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HVACR ELECTRICAL COMPONENTS
PG 1 OF
99% OF ALL ELECTRICAL COMPONENTS CAN BE CLASSIFIED INTO 1 OF
3 CATEGORIES:
1) SOURCE: DEVICES THAT SUPPLY ELECTRICAL POWER TO AN ELECTRICAL
CIRCUIT.
2) CONTROLLING DEVICES ( SWITCHES ): THESE DEVICES WILL DETERMINE
WHEN & HOW A LOAD IS TO BE ‘ENERGIZED’ ( TURNED-ON ),
AS WELL AS WHEN & HOW THE LOAD IS TO BE ‘DE-ENERGIZED’ ( TURNED-OFF ).
3) LOADS: DEVICES THAT USE ELECTRICAL POWER TO PERFORM SOME KIND OF
‘WORK’. LOADS CHANGE ENERGY FROM ONE FORM TO ANOTHER.
EVERY ELECTRICAL COMPONENT THAT WE WILL DISCUSS IN ACR-123 WILL
FALL INTO ONE OF THESE CATEGORIES. ( SOME MAY FALL INTO MORE
THAN ONE CATEGORY ).
THE PURPOSE OF AN ELECTRICAL CIRCUIT: TO SUPPLY A ‘LOAD’ WITH THE
‘TOTAL’ ELECTRICAL POWER ( VOLTAGE & CURRENT ) THAT IT NEEDS TO PERFORM
ITS ‘FUNCTION’.
ELECTRICITY IS ALL ABOUT GETTING THE RIGHT ‘VOLTAGE’ TO A ‘LOAD’,
& HAVING THAT LOAD ‘DRAW’ THE RIGHT AMOUNT OF CURRENT THAT
IT NEEDS TO PERFORM ITS ‘JOB’.
THE DESIGNER OF ANY ELECTRICAL CIRCUIT, WILL ‘DRAW’ THE ELECTRICAL
CIRCUIT SO THAT SOMEONE ELSE CAN ‘READ’ & ‘UNDERSTAND’ HOW
( & WHEN ) THE CIRCUIT IS SUPPOSE TO OPERATE.
THESE ELECTRICAL ‘DRAWINGS’ ARE CALLED ‘DIAGRAMS’.
THERE ARE SEVERAL TYPES OF ELECTRICAL ‘DIAGRAMS’.
THE DIAGRAM MOST OFTEN USED BY TECHNICIANS IS CALLED THE
‘SCHEMATIC’ DIAGRAM.
THE TECHNICIAN USES ( READS ) THE ELECTRICAL ‘SCHEMATIC’ DIAGRAM TO
UNDERSTAND HOW ANY ELECTRICAL CIRCUIT WORKS, & TO DIAGNOSE
ANY PROBLEMS ENCOUNTERED WITH AN ELECTRICAL CIRCUIT.
ON A SCHEMATIC DIAGRAM, ‘SYMBOLS’ ARE USED TO REPRESENT THE ACTUAL
ELECTRICAL COMPONENTS.
IT IS IMPERATIVE THAT A TECHNICIAN KNOW THE PROPER ‘SYMBOL’ FOR
EACH OF THE ELECTRICAL COMPONENTS.
IT IS THE ONLY WAY TO ‘READ’ A SCHEMATIC DIAGRAM.
THE COMPONENTS, TO BE DISCUSSED IN THIS SECTION, WILL BE SHOWN
WITH THEIR APPROPRIATE ‘SYMBOL’.
THOUGH THE ‘SYMBOLS’ SHOWN IN THIS SECTION ARE GENERALLY ACCEPTED,
THESE ‘SYMBOLS’ ARE NOT UNIVERSALLY USED. HVACR MANUFACTURERS ARE
NOT REQUIRED TO USE ANY PARTICULAR ‘SYMBOL’.
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PG 2 OF
SOURCE:
THERE IS ONLY ONE TRUE ‘SOURCE’ OF POWER, FOR ALL ELECTRICAL
CIRCUITS, THAT TECHNICIANS WILL ENCOUNTER.
A ‘TRANSFORMER’.
A TRANSFORMER IS A DEVICE THAT CHANGES THE VOLTAGE ( & ULTIMATELY,
THE CURRENT ) OF THE INCOMING ELECTRICAL POWER.
A ‘GENERATOR’ PRODUCES ELECTRICAL POWER, & A ‘TRANSFORMER’,
TRANSFORMS THE GENERATOR POWER INTO OTHER, MORE USEFUL, POWER.
A TRANSFORMER CAN INCREASE THE VOLTAGE OF AN INCOMING POWER SOURCE,
OR IT CAN DECREASE THE VOLTAGE OF AN INCOMING POWER SOURCE.
THE TRANSFORMER IS, SIMPLY, TWO INDUCTORS ( REMEMBER THE TERM ? ),
OR COILS OF WIRE ( CONDUCTORS ), THAT USE THE PRINCIPLE OF
‘INDUCTANCE’ TO TRANFER POWER ( ENERGY ) FROM ONE ‘COIL’
TO THE OTHER ‘COIL’.
THE 1ST INDUCTOR IS CALLED THE PRIMARY WINDING.
THE 1ST INDUCTOR IS ACTUALLY A ‘LOAD’ TO THE POWER SOURCE THAT ‘FEEDS’
THE TRANSFORMER.
THE PRIMARY WINDING DRAWS ITS POWER FROM ITS SOURCE & TRANSFERS THAT
POWER TO THE 2ND INDUCTOR BY ‘INDUCTANCE’.
THE 2ND INDUCTOR IS CALLED THE SECONDARY WINDING.
THE SECONDARY WINDING IS THE ‘SOURCE’ OF POWER FOR ALL ELECTRICAL
COMPONENTS THAT ARE CONNECTED TO THE 2ND INDUCTOR.
SO, THE TRANSFORMER IS ACTUALLY A ‘LOAD’ ( PRIMARY WINDING ),
& A ‘SOURCE’ ( SECONDARY WINDING ).
THE WINDINGS OF A TRANSFORMER ARE WOUND TOGETHER AROUND AN IRON
CORE. THE IRON CORE CONCENTRATES THE MAGNETIC FIELD OF THE
PRIMARY WINDING TO PROVIDE A GREATER TRANSFER OF ENERGY FROM’
THE PRIMARY WINDING TO THE SECONDARY WINDING.
THE SYMBOL FOR A TRANSFORMER:
PRIMARY WINDING
IRON CORE
SECONDARY WINDING
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PG 3 OF
TRANSFORMER CONTINUED:
TO UNDERSTAND HOW A TRANFORMER OPERATES, WE MUST REVIEW &
EXPAND OUR DISCUSSION OF INDUCTANCE.
INDUCTANCE: THE ABILITY OF A MAGNETIC FIELD TO TRANSFER ITS ENERGY TO
A CONDUCTIVE MATERIAL WITHOUT TOUCHING IT.
THE STRENGTH OF THE MAGNETIC FIELD PRODUCED BY THE PRIMARY WINDING
( INDUCTOR ) IS DEPENDANT UPON:
1) THE AMOUNT OF CURRENT FLOW IN THE PRIMARY WINDING.
( THIS IS A PRODUCT OF THE DC RESISTANCE OF THE WIRE & THE INDUCTIVE
REACTANCE PRODUCED BY THE INDUCTANCE OF THE WINDING ).
2) THE NUMBER OF TURNS OF WIRE IN THE WINDING ( INDUCTOR ).
( THE GREATER THE NUMBER OF TURNS, THE GREATER THE INDUCTANCE )
3) THE CORE MATERIAL.
( THE CORE CONCENTRATES THE MAGNETIC FIELD, MAKING IT STRONGER )
THE STRENGTH OF THE ‘INDUCED’ POWER THAT THE SECONDARY WINDING
RECEIVES IS DEPENDANT UPON:
1) THE ‘COEFFICIENT OF COUPLING’ BETWEEN THE PRIMARY & SECONDARY
WINDING. ( HOW CLOSE EACH WINDING IS TO EACH OTHER ).
2) THE CORE MATERIAL OF THE SECONDARY WINDING.
( AGAIN, TO CONCENTRATE THE MAGNETIC FIELD IN THE SECONDARY WINDING )
3) THE NUMBER OF TURNS IN THE SECONDARY WINDING.
IN REALITY, THE PRIMARY & SECONDARY WINDINGS ARE WOUND,TOGETHER,
ON THE SAME CORE MATERIAL ( USUALLY IRON ).
THIS MAKES FOR A VERY HIGH ‘COEFFICIENT OF COUPLING’.
WHICH IS A TECHNICAL WAY OF SAYING THAT:
ALL THE ENERGY ( POWER ) FROM THE PRIMARY WINDING IS TRANSFERRED TO
THE SECONDARY WINDING .
WHAT THIS MEANS IS THAT:
THE POWER RECEIVED BY THE SECONDARY WINDING IS, EXACTLY THE SAME
AS, THE POWER PRODUCED BY THE PRIMARY WINDING.
IN OTHER WORDS: Pp = Ps ( POWER IN THE PRIMARY, Pp IS EQUAL TO THE
POWER IN THE SECONDARY, Ps ).
SINCE POWER IS A PRODUCT OF VOLTAGE & CURRENT, THEN WE CAN SAY:
Ep x Ip = Es x Is ( FROM OHMS LAW )
VERY IMPORTANT: POWER ( ‘P’ ) = E x I . CHANGING EITHER ‘E’ OR ‘I’, CHANGES
THE POWER (‘P’). SO, IF WE DOUBLE THE VOLTAGE AND, AT THE SAME TIME, CUT
THE CURRENT IN HALF ( ½ ), THEN THE RESULTING POWER WILL STAY THE SAME.
EG: 100W = 10V x 10A OR 100W = 20V x 5A
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PG 4 OF
TRANSFORMER CONTINUED:
AS STATED BEFORE, A TRANSFORMER SIMPLY CHANGES VOLTAGE.
THE PRIMARY WINDING IS SUPPLIED WITH ITS OPERATING VOLTAGE & THIS
VOLTAGE IS TRANFERRED TO THE SECONDARY, WITH THE
SECONDARY VOLTAGE EITHER,
1) BEING HIGHER THAN THE PRIMARY ( A STEP-UP TRANSFORMER ), OR
2) BEING LOWER THAN THE PRIMARY VOLTAGE.
( A STEP-DOWN TRANSFORMER )
3) BEING THE SAME AS THE PRIMARY ( AN AUTOTRANSFORMER )
THE 2 TYPES OF TRANSFORMERS THAT HVAC TECHNICIANS
WILL COMMONLY SEE IS:
1) THE STEP-UP TRANFORMER
SECONDARY VOLTAGE MORE THAN PRIMARY VOLTAGE
( USED IN GAS FURNACES )
2) THE STEP-DOWN TRANFORMER
SECONDARY VOLTAGE LESS THAN PRIMARY VOLTAGE
( USED AS THE CONTROL TRANFORMER IS ALMOST ALL CENTRAL HEAT & AIR
SYSTEMS )
SINCE THE SECONDARY WINDING RECEIVES THE SAME POWER, FROM THE
PRIMARY WINDING, AS THE PRIMARY WINDING ‘DRAWS’ FROM ITS SOURCE, THEN
THE POWER (‘P’), IN THE OHMS LAW FORMULA, MUST STAY THE SAME FOR BOTH
THE PRIMARY & SECONDARY WINDINGS.
A TRANSFORMER IS RATED ACCORDING TO THE POWER THAT THE PRIMARY
WINDING CAN ‘DRAW’ FROM ITS SOURCE, WITHOUT DAMAGE.
THIS SAME POWER IS THEN TRANSFERRED TO THE SECONDARY WINDING, &
IS AVAILABLE TO BE USED BY THE ‘LOADS’ CONNECTED TO THE
SECONDARY WINDING.
( THE SECONDARY WINDING IS THE ‘SOURCE FOR ANYTHING CONNECTED TO IT )
IN TRANSFORMER TERMS:
THE TRANSFORMER IS RATED FOR THE VA ( VOLTS x AMPS = POWER ) THAT
THE PRIMARY ‘DRAWS’ & THE SECONDARY USES, AS WELL AS THE VOLTAGE
OF THE PRIMARY WINDING & THE VOLTAGE THAT THE SECONDARY ‘PUTS OUT’.
THE SIZE OF A TRANSFORMER IS ITS ‘VA’ RATING:
EACH SIDE OF A TRANSFORMER IS ‘LIMITED’ TO THE AMOUNT OF POWER THAT IT
IS ‘RATED’ FOR.
IN OTHER WORDS, EACH WINDING, PRIMARY OR SECONDARY, IS ‘LIMITED’ TO
THE COMBINATION OF VOLTAGE & CURRENT THAT WILL PRODUCE THE
‘RATED’ ( MAXIMUM ) VA ( POWER ).
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PG 5 OF
TRANSFORMER CONTINUED:
NOW THAT WE UNDERSTAND THE ‘RATINGS’ OF A TRANSFORMER, LETS SEE HOW
A TRANSFORMER ‘PUTS OUT’ DIFFERENT VOLTAGES.
VERY IMPORTANT POINT: ANY INDUCTOR ( OR COIL OF WIRE ), WILL HAVE A
CERTAIN ‘NUMBER OF TURNS’ THAT THE WIRE WILL BE COILED INTO.
THERE IS A DIRECT RELATIONSHIP BETWEEN THE ‘NUMBER OF TURNS’ OF
THE PRIMARY WINDING VERSUS, THE ‘NUMBER OF TURNS’ OF WIRE IN
THE SECONDARY WINDING, AND THE AMOUNT OF VOLTAGE THAT IS
TRANSFERRED BETWEEN THE PRIMARY &THE SECONDARY.
EG: IF THE SECONDARY WINDING HAS 1/2 THE ‘NUMBER OF TURNS’ OF WIRE AS
DOES THE PRIMARY WINDING, THE VOLTAGE OF THE SECONDARY WILL
BE ½ OF THE PRIMARY VOLTAGE.
IF THE SECONDARY WINDING HAS TWICE THE ‘NUMBER OF TURNS’ OF WIRE
AS THE PRIMARY WINDING, THE VOLTAGE OF THE SECONDARY WINDING
WILL BE TWICE AS HIGH AS THE PRIMARY VOLTAGE.
SO, IF A TRANSFORMER HAS 100 TURNS OF WIRE, IN THE PRIMARY WINDING,
& 50 TURNS OF WIRE, IN THE SECONDARY WINDING,
THEN THE SECONDARY VOLTAGE WOULD BE ½ OF THE PRIMARY VOLTAGE.
IF 240 VAC FED THE PRIMARY WINDING, THEN 120 VAC WOULD BE THE
VOLTAGE PROVIDED FROM THE SECONDARY WINDING.
IN MATHEMATICAL FORM: Np / Ns = Vp / Vs
THE RATIO OF THE NUMBER OF TURNS OF WIRE IN THE PRIMARY VERSUS THE
NUMBER OF TURNS IN THE SECONDARY IS THE SAME AS THE RATIO OF:
THE VOLTAGE OF THE PRIMARY VERSUS THE VOLTAGE OUTPUT OF THE
SECONDARY.
EG: IF THE RATIO OF THE TRANSFORMER IS THAT THE PRIMARY HAS 10 TIMES
THE NUMBER OF TURNS OF WIRE THAN THE SECONDARY, THEN THE PRIMARY
VOLTAGE WILL BE 10 TIMES GREATER THAN THE SECONDARY VOLTAGE.
ALRIGHT, LETS REVIEW WHAT WE HAVE LEARNED SO FAR:
1) A TRANFORMER IS ‘RATED’ FOR THE AMOUNT OF POWER ( IN ‘VA’ ) THAT
IT CAN HANDLE. ( BOTH PRIMARY & SECONDARY ) & THE VOLTAGE OF THE
WINDINGS.
2) THE PRIMARY WINDING ‘INDUCES’ THE SAME POWER INTO THE
SECONDARY WINDING.
SO, THE PRIMARY WINDING MUST PRODUCE THE SAME VA ( POWER )
THAT THE SECONDARY WINDING ‘DRAWS’ ( PUTS OUT ).
3) THE RATIO OF THE NUMBER OF TURNS BETWEEN THE PRIMARY & SECONDARY
WINDING IS THE SAME AS THE VOLTAGE RATIO BETWEEN THE TWO WINDINGS.
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PG 6 OF
TRANSFORMER CONTINUED:
TRANSFORMER RATINGS & CURRENT:
A TRANSFORMER IS RATED FOR:
1) THE MAXIMUM AMOUNT OF POWER THAT EACH WINDING CAN HANDLE,
IN ‘VA’ ( VOLT / AMPS )
2) THE VOLTAGE OFTHE PRIMARY WINDING.
3) THE VOLTAGE OF THE SECONDARY WINDING.
THE CURRENT DRAWN BY THE PRIMARY WINDING OR AVAILABLE TO BE USED BY
THE SECONDARY WINDING IS SIMPLY AN ‘OHMS LAW’ RESULT OF THE
RATED POWER ( IN ‘VA’ ) DIVIDED BY THE RATED VOLTAGE.
P ( VA )
I=E
SO, LETS TAKE A COMMON CONTROL POWER TRANSFORMER, RATED AT 40VA, WITH
A 240 VAC PRIMARY & A 24 VAC SECONDARY
40 VA / 240 VAC = .167 AMPS
THIS MEANS THAT THE MAXIMUM PRIMARY CURRENT THAT A 40 VA
TRANSFORMER CAN PRODUCE( WITHOUT DAMAGE ) IS .167 AMPS.
THE SECONDARY CURRENT CAN BE : 40 VA / 24 VAC = 1.67 AMPS
THIS MEANS THAT THE MAXIMUM CURRENT THAT THE SECONDARY WINDING &
THE CIRCUIT THAT IT SERVES CAN DRAW FROM THE TRANSFORMER ( WITHOUT
DAMAGE ) IS 1.67 AMPS.
LOOKING AT THE RATIO OF ‘NUMBER OF TURNS’, ‘VOLTAGES’ & CURRENTS
TOGETHER, WE SEE THAT :
NP
=
EP
=
IS
NS
ES
IP
WHICH MEANS THAT, IF THE ‘NUMBER OF TURNS’ OF THE PRIMARY IS MORE THAN
THE ‘NUMBER OF TURNS’ OF THE SECONDARY,
THEN THE VOLTAGE OF THE PRIMARY WILL BE GREATER THAN THE VOLTAGE OF
THE SECONDARY ( STEP-DOWN ), &
THE CURRENT OF THE PRIMARY WILL BE LESS THAN THE CURRENT OF THE
SECONDARY ( OPPOSITE THE OTHER TWO ).
WHEN REPLACING A TRANSFORMER, ALWAYS REPLACE WITH THE SAME SIZE OR
GREATER SIZE ( IN ‘VA’ ) TO ENSURE THAT THE SECONDARY SIDE OF THE
TRANSFORMER WILL HAVE ENOUGH AVAILABLE CURRENT TO ‘SUPPLY’
THE ELECTRICAL CIRCUITRY CONNECTED TO IT.
WHEN ADDING ‘LOADS’ TO THE SECONDARY SIDE OF ANY TRANSFORMER, WE
MUST INSURE THAT WE DO NOT ‘OVERLOAD’ THE TRANSFORMERS ‘VA’RATING.
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PG 7 OF
TRANSFORMER CONTINUED:
MULTI-TAP TRANSFORMER WINDINGS:
A TECHNICIAN WILL EVENTUALLY NOTICE THAT SOME TRANSFORMERS ARE
‘RATED’ FOR MORE THAN 1 VOLTAGE ON A WINDING.
THIS USUALLY OCCURS ON THE PRIMARY WINDING, WHERE THE TRANSFORMER
PRIMARY CAN BE ‘FED’ WITH 120 VAC, 208 VAC, OR 240 VAC.
THE TECHNICIAN MUST INSURE THAT THE TRANSFORMER WINDING IS CONNECTED
TO THE PROPER ‘TAP’ FOR THE ‘INPUT’ VOLTAGE THAT IS USED.
OTHERWISE, THE VOLTAGE ‘OUTPUT’ OF THE SECONDARY WINDING WILL NOT BE
WHAT IT IS RATED FOR.
LETS LOOK AT A TRANSFORMER & SEE WHY…
240 VAC
VOLTAGE
‘TAPS’
FOR
USING
DIFFERENT
VOLTAGES
208 VAC
120 VAC
RATED AT
120 VAC OUTPUT
IN THE ABOVE TRANSFORMER THERE ARE 20 TURNS OF WIRE ( CIRCLES ) IN THE
PRIMARY WINDING & 10 TURNS OF WIRE, IN THE SECONDARY WINDING.
THAT MAKES THIS TRANSFORMER HAVE A 2 ( PRIMARY ) TO
1 ( SECONDARY ) RATIO,
( IF WE USE THE ENTIRE PRIMARY WINDING WITH 240 VAC PRIMARY )
IF WE USE THE 120 VAC PRIMARY ‘TAP’, THEN THE RATIO OF ‘NUMBERS OF TURNS’
WOULD BE 1 TO 1.
( 10 TURNS IN PRIMARY & 10 TURNS IN SECONDARY )
SO THE SECONDARY VOLTAGE WOULD STILL BE 120 VAC.
IF WE USE THE 208 VAC ‘TAP’, THEN THE RATIO WOULD BE 1.73 ( PRIMARY )
TO 1 ( SECONDARY ).
& THE SECONDARY VOLTAGE WOULD REMAIN AT 120 VAC.
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PG 8 OF
TRANSFORMER CONTINUED:
MULTI-TAP TRANSFORMER WINDINGS:
NOW, LOOKING AT THE TRANSFORMER ABOVE, WHAT WOULD HAPPEN IF WE
CONNECTED 240 VAC TO THE 208 VAC ‘TAP’ ??
BECAUSE THE NUMBER OF TURNS ‘RATIO’ DICTATES THE OUTPUT VOLTAGE,
( BY THE SAME RATIO – INPUT VOLTAGE TO OUTPUT VOLTAGE ), THEN
THE OUTPUT VOLTAGE WOULD STILL BE AT THE 208 VAC ‘RATIO’ OR 1.73 TO 1.
( SINCE AT THIS ‘TAP’, THERE WILL BE 1.73 MORE TURNS IN THE
PRIMARY WINDING THAN THE SECONDARY WINDING ).
THEN THE SECONDARY VOLTAGE WOULD STILL REFLECT THE ‘NUMBER OF TURNS’
RATIO OR:
240 VAC / 1.73 = 138 VAC
SO, THE SECONDARY VOLTAGE WOULD BE 138 VAC INSTEAD OF THE 120 VAC THAT
THE SECONDARY IS ‘RATED’ FOR.
WHAT WOULD HAPPEN, THEN, IF WE CONNECTED A 208 VAC SOURCE TO THE
240 VAC ‘TAP’ ON THE PRIMARY WINDING??
IN THIS CASE, WE WOULD BE USING ALL OF THE PRIMARY WINDING, SO THE
‘NUMBER OF TURNS’ OF THE PRIMARY WINDING WOULD BE 20 & THE
‘NUMBER OF TURNS’ OF THE SECONDARY WOULD BE 10, SO WE HAVE A 2 – 1 RATIO.
SO, AT THIS TAP, THE SECONDARY VOLTAGE WOULD BE EXACTLY ½ OF THE
PRIMARY VOLTAGE BECAUSE IT IS THE SAME ‘RATIO’.
NP / NS = EP / ES
THE PRIMARY VOLTAGE THEN WOULD BE TWICE THE VOLTAGE OF THE
SECONDARY, OR IN OTHER WORDS, THE SECONDARY VOLTAGE WOULD BE
ONE-HALF THE PRIMARY VOLTAGE.
THE PRIMARY VOLTAGE WOULD BE 208 VAC, SO THE SECONDARY VOLTAGE WOULD
BE ½ OF 208 OR 104 VAC ( INSTEAD OF 120 VAC ).
IMPORTANT: THE ‘VA’ RATING, OF THE TRANSFORMER, IS THE MAXIMUM
AMOUNT OF POWER ( ‘VA’ ) THAT A TRANSFORMER CAN ‘DRAW’ ( PRIMARY
WINDING ) OR ‘SUPPLY’ ( SECONDARY WINDING ).
THE ACTUAL ‘VA’ ( VOLTS & AMPS ) THAT A TRANSFORMER
USES AT ANY MOMENT IS A RESULT OF HOW MUCH CURRENT THE ELECTRICAL
CIRCUIT, ( THAT THE SECONDARY IS THE ‘SOURCE’ FOR ) ‘DRAWS’.
THE PRIMARY ONLY ‘PUTS OUT’ THE POWER ( IN VOLT x AMPS – VA ) THAT
THE SECONDARY NEEDS TO POWER THE ELECTRICAL CIRCUIT THAT IT ‘FEEDS’.
iN OTHER WORDS, IF THE ELECTRICAL CIRCUIT THAT THE SECONDARY WINDING
SERVES, ONLY NEEDS 30 ‘VA’S OF POWER, THE PRIMARY WINDING WILL
ONLY ‘PUT OUT’ THE SAME 30 ‘VA’.
( THE PRIMARY WINDING WILL ONLY ‘DRAW’ 30 VA OF POWER FROM ITS SOURCE )
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PG 9 OF
CONTROLLING DEVICES:
THERE ARE 2 CATEGORIES OF DEVICES USED TO CONTROL THE OPERATION
OF AN ELECTRICAL ‘LOAD’.
1) OPERATING CONTROL: THESE ARE THE SWITCHES & CONTACTS THAT ARE
USED TO ‘TELL’ THE LOAD WHEN TO START & WHEN TO STOP, UNDER
‘NORMAL’ OPERATING CONDITIONS.
2) PROTECTION CONTROL: THESE DEVICES ALLOW THE ‘LOAD’ TO START, IF
CONDITIONS ARE SAFE, & WILL STOP THE ‘LOAD’ IF CONDITIONS ARE UNSAFE.
MANY DEVICES CAN BE USED FOR EITHER CATEGORY, OPERATING OR
PROTECTION.
EG: A TEMPERATURE SWITCH CAN BE USED TO, NORMALLY START OR STOP A
‘LOAD’ ( OR LOADS ) TO CONTROL THE TEMPERATURE ( WATER HEATER ), OR
A TEMPERATURE SWITCH MAY BE USED TO SHUT OFF THE DEVICE IF THE
TEMPERATURE GETS TOO HIGH. ( ALSO ON A WATER HEATER ).
THERE ARE 2 BASIC GROUPS OF CONTROLLING DEVICES.
1) SWITCHES: DEVICES THAT WILL CLOSE ( ALLOWING CURRENT FLOW ) OR
OPEN ( NOT ALLOWING CURRENT FLOW ). THE OPERATION OF A ‘SWITCH’
CAN BE CONTROLLED BY ANY OF THE FOLLOWING NON-ELECTRICAL ‘MEANS’.
A) MANUAL: THE SWITCH IS OPERATED BY THE ‘FORCE’ OF ‘MOVEMENT’.
B) TEMPERATURE: THE SWITCH IS OPERATED BY ‘HEAT’.
C) PRESSURE: THE SWITCH IS OPERATED BY ‘FLUID PRESSURE’.
( FLUID IS WATER, REFRIGERANT, OR AIR )
D) FLOW: THE SWITCH IS OPERATED BY THE MOVEMENT OF FLUIDS.
E) LEVEL / FLOAT: THIS SWITCH IS OPERATED BY THE ‘LEVEL’ OF A FLUID.
THE ‘BASIC’ SYMBOL
FOR A SWITCH
TOP: CLOSED
BOTTOM: OPEN
THERE ARE 2 PARTS TO
A SWITCH:
1) POLE
2) ‘THROW’
2) CONTACTS: THE DEVICES OPERATE SIMILAR TO SWITCHES, IN THAT THEY
CLOSE TO ALLOW CURRENT TO FLOW IN THE CIRCUIT, OR OPEN TO STOP
CURRENT FROM FLOWING IN THE CIRCUIT.
WHAT MAKES THE ‘CONTACT’ DIFFERENT FROM A SWITCH IS THAT A CONTACT
CLOSES OR OPENS BASED ON AN ELECTRICAL ‘MEANS’.
THE SYMBOL FOR A
CONTACT.
OPEN
CLOSED
LEFT: OPEN
RIGHT: CLOSED
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PG 10 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT SIMILARITIES:
SWITCHES & CONTACTS OPERATE, IN AN ELECTRICAL CIRCUIT, EXACTLY THE
SAME. THEY ARE WIRED IN THE SAME MANNER, THEY ARE TESTED IN THE SAME
MANNER.
TO UNDERSTAND HOW A SWITCH OR A CONTACT OPERATES WITHIN AN
ELECTRICAL CIRCUIT, THINK OF THE ELECTRICAL CIRCUIT AS A ROADWAY, WITH
THE SWITCH OR CONTACT AS A DRAW-BRIDGE.
WHEN THE DRAW-BRIDGE IS ‘DOWN’ ( SWITCH OR CONTACT CLOSED ), CARS CAN
CROSS THE BRIDGE ( CURRENT CAN FLOW THROUGH ).
WHEN THE DRAW-BRIDGE IS ‘UP’ ( SWITCH OR CONTACT OPEN ), CARS CANNOT PASS
THROUGH ( NO CURRENT CAN FLOW THROUGH ).
A SWITCH OR CONTACT CAN HAVE 2 POSSIBLE ‘NORMAL’ POSITIONS:
1) NORMALLY-CLOSED
2) NORMALLY-OPEN
THE ‘NORMAL’ POSITION OF THE SWITCH OR CONTACT IS:
THE POSITION OF THE SWITCH WHEN THERE IS NO ELECTRICAL POWER APPLIED.
OR: THE SWITCH OR CONTACT POSITION WHEN THE SWITCH OR CONTACT IS
HELD IN YOUR HAND ( NOT CONNECTED ELECTRICALLY ).
THE ‘NORMAL’ POSITION OF A DRAW-BRIDGE IS ‘DOWN’ ( CLOSED ).
IN OTHER WORDS, THE DRAW-BRIDGE IS NORMALLY ‘DOWN’ ( CLOSED ) & MUST BE
PHYSICALLY MOVED TO CHANGE ITS POSITION – TO ‘UP’ ( OPEN ).
ALL SWITCHES OR CONTACTS HAVE AN ‘INPUT’ & AN ‘OUTPUT’.
ELECTRICAL POWER ( VOLTAGE & CURRENT ) IS ‘NORMALLY’ SITTING AT THE
‘INPUT’ SIDE OF A SWITCH OR CONTACT, WAITING FOR THE SWITCH OR CONTACT
TO CLOSE, WHICH ALLOWS THE VOLTAGE & THE CURRENT TO GET THROUGH
THE SWITCH ( OUTPUT ).
AGAIN, REFER TO THE DRAW-BRIDGE:
WHEN THE DRAW-BRIDGE IS ‘UP’ ( OPEN ), THE CARS THAT ARE TRYING TO TAKE
THAT ‘ROAD’ ( PATH ) TO THEIR DESTINATION ( LOAD ), MUST SIT & WAIT FOR THE
BRIDGE TO ‘CLOSE’ ( DOWN ). THEY ARE AT THE ‘INPUT’ TO THE BRIDGE.
WHEN THE DRAW-BRIDGE COMES DOWN ( CLOSES ), THE CARS CAN TRAVEL
( FLOW ) THROUGH THE DRAW-BRIDGE ( OUTPUT ) & CONTINUE ON THEIR
WAY TO THEIR DESTINATION ( LOAD ).
IN AN ELECTRICAL CIRCUIT, THERE IS, USUALLY, MORE THAN 1 ‘DRAW-BRIDGE’
THAT THE POWER ( VOLTAGE & CURRENT ) MUST FLOW THROUGH BEFORE
REACHING ITS DESTINATION, WHICH IS THE ‘LOAD’ THAT THEY ARE TRYING TO
CONTROL.
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PG 11 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT SIMILARITIES CONTINUED:
SWITCHES & CONTACTS CAN BE ‘TESTED’ IN EXACTLY THE SAME
MANNER.
1) OHMMETER: USE AN OHMMETER TO TEST THE CONTINUITY OF THE SWITCH
OR CONTACT.
( INSURE SWITCH IS ‘ISOLATED’ FROM ITS ELECTRICAL CIRCUIT )
A ‘CLOSED’ SWITCH SHOULD READ VERY CLOSE TO ‘ZERO’ OHMS ( VERY LOW
RESISTANCE )
AN ‘OPEN’ SWITCH SHOULD READ ‘INFINITE’ ( EXTREMELY HIGH RESISTANCE )
OR ‘OVERLOAD’ ( TOO MUCH RESISTANCE FOR METER TO READ )
2) VOLTMETER: THERE ARE 2 WAYS TO USE A VOLTMETER TO DETERMINE THE
CONDITION ( OPEN OR CLOSED ) OF A SWITCH OR CONTACT.
A) A TECHNICIAN CAN USE A VOLTMETER TO DETERMINE IF POWER IS AVAILABLE
AT THE ‘INPUT’ TO THE SWITCH OR CONTACT, &
IF IT IS BEING ALLOWED OUT OF ( ‘OUTPUT’ ) THE SWITCH OR CONTACT,
IF THE SWITCH OR CONTACT IS ‘CLOSED’.
PLACE THE 1ST LEAD OF THE VOLTMETER ON THE SIDE OF THE POWER SOURCE
THAT IS NOT GOING THROUGH THE SWITCH OR CONTACT.
USING THE 2ND VOLTMETER LEAD, DETERMINE IF THE OTHER SIDE OFTHE POWER
SOURCE IS AT THE ‘INPUT’ TO THE SWICTH OR CONTACT.
IF THE VOLTAGE IS AT THE ‘INPUT’, DETERMINE IF THE VOLTAGE IS AT THE
‘OUTPUT’, OF THE SWITCH OR CONTACT.
B) THE 2ND METHOD OF USING A VOLTMETER IS TO PLACE THE VOLTMETER
LEADS ON BOTH SIDES OF THE SWITCH OR CONTACT [ ACROSS ( PARALLEL WITH )
THE SWITCH OR CONTACT ].
IF THE SWITCH OR CONTACT IS ‘CLOSED’, THE VOLTMETER WILL READ
‘ZERO’ VOLTS.
IF THE SWITCH OR CONTACT IS ‘OPEN’, THE VOLTMETER WILL READ THE
SOURCE ( OR SUPPLIED ) VOLTAGE.
VERY IMPORTANT NOTE: THIS 2ND METHOD IS ONLY ACCURATE WHEN THE 1
SWITCH OR CONTACT IS THE ONLY SWITCH OR CONTACT THAT IS ‘OPEN’ IN THE
CIRCUIT.
THIS METHOD SHOULD NOT BE USED UNLESS THE TECHNICIAN UNDERSTANDS THE
ELECTRICAL DIAGRAM & CAN INSURE THAT ALL OTHER SWITCHES & CONTACTS IN
THE CIRCUIT ARE ‘CLOSED’.
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PG 12 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT OPERATION:
LETS LOOK AT THE ‘PARTS’ OF A SWITCH.
‘INPUT’
POST
‘POLE’
‘OUTPUT’ POST
REFERRED TO AS
A ‘THROW’
NORMALLY
CLOSED
SWITCH
‘POLE’
LAYS ON TOP
OF ‘OUTPUT
POST’.
THE ‘POLE’ ( MOVING PART OF SWITCH ) IS ATTACHED TO THE ‘INPUT POST’ IN A
MANNER THAT WILL ALLOW THE ‘POLE’ TO MOVE.
THE OTHER END OF THE ‘POLE’ LAYS ON TOP OF THE OUTPUT POST, CALLED A
‘THROW’, MAKING IT A NORMALLY-CLOSED SWITCH.
IN ACTUALITY, A SWITCH DOESN’T CARE WHICH WAY CURRENT FLOWS OR
WHICH ‘POST’ IS AN INPUT NOR WHICH IS AN OUTPUT.
IT IS VERY IMPORTANT TO ‘SEE’ HOW THE ‘POLE’ IS LOCATED, IN REFERENCE TO
THE ‘OUTPUT POST’, OR ‘THROW.
IS POLE ‘SITTING ON TOP OF’ ( NORMALLY-CLOSED ) OR
‘BELOW’ ( NORMALLY-OPEN ) THE OUTPUT POSTS?
THE PROPER TERMINOLOGY TO USE IN DESCRIBING THE ABOVE SWITCH IS:
A ‘NORMALLY-CLOSED’, SINGLE-POLE, SINGLE ‘THROW’ SWITCH.
THIS SWITCH WILL ALOW CURRENT TO FLOW, AS THERE IS A COMPLETE
CONNECTION BETWEEN THE ‘INPUT POST’ & THE ‘OUTPUT POST’.
THIS SWITCH WOULD HAVETO BE ‘FORCED’ OPEN TO STOP THE FLOW OF CURRENT.
BELOW IS THE ‘SYMBOL’ FOR A NORMALLY-OPEN, SINGLE-POLE, SINGLE-THROW
SWITCH.
SWITCH ‘OPEN’
NOTE THAT THE ‘POLE’ IS NOW LAYING UNDER THE ‘OUTPUT POST’ ( THROW ).
THE ‘INPUT POST’ & THE ‘OUTPUT POST’ ( THROW ) ARE THE SAME AS BEFORE.
THE ONLY DIFFERENCE IS THAT THE ‘POLE’ IS ‘HANGING’ BELOW THE POST,
WHICH LEAVES AN OPEN CONNECTION BETWEEN THE ‘POLE’ & THE ‘OUTPUT POST’.
THIS SWITCH MUST BE ‘FORCED’ TO ‘CLOSE’ BEFORE CURRENT WILL FLOW
THROUGH THIS SWITCH.
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 13 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT OPERATION:
DID YOU NOTICE THE TERMS SINGLE-POLE, SINGLE-THROW FROM ABOVE ?
WHEN REFERRING TO A SWITCH & SOMETIMES A CONTACT, WE MUST
KNOW HOW MANY ‘POLES’ ARE NEEDED OR USED BY THE ELECTRICAL CIRCUIT.
( EACH ‘POLE’ CAN BE CONSIDERED A SEPARATE SWITCH )
WE MUST ALSO DETERMINE HOW MANY ‘THROWS’, ( ‘OUTPUTS’ ) ARE NEEDED OR
USED BY THE ELECTRICAL CIRCUIT..
A ‘THROW’ IS AN ‘OUTPUT POST’ OF THE SWITCH
( REMEMBERING THAT A SWITCH OR CONTACT DOESN’T CARE WHICH SIDE IS ‘INPUT’
OR OUTPUT’ )
A SINGLE SWITCH OR CONTACT CAN HAVE 1 ‘POLE’ & UP TO 2 ‘THROWS’.
A DEVICE CAN CONTAIN MORE THAN 1 SINGLE SWITCH OR CONTACT
& OPERATE ALL OF THEM BY THE SAME MECHANISM ( OPERATOR ).
A SWITCH OR CONTACT CAN BE:
1) SINGLE-POLE / SINGLE-THROW:
‘CONTACT’ SYMBOL
1 INPUT & 1 OUTPUT
‘SWITCH; SYMBOL
NORMALLY CLOSED ( N/C )
OR:
NORMALLY OPEN ( N/O )
OR:
SINGLE ‘POLE’
2) SINGLE-POLE / DOUBLE-THROW:
‘CONTACT’ SYMBOL
SINGLE ‘THROW’
1 ‘INPUT’ & 2 ‘OUTPUTS’ OR:
2 ‘INPUTS’ & 1 ‘OUTPUT’
‘SWITCH’ SYMBOL
NORMALLY OPEN ( N/O)
SIDE OF
SWITCH / CONTACT
NORMALLY-CLOSED ( N/C )
SIDE OF
SWITCH / CONTACT
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 14 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT OPERATION:
WITH THE SINGLE-POLE / DOUBLE-THROW SWITCH OR CONTACT, THE NORMALLYCLOSED PATH, THROUGH THE SWITCH, WILL ALLOW
CURRENT TO FLOW, UNTIL THE SWITCH / CONTACT ‘OPERATOR’, CAUSES
THE SWITCH OR CONTACT TO CHANGE POSITION.
( THE ‘OPERATOR’ OF THE SWITCH WILL FORCE THE NORMALLY-CLOSED
CONTACT TO ‘OPEN’ & FORCE THE ‘POLE’ TO CONNECT TO THE NORMALLY-OPEN
CONTACT CAUSING IT TO ‘CLOSE’. )
A 3-WAY SWITCH, LIKE THE ONES IN MOST RESIDENCES, ARE
SINGLE-POLE / DOUBLE-THROW SWITCHES.
A DEVICE CAN CONTAIN & OPERATE MORE THAN 1 SWITCH, AT THE SAME TIME.
A DEVICE CAN CONTAIN 1 SWITCH & WILL BE REFERRED TO AS SHOWN IN THE
ABOVE SYMBOLS.
A DEVICE CAN ALSO CONTAIN MORE THAN 1 SWITCH OR CONTACT & BE REFRRED
TO AS THE FOLLOWING:
3) DOUBLE-POLE / SINGLE-THROW: 2 ‘INPUTS’ & 2 ‘OUTPUTS’
EACH ‘POLE’ HAS ONLY 1 OUTPUT
THE ‘DOTTED’
LINE
INDICATES
THAT THE
SWITCHES
OPERATE
AT THE
SAME TIME,
BY THE SAME
OPERATOR
THIS ARRANGEMENT IS
SIMPLY 2 SINGLE-POLE /
SINGLE-THROW
SWITCHES ‘TIED’
TOGETHER SO THAT
THE ‘OPERATOR’ CAN
OPERATE BOTH
SWITCHES AT THE SAME
TIME
OR:
ANY COMBINATION
OF NORMALLY-OPEN
OR NORMALLYCLOSED SWITCHES
CAN BE USED
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 15 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT OPERATION:
THE ABOVE SYMBOL, WITH THE 2 NORMALLY-OPEN SWITCHES, IS HOW A
RESIDENTIAL 4-WAY SWITCH IS ARRANGED.
4) DOUBLE-POLE / DOUBLE-THROW: 2 ‘INPUTS’ & 4 POSSIBLE ‘OUTPUTS’
OR: 4 POSSIBLE ‘INPUTS’ & 2 ‘OUTPUTS’
AS YOU SHOULD BE ABLE TO SEE, THE ABOVE SYMBOLS ARE JUST ‘SINGLE-POLE /
DOUBLE-THROW’ SWITCHES THAT ARE CONNECTED TOGETHER & OPERATE
AT THE SAME TIME, BY THE SAME ‘OPERATOR’.
SOME DEVICES, USED IN HAVCR, MAY USE AS MANY AS 3, SINGLE-POLE / DOUBLETHROW SWITCHES CONNECTED TOGETHER.
( COULD BE CALLED A : TRIPLE-POLE / DOUBLE-THROW DEVICE )
IN ELECTRICAL SYTEMS, AS MANY SWITCHES CAN BE ‘TIED’ TOGETHER WITH
THE SAME OPERATOR, AS ARE NEEDED FOR A PARTICULAR CIRCUIT.
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 16 OF
CONTROLLING DEVICES CONTINUED:
SWITCH & CONTACT OPERATION:
THOUGH THE ACTUAL SWITCHES & CONTACTS CAN BE DRAWN THE SAME, & CAN
BE SHOWN AS THE SAME SYMBOL ( BY SOME MANUFACTURERS ),
THE ‘OPERATOR’ MECHANISM IS QUITE DIFFERENT.
AS STATED BEFORE, MOST SWITCHES ARE OPERATED BY SOME ‘MECHANICAL’
MEANS, WHILE CONTACTS ARE OPERATED BY ‘ELECTRICAL’ MEANS.
( THOUGH THE ACTUAL MOVEMENT OF BOTH SWITCHES & CONTACTS ARE
MECHANICAL, WHAT CAUSES THE MECHANICAL MOVEMENT OF THE
SWITCH OR CONTACT CAN BE EITHER MECHANICAL OR ELECTRICAL ).
LET’S SEE WHAT MAKES EACH TYPE OF SWITCH OR CONTACT KNOW ‘WHEN TO
CHANGE’ ( MOVE ).
SWITCH OPERATION: SWITCH ‘OPERATORS’:
1) PRESSURE: A SWITCH MAY BE ‘OPERATED’ BY A CHANGE IN PRESSURE.
THIS PRESSURE CAN BE REFRIGERANT PRESSURE, WATER ( LIQUID ) PRESSURE,
GAS ( VAPOR ) PRESSURE, OR EVEN AIR ( ALSO A GAS OR VAPOR ) PRESSURE.
THERE ARE 2 TYPES OF PRESSURE SWITCHES:
A) HIGH-PRESSURE
WE CAN OPEN A SWITCH BECAUSE THE PRESSURE RISES TOO HIGH OR WE CAN
CLOSE A SWITCH IF THE PRESSURE RISES TO HIGH.
B) LOW-PRESSURE
WE CAN OPEN A SWITCH IF THE PRESSURE DROPS TOO LOW, OR WE CAN
CLOSE A SWITCH IF THE PRESSURE DROPS TOO LOW.
SYMBOL FOR
PRESSURE
A NORMALLY-OPEN SWITCH
THIS SWITCH, WILL ‘CLOSE’
ON AN INCREASE IN PRESSURE
NOTICE:
THE SWITCH
ITSELF IS DRAWN
THE SAME,
BUT THE
OPERATOR
( ATTACHED TO
THE SWITCH )
WILL CHANGE,
A NORMALLY-CLOSED SWITCH
DEPENDING ON
THIS SWITCH WILL ‘OPEN’ ON
WHAT ‘OPERATES’
AN INCREASE IN PRESSURE
THE SWITCH
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 17 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
THE PRESSURE SWITCH WILL BE ATTACHED TO THE SYSTEM THAT IS BEING
MEASURED BY A SMALL TUBE THAT MUST SENSE THE SYSTEM PRESSURE.
REFRIGERANT LINE
PS
AIR DUCT
PRESSURE SWITCH ( PS )
CONNECTED TO REFRIGERANT LINE OR
AIR DUCT
A
SWITCH
‘DIAPHRAM’
SPRING
B
A PRESSURE SWITCH WILL HAVE SOME KIND OF ‘DIAPHRAM’ WHICH, WILL
‘FLEX’ WHEN PRESSURE IS APPLIED INSIDE THE SWITCH BODY.
A SPRING, CONNECTED TO THE DIAPHRAM & THE SWITCH BODY, WILL
PROVIDE A CERTAIN AMOUNT OF ‘TENSION’ ON THE DIAPHRAM.
THE ‘TENSION’ ON THE SPRING IS WHAT IS USED TO DETERMINE AT WHAT PRESSURE
THE SWITCH WILL RESPOND AT. THE SPRING CAN BE FIXED OR ADJUSTABLE.
THE GREATER THE SPRING TENSION, THE GREATER THE PRESSURE HAS TO BE TO
CAUSE THE DIAPHRAM TO ‘FLEX’ & THE SWITCH TO MOVE.
DRAWING ‘A’, ON LEFT SIDE, SHOWS THE SWITCH WITH NO PRESSURE APPLIED.
DRAWING ‘B’, ON RIGHT SIDE, SHOWS THE DIAPHRAM ‘FLEX’, CAUSING THE SWITCH
TO CHANGE POSITION ( FROM OPEN TO CLOSED ) WHEN PRESSURE ( BLACK DOTS )
IS APPLIED. THE SWITCH CAN BE A N/O OR A N/C CONTACT OR BOTH.
ACR-123
HVACR ELECTRICAL COMPONENTS
PG 18 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
2) TEMPERATURE: A SWITCH MAY BE ‘OPERATED’ BY A CHANGE IN
TEMPERATURE
THE TEMPERATURE CAN BE GENERATED BY ANYTHING: LIQUIDS, AIR, METAL,
ETC. ALL WE HAVE TO BE ABLE TO DO IS MEASURE A TEMPERATURE.
THERE ARE 2 TYPES OF TEMPERATURE SWITCHES:
A) HIGH TEMPERATURE
WE CAN OPEN OR CLOSE A SWITCH WHEN A TEMPERATURE GETS TOO HIGH,
OR INCREASES ABOVE A PARTICULAR TEMPERATURE.
B) LOW TEMPERATURE
WE CAN OPEN OR CLOSE A SWITCH WHEN A TEMPERATURE GETS TOO LOW,
OR DECREASES BELOW A PARTICULAR TEMPERATURE.
SYMBOL FOR
TEMPERATURE
A NORMALLY-OPEN SWITCH
THIS SWITCH WILL ‘CLOSE’ ON
AN INCREASE IN
TEMPERATURE
AGAIN, NOTICE
THE SWITCH
ITSELF IS
DRAWN THE
SAME
ONLY THE TYPE
OF OPERATOR
( SYMBOL )
CHANGES
A NORMALLY-CLOSED
SWITCH
THE SWITCH WILL ‘OPEN’ ON
AN INCREASE IN
TEMPERATURE
THERE ARE 2 BASIC METHODS THAT ARE USED TO MEASURE THE TEMPERATURE OF
A SUBSTANCE, AND CAUSE THE MOVEMENT OF A SWITCH.
A) BI-METAL TEMPERATURE SWITCH: ( THE MOST COMMON KIND )
THE BI-METAL TYPE OF TEMPERATURE SENSOR CONSISTS OF 2 DISSIMILAR
( DIFFERENT ) TYPES OF METAL ‘GLUED’ TOGETHER.
METALS WILL EXPAND WHEN HEATED & CONTRACT WHEN COOLED.
DIFFERENT METALS WILL EXPAND & CONTRACT AT DIFFERENT RATES & AT
DIFFERENT TEMPERATURES.
WHEN 2 DISSIMILAR METALS ARE PLACED TOGETHER & ARE HEATED OR COOLED,
THEY WILL TRY TO EXPAND & CONTRACT AT DIFFERENT RATES, BUT SINCE THEY
ARE ‘GLUED’ TOGETHER, THEY WILL RESPOND TO A CHANGE IN TEMPERATURE BY
A ‘SNAP-ACTION’ MOVEMENT.
HVACR ELECTRICAL COMPONENTS
PG 19 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
SAME
SWITCH
ACR-123
DISSIMILAR
METALS
HEAT SOURCE
WHEN THE 2 DISSIMILAR METALS ARE HEATED, AT SOME TEMPERATURE,
THE REACTION OF THE 2 METALS WILL CAUSE A ‘SNAP-ACTION’
( VERY QUICK MOVEMENT ) ‘FLEXING’ OF THE METALS.
IF THE POLE OF A SWITCH IS ATTACHED TO THE METALS, THE ‘SNAP-ACTION’
MOVEMENT OF THE METALS WILL CAUSE MOVEMENT OF THE SWITCH.
THE SWITCH CAN BE MADE TO ‘OPEN’ WHEN THE TEMPERATURE IS REACHED
OR ‘CLOSE’ WHEN THE TEMPERATURE IS REACHED ( AS SHOWN ABOVE ).
THE TYPES & THE AMOUNTS OF EACH METAL CAN BE ALTERED TO CAUSE THE
METALS TO ‘RESPOND’ ( SNAP-ACTION ) AT ANY SPECIFIC TEMPERATURE.
EG: A 140* ‘F’ TEMPERATURE SWITCH MEANS THAT THE METALS, THAT MAKE UP
THE SENSOR PORTION OF THE SWITCH WILL RESPOND & CAUSE A SNAP-ACTION OF
THE SWITCH WHEN THE TEMPERATURE JUST EXCEEDS 140*’F’.
IMPORTANT: THE METALS HAVE TO BE AT A CERTAIN TEMPERATURE BEFORE
THEY WILL ‘RESPOND’, BUT IF THE HEAT SOURCE IS REMOVED, THE METALS WILL
TAKE A CERTAIN AMOUNT OF TIME, TO COOL DOWN, BEFORE THEY WILL RETURN
TO THEIR ORIGINAL POSITION.
THIS IS A ‘TIME-DELAY’ EFFECT.
THE TEMPERATURE THAT WILL ALLOW THE SWITCH TO RETURN TO ITS ‘NORMAL’
POSITION WILL BE LOWER THAN THE TEMPERATURE AT WHICH THEY ‘SNAPPED’.
EG: THE SWITCH, AS PICTURED ABOVE, WILL ‘SNAP’ & CAUSE THE SWITCH TO
CLOSE AT, SAY, 140* ‘F’, BUT IT WILL NOT RETURN TO ITS ORIGINAL POSITION
( FLAT ), UNTIL THE METALS COOL DOWN TO, MAYBE, 100* ‘F’.
HVACR ELECTRICAL COMPONENTS
PG 20 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
2ND METHOD OF SENSING TEMPERATURE & MAKING A SWITCH MOVE.
B) REMOTE-BULB TEMPERATURE SWITCH:
THE REMOTE-BULB TYPE OF TEMPERATURE SWITCH IS ACTUALLY A PRESSURE
SWITCH, JUST LIKE THE ONE DESCRIBED ABOVE.
THE ONLY DIFFERENCE IS THAT THE SMALL TUBE THAT EXTENDS FROM THE
SWITCH BODY IS CONNECTED TO A BULB THAT IS FILLED WITH EITHER A LIQUID
OR A GAS. THE LIQUID OR GAS WILL EXPAND WHEN HEATED, CAUSING AN
INCREASE IN PRESSURE IN THE TUBE, OR IT WILL CONTRACT WHEN COOLED &
REDUCE THE PRESSURE THAT IT ASSERTS IN THE TUBE.
THIS ‘BULB’ IS, PHYSICALLY, ATTACHED TO WHATEVER WE NEED TO TAKE THE
TEMPERATURE OF.
THE ‘BULB’ FEELS THE TEMPERATURE OF THE SUBSTANCE THAT IT IS ATTACHED
TO, CREATING A PRESSURE WITHIN THE BULB, THAT IS TRANSMITTED TO THE
SWITCH BODY, BY THE SMALL TUBE.
THE PRESSURE, CREATED BY THE LIQUID OR VAPOR WITHIN THE BULB, IS
DIRECTLY RELATED TO THE TEMPERATURE THAT THE BULB SENSES.
TEMPERATURE INCREASES - PRESSURE INCREASES
TEMPERATURE DECREASES - PRESSURE DECREASES
THIS TYPE OF TEMPERATURE SWITCH CAN BE EITHER FIXED OR
ADJUSTABLE.
IF ‘FIXED’, THE SPRING CONNECTED TO THE DIAPHRAM IS SET AT A CERTAIN
PRESSURE, MEANING THAT IT WILL TAKE A CERTAIN TEMPERATURE TO CREATE
THE PRESSURE NEEDED TO ‘FLEX’ THE DIAPHRAM & MOVE THE SWITCH.
IF ‘ADJUSTABLE’, THE ‘ADJUSTMENT’ IS THE TENSION ON THE SPRING WHICH WILL
CHANGE THE PRESSURE THAT THE DIAPHRAM NEEDS TO CAUSE IT TO ‘FLEX’.
INCREASING THE TENSION ON THE SPRING MEANS THAT THE ‘BULB’ WILL HAVE TO
SENSE MORE HEAT & CREATE MORE PRESSURE TO SEND TO THE DIAPHRAM TO
CAUSE IT TO ‘FLEX’ & CHANGE THE POSITION OF THE SWITCH.
INCREASING SPRING TENSION = INCREASING THE TEMPERATURE AT WHICH THE
SWITCH WILL OPERATE ( CHANGE POSITION ).
DECREASING SPRING TENSION = DECREASING THE TEMPERATURE AT WHICH THE
SWITCH WILL OPERATE ( CHANGE POSITION ).
THE SWITCH THAT IS ATTACHED TO THE DIAPHRAM CAN BE A NORMALLY-OPEN
SWITCH, A NORMALLY-CLOSED SWITCH, OR A SINGLE-POLE / DOUBLE THROW TYPE
OF SWITCH.
N/O – CLOSES ON TEMP. RISE
N/C – OPENS ON TEMP. RISE
HVACR ELECTRICAL COMPONENTS
PG 21 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
A REMOTE-BULB TEMPERATURE SWITCH:
DIAPHRAM
‘TUBE’
CALLED A
CAPILLARY TUBE
SENSING
‘BULB’
REFRIGERANT LINE
THE SENSING ‘BULB’ SENSES THE TEMPERATURE OF THE REFRIGERANT LINE,
CAUSING A CHANGE IN THE PRESSURE INSIDE THE ‘BULB’.
THIS PRESSURE IS SENT TO THE SWITCH BODY WHERE IT WILL ACT UPON THE
DIAPHRAM.
WHEN THE PRESSURE, SENT BY THE BULB, OVERCOMES THE TENSION OF THE
SPRING, THE DIAPHRAM WILL ‘FLEX’ & THE SWITCH WILL CHANGE POSITION.
( IN THIS CASE, THE SWITCH WILL OPEN )
THIS IS A HIGH TEMPERATURE ‘LIMIT’ SWITCH WHICH WILL OPEN & SHUT POWER
OFF ( STOP CURRENT FLOW ) IF THE TEMPERATURE EXCEEDS THE ‘SET POINT’ OF
THE SWITCH.
SET-POINT: THE TEMPERATURE ( OR PRESSURE ) THAT A SWITCH IS ‘SET AT’
TO OPERATE.
THE SET-POINT MAY BE FIXED BY THE MANUFACTURER OR ADJUSTABLE, IN THE
FIELD, BY THE TECHNICIAN.
A TEMPERATURE SWITCH RATED AT 140* ‘F’ – THE SET-POINT IS 140 * ‘F’.
WHEN A PERSON ‘SETS’ HIS HEATING & COOLING SYSTEM THERMOSTAT AT A
CERTAIN TEMPERATURE, THAT TEMPERATURE IS THE SET-POINT OF THE SYSTEM,
AT THAT TIME, IF THE PERSON CHANGES THE TEMPERATURE, THEN THE SET-POINT
IS CHANGED.
IMPORTANT: A TEMPERATURE SWITCH IS ALSO CALLED A THERMOSTAT, AS IT
RESPONDS TO A CHANGE IN TEMPERATURE.
THE THERMOSTAT THAT CONTROLS A HEATING & COOLING SYSTEM IS SIMPLY ONE
OR MORE TEMPERATURE SWITCHES, DESIGNED TO OPERATE THE
COOLING SYSTEM IF THE TEMPERATURE INCREASES ABOVE THE ‘SETPOINT’,
OR OPERATE THE HEATING SYSTEM IF THE TEMPERATURE DECREASES BELOW
THE ‘SET-POINT’.
HVACR ELECTRICAL COMPONENTS
PG 22 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
3) FLOAT SWITCH: A SWITCH THAT IS OPERATED BY THE ‘LEVEL’ OF LIQUID
WITHIN A CONTAINER.
USUALLY, A FLOAT SWITCH CONSISTS OF A ‘BALL’, THAT FLOATS ON A LIQUID,
CONNECTED BY A ‘ROD’ TO A SWITCH.
THE SWITCH MAY BE A NORMALLY-CLOSED SWITCH, WHICH WILL OPEN & SHUT
OFF CURRENT FLOW, IF THE LIQUID LEVEL REACHES A CERTAIN POINT.
EG: SIMILAR TO THE FLOAT ‘VALVE’ IN A TOILET, THAT SHUTS OFF THE
WATER WHEN THE WATER LEVEL, IN THE TANK, IS HIGH ENOUGH.
OR, THE SWITCH COULD BE A NORMALLY-OPEN SWITCH WILL WILL CLOSE
& ALLOW CURRENT TO FLOW, IF THE WATER LEVEL REACHES A CERTAIN POINT.
EG: A SUMP PUMP, IN WHICH THE SWITCH WILL CLOSE & TURN ON THE PUMP
MOTOR WHEN THE WATER LEVEL, IN THE SUMP, REACHES A CERTAIN POINT.
FLOAT SWITCH SYMBOL:
AGAIN, THE SWITCH
SYMBOL
IS THE SAME
NORMALLY-OPEN SWITCH
CLOSES ON RISE IN
LIQUID LEVEL
ONLY THE
OPERATOR HAS
CHANGED
NORMALLY-CLOSED SWITCH
OPENS ON RISE IN LIQUID
LEVEL
4) FLOW SWITCH: SOMETIMES CALLED A ‘SAIL SWITCH’:
A SWITCH THAT IS OPERATED BY THE MOVEMENT ( FLOW ) OF A FLUID ( AIR OR
LIQUID ). USUALLY, A FLOW SWITCH CONSISTS OF A ‘PADDLE’ OR ‘SAIL’ DEVICE
THAT IS LOCATED INSIDE THE PIPE OR DUCT THAT THE FLUID IS GOING TO MOVE
THROUGH. WHEN MOVING, THE FLUID PHYSICALLY CONTACTS THE ‘PADDLE’ OR
‘SAIL’ & CAUSE THE ‘PADDLE’ OR ‘SAIL’ TO MOVE. THE ‘PADDLE’ OR ‘SAIL’ IS
ATTACHED BY A ROD TO A SWITCH. WHEN THE FLUID MOVES, IT MAKES THE
‘PADDLE’ OR ‘SAIL’ MOVE, WHICH MOVES THE ROD, WHICH CHANGES THE
POSITION OF THE SWITCH.
FLOW SWITCH SYMBOL:
NORMALLYOPEN
CLOSES ON
FLOW
THE SWITCH IS THE
SAME
ONLY THE
OPERATOR
CHANGES
NORMALLYCLOSED
OPENS ON
FLOW
HVACR ELECTRICAL COMPONENTS
PG 23 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
MOST SWITCHES & CONTACTS, USED IN HVACR, ARE ‘SPRING LOADED’.
THIS MEANS THAT A SPRING ‘HOLDS’ THE POLE, IN ITS ‘NORMAL’ POSITION,
( EITHER CLOSED OR OPEN ).
THE OPERATOR ( PRESSURE, TEMPERATURE, ETC ) MUST OVERCOME THE
‘PRESSURE’ OF THE SPRING BEFORE THE SWITCH WILL CHANGE POSITION.
‘RETURN’ SPRINGS
THE SPRINGS ARE USED TO ‘RETURN’ THE SWITCH TO ITS ‘NORMAL’ POSITION,
WHEN THE ‘OPERATOR’ RELEASES ITS ‘FORCE’ UPON THE SWITCH.
IN AN ELECTRICAL DRAWING ( SCHEMATIC ), SWITCHES CAN BE SYMBOLIZED WITH
4 DIFFERENT SYMBOLS.
EVEN THOUGH THERE ARE ONLY 2 TYPES OF SWITCHES, NORMALLY-OPEN OR
NORMALLY-CLOSED, THESE 2 SWITCHES CAN BE ‘HELD’ IN 4 POSITIONS.
THESE 4 POSITIONS ARE SHOWN BELOW:
NORMALLY-OPEN
NOTICE: THE ‘POLE’ IS
LAYING UNDER THE ‘POST’
IN A RELAXED POSITION
NORMALLY-CLOSED
NOTICE: THE ‘POLE’ IS
LAYING ON TOP OF THE POST
AGAIN, IN A RELAXED POSITION
THIS WOULD BE THE NORMAL POSITION OF JUST THE SWITCH, IF IT WERE LAYING
IN YOUR HAND ( NOT ELECTRICALLY CONNECTED )
BUT:
IF THE SWITCH WAS A PRESSURE SWITCH OR A TEMPERATURE SWITCH
( THERMOSTAT ), OR EVEN A FLOW OR FLOAT SWITCH, THE SWITCH COULD
BE ‘HELD’ IN THE OPPOSITE ( NOT ‘NORMAL’ ) POSITION BY THE OPERATOR.
EG: IMAGINE, IF YOU WILL, A NORMALLY-OPEN TEMERATURE SWITCH THAT IS
INSTALLED OUTSIDE TO MEASURE THE OUTDOOR TEMPERATURE. THE PURPOSE OF
THE SWITCH IS TO OPEN WHEN THE OUTSIDE TEMPERATURE DROPS TO, SAY, 30*’F’.
THIS WOULD BE A LOW-TEMPERATURE SWITCH.
DURING ‘NORMAL’ TEMPERATURES, WHICH WOULD BE ABOVE 30* ‘F’, THE
TEMPERATURE WOULD ‘HOLD’ THE SWITCH CLOSED.
HVACR ELECTRICAL COMPONENTS
PG 24 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
HOW DO WE DRAW THIS SWITCH, SO THAT THE TECHNICIAN THAT READS OUR
DRAWING CAN UNDERSTAND THAT THE SWITCH IS A LOW-TEMPERATURE SWITCH,
& NOT A HIGH-TEMPERATURE SWITCH?
IF WE DRAW THE SWITCH IN ITS NORMAL POSITION IT WOULD BE:
THIS NORMALLY-OPEN SWITCH WILL ‘CLOSE’ ON AN INCREASE IN TEMPERATURE.
THE TECHNICIAN DOESN’T KNOW AT WHAT TEMPERATURE THIS SWITCH
OPERATES, & BY THE DRAWING, MAY THINK THAT THE SWITCH IS SUPPOSE TO
CLOSE ON AN INCREASE IN TEMPERATURE ( AKA: HIGH-TEMP. SWITCH ).
ALSO, REALIZE THAT THE ‘NORMAL’ OUTSIDE TEMPERATURE WILL BE ABOVE
30*’F’, SO THE SWITCH WOULD BE ‘HELD-CLOSED’ DURING MOST OF THE YEAR.
SO, THE SWITCH WOULD BE DRAWN IN ‘ITS NORMAL OPERATING POSITION’ WHICH
WOULD BE THE POSITION IT WOULD BE IN AT ANY TEMPERATURE ABOVE 30* ‘F’.
THIS SWITCH IS BEING
‘HELD’ IN A CLOSED
POSITION BY THE FORCE
OF THE OPERATOR.
( IN THIS CASE –
TEMPERATURE )
IMPORTANT:
NOTICE THAT THE ‘POLE’ IS
SITUATED ‘UNDER’ THE OUTPUT
POST.
( NOT ON TOP – LIKE A
NORMALLY-CLOSED SWITCH )
THIS SWITCH IS CALLED A:
NOMALLY-OPEN / HELD CLOSED
SWITCH
IT IS A NORMLLY-OPEN TYPE OF SWITCH THAT, IN ITS NORMAL POSITION WITHIN
THE SYSTEM, IS UNDER A TEMPERATURE GREATER THAN ITS SETPOINT &
THEREFORE THE SWITCH WOULD BE HELD-CLOSED BY THE FORCE OF
THE HIGHER TEMPERATURE.
THE ‘POLE’ OF THE SYMBOL, SHOWS THAT IT IS BEING ‘HELD’ AGAINST THE
BOTTOM OF THE OUTPUT ‘POST’.
IF THE FORCE, OF THE TEMPERATURE, WERE TO BE ELIMINATED, THE ‘POLE’
WOULD ‘DROP’ ( FALL ) TO ITS OPEN POSITION.
HVACR ELECTRICAL COMPONENTS
PG 25 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
IF A TECHNICIAN WERE TO BUY JUST THE SWITCH FROM A SUPPLIER, HE/SHE
WOULD GET A NORMALLY-OPEN SWITCH.
WHEN THE TECHNICIAN INSTALLED THE SWITCH INTO THE TEMPERATURE
OPERATED MECHANISM, THE TEMPERATURE, THAT THE MECHANISM ‘FEELS’,
WHICH WOULD BE THE ‘AMBIENT TEMPERATURE’ OF THE AREA SURROUNDING THE
MECHANISM, WOULD CAUSE THE SWITCH TO CLOSE, AFTER IT WAS INSTALLED.
( IF THE TEMP. WAS ABOVE 40*’F’, WHEN HE/SHE INSTALLED IT )
THE SAME SENARIO CAN OCCUR WITH A NORMALLY-CLOSED SWITCH, WHICH
MIGHT BE ‘HELD-OPEN’ BY THE PRESSURE OR TEMPERATURE THAT ‘NORMALLY’
OCCURS IN A PARTICULAR SYSTEM.
SUCH A SWITCH WOULD BE SHOWN AS FOLLOWS:
NORMALLY-CLOSED / HELD-OPEN
TEMPERATURE SWITCH
PRESSURE SWITCH
THE SWITCH IS ACTUALLY A NORMALLY-CLOSED SWITCH, BUT IN
THE NORMAL OPERATION OF A PARTICULAR SYSTEM, THIS MAY BE ITS
‘NORMAL’ POSITION ( WHEN THE SYSTEM IS OPERATING ).
THE TEMPERATURE OR PRESSURE WOULD, NORMALLY, BE HIGHER THAN THE
SET-POINT OF THE SWITCH, & WOULD ‘HOLD’ THE SWITCH OPEN.
THESE SWITCHES WILL ‘CLOSE’ ON A ‘DROP’ IN TEMPERATURE OR PRESSURE.
ONE REASON FOR SEEING THESE SYMBOLS ON AN ELECTRICAL DRAWING
WOULD BE TO TURN ON AN ALARM ( LIGHT OR BELL ) IF THE TEMPERATURE
OR THE PRESSURE DROPPED BELOW THE SET-POINT OF THE SWITCH.
AS BEFORE, IF A TECHNICIAN WENT TO A SUPPLY HOUSE TO GET A SWITCH
REPLACEMENT TO INSTALL IN THE MECHANISM, THE SWITCH THAT THE
TECHNICIAN WOULD GET WOULD BE A NORMALLY-CLOSED SWITCH.
BUT AS SOON AS THE TECHNICIAN INSTALLED THE SWITCH IN THE MECHANSIM
& INSTALLED THE MECHANISM INTO THE SYSTEM, THE SYSTEMS ‘NORMAL’
TEMPERATURE OR PRESSURE WOULD CAUSE THE SWITCH TO BE ‘HELD-OPEN’.
HVACR ELECTRICAL COMPONENTS
PG 26 OF
CONTROLLING DEVICES CONTINUED:
SWITCH OPERATION:
NOTICE HOW THE ‘POLE’ IS ABOVE THE ‘OUTPUT POST’.
IF THE OPERATOR WAS REMOVED, THE ‘POLE’ WOULD DROP ( FALL )
BACK TO THE TOP OF THE POST, IN A NORMALLY-CLOSED POSITION.
SO, IN READING AN ELECTRICAL DIAGRAM ( SCHEMATIC ), IT IS IMPORTANT TO
ACCURATELY ‘READ’ THE POSITION OF THE POLE AS IT RELATES TO THE ‘OUTPUT
POST’ TO DETERMINE WHICH TYPE OF SWITCH A SYMBOL REFERS TO.
AN EXAMPLE OF SWITCHES CONTROLLING A LOAD.
SOURCE OF POWER
ON / OFF SWITCH
HIGH TEMP.
SWITCH
LOW PRESS.
SWITCH
HIGH PRESS.
SWITCH
COMPRESSOR MOTOR
REMEMBER: THE PURPOSE OF ELECTRICITY IS TO APPLY POWER TO A LOAD,
( WHICH WILL USE THAT POWER TO PERFORM SOME ‘ACTION’ ), & TO
‘CONTROL’ & PROTECT THE ‘LOAD’.
IN THE EXAMPLE ABOVE, A COMPRESSOR MOTOR IS THE LOAD THAT WE ARE
ATTEMPTING TO OPERATE.
BECAUSE THE LOAD NEEDS A PATH FOR POWER TO GET TO THE LOAD & A PATH
FOR POWER TO RETURN TO THE SOURCE, THERE MUST BE AT LEAST 2 CONDUCTOR
‘PATHS’. ONE ‘PATH’ IS CONNECTED DIRECTLY TO THE LOAD FROM THE SOURCE.
WE WILL CALL THIS PATH, THE RETURN PATH.
THE OTHER PATH IS THE ONE THAT WE WILL ‘CONTROL’ GETTING TO THE ‘LOAD’.
NOW, IN THE OPERATION OF THE COMPRESSOR MOTOR, THERE ARE SEVERAL
CONDITIONS THAT CAN CAUSE HARM TO THE COMPRESSOR MOTOR.
ITS OUTPUT TEMPERATURE CAN BE TOO HIGH – PROTECTED BY THE HIGH
TEMPERATURE SWITCH.
THE PRESSURES CREATED BY THE COMPRESSOR CAN CAUSE PROBLEMS WITH THE
MOTOR OPERATION - PROTECTED BY THE LOW PRESSURE SWITCH & THE HIGH
PRESSURE SWITCH.
NOW WE HAVE A COMPLETE ELECTRICAL CIRCUIT TO CONTROL & PROTECT THE
COMPRESSOR MOTOR.
HVACR ELECTRICAL COMPONENTS
PG 27 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
A CONTACT IS A TYPE OF SWITCH THAT IS OPERATED BY AN ELECTRICAL MEANS.
THE ‘ELECTRICAL MEANS’ IS A SOLENOID.
A SOLENOID IS AN INDUCTOR ( COIL OF WIRE ) WHOSE SOLE PURPOSE IS TO
CREATE AN ELECTROMAGNET ( WHEN CURRENT FLOWS THROUGH IT ) &, THROUGH
THE PRINCIPLE OF THE ‘LAW OF CHARGES’, ATTRACT A PIECE OF METAL.
WE CAN ATTACH SWITCHES TO THE ‘PIECE OF METAL’, THAT WILL CHANGE
POSITIONS WHEN THE ‘METAL’ IS MOVED.
SPRING
SPRING
‘STRETCHED’
SWITCH
SOURCE
OF
POWER
INDUCTOR
‘SOLENOID’
SOURCE
WHEN THE SWITCH IS CLOSED, THE INDUCTOR
BECOMES AN ELECTROMAGNET, WHICH ATTRACTS
THE METAL OF THE ‘SWITCH POLE’, CLOSING THE
‘CONTACT’
WHEN POWER IS REMOVED FROM THE ‘SOLENOID’, THE
SPRING WILL PULL THE SWITCH ‘POLE’ OPEN AGAIN.
THERE ARE 2 PARTS TO THE OPERATION OF A ‘CONTACT’.
1) THE SOLENOID ( COIL ) - THE SOLENOID IS A ‘LOAD’ TO THE ELECTRICAL
CIRCUIT FROM WHICH IT GETS ITS POWER ( VOLTAGE & CURRENT ).
WE WILL DICUSS ‘SOLENOIDS’, FURTHER, IN THE ‘LOADS’ SECTION OF THE COURSE.
2) THE ‘CONTACTS’ - JUST AS WITH ‘SWITCHES’, IN THE PREVIOUS DISCUSSION,
A ‘CONTACT’ CAN BE A NORMALLY-OPEN OR A
NORMALLY-CLOSED SWITCH.
IT CAN BE SINGLE-POLE, SINGLE-THROW, OR DOUBLE-POLE – SINGLE-THROW,
OR DOUBLE-POLE – DOUBLE-THROW TYPE OF SWITCH.
AND JUST LIKE SWITCHES, THERE CAN BE AS MANY ‘CONTACTS’ THAT CAN BE
CHANGED BY THE ACTION OF THE SOLENOID AS THERE IS A NEED FOR, IN
THE ELECTRICAL CIRCUIT.
HVACR ELECTRICAL COMPONENTS
PG 28 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
VERY IMPORTANT: THERE ARE 3 DEVICES THAT USE SOLENOIDS & ‘CONTACTS’
AS THEIR MEANS OF OPERATION.
1) RELAY:
2) CONTACTOR:
3) MAGNETIC ‘STARTER’:
EACH OF THESE DEVICES USE AN ELECTROMAGNET AS A ‘LOAD’ TO CAUSE THE
MOVEMENT OF THE CONTACT OR CONTACTS ( CONTROL ) .
ALL 3 OF THESE DEVICES OPERATE IN EXACTLY THE SAME WAY ( THOUGH THE
METHOD OF MOVING THE ‘POLES’ DIFFER AS WELL AS THE TYPES & NUMBERS OF
SWITCHES DIFFER ).THE ‘PRINCIPLE OF OPERATION’ IS THE SAME.
THERE ARE 2 ‘RATINGS’ THAT MUST BE CONSIDERED WHEN APPLYING ANY OF
THE 3 DEVICES FROM ABOVE.
1) CONTACT ( SWITCH ) CURRENT RATING: THE SWITCH PORTION OF THE
DEVICE CAN ONLY ‘SAFELY’ HANDLE A CERTAIN AMOUNT OF CURRENT FLOW, &
THE AMOUNT OF ‘HEAT’ PRODUCED BY THE CURRENT FLOW.
THE ABILITY OF A ‘CONTACT’ OR SWITCH TO HANDLE THE HEAT IS DUE TO THE
SIZE OF THE ‘POLE’ & ‘POSTS’, TYPE OF METAL USED, & ITS SHAPE, AMOUNG OTHER
THINGS.
2) THE VOLTAGE RATING OF THE SOLENOID ( COIL ): THE SOLENOID
MUST HAVE THE PROPER VOLTAGE APPLIED TO IT, SO THAT IT CAN PRODUCE THE
CORRECT AMOUNT OF CURRENT FLOW, WHICH IS NECESSARY TO PRODUCE THE
NECESSARY AMOUNT OF ATTRACTION TO ‘PULL IN’ THE CONTACT.
REMEMBER THE PRINCIPLES OF INDUCTION: THE NUMBER OF TURNS OF
WIRE & THE AMOUNT OF CURRENT FLOW, DICTATES THE STRENGTH OF THE
ELECTROMAGNET. ( THE ABILITY OF THE ‘COIL’ TO MOVE THE ‘POLE’ )
ALL ‘LOADS’ ARE RATED BY THE VOLTAGE THAT THEY NEED,
APPLIED TO THEM, TO OPERATE PROPERLY.
THE DIFFERENCES BETWEEN A RELAY, A CONTACTOR,
& A MAGNETIC ‘STARTER’.
1) RELAY: A RELAY IS GENERALLY, RATED AT LESS THAN 20 AMPERES OF
CURRENT THAT CAN FLOW THROUGH ITS CONTACTS ( SWITCHES ).
DIFFERENT RELAYS WILL BE RATED AT DIFFERENT CURRENTS.
THE CONTACTS ( SWITCHES ) OF A RELAY CAN BE NORMALLY-OPEN OR
NORMALLY-CLOSED & CAN CONTAIN SEVERAL DIFFERENT TYPES OF CONTACTS
( SWITCHES ).
HVACR ELECTRICAL COMPONENTS
PG 29 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
2) CONTACTOR: A CONTACTOR IS, GENERALLY, RATED AT, APPROXIMATELY,
30 TO 50 AMPERES OF CURRENT FLOW THAT ITS CONTACTS CAN SAFELY
HANDLE.
CONTACTORS, USUALLY, HAVE ONLY NORMALLY-OPEN CONTACTS & ARE USED TO
SUPPLY POWER TO THE ‘MAJOR’ LOADS, IE: COMPRESSOR MOTORS.
3) MAGNETIC STARTERS: A MAGNETIC STARTER IS, GENERALLY, RATED AT
MORE THAN 50 AMPERES, THAT THE CONTACTS CAN HANDLE.
THE MAIN DIFFERENCE BETWEEN A CONTACTOR & A MAGNETIC STARTER IS THAT
A MAGNETIC STARTER ALSO INCLUDES ITS OWN OVERLOADS FOR THE DEVICE
CONTROLLED BY THE MAGNETIC STARTER.
A MAGNETIC STARTER WILL, USUALLY, HAVE NORMALLY-OPEN CONTACTS, BUT
CAN HAVE ‘AUXILLARY CONTACTS’ ATTACHED TO IT THAT COULD BE
NORMALLY-OPEN OR NORMALLY-CLOSED.
THE COILS ( INDUCTORS ) OF A RELAY, CONTACTOR, OR MAGNETIC STARTER CAN
BE RATED AT 24 VAC, 120 VAC, 240 VAC, 277 VAC, OR 480 VAC.
THERE ARE CERTAIN RELAYS THAT ARE USED WITH DIRECT CURRENT ( DC )
CIRCUITS, SO THE COIL VOLTAGE WILL BE 20 – 24 VDC.
WHEN REPLACING A RELAY, CONTACTOR, OR MAGNETIC STARTER, IT IS
IMPERATIVE THAT THE REPLACEMENT DEVICE HAVE THE SAME COIL
VOLTAGE RATING & THE SAME ( OR GREATER ) CONTACT CURRENT RATING
AS THE ORIGINAL DEVICE.
RELAY CONTACTS WILL, GENERALLY, BREAK ONLY ON ONE ‘LEG’ OF THE POWER
SOURCE.
CONTACTOR CONTACTS WILL, NORMALLY, BREAK EACH ‘LEG’ OF THE POWER
SOURCE. HOWEVER, IN HVACR, THERE ARE REASONS THAT SOME CONTACTOR
CONTACTS WILL ONLY BREAK ONE ‘LEG’ OF THE POWER SOURCE.
MAGNETIC STARTERS WILL, GENERALLY, BREAK ALL ‘LEGS’ OF THE POWER
SOURCE.
NOTICE:
COIL ( INDUCTOR OR WINDING )
THE COIL & ITS ASSOCIATED
NOTE:
SYMBOLS:
CONTACTS WILL BE
THE ‘COIL’ WILL BE
‘LABELED’ ( CC )
CC
POWERED BY SINGLE-PHASE
THE SAME ON AN
POWER, SO THERE WILL ONLY BE 2
ELECTRICAL DRAWING.
WIRES CONNECTED TO IT.
CC
NORMALLY-OPEN CONTACT
CC
NORMALLY-CLOSED CONTACT
HVACR ELECTRICAL COMPONENTS
PG 30 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
A ‘RELAY’
CONTACT
CONTROLLING
THE POWER TO A
SINGLE-PHASE
BLOWER MOTOR
A THERMOSTAT
CONTROLLING
POWER TO THE
RELAY ‘COIL’
SOURCE
MOTOR SYMBOL
BR
SOURCE
BR
THE ‘COIL’ WILL NOT
BE LOCATED,
AT THE SAME PLACE
AS THE CONTACT, ON
AN ELECTRICAL
DRAWING.
WHEN THE ‘THERMOSTAT SWITCH’ CLOSES ( ON A RISE IN TEMP. )
THE ‘BR’ COIL WILL RECEIVE POWER, CAUSING CURRENT TO FLOW
THROUGH THE ‘INDUCTOR’, CREATING AN ELECTROMAGNET, WHICH
CAUSES THE CONTACT, IN THE BLOWER MOTOR CIRCUIT, TO CLOSE,
SENDING THE POWER TO THE BLOWER MOTOR.
VERY IMPORTANT:
THE ‘COIL’ VOLTAGE MAY OR MAY NOT BE THE SAME AS THE VOLTAGE OF THE
CIRCUIT THAT THE ‘CONTACT’ IS IN.
IN OTHER WORDS, THE BLOWER MOTOR THAT THE ‘CONTACT’ CONTROLS MAY BE
240 VAC, BUT THE VOLTAGE OF THE ‘COIL’ MAY BE ONLY 24 VAC, OR 120 VAC.
( BUT, THE COIL VOLTAGE COULD BE 240 VAC. )
UNDERSTAND THAT EVEN THOUGH THE CONTACT IS OPERATED BY THE ACTION OF
THE COIL ( ELECTROMAGNET ), & THEY ARE CONTAINED WITHIN ONE SINGLE
DEVICE, THE ‘COIL’ & THE ‘CONTACTS’ ARE
TWO, COMPLETELY DIFFERENT COMPONENTS,
IN AN ELECTRICAL CIRCUIT. ONE BEING A ‘LOAD’ & ONE BEING A ‘SWITCH’, OR
SWITCHES.
HVACR ELECTRICAL COMPONENTS
PG 31 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
A CONTACTOR CONTROLLING POWER TO A SINGLE-PHASE, 240 VAC MOTOR,
WITH A 24 VAC ‘COIL’.
ONE OR TWO CONTACTS CAN BE USED.
240 VAC SOURCE
CC
CC
24 VAC SOURCE
CC
NOTICE THAT, IN THIS CASE, THE CONTROLLING ( THERMOSTAT ) & PROTECTIVE
DEVICES ( HIGH PRESS. SWITCH ),ARE IN SERIES WITH THE CONTACTOR COIL.
WHATEVER CONTROLS THE ‘COIL’, CONTROLS THE MOTOR, SINCE THE ‘COIL’
IS WHAT CONTROLS THE CONTACTS THAT CONTROL THE MOTOR.
SINGLE-PHASE
CONTACTOR ( OR
MAGNETIC
STARTER ) COIL
CONTROLLING
THE POWER ( BY
THE CONTACTS )
TO A 3-PHASE
MOTOR
CC
3 PHASE
POWER
SOURCE
CC
CC
HVACR ELECTRICAL COMPONENTS
PG 32 OF
CONTROLLING DEVICES CONTINUED:
‘CONTACT’ OPERATION:
EACH ‘CONTACT’, IN A CONTACTOR OR MAGNETIC STARTER, IS A ‘POLE’ OF THE
SWITCH. SO, THERE IS A 1-POLE CONTACTOR, A 2-POLE CONTACTOR, OR A 3-POLE
CONTACTOR.
( THERE IS EVEN A 4-POLE CONTACTOR, USED FOR SPECIAL PURPOSES ).
EXPLANATION OF TIME-DELAY RELAY OPERATION:
SINCE, BY NOW, YOU SHOULD UNDERSTAND THAT A RELAY ( OR A CONTACTOR ) IS
MADE UP OF 2 INDIVIDUAL PARTS CONNECTED TOGETHER BY A MECHANICAL
LINKAGE. ( THE ELECTRICAL ‘COIL’ & THE ‘CONTACTS’ )
A TIME-DELAY RELAY OPERATES A LITTLE DIFFERENTLY.
THERE ARE 2 TYPES OF TIME-DELAY RELAYS USED IN HVACR:
1) MECHANICAL RELAY
2) ELECTRONIC RELAY
THE MECHANICAL TIME-DELAY:
THE RELAY OPERATES SIMILAR TO ANY OTHER TYPE OF RELAY, EXCEPT THAT THE
MECHANICAL TIME-DELAY RELAY DOES NOT USE A
‘COIL’ TO ENERGIZE ITS CONTACTS.
THE TIME-DELAY RELAY USES A ‘HEATER’, IN PLACE OF A COIL.
THE TIME-DELAY RELAY USES NORMALLY-OPEN, BI-METAL TEMPERATURE
SWITCHES AS ITS ‘CONTACTS’.
WHEN VOLTAGE IS APPLIED TO THE ‘HEATER’ ( & CURRENT FLOWS, OF COURSE ),
THE ‘HEATER’ PRODUCES HEAT, WHICH IS ‘FELT’ BY THE BI-METAL CONTACTS
( THERMOSTATS OR TEMPERATURE SWITCHES ).
REMEMBERING WHAT WE HAVE LEARNED ABOUT BI-METAL TEMPERATURE
SWITCHES, WE SHOULD REALIZE THAT AS THE SWITCHES ‘FEEL’ THE HEAT FROM
THE ‘HEATER’, AT SOME TEMPERATURE THEY WILL EXPAND & ‘SNAP’ CLOSED.
THE DIFFERENCE BETWEEN THE TIME THE POWER IS APPLIED TO THE ‘HEATER’ &
THE TIME THE CONTACTS CLOSE IS THE TIME-DELAY.
FOR A LONGER TIME-DELAY, WE JUST MAKE THE CONTACT TO CLOSE AT A HIGHER
TEMPERATURE, WHICH WILL TAKE LONGER TO ACHIEVE.
TO GET A SHORTER TIME-DELAY, WE JUST MAKE THE CONTACT TO CLOSE AT A
LOWER TEMPERATURE.
AS IN A ‘COIL’ OPERATED RELAY, THE ‘HEATER’ OF THE TIME-DELAY RELAY IS
ELECTRICALLY SEPARATE FROM THE CONTACTS.
THE ‘HEATER’ IS A LOAD TO THE SOURCE FROM WHERE IT GETS ITS POWER.
THE CONTACTS ARE JUST TEMPERATURE SWITCHES, IN LINE WITH THE LOAD
THAT THEY ARE DESIGNED TO CONTROL.
HVACR ELECTRICAL COMPONENTS
PG 33 OF
CONTROLLING DEVICES CONTINUED:
‘TIME-DELAY’ MECHANICAL RELAY OPERATION CONTINUED:
THE SYMBOL FOR A TIME-DELAY, MECHANICAL, RELAY IS:
TDR-1
THE ‘CONTACTS’
TDR
TDR-2
THERE MAY BE 1, 2, 3
OR 4 SETS OF
CONTACTS
THE ‘ARROW’
INDICATES A
TIME-DELAY
THE ‘HEATER’
IN MOST HVACR SYSTEMS, MECHANICAL TIME-DELAY RELAYS ARE USED FOR
2 PURPOSES:
1) BLOWER MOTOR TIME-DELAY: USED TO DELAY THE START OF THE
BLOWER MOTOR. THIS WILL BE A SINGLE NORMALLY OPEN CONTACT
OR A SINGLE-POLE / DOUBLE-THROW TYPE OF CONTACT.
2) AS A HEAT ‘SEQUENCER’: USED TO ‘STAGE’ ON VARIOUS HEAT ELEMENTS.
EACH ‘CONTACT’ OF THE ‘SEQUENCER’ WILL BE RATED FOR ENOUGH CURRENT
TO OPERATE ONE. – 5KW HEATING ELEMENT.
( HEATING ELEMENTS ARE RATED AT EITHER 2.5 OR 5 THOUSAND WATTS –KW )
MOST, BY FAR, ARE RATED AT 5KW ( 5,000 WATTS ).
MOST MODERN HEAT SEQUENCERS HAVE 1 OR 2 CONTACTS, WHICH CAN HANDLE
1 OR 2 HEAT ELEMENTS, ( 5KW OR 10KW OF ELECTRIC HEAT ).
SOME OLDER ‘SEQUENCERS’ CONTAINED AS MANY AS 4 SWITCHES FOR 4 ELEMENTS.
THE MODERN METHOD USED BY MANUFACTURERS TO PRODUCE 15 OR 20 KW
HEAT SEQUENCERS IS TO PARALLEL THE ‘HEATERS’ OF TWO SEQUENCERS
TOGETHER TO ACHIEVE THE NEEDED NUMBER OF ‘CONTACTS’.
15KW SEQUENCER
20 KW SEQUENCER
HVACR ELECTRICAL COMPONENTS
PG 34 OF
CONTROLLING DEVICES CONTINUED:
‘TIME-DELAY’ MECHANICAL RELAY OPERATION CONTINUED:
THE ‘HEATER’ OF THE MECHANICAL TIME-DELAY RELAY ( LIKE A ‘COIL’ OF A
ELECTROMAGNETIC RELAY ), CAN OPERATE ON DIFFERENT VOLTAGES, SUCH AS
24 VAC, 120 VAC, 0R 240 VAC.
THE ‘CONTACTS’ OF THE MECHANICAL TIME-DELAY RELAY ARE, USUALLY, RATED
AT 20+ AMPERES OF CURRENT FLOW.
( PER OHMS LAW – A 5KW HEATER AT 240 VAC DRAWS 20.8 AMPS )
ALRIGHT, LETS DISCUSS THE ‘CONTACT’ SYMBOL:
NOTICE THAT THE ‘LEGS’ OF THE SYMBOL FORM AN ARROW, POINTING UP, IN THE
DIRECTION OF THE SWITCH ‘POLE’.
‘ARROW’ POINTING UP
TOWARDS SWITCH ‘POLE’
THE UPWARDS POINTING ARROW INDICATES THAT THE ACTION OF THE
TIME-DELAY STARTS WHEN THE ‘HEATER’ IS ENERGIZED.
IN OTHER WORDS, WHEN THE ‘HEATER’ IS ENERGIZED, THE ‘CONTACT’ STARTS
TIMING ITSELF TO CLOSE.
( THE ‘HEATER’ HEATS THE BI-METAL & AFTER A TIME, THE BI-METAL WILL ‘SNAP’
& THE SWITCH WILL ‘CLOSE’ )
THIS IS CALLED A ‘DELAY-ON-MAKE’ TYPE OF TIME-DELAY ‘CONTACT’.
( THE TIME-DELAY STARTS UPON THE ELECTRICAL CIRCUIT BEING MADE TO THE
HEATER )
ALL MECHANICAL TIME-DELAY RELAYS WILL BE OF THE ‘DELAY-ON-MAKE’ TYPE:
ELECTRONIC TIME-DELAY RELAYS:
ELECTRONIC TIME-DELAY RELAYS ARE USED TO:
1) PROVIDE TIME DELAY FOR SMALL MOTORS
( BLOWER & CONDENSER FAN MOTORS ), EITHER DIRECTLY OR BY CONTROLLING
A RELAY ‘COIL’.
2) PROVIDE TIME DELAY FOR THE STARTING OF A LARGER MOTOR
( COMPRESSOR ), BY CONTROLLING THE CONTACTOR ‘COIL’.
THE CONTACTS OF THE ELECTRONIC TIME-DELAY RELAY CANNOT CARRY LARGE
CURRENTS. THEY ARE LIMITED TO THE SMALLER CURENTS DRAWN BY
RELAY & CONTACTOR COILS.
HVACR ELECTRICAL COMPONENTS
PG 35 OF
CONTROLLING DEVICES CONTINUED:
ELECTRONIC ‘TIME-DELAY’ RELAY OPERATION CONTINUED:
THERE ARE 2 WAYS THAT AN ELECTRONIC TIME-DELAY CONTACT CAN
OPERATE:
1) DELAY-ON-MAKE: SAME AS THE MECHANICAL TIME-DELAY.
THE CONTACT TIMING STARTS WHEN POWER IS APPLIED TO THE ELECTRONIC
DEVICE.
CONTACT SYMBOL
NOTICE THE ‘ARROW’ POINTS UP
THE ‘TIMING’ OF THE CONTACT STARTS AS SOON AS POWER IS APPLIED TO THE
ELECTRONIC TIMING DEVICE.
IN THE CASE OF THE NORMALLY-OPEN CONTACT SHOWN ABOVE, THE CONTACT
WILL ‘TIME CLOSED’ AFTER THE ELECTRONIC CONTROL IS ENERGIZED
( HAS POWER APPLIED TO IT ).
EXAMPLE OF A 3 TO 5 MINUTE TIME-DELAY: ( COMPRESSOR SHORT-CYCLE
PROTECTION )
WHEN POWER IS APPLIED TO THE ELECTRONIC CONTROL, THE CONTACT WILL
‘CLOSE’ AFTER 3 TO 5 MINUTES.
SO, THE COMPRESSOR, OPERATED BY THE TIMED CONTACT, WILL HAVE A 3 TO 5
MINUTE DELAY BEFORE IT WILL BE ENERGIZED, EVERY TIME THAT ITS CONTROL
CALLS FOR IT TO OPERATE.
2) DELAY-ON-BREAK: WITH THIS TYPE OF RELAY, THE CONTACT
DOESN’T START ITS ‘TIMING’ UNTIL AFTER POWER HAS BEEN REMOVED
FROM THE ELECTRONIC DEVICE.
CONTACT SYMBOL
NOTICE THE ‘ARROW’ POINTS DOWN
THE DELAY-ON-BREAK CONTACT IS A LITLE HARDER TO UNDERSTAND.
IN THE CONTACT ABOVE, THE CONTACT WILL STAY IN ITS ‘CLOSED’ POSITION
WHEN POWER IS APPLIED TO THE ELECTRONIC CONTROL. BUT, WHEN THE POWER
IS REMOVED FROM THE ELECTRONIC CONTROL, THE CONTACT WILL ‘SNAP’ OPEN,
& THEN ‘TIME ITSELF CLOSED’ AGAIN.
EXAMPLE OF A 3 TO 5 MINUTE TIME-DELAY : ( COMPRESSOR SHORT-CYCLE
PROTECTION )
WHEN POWER IS APPLIED TO THE COMPRESSOR, THE COMPRESSOR WILL OPERATE.
BUT, WHEN THE COMPRESSOR IS STOPPED BY ITS CONTROL, THE ‘TIMED CONTACT’
WILL OPEN & KEEP THE COMPRESSOR FROM COMING BACK ON BEFORE 3 TO 5
MINUTES HAVE ELAPSED. ONCE THE COMPRESSOR HAS BEEN OFF FOR THE 3 TO 5
MINUTES, THE ‘TIMED CONTACT’ WILL CLOSE AGAIN, ALLOWING THE
COMPRESSOR TO RESTART, IF CALLED FOR BY ITS CONTROL.
HVACR ELECTRICAL COMPONENTS
PG 36 OF
CONTROLLING DEVICES CONTINUED:
ELECTRONIC BOARD OPERATION:
ALL ELECTRONIC DEVICES ( BOARDS ) MUST HAVE POWER APPLIED TO
THEM FOR THEIR ELECTRONIC PARTS TO OPERATE.
THINK OF THIS POWER AS THE POWER TO A CONTROLLING ‘COIL’
( LIKE A RELAY, OR A CONTACTOR HAS , OR LIKE THE ‘HEATER’ OF A MECHANICAL
TIME-DELAY RELAY )
MOST ELECTRONIC DEVICES, USED IN HVACR, USE 24 VAC AS THE
‘OPERATING POWER’
THE MAIN ADVANTAGE THAT ELECTRONIC BOARDS HAVE IN HVACR CIRCUITS IS
THE ABILITY TO PROVIDE ‘TIMING’ FUNCTIONS.
ALMOST ALL ELECTRONIC CONTROL BOARDS USED IN HVACR PROVIDE
SOME KIND OF ‘TIMING’.
ELECTRONIC BOARDS ARE NOT SOME KIND OF ‘MAGICAL’ DEVICE:
THEIR OPERATION IS VERY SIMILAR TO RELAYS, CONTACTORS, ETC.
ELECTRONIC BOARDS MUST HAVE POWER SUPPLIED TO THEM TO OPERATE.
THIS CAN BE CONSIDERED THE SAME AS THE COIL OF A RELAY OR CONTACTOR,
OR THE HEATER OF A MECHANICAL TIME-DELAY RELAY.
THIS MEANS THAT 2 CONDUCTORS ( WIRES ) CONNECT TO EVERY BOARD TO SUPPLY
POWER FROM THE SOURCE & TO RETURN THE POWER BACK TO THE SOURCE.
THE REST OF THE ELECTRONIC BOARD IS NOTHING MORE THAN A SWITCH OR A
SERIES OF SWITCHES TO CONTROL SOME DEVICE OR DEVICES – OUTSIDE THE
BOARD ITSELF.
EVERY CONDUCTOR ( WIRE ) CONNECTED TO AN ELECTRONIC BOARD IS
EITHER AN ‘INPUT’ TO THE BOARD, OR AN ‘OUTPUT’ FROM THE BOARD.
SO, AN ELECTRONIC BOARD OPERATES JUST LIKE A RELAY OR CONTACTOR.
THERE ARE ‘INPUTS’, LIKE THE POWER SUPPLIED TO THE COIL ( OR BOARD ) WHICH
IS AN ‘INPUT’ TO THE DEVICE TO ALLOW IT TO OPERATE.
THERE ARE ‘INPUTS’ TO EACH SWITCH CONTAINED WITHIN THE RELAY OR
CONTACTOR ( OR ELECTRONIC BOARD ).
ABD THERE ARE ‘OUTPUTS’ FROM EACH SWITCH ( WHEN THE SWITCH IS CLOSED ),
TO PROVIDE THE POWER FOR SOME DEVICE, OUTSIDE THE RELAY, CONTACTOR, OR
ELECTRONIC BOARD, TO OPERATE.
SO, ELECTRONIC BOARDS, LIKE RELAYS & CONTACTORS, ARE BOTH A ‘LOAD’ ( TO
THE SOURCE ) & ‘SWITCHES’ ( CONTROLLING DEVICES ).
A TECHNICIAN TROUBLESHOOTS AN ELECTRONIC BOARD JUST LIKE HE/SHE WILL
TROUBLESHOOT A RELAY OR CONTACTOR.
ST
1 : SEE IF POWER IS APPLIED ( TO THE BOARD OR TO THE ‘COIL’ )
2ND: INSURE THAT EACH INPUT REQUIRED IS AVAILABLE
3RD: VERIFIY THE OUTPUT OF ‘THE SWITCH’ OR BOARD.
HVACR ELECTRICAL COMPONENTS
PG 37 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
THOUGH ALL THERMOSTATS ARE TEMPERATURE SWITCHES & ALL TEMPERATURE
SWITCHES ARE THERMOSTATS, IN THIS SECTION WE NEED TO UNDERSTAND HOW A
HEATING &/OR COOLING SYSTEM IS CONTROLLED.
THEY ARE CONTROLLED BY TEMPERATURE SWITCHES, CONTAINED WITHIN A
DEVICE, COMMONLY CALLED A ‘THERMOSTAT’.
THIS DEVICE IS USED TO CONTROL THE OPERATION OF THE ENTIRE HEATING OR
COOLING SYSTEM ( NOTE: A COOLING SYSTEM CAN BE A REFRIGERATOR OR A
FREEZER OR AN ICE MACHINE, ETC. ).
SINCE THE ENTIRE PURPOSE OF A HEATING OR COOLING SYSTEM IS TO:
CONTROL THE TEMPERATURE OF A ‘MEDIUM’ ( SUBSTANCE ).
TO ‘CONTROL THE TEMPERATURE’ OF A MEDIUM, MEANS THAT WE MUST MEASURE
THE TEMPERATURE OF THE MEDIUM & BY THE USE OF SWITCHES, CONTROL THAT
TEMPERATURE. ( THE ‘MEDIUM’ CAN BE AIR OR WATER )
THERE ARE 2 TYPES OF ‘THERMOSTATS’ USED IN HVACR:
1) LINE-VOLTAGE: THESE THERMOSTATS OPERATE ON THE SAME VOLTAGE
THAT THE HEATING OR COOLING UNIT OPERATES ON.
EG: REFRIGERATOR &/OR FREEZER – THE UNIT IS 120 VAC, SO THE THERMOSTAT
CONTROLS 120 VAC TO OPERATE THE COOLING SYSTEM.
ELECTRIC SPACE HEATER – THE THERMOSTAT OPERATES THE 120 VAC
GOING TO THE HEAT STRIPS.
240 VAC
CONTROLLING
THERMOSTAT
RATED AT 240 VAC
& 25 AMPERES
5KW ( 5000W )
WALL INSERT SPACE
HEATER
WITH A LINE-VOLTAGE THERMOSTAT, THE THERMOSTAT SWITCH IS,PHYSICALLY,
LOCATED IN THE SAME ELECTRICAL PATH AS THE LOAD ( HEATER, IN THIS CASE ).
THIS MEANS THAT THE SWITCH MUST BE ABLE TO HANDLE THE FULL CURRENT
DRAW OF THE LOAD THAT IT IS CONTROLLING.
IN THIS CASE: HEATER POWER ( 5000 W ) DIVIDED BY HEATER VOLTAGE ( 240 VAC ),
EQUALS 20.83 AMPS DRAWN BY HEATER & CONTROLLED BY THERMOSTAT.
HVACR ELECTRICAL COMPONENTS
PG 38 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
2) LOW-VOLTAGE: THESE THERMOSTAT OPERATE ON A LOWER-THAN-SUPPLY
VOLTAGE ( WHICH IS PRODUCED BY A TRANSFORMER ).
FOR THE PROTECTION OF PEOPLE OPERATING THE THERMOSTAT, IN RESIDENTIAL
& COMMERCIAL SPACE HEATING & COOLING SYSTEMS, THERE IS A LOW-VOLTAGE
CONTROL CIRCUIT, IN WHICH THE THERMOSTAT OPERATES.
THE LOWER-THAN-SUPPLY VOLTAGE, THAT THE ‘CONTROL SYSTEM’ OPERATES
WITH, IS PRODUCED BY A STEP-DOWN TRANSFORMER.
THIS TRANSFORMER PRODUCES A LOWER-THAN-SUPPLY ( OR SOURCE ) VOLTAGE
TO BE USED BY THE CONTROLLING SECTION OF THE ELECTRICAL CIRCUITRY.
THIS IS CALLED THE ‘CONTROL’ SECTION OF AN ELECTRICAL
SCHEMATIC DIAGRAM
(A SCHEMATIC DIAGRAM, FOR A SPACE HEATING & COOLING SYSTEM, CONSISTS OF
A ‘POWER’ SECTION & A ‘CONTROL’ SECTION )
IN THIS CASE, THE THERMOSTAT IS PART OF THE LOW-VOLTAGE CONTROL
SECTION OF THE ELECTRICAL CIRCUIT.
THE ‘CONTROL’ OR ‘LOW-VOLTAGE’ SECTION OF THE ELECTRICAL CIRCUIT IS
WHERE WE USE RELAYS & CONTACTORS TO CONTROL THE OPERATION OF THE
MAIN ‘LOADS’, WHICH ARE POWERED BY THE SUPPLY ( SOURCE ) VOLTAGE.
240 VAC
‘POWER
SECTION’
OF THE
ELECTRICAL
CIRCUIT
CONTROLS
SUPPLY
( SOURCE )
POWER TO
MAIN LOADS
HR
5KW ( 5000W )
HEATING ELEMENT
OF CENTRAL HEATING
UNIT
‘CONTROL’ CONTACT
FROM
‘HEAT SEQUENCER’
T1
TRANSFORMER
‘CONTROL’
SECTION OF
ELECTRICAL
CIRCUIT
TRANSFORMER
PRODUCES LOW
VOLTAGE
TH
24 VAC
HEATING THERMOSTAT ( TH )
HR
HEAT SEQUENCER ( HR )
RELAY ‘HEATER’
HVACR ELECTRICAL COMPONENTS
PG 39 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
WITH A LOW-VOLTAGE THERMOSTAT, THE THERMOSTAT SWITCH IS, PHYSICALLY,
LOCATED IN THE SAME ELECTRICAL PATH AS THE 24 VAC CONTROL RELAY ‘COIL’.
THIS MEANS THAT THE SWITCH NEED ONLY TO BE ABLE TO HANDLE THE CURRENT
THAT IS DRAWN BY THE ‘COIL’ OF THE CONTROL RELAY, WHICH IS USUALLY LESS
THAN 1 AMP.
SYSTEM CONTROLLING THERMOSTATS CAN BE OF THE:
1) MECHANICAL TYPE: ONE STYLE OF THESE THERMOSTATS USE A BI-METAL
TEMPERATURE SWITCH WITH A ‘BULB’ CONTAINING A ‘DROP’ OF MERCURY
( LIQUID METAL ). THE BI-METAL TEMPERATURE SWITCH CONSISTS OF A BI-METAL
STRIP WOUND INTO A COIL, WITH THE ‘BULB’, CONTAINING THE MERCURY
ATTACHED TO THE BI-METAL STRIP.
AS THE BI-METAL STRIP ‘FEELS’ THE TEMPERATURE, THE BI-METAL ‘COIL’, EITHER
WINDS TIGHTER OR LOOSENS, THUS MOVING THE ‘BULB’.
THE ‘BULB’ ( & THE MERCURY INSIDE ) CONSTITUTES THE SWITCH PORTION OF THE
THERMOSTAT.
WHEN THE TEMPERATURE IS COOLER THAN THE SET-POINT OF THE THERMOSTAT,
THE MERCURY FALLS TO ONE END OF THE ‘BULB’ COMPLETING THE ‘HEAT’
CONTROL ELECTRICAL CIRCUIT.
WHEN THE TEMPERATURE IS WARMER THAN THE SET-POINT OF THE THERMOSTAT,
THE MERCURY FALLS TO THE OTHER END OF THE ‘BULB’ & COMPLETES THE
‘COOLING’ CONTROL ELECTRICAL CIRCUIT.
‘HEATING’ CYCLE
ELECTRICAL
CONTROL
CONDUCTORS
COOLING CYCLE
ELECTRICAL
CONTROL
CONDUCTORS
‘DROP’ OF MERCURY( LIQUID METAL )
INSIDE GLASS ‘BULB’
BI-METAL TEMPERATURE
SENSOR
HEATING
CYCLE
COOLING
CYCLE
HVACR ELECTRICAL COMPONENTS
PG 40 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
MECHANICAL TYPE CONTINUED:
A SECOND TYPE OF MECHANICAL THERMOSTAT USES MAGNETS TO PRODUCE THE
SWITCH ACTION, INSTEAD OF A MERCURY FILLED BULB.
THIS TYPE USES THE SAME BI-METAL TEMPERATURE SENSOR, WOUND INTO A
‘COIL’. ITS ONLY THE SWITCH ACTION THAT IS DIFFERENT.
CONDUCTORS
FOR ‘HEATING’
CYCLE CONTROL
CONDUCTORS FOR
‘COOLING’ CYCLE
CONTROL
PERMANENT MAGNETS
WITH METAL PLATES
ATTACHED
AS THE BI-METAL SENSOR, SENSES THE TEMPERATURE, THE ‘MIDDLE’ MAGNET,
WITH BOTH METAL PLATES, WILL MOVE TOWARDS EITHER OF THE 2 ‘CONTROL’
MAGNETS.
AS THE ‘MIDDLE’ MAGNET NEARS THE ‘CONTROL’ MAGNET, THE ACTION OF THE
MAGNETS ‘POLE’ WILL ATTRACT THE OTHER MAGNETS ‘POLE’
( LAW OF CHARGES ) & THE SWITCH WILL ‘SNAP’ CLOSED.
VERY IMPORTANT POINT:
ALL SWITCHES MUST INCORPORATE A ‘SNAP ACTION’, IN SOME MANNER.
THIS IS BECAUSE THE VOLTAGE CAN ( & WILL ) ‘ARC’ ACROSS AN ‘AIR SPACE’.
THE GREATER THE VOLTAGE, THE WIDER THE ‘AIR SPACE’ THAT THE VOLTAGE
CAN ‘ARC’ ACROSS.
AS THE SIDES OF THE SWITCH OR CONTACT COME CLOSE TOGETHER, IF THE
ACTION IS NOT QUICK ENOUGH, THE VOLTAGE WILL CAUSE AN ‘ARC’, WHICH
CAN CAUSE PITTING OF THE CONTACT OR SWITCH SURFACE.
THIS CAN CREATE A BAD CONNECTION, WHICH CAUSES A RESISTANCE TO FORM,
WHICH, WHEN CURRENT FLOWS WILL ALLOW VOLTAGE TO ‘DROP’ ACROSS THE
SWITCH OR CONTACT, TAKING THE VOLTAGE AWAY FROM THE LOAD.
( SINCE THE SWITCH OR CONTACT IS IN SERIES WITH THE LOAD, THE RESISTANCE
OF THE ‘BAD CONNECTION’ WILL ALSO BE IN SERIES WITH THE LOAD )
HVACR ELECTRICAL COMPONENTS
PG 41 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
THERE ARE A FEW ADDITIONAL TERMS THAT TECHNICIANS NEED TO BE FAMILIAR
WITH IN REGARDS TO A MECHANICAL THERMOSTAT.
1) COOLING ANTICIPATOR
2) SYSTEM LAG
3) HEAT ANTICIPATOR
4) SYSTEM OVERSHOOT
SYSTEM ‘LAG’ & SYSTEM ‘OVERSHOOT’ ARE TERMS THAT APPLY TO THE ABILITY OF
A THERMOSTAT TO ACCURATELY MAINTAIN THE ‘SET-POINT’ TEMPERATURE.
THE COOLING ANTICIPATOR REDUCES SYSTEM ‘LAG’.
THE TERM, SYSTEM LAG, APPLIES TO THE FACT THAT, IN A COOLING CYCLE, THE
THERMOSTAT DETERMINES THE NEED TO ENERGIZE THE COOLING CYCLE WHEN
THE SPACE TEMPERATURE INCREASES ABOVE THE SET-POINT OF THE
THERMOSTAT.
BUT, IT TAKES SOME ‘TIME’ FOR THE EQUIPMENT THAT MAKES UP THE COOLING
CYCLE TO ‘START’ & ACTUALLY PROVIDE COLD AIR TO THE SPACE.
BY THE TIME, THE AIR FLOW INTO THE SPACE ACTUALLY BECOMES ‘COOL’, THE
TEMPERATURE INSIDE THE SPACE CAN HAVE INCREASED WELL ABOVE THE
SET-POINT OF THE THERMOSTAT. SO, IF EFFECT, THE RESPONSE OF THE COOLING
CYCLE ‘LAGS’ BEHIND THE THERMOSTAT SENSOR.
EG: SET-POINT AT 75* ‘F’ – AT 76*’F’, THE THERMOSTAT CLOSES THE SWITCH TO
ENERGIZE THE COOLING CYCLE. THIS ‘SIGNAL’ IS SENT TO THE BLOWER MOTOR &
TO THE COMPRESSOR & CONDENSER FAN. IT TAKES SEVERAL MINUTES FOR THE
COMPRESSOR TO COMPLETELY ‘COOL’ THE EVAPORATOR COIL, WHICH PROVIDES
COOL AIR TO THE SPACE.
BY THIS TIME, THETEMPERATURE WITHIN THE SPACE CAN INCREASE BY SEVERAL
MORE DEGREES – 77 – 79* ‘F’. THIS COULD BE NOTICABLE TO THE USER.
THE COOLING ANTICIPATOR IS A SMALL, FIXED, RESISTOR THAT ACTUALLY HEATS
THE BI-METAL TEMPERATURE SENSOR, TO MAKE THE THERMOSTAT THINK THAT
THE TEMPERATURE IT IS RESPONDING TO IS A LITTLE WARMER THAN WHAT IT
ACTUALLY IS. THIS CAUSES THE THERMOSTAT SWITCH TO CLOSE A LITTLE
SOONER, TO CALL FOR THE COOLING CYCLE.
THIS GIVES TIME FOR THE COOLING CYCLE TO BEGIN COOLING THE SPACE BEFORE
THE ACTUAL TEMPERATURE, IN THE SPACE, INCREASES TOO MUCH ABOVE THE
SET-POINT.
SO, THE COOLING ANTICIPATOR IS HEATING UP THE BI-METAL THERMOSTAT
BEFORE THE SYSTEM ‘CALLS FOR’ THE COOLING CYCLE.
THE ‘COOLING ANTICIPATOR’ IS IN PARALLEL WITH THE BI-METAL THERMOSTAT.
HVACR ELECTRICAL COMPONENTS
PG 42 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
THE HEATING ANTICIPATOR REDUCES SYSTEM ‘OVERSHOOT’.
THE TERM, SYSTEM OVERSHOOT, APPLIES TO THE FACT THAT, IN A HEATING
CYCLE, HEAT DOES NOT ‘END’ QUICKLY. WHEN THE TEMPERATURE WITHIN A
SPACE BECOMES COLDER THAN THE SET-POINT OF THE THERMOSTAT, THE
THERMOSTAT ‘CALLS FOR’ THE HEATING CYCLE TO ENERGIZE & PRODUCE HEAT,
TO WARM UP THE SPACE.
AS THE TEMPERATURE WITHIN THE SPACE RISES ABOVE THE SET-POINT OF THE
THERMOSTAT, THE THERMOSTAT BI-METAL WILL RESPOND BY SHUTTING OFF THE
HEAT CYCLE.
BUT, JUST BECAUSE THE POWER IS REMOVED FROM WHATEVER IS DOING THE
HEATING, DOESN’T MEAN THAT THE ‘HEAT’ SUDDENLY STOPS.
THE MOMENT THAT THE POWER IS REMOVED FROM THE HEATING COMPONENT,
THE COMPONENT IS STILL ‘HOT’ & WILL TAKE SOME TIME FOR THE COMPONENT
TO COOL DOWN.
DURING THIS COOL-DOWN PERIOD, HEAT IS STILL BEING PRODUCED & THE AIR
THAT ‘FEEDS’ THE SPACE WILL STILL FEEL THIS HEAT. THIS CAN CAUSE THE
TEMPERATURE WITHIN THE SPACE TO RISE WELL ABOVE THE SET-POINT OF THE
THERMOSTAT. IT CAN ‘OVERSHOOT’ THE SET-POINT OF THE THERMOSTAT.
EG: AN ELECTRIC HEATER WITH THE THERMOSTAT SET AT 70*’F’. AT 69*’F’, THE
THERMOSTAT WILL ‘CALL FOR’ THE HEATING CYCLE TO ENERGIZE. THE ELECTRIC
HEAT STRIPS WILL BE ENERGIZED & THE BLOWER MOTOR WILL COME ON, MOVING
THE WARM AIR WITHIN THE SPACE. AS THE SPACE TEMPERATURE INCREASES, AT
SOME POINT IT WILL RISE TO 71*’F’, WHICH WILL CAUSE THE BI-METAL
THERMOSTAT TO OPEN, SHUTTING OFF THE POWER TO THE HEATING ELEMENTS.
BUT, THE HEATING ELEMENTS ARE STILL ‘HOT’ AT THAT MOMENT & THE BLOWER
MOTOR WILL STILL BE MOVING AIR ACROSS THE HEATERS. THIS WILL CAUSE
WARM AIR TO STILL BE DELIVERED TO THE SPACE, WHICH CAN CAUSE THE SPACE
TEMPERATURE TO RISE ABOVE 71*’F’.
THE HEATING ANTICIPATOR IS A SMALL, VARIABLE, RESISTANCE THAT ACTUALLY
PRODUCES HEAT, WHICH IS USED TO HEAT THE BI-METAL TEMPERATURE SWITCH.
THE HEAT ANTICIPATOR IS IN SERIES WITH THE HEATING THERMOSTAT, SO IT
OPERATES AT THE SAME TIME THAT THE HEAT CYCLE IS ‘CALLED FOR’.
SO, WHEN THE HEATING THERMOSTAT ‘CALLS FOR’ THE HEAT CYCLE, THE
ANTICIPATOR STARTS TO HEAT UP THE BI-METAL THERMOSTAT & MAKE IT ‘THINK’
THAT THE TEMPERATURE IS A LITTLE WARMER THAN WHAT IT ACTUALLY IS.
THIS CAUSES THE BI-METAL THERMOSTAT TO OPEN WHEN THE SPACE
TEMPERATURE, WHEN THE ACTUAL TEMPERATURE IS ONLY 70*’F’.
( THE ANTICIPATOR ‘HEATS’ THE SWITCH WHICH CAUSES THE SWITCH TO ‘FEEL’
71*’F’ TEMPERATURE INSTEAD OF THE 70*’F’ TEMPERATURE THAT THE SPACE
ACTUALLY IS. )SO, THE THERMOSTAT SHUTS OFF THE POWER TO THE HEATING
ELEMENTS AT 70*’F’, SO THAT BY THE TIME, THE ELEMENTS COOL DOWN, THE
ACTUAL TEMPERATURE WITHIN THE SPACE RISES TO ONLY 71.5*’F’.
HVACR ELECTRICAL COMPONENTS
PG 43 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
STANDARD HEAT & COOL THERMOSTAT, SCHEMATIC DIAGRAM
COOLING ANTICIPATOR
BI-METAL TEMPERATURE
SWITCH - THERMOSTAT
HEATING ANTICIPATOR
OFF
HEAT
ON
COOL
AUTO
R
G
W
Y
INPUT
OUTPUT
OUTPUT
OUTPUT
FROM
SOURCE
FOR
BLOWER
MOTOR
FOR HEATING
CYCLE
FOR COOLING
CYCLE
SIMPLIFIED DIAGRAM OF THERMOSTAT
R
G
W
Y
THE ‘DOTTED’
LINE INDICATES
THAT ALL
COMPONENTS
WITHIN THE
DOTTED LINE
ARE
CONTAINED
WITHIN
ONE DEVICE
HVACR ELECTRICAL COMPONENTS
PG 44 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
THE 2ND KIND OF SYSTEM CONTROLLING THERMOSTAT IS THE:
2) ELECTRONIC THERMOSTAT:
MECHANICAL THERMOSTATS FOR RESIDENTIAL & COMMERCIAL HVAC SYSTEMS
ARE BEING PHASED OUT IN FAVOR OF THE ELECTRONIC THERMOSTAT.
THE ELECTRONIC THERMOSTAT CONSISTS OF AN ELECTRONIC CIRCUIT BOARD
THAT PERFORMS THE SAME FUNCTION AS A MECHANICAL THERMOSTAT, BUT HAS
MANY ADDITIONAL ABILITIES.
ALL ELECTRONIC CIRCUIT BOARDS, USED IN HVACR, PROVIDE ‘TIMING’
FUNCTIONS.
SUCH AS: PROVIDING A 5 MINUTE TIME-DELAY SO THAT ONCE THE SYSTEM STOPS,
IT CAN’T RESTART FOR 5 MINUTES ( CALLED A ANTI SHORT-CYCLE FEATURE ).
ALL ELECTRONIC CIRCUIT BOARDS PROVIDE ‘COUNTING’ FUNCTIONS.
( ACTUALLY, THE WAY AN ELECTRONIC BOARD ‘TIMING’ FUNCTION WORKS IS
THAT THE BOARD ‘COUNTS’ TO DETERMINE THE ‘TIME’.)
THE CIRCUIT BOARD MAY ‘COUNT’ THE NUMBER OF ON OF OFF CYCLES OF THE
EQUIPMENT.
OR IT MAY ‘COUNT’ THE NUMBER OF TIMES THAT A ‘FAULT’ HAS OCCURRED.
IN REALITY, ANYTHING THAT A MANUFACTURER OR A TECHNICIAN MIGHT
WANT OR NEED TO BE ‘COUNTED’, CAN BE ACCOMPLISHED WITH THE
ELECTRONIC CIRCUIT BOARD.
MOST ELECTRONIC CIRCUIT BOARDS CAN BE ‘PROGRAMMED’ TO
RESPOND IN A SPECIFIC MANNER ( WITHIN THE ABILITIES OF THE BOARD ), TO
SATISFY SPECIFIC CONDITIONS OR NEEDS.
MOST ELECTRONIC BOARDS, USED IN HVACR, WILL HAVE SWITCHES, ON THE
BOARD, TO SET FOR A SPECIFIC ‘PROGRAM’ OF FUNCTIONS.
BY PROGRAMMING, A TECHNICIAN CAN CHANGE MANY OF THE ASPECTS OF
OPERATING AN HVACR SYSTEM.
DO NOT CONFUSE PROGRAMMING ELECTRONIC CIRCUIT BOARDS, WITH:
PROGRAMMABLE THERMOSTATS
A PROGRAMMABLE THERMOSTAT IS AN ELECTRONIC THERMOSTAT THAT CAN BE
‘PROGRAMMED’ WITH DIFFERENT ‘SET-POINTS’ FOR VARIOUS TIMES OF THE DAY.
EG: THE THERMOSTAT CAN BE PROGRAMMED TO RESPOND TO A COOLING
SYSTEM SET-POINT TEMPERATURE OF 72* ‘F’ WHILE THE OCCUPANTS ARE,
NORMALLY, AT HOME, SAY BETWEEN THE HOURS OF 5:00 PM & 6:00 AM, BUT AT 6
AM, WHEN THE OCCUPANTS LEAVE FOR WORK, THE SET-POINT CAN BE SET BACK
TO 78* ‘F’. SO, THE SYSTEM WILL MAINTAIN 78* ‘F’ DURING THE DAY &
AUTOMATICALLY ‘SET BACK’ TO 72* ‘F’, BEFORE THE OCCUPANTS GET HOME.
HVACR ELECTRICAL COMPONENTS
PG 45 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS CONTINUED:
THE TERM ‘SET BACK’, AS USED WITH PROGRAMMABLE THERMOSTATS, SIMPLY
MEANS THAT THE SET-POINT TEMPERATURE, THAT A SYSTEM RESPONDS TO, WILL
BE CHANGED TO A DIFFERENT SET-POINT TEMPERATURE DURING ONE PART OF A
24 HR PERIOD, & THEN ‘SET BACK’ TO ITS ORIGINAL TEMPERATURE DURING
ANOTHER PART OF THE 24 HR PERIOD.
SOME PROGRAMMABLE THERMOSTATS MAY ONLY HAVE THE ABILITY TO
PROGRAM ONLY A COUPLE OF DIFFERENT TEMPERATURES FOR ONLY A COUPLE OF
TIMES A DAY, OR THERE CAN BE SEVERAL DIFFERENT TEMPERATURES THAT CAN
BE PROGRAMMED INTO A PROGAMMABLE THERMOSTAT AS ‘SET BACK’
TEMPERATURES, WITH SEVERAL DIFFERENT TIMES PER DAY.
AS FAR AS A SERVICE TECHNICIAN IS CONCERNED, THE OPERATION OF AN
ELECTRONIC THERMOSTAT ( PROGRAMMABLE OR NOT ) OPERATES & IS ‘TESTED’,
IN THE SAME MANNER, AS A MECHANICAL THERMOSTAT.
( WITH THE EXCEPTION OF THE PROGRAMMING OF THE THERMOSTAT )
THERE IS ONLY ONE REAL DIFFERENCE BETWEEN THE OPERATION & TESTING OF
AN ELECTRONIC THERMOSTAT WHEN COMPARED TO A MECHANICAL
THERMOSTAT.
ALL ELECTRONIC BOARDS REQUIRE POWER TO FUNCTION.
TO ACCOMPLISH ANY TIMING OR COUNTING ( OR PROGRAMS ), THE ELECTRONIC
BOARD, WITHIN THE ELECTRONIC THERMOSTAT, MUST HAVE OPERATING POWER
( VOLTAGE & CURRENT ) TO OPERATE THESE FUNCTIONS.
THE OPERATING POWER, THAT MUST BE CONNECTED TO THE BOARD,
IS A ‘LOAD’ TO THE SOURCE PROVIDING THE POWER.
( THOUGH A VERY SMALL ‘LOAD’ AS ELECTRONIC DEVICES REQUIRE VERY LITTLE
POWER TO OPERATE ).
OTHER THAN PROVING OPERATING POWER, THE REMAINDER OF ALL ELECTRICAL
CONNECTIONS TO THE ELECTRONIC BOARD, ARE EITHER INPUTS TO THE BOARD
( WHICH LET THE BOARD KNOW WHEN TO SEND AN OUTPUT ) OR OUTPUTS, FROM
THE BOARD TO OPERATE ELECTRICAL CONTROL DEVICES, SUCH AS A RELAY OR
CONTACTOR COIL.
SOME ELECTRONIC THERMOSTATS USE THE SYSTEM POWER FOR ITS OPERATION
( USUALLY 24 VAC ), & SOME USE A BATTERY AS ITS OPERATING POWER SOURCE.
( 3 TO 9 VDC )
IF USING SYSTEM POWER AS THE OPERATING POWER, AN EXTRA WIRE MUST BE
CONNECTED TO THE THERMOSTAT FROM A SYSTEM DEVICE, WHICH PROVIDES THE
POWER.
HVACR ELECTRICAL COMPONENTS
PG 46 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS CONTINUED:
SIMPLIFIED ELECTRICAL SCHEMATIC DIAGRAM FOR AN ELECTRONIC
THERMOSTAT. BATTERY OPERATED:
R
G
W
Y
NOTICE: THIS DIAGRAM IS EXACTLY THE SAME AS THE DIAGRAM FOR A
MECHANICAL THERMOSTAT.
JUST FOR YOUR INFORMATION:
‘R’ = INPUT - BRINGS ONE ‘LEG’ OF POWER IN TO THE THERMOSTAT FOR USE BY
EACH SWITCH.
‘G’ = OUTPUT - TAKES THE POWER, FROM THE ‘R’ TERMINAL & SENDS THE
POWER TO THE BLOWER MOTOR CONTROLLING DEVICE,
( USUALLY A RELAY COIL ), WHEN NEEDED.
‘W’ = OUTPUT - TAKES THE POWER FROM THE ‘R’ TERMINAL & WHEN ‘HEAT’ IS
NEEDED, SENDS IT TO THE HEAT CONTROL DEVICE.
‘Y’ = OUTPUT - TAKES THE POWER FROM THE ‘R’ TERMINAL & WHEN COOLING
IS NEEDED, SENDS IT TO THE COOLING CONTROL DEVICE.
SIMPLIFIED ELECTRICAL SCHEMATIC DIAGRAM FOR AN ELECTRONIC
THERMOSTAT. SYSTEM OPERATED.
OPERATING POWER
C
R
G
W
Y
HVACR ELECTRICAL COMPONENTS
PG 47 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS CONTINUED:
NOTICE: IN THE ABOVE SCHEMATIC DIAGRAM, THERE IS ONLY ONE ADDITION TO
THIS DIAGRAM THAN WAS SEEN ON THE PREVIOUS DIAGRAMS.
AN ADDITIONAL WIRE ( CONDUCTOR ) WAS ADDED TO BRING THE 2ND ‘LEG’ OF
POWER TO THE THERMOSTAT, SO THAT THE THERMOSTAT WOULD HAVE THE
SOURCE POWER TO USE FOR ITS OPERATION.
IN THE ABOVE DIAGRAM, THIS WOULD BE THE 24 VAC ‘COMMON’ ( C ) SIDE OF THE
SOURCE POWER. THE ‘R’ WAS THE ‘HOT’ SIDE ( & IS APPLIED TO ALL
THERMOSTATS ) & ‘C’ IS THE ‘COMMON’ SIDE, OR THE OTHER SIDE OF THE 24 VAC
POWER SOURCE.
OTHERWISE, THE OPERATION OF & THE DIAGRAM OF, THE THERMOSTAT, IS THE
SAME AS FOR ANY OTHER THERMOSTAT.
ONE MORE POINT THAT NEEDS TO BE ADDRESSED ABOUT ELECTRONIC
THERMOSTATS:
WHAT SENSES THE TEMPERATURE IN AN ELECTRONIC THERMOSTAT??
WE KNOW THAT THE TEMPERATURE SENSOR, IN A MECHANICAL THERMOSTAT, IS A
BI-METAL SENSOR, WHICH EXPANDS OR CONTRACTS, DUE TO CHANGES IN
TEMPERATURE, TO CAUSE MOVEMENT OF THE SWITCHES.
BUT, WHAT ABOUT THE ELECTRONIC THERMOSTAT??
IN THE ELECTRONIC THERMOSTAT A DEVICE KNOWN AS A THERMISTOR SENSES
THE TEMPERATURE, & CAUSES MOVEMENT OF THE SWITCHES.
A THERMISTOR IS A SPECIAL TYPE OF DEVICE WHO’S:
RESISTANCE CHANGES WITH A CHANGE IN TEMPERATURE
THERMISTERS ARE USED ONLY WITH ELECTRONIC BOARDS.
THE ELECTRONIC BOARD APPLIES A DC VOLTAGE ACROSS THE THERMISTOR, &
ACCORDING TO ITS TEMPERATURE, WILL PRODUCE A CERTAIN CURRENT FLOW
THAT THE ELECTRONICS CAN READ TO DETERMINE THE TEMPERATURE.
THERE ARE 2 TYPES OF THERMISTORS USED IN HVACR.
1) PTC – POSITIVE TEMPERATURE COEFFICIENT: WITH A PTC, THE
RESISTANCE &TEMPERATURE ARE DIRECTLY RELATED, IN OTHER WORDS, IF THE
TEMPERATURE INCREASES, SO DOES THE RESISTANCE & VISE VERSA.
2) NTC - NEGATIVE TEMPERATURE COEFFICIENT: WITH AN NTC, THE
RESISTANCE & TEMPERATURE ARE INVERSELY RELATED. IN OTHER WORDS, IF THE
TEMPERATURE INCREASES, THE RESISTANCE DECREASES & VISE VERSA.
HVACR ELECTRICAL COMPONENTS
PG 48 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS-THERMISTORS CONTINUED:
THERMISTORS ARE NOT EASY TO TROUBLESHOOT. A TECHNICIAN WOULD NEED TO
KNOW THE EXACT RESISTANCE OF THE THERMISTOR AT A CERTAIN
TEMPERATURE.
HE/SHE WOULD THEN HAVE TO APPLY THAT TEMPERATURE TO THE THERMISTOR
& READ ITS RESISTANCE, TO KNOW IF IT IS GOOD OR NOT.
NORMALLY, THERMISTORS ARE ‘SOLDERED’ TO THE ELECTRONIC BOARD, SO THAT
IF THE BOARD OR THE THERMISTOR IS SUSPECTED AS BEING ‘BAD’, BOTH HAVE TO
BE REPLACED.
ONE LAST POINT ABOUT ALL THERMOSTATS – ‘STAGING’:
‘STAGING’ IS A TERM USED IN HVACR & ELECTRICAL SYSTEMS TO DENOTE THAT
THERE IS MORE THAN ONE ‘PART’ TO A HVACR OR ELECTRICAL SYSTEM THAT IS
AVAILABLE TO ACCOMPLISH THE PURPOSE OF A PARTICULAR SYSTEM.
‘STAGING’ CAN BE ACCOMPLISHED BY THE USE OF DIFFERENT ‘TEMPERATURES’ OR
THE USE OF DIFFERENT ‘TIMES’.
EACH ‘PART’ OF THE SYSTEM WILL RESPOND AT A DIFFERENT ‘TEMPERATURE’, OR
TO A DIFFERENT ‘TIME’.
SINCE WE ARE SPECIFICALLY REFRRING TO THERMOSTATS HERE, WE WILL LIMIT
THIS DISCUSSION TO DIFFERENT ‘TEMPERATURES’.
SO, THE THERMOSTAT, FOR A MULTI-STAGE ( MORE THAN 1 STAGE ) SYSTEM WILL
HAVE MORE THAN ONE TEMPERATURE TO SENSE SO THAT IT CAN KNOW WHEN TO
ENERGIZE EACH ‘PART’ OF THE SYSTEM.
SO, A MULTI-STAGE THERMOSTAT WILL HAVE MORE THAN 1 TEMPERATURE
SENSOR. THERE WILL BE A SEPERATE TEMPERATURE SENSOR FOR EACH ‘STAGE’
( OR ‘PART’ ) OF THE SYSTEM OPERATION.
EG: IN A HEAT PUMP SYSTEM, THERE ARE 2 STAGES OF HEAT. ONE COMES FROM
THE HEAT PRODUCED BY THE COMPRESSOR, & ONE COMES FROM ELECTRIC STRIP
HEAT USED AS ‘BACK-UP’ OR ADDITIONAL HEAT, IF NECESSARY.
THE 1ST STAGE OF THE THERMOSTAT, WHICH IS ONE TEMPERATURE SENSOR, WILL
RESPOND AT THE SET-POINT TEMPERATURE OF THE THERMOSTAT.
( AGAIN, THE SET-POINT IS THE TEMPERATURE THAT THE OPERATOR SETS THE
THERMOSTAT TO MAINTAIN ).
IN THIS CASE, THE 1ST STAGE THERMOSTAT WILL ENERGIZE THE COMPRESSOR
‘PART’ OF THE HEATING SYSTEM.
IF THE COMPRESSOR ‘PART’ OF THE SYSTEM CANNOT SATISFY THE SET-POINT
TEMPERATURE OF THE THERMOSTAT, THEN THE TEMPERATURE AROUND THE
THERMOSTAT MAY DROP. IF THE AMBIENT TEMPERATURE AROUND THE
THERMOSTAT DROPS TO THE SET-POINT OF THE 2ND TEMPERATURE SENSOR, THE 2ND
‘PART’ OF THE HEATING SYSTEM ( THE HEAT STRIPS ) WILL BE ENERGIZED,
TO PROVIDE ADDITIONAL HEATING.
HVACR ELECTRICAL COMPONENTS
PG 49 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS-‘STAGING’ CONTINUED:
TO FULLY UNDERSTAND THE CONCEPT OF ‘STAGING’, WE MUST UNDERSTAND THE
CONCEPT OF ‘CAPACITY’.
THE ‘TOTAL CAPACITY’ OF A COOLING SYSTEM IS THE TOTAL AMOUNT OF BTU’S OF
HEAT THAT THE COOLING SYSTEM CAN ABSORB FROM A ‘SPACE’.
THE ‘TOTAL CAPACITY’ OF A HEATING SYSTEM, IS THE TOTAL AMOUNT OF BTU’S OF
HEAT THAT A HEATING SYSTEM CAN REJECT INTO THE ‘SPACE’.
THE ‘CAPACITY’ OF THE SPACE WITHIN A STRUCTURE DEPENDS UPON THE AMOUNT
OF BTU’S THAT IT TAKES TO HEAT OR COOL THE ‘SPACE’ AT ANY ‘TIME’.
THE CAPACITY OF THE SPACE IS DEPENDANT UPON:
1) HOW BIG THE ‘SPACE’ IS ( THE VOLUME OF THE ‘SPACE’ ).
( THE LARGER THE ‘SPACE’, THE MORE BTU’S REQUIRED TO HEAT OR COOL )
2) THE TEMPERATURE DIFFERENCE BETWEEN THE OUTDOOR TEMPERATURE &
THE INDOOR ( OR ‘SPACE’ ) TEMPERATURE ( DELTA ‘T’ ).
( THE GREATER THE ‘DELTA’ ‘T’, THE MORE BTU’S NEEDED TO HEAT OR COOL )
3) THE AMOUNT OF INSULATION BETWEEN THE INDOOR ‘SPACE’ & THE OUTDOOR.
( THE MORE INSULATION THERE IS, THAT SEPERATES THE OUTDOOR
TEMPERATURE FROM THE INDOOR TEMPERATURE, THE LESS BTU’S THAT ARE
NEEDED TO HEAT OR COOL THE SPACE, AT A CERTAIN TEMPERATURE )
SINCE THE ‘VOLUME OF SPACE’ DOESN’T, NORMALLY, CHANGE, NOR DOES THE
AMOUNT OF INSULATION, THEN THE ONLY VARIABLE THAT DOES CHANGE DURING
THE COURSE OF ‘TIME’ ( HOURLY ), IS THE DIFFERENCE IN THE ‘DELTA ‘T’
BETWEEN THE OUTDOOR TEMPERATURE &THE INDOOR TEMPERATURE.
SO, THE AMOUNT OF HEATING OR COOLING NEEDED TO SATISFY THE SET-POINT OF
THE THERMOSTAT WILL VARY, DEPENDANT UPON WHAT TEMPERATURE IT IS
OUTSIDE & WHAT TEMPERATURE WE ARE TRYING TO MAINTAIN INSIDE.
SINCE THE OUTDOOR TEMPERATURE CAN CHANGE 20 – 30 ( OR MORE ) DEGREES
WITHIN A SINGLE 24 HOUR PERIOD ( A DAY ), THE ‘CAPACITY’ NEED OF THE ‘SPACE’
ALSO CHANGES.
IN OTHER WORDS, IN THE SUMMER TIME, THE HOTTEST PART OF THE DAY IS IN THE
AFTERNOON, WHEN WE SEE THE HIGHEST OUTDOOR TEMPERATURES. THE LOWEST
OUTDOOR TEMPERATURES ARE JUST BEFORE SUNRISE, IN THE MORNING.
SO WE NEED MORE CAPACITY FROM THE COOLING SYSTEM DURING THE
AFTERNOON TO MAINTAIN THE THERMOSTATS SET-POINT TEMPERATURE THAN WE
NEED IN THE MORNING.
THE EXACT OPPOSITE IS TRUE DURING WINTER TIMES, WHEN THE COLDEST
OUTDOOR TEMPERATURE IS USUALLY RIGHT BEFORE SUNRISE & THE WARMEST
OUTDOOR TEMPERATURE IS IN THE AFTERNOON.
IN THIS CASE, WE NEED MORE HEAT INTHE EARLY MORNING TIME THAN IN THE
AFTERNOON.
HVACR ELECTRICAL COMPONENTS
PG 50 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
ELECTRONIC THERMOSTATS-‘STAGING’ CONTINUED
CAPACITY CONTINUED:
THE POINT OF ALL OF THIS IS THAT IF THE CAPACITY OF THE ‘SPACE’ CHANGES, &
IF WE CAN CHANGE THE AMOUNT OF BTU’S THAT WE REMOVE FROM ( ABSORB ) OR
DELIVER TO ( REJECT ) THE ‘SPACE’, THEN WE CAN HEAT OR COOL THE ‘SPACE’
MORE EFFICIENTLY ( LESS COST ) BY DOING IT WITH LESS BTU’S.
IN THE EXAMPLE OF THE HEAT PUMP FROM ABOVE, THE ‘TOTAL CAPACITY’ OF THE
HEATING SYSTEM IS THE SUM OF THE BTU’S PRODUCED BY THE COMPRESSOR &
THE BTU’S PRODUCED BY THE HEAT STRIPS.
WE SEPERATE THE TOTAL CAPACITY OF THE SYSTEM INTO 2 ‘PARTS’.
THE COMPRESSOR IS 1ST PART & THE HEAT STRIPS ARE THE 2ND ‘PART’ OF THE
HEATING SYSTEM.
SO, IN THE AFTERNOON, WHEN THE CAPACITY OF OUR ‘SPACE’ IS LESS ( DUE TO
HIGHER OUTDOOR TEMPERATURES ), THEN, MAYBE, WE ONLY NEED THE CAPACITY
( AMOUNT OF BTU’S ) OF THE COMPRESSOR TO HEAT THE ‘SPACE’.
BUT, IN THE EARLY MORNING, WE NEED THE ADDITIONAL CAPACITY ( AMOUNT OF
BTU’S ) TO BE ABLE TO HEAT THE ‘SPACE’.
SO, WE SPLIT THE ‘TOTAL CAPACITY’ OF OUR HEATING SYSTEM INTO 2 ‘STAGES’ OF
HEAT & CONTROL EACH STAGE WITH DIFFERENT TEMPERATURE SENSORS INSIDE
OUR THERMOSTAT.
EG: ANOTHER EXAMPLE IS MULTI-STAGE COOLING SYSTEMS. LETS SAY THAT WE
HAVE A 10 TON AIR CONDITIONER SERVING A PARTICULAR ‘SPACE’.
AND LETS FURTHER SAY THAT THERE ARE 2 COMPRESSORS IN THE COOLING UNIT.
WE CAN, THEN, SEPERATE EACH COMPRESSOR INTO 2 ‘STAGES’ OF COOLING.
EACH ‘STAGE’ OPERATED BY A SEPERATE TEMPERATURE SENSOR INSIDE THE
THERMOSTAT.
ONE LAST POINT ABOUT ‘STAGING’.
GENERALLY, WITH A MULTI-STAGE THERMOSTAT, THE 1ST STAGE IS ALWAYS
ENERGIZED 1ST, WITH THE 2ND STAGE ENERGIZING 2ND, ETC.
BUT, WHEN DEENERGIZING, THE 2ND STAGE DEENERGIZES 1ST, & THE 1ST STAGE
DEENERGIZES LAST.
IN OTHER WORDS, 1ST STAGE ‘ON’, IS THE LAST STAGE ‘OFF; 2ND STAGE THAT COMES
‘ON’, IS THE NEXT-TO-LAST STAGE THAT TURNS ‘OFF’. ETC.
( SIMPLIFIED: 1ST ON, LAST OFF : LAST ON, 1ST OFF )
HOPEFULLY, BY NOW, YOU HAVE AN UNDERSTANDING OF ‘STAGING’ & ‘CAPACITY’.
BELOW IS THE SCHEMATIC DIAGRAM OF A 2-STAGE COOLING & 2-STAGE HEATING
MECHANICAL THERMOSTAT.
HVACR ELECTRICAL COMPONENTS
PG 51 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
MULTI-STAGE MECHANICAL THERMOSTAT:
BI-METAL TEMPERATURE
SWITCHES - (THERMOSTATS)
OFF
COOL
ON
AUTO
HEAT
R
G
INPUT
OUTPUT
FROM
SOURCE
FOR
BLOWER
MOTOR
W2
2ND STAGE
HEAT
Y2
W1
Y1
2ND
OUTPUT
OUTPUT
STAGE
ST
FOR
1
STAGE
OF
FOR
1ST STAGE OF
COOLING
HEATING CYCLE
COOLING
CYCLE
NOTICE THAT IN THE ABOVE DIAGRAM, THAT THERE ARE 2 TEMPERATURE
SWITCHES THAT ARE SENSING THE TEMPERATURE INSIDE THE ‘SPACE’.
NOTICE, ALSO, THAT THERE ARE 2 ADDITIONAL ‘OUTPUTS’ OF THE THERMOSTAT.
NOW, INSTEAD OF JUST ‘W’ & ‘Y’, WE HAVE DESIGNATED STAGE 1 AS ‘W1’ & ‘Y1’,
WITH STAGE 2 DESIGNATED AS ‘W2’ & ‘Y2’.
THERE IS ALSO AN ADDITIONAL SET OF MANUAL ‘HEAT-OFF-COOL’ SWITCHES THAT
ARE NECESSARY TO ACCOMODATE THE 2 NEW ‘STAGES’.
HVACR ELECTRICAL COMPONENTS
PG 52 OF
CONTROLLING DEVICES CONTINUED:
OPERATING THERMOSTATS:
MULTI-STAGE MECHANICAL THERMOSTAT:
LOOKING AT THE ‘COOLING CYCLE’ SET-POINTS:
THE 1ST STAGE SENSOR’S SET-POINT IS AT, SAY 72* ‘F’.
THE 2ND STAGE SENSOR’S SET-POINT WOULD BE AT, SAY, 74* ‘F’.
IF THE TEMPERATURE INSIDE THE ‘SPACE’ EXCEEDS 72* ‘F’, THE 1ST STAGE COOLING
CYCLE WOULD ENERGIZE.
IF THE TEMPERATURE THEN ‘COOLED’ BACK DOWN TOWARDS 72* ‘F’, THEN 1
STAGE IS ALL THAT WOULD BE NEEDED.
BUT, IF THE ‘SPACE’ TEMPERATURE CONTINUED TO CLIMB, INDICATING THAT THE
CAPACITY OF THE SYSTEM WAS TOO SMALL TO MAINTAIN THE SET-POINT
TEMPERATURE, THEN THE 2ND STAGE SENSOR WOULD SENSE IF THE TEMPERATURE
ROSE ABOVE 74* ‘F’, & IT WOULD THEN ENERGIZE THE 2ND STAGE COOLING CYCLE.
THIS WOULD PROVIDE THE MAXIMUM CAPACITY THAT THE COOLING SYSTEM CAN
PRODUCE ( MAXIMUM BTU’S – BOTH STAGES ‘ON’ ).
NOW, IF THE ‘TOTAL CAPACITY’ OF THE SYSTEM IS ENOUGH, THE TEMPERATURE
INSIDE THE ‘SPACE’ SHOULD DECREASE.
WHEN THE SPACE TEMPERATURE ‘DROPS’ TO LESS THAN 74* ‘F’, THE 2ND STAGE
COOLING CYCLE WILL BE DEENERGIZED, LEAVING ONLY THE 1ST STAGE TO FINISH
COOLING THE SPACE.
STANDARD THERMOSTATS, MECHANICAL OR ELECTRONIC, CAN HAVE AS MANY
‘STAGES’ AS IS NEEDED. MOST THERMOSTATS WILL HAVE:
1)
2)
3)
4)
1 STAGE COOLING & 1 STAGE HEAT
1 STAGE COOLING & 2 STAGE HEAT
2 STAGE COOLING & 2 STAGE HEAT
2 STAGE COOLING & 3 STAGE HEAT
SYSTEM PROTECTIVE DEVICES ARE JUST SWITCHES:
THERE ARE 2 TYPES OF SYSTEM PROTECTIVE DEVICES:
1) CIRCUIT BREAKERS: THESE ARE SWITCHES ( ONE SWITCH, CALLED A POLE,
FOR EACH ‘HOT’ CONDUCTOR OF THE ELECTRICAL CIRCUIT ), THAT
AUTOMATICALLY OPEN IF THE ELECTRICAL CIRCUIT DRAWS TOO MUCH CURRENT.
THESE SWITCHES MUST BE MANUALLY CLOSED, ( & CAN BE MANUALLY OPENED ),
BUT WILL AUTOMATICALLY OPEN UPON A ‘FAULT’ CONDICTION.
2) FUSES: THESES ARE SIMPLY ‘ONE-TIME’ ( MEANING THAT THEY HAVE TO BE
REPLACED IF OPENED ) DEVICES THAT ACT LIKE A ‘CLOSED’ SWITCH, WHEN
CONDITIONS ARE NORMAL. BUT, IF A FAULT OCCURS ( OVERCURRENT ), THE
‘CONTACT’ MELTS ‘OPEN’.
EITHER TYPE OF DEVICE IS ONLY A SWITCH IN THE ELECTRICAL CIRCUIT & CAN BE
TROUBLESHOT THE SAME AS ANY OTHER SWITCH.
HVACR ELECTRICAL COMPONENTS
PG 53 OF
LOADS:
A ‘LOAD’ IS ANY DEVICE WHICH USES POWER ( VOLTAGE & CURRENT ) TO PRODUCE
WORK. ( ANY KIND OF WORK )
A ‘LOAD’ CHANGES ENERGY FROM ONE FORM TO ANOTHER.
EG: 1) ELECTRICAL ENERGY TO MECHANICAL ENERGY. ( MOTOR, SOLENOID )
2) ELECTRICAL ENERGY TO ELECTRICAL ENERGY ( TRANSFORMER )
3) ELECTRICAL ENERGY TO LIGHT ENERGY ( LIGHT BULBS )
4) ELECTRICAL ENERGY TO HEAT ENERGY. ( HEATERS )
‘LOADS’ CAN BE CLASSIFIED ACCORDING TO THE TYPE OF POWER
SUPPLIED TO THE LOAD:
1) SINGLE-PHASE LOAD: ALL SINGLE-PHASE LOADS WILL HAVE TWO ( 2 )
CONDUCTORS FEEDING THE POWER TO THE LOAD. ONE CONDUCTOR BRINGS THE
POWER TO THE LOAD & ONE CONDUCTOR RETURNS THE POWER TO THE SOURCE.
( ALL SINGLE-PHASE LOADS WILL HAVE 2 CONDUCTORS CONNECTED TO
IT )
THE WIRING OF & THE TROUBLESHOOTING OF, A SINGLE-PHASE LOAD IS EXACTLY
THE SAME, NO MATTER WHAT TYPE OF LOAD IT IS.
2) 3-PHASE LOAD: 3-PHASE LOADS WILL HAVE 3 CONDUCTORS THAT DELIVER
THE POWER TO THE LOAD. THE LOAD MAY BE CONNECTED IN EITHER A ‘WYE’ OR A
‘DELTA’ CONFIGURATION. THERE WILL BE ONE CONDUCTOR FOR EACH ‘PHASE’ OF
THE 3-PHASE POWER SOURCE.
( ALL 3-PHASE LOADS WILL HAVE 3 CONDUCTORS CONNECTED TO IT )
THE WIRING OF & THE TROUBLESHOOTING OF, A 3-PHASE LOAD, IS EXACTLY THE
SAME, NO MATTER WHAT TYPE OF LOAD IT IS.
‘LOADS CAN ALSO BE CLASSIFIED AS TO THEIR EFFECT ON THE
ELECTRICAL CIRCUIT:
1) RESISTIVE: A RESISTIVE LOAD IS ONE THAT PRODUCES THE SAME CURRENT
FLOW IF CONNECTED TO AN AC CIRCUIT AS IT WOULD IF CONNECTED TO A DC
CIRCUIT.
2) INDUCTIVE: AN INDUCTIVE LOAD IS ONE THAT WILL PRODUCE A DIFFERENT
CURRENT FLOW IF CONNECTED TO AN AC CIRCUIT THAN IT WOULD IF CONNECTED
TO A DC CIRCUIT.
THE DIFFERENCE BETWEEN A RESISTIVE LOAD & AN INDUCTIVE LOAD IS, SIMPLY,
THE AMOUNT OF ‘RESISTANCE’ THAT THE LOAD ‘EFFECTIVELY’ PRODUCES
AGAINST THE FLOW OF CURRENT.
HVACR ELECTRICAL COMPONENTS
PG 54 OF
LOADS:
REMEMBER: A DC CIRCUIT CAN ONLY BE AFFECTED BY THE ACTUAL DC
RESISTANCE ( AS MEASURED WITH AN OHMMETER ) OF THE CIRCUIT.
AN AC CIRCUIT IS AFFECTED BY THE IMPEDANCE OF THE CIRCUIT.
IMPEDANCE BEING THE ALGEBRAIC SUM OF THE DC RESISTANCE OF THE CIRCUIT
& THE INDUCTIVE &/OR CAPACITIVE REACTANCES.
RESISTIVE LOADS:
1) HEATERS: ELECTRIC HEATERS ARE CONSIDERED AS RESISTIVE LOADS.
IF THE RESISTANCE IS MEASURED WITH AN OHMMETER, & THE SUPPLIED
VOLTAGE IS MEASURED WITH A VOLTMETER, THEN THE ‘CALCULATED’ CURRENT
FLOW ( CALCULATED BY THE DC ‘OHMS LAW’ ) WOULD BE VERY CLOSE TO THE
ACTUAL CURRENT FLOW THROUGH THE ‘HEATER’.
SO, ALL ELECTRIC HEATERS ARE RESISTIVE LOADS – EVEN THE ‘HEATER’ THAT IS
USED AS A ‘COIL’ IN A ‘HEAT SEQUENCER RELAY’.
INDUCTIVE LOADS:
1) TRANSFORMER PRIMARY:
2) LIGHT BULBS ( FIXTURES ):
3) SOLENOIDS:
4) MOTORS:
ALL OF THE ABOVE ‘INDUCTIVE LOADS’ USE THE PRINCIPLE OF INDUCTANCE TO
PRODUCE ‘INDUCTIVE REACTANCE’, WHICH IS AN ADDITIONAL RESISTANCE
THAT WOULD BE ALGEBRAICALLY ADDED TO THE ‘DC RESISTANCE’ OF THE
CONDUCTORS TO DETERMINE THE ‘TOTAL RESISTANCE’ OF THE ‘LOAD’,
& THEREFORE DETERMINE THE AMOUNT OF CURRENT THAT WOULD FLOW
THROUGH THE ‘LOAD’.
1) TRANSFORMER PRIMARY:
AS WAS DISCUSSED PREVIOUSLY, THE PRIMARY WINDING OF A TRANSFORMER IS A
‘LOAD’ TO THE SOURCE THAT PROVIDES POWER TO THE PRIMARY WINDING.
THE SECONDARY WINDING IS A ‘SOURCE’ OF POWER TO THE ELECTRICAL CIRCUIT
THAT IS CONNECTED TO IT.
THE AMOUNT OF POWER ( VA ) THAT THE PRIMARY WINDING ‘DRAWS’ FROM ITS
SOURCE IS DEPENDANT UPON THE AMOUNT OF POWER USED BY THE SECONDARY
WINDINGS ELECTRICAL CIRCUIT.
IN OTHER WORDS, THE PRIMARY WINDING WILL ONLY ‘DRAW’ FROM ITS SOURCE,
THE EXACT SAME AMOUNT OF POWER THAT THE SECONDARY SIDE USES,
UP TO THE MAXIMUM POWER THAT THE TRANSFORMER CAN PRODUCE, WHICH IS
THE ‘RATED’ ‘VA’ OF THE TRANSFORMER.
HVACR ELECTRICAL COMPONENTS
PG 55 OF
LOADS – TRANSFORMER PRIMARY CONTINUED:
THE PRIMARY WINDING OF THE TRANSFORMER IS, SIMPLY, AN INDUCTOR.
IN THE CASE OF THE TRANSFORMER, THE INDUCTOR IS USED TO TRANSFER POWER
TO THE SECONDARY WINDING.
( IN THIS CASE, THE WINDING IS NOT USED AS AN ELECTROMAGNET )
BEING AN INDUCTOR, THE RESISTANCE THAT THE PRIMARY WINDING HAS IS A
COMBINATION OF THE DC RESISTANCE OF THE CONDUCTOR & THE INDUCTIVE
REACTANCE PRODUCED BY THE AC FLOWING THROUGH THE INDUCTOR.
THE TOTAL OPPOSITION TO THE FLOW OF CURRENT PRODUCED BY THE PRIMARY
WINDING IS CALLED IMPEDANCE.
THIS IMPEDANCE IS FELT BY THE SOURCE THAT PROVIDES THE POWER TO THE
PRIMARY WINDING.
REVIEW: THE PRIMARY WINDING, OF A TRANSFORMER IS A ‘LOAD’ TO ITS
SOURCE.
THE SECONDARY WINDING IS THE ‘SOURCE’ OF POWER TO THE ELECTRICAL
CIRCUIT THAT IT SUPPLIES THE POWER FOR.
THE SYMBOL FOR A TRANSFORMER:
A TRANSFORMER IS
RATED FOR ITS
MAXIMUM ‘VA’ THAT
IT CAN PRODUCE &
THE PRIMARY &
SECONDARY
VOLTAGES
STEP-DOWN
TRANSFORMER
PRIMARY
WINDING
SECONDARY
WINDING
2) LIGHT BULBS ( FIXTURES ):
THERE ARE MANY DIFFERENT TYPES OF ‘LIGHT BULBS’:
INCANDESCENT LIGHT BULBS: THE MOST COMMON KIND ( AS OF TODAY ) ARE,
SIMPLY, A SPECIAL TYPE OF CONDUCTOR MATERIAL, CALLED A ‘FILAMENT’, THAT
PRODUCES A WHITE-HOT HEAT THAT PRODUCES ‘LIGHT’.
INCANDESCENT BULBS ‘SCREW’ INTO THE LIGHT SOCKET.
THIS ‘FILAMENT WIRE’ IS WOUND INTO A ‘COIL’, MAKING IT OPERATE LIKE AN
INDUCTOR.
WINDING THE ‘FILAMENT’ INTO A COIL PROVIDES FOR A LOWER CURRENT DRAW,
DUE TO THE REACTANCE OF THE ‘COIL’ AS WELL AS ‘CONCENTRATING’ THE HEAT
PRODUCED, MAKING IT HOTTER, THEREBY GIVING OUT MORE ‘LIGHT’.
SO, BY WINDING THE FILAMENT, THE BULB CAN EMIT MORE LIGHT WITH LESS
CURRENT FLOW.
HVACR ELECTRICAL COMPONENTS
PG 56 OF
LOADS – LIGHT BULBS ( FIXTURES ) CONTINUED:
FLOURESCENT LIGHTS, MERCURY VAPOR LIGHTS, SODIUM VAPOR LIGHTS,
METAL HALYDE LIGHTS, ETC.
MOST OF THE REMAINING TYPES OF LIGHT BULBS, USE A TYPE OF STEP-UP
TRANSFORMER, CALLED A ‘BALLAST’, TO INCREASE THE VOLTAGE OF THE
INCOMING POWER, WHICH IS THEN USED TO ‘IGNITE’ A GAS WITHIN THE LIGHT
BULBS TO CREATE ‘LIGHT’.
SO, THE ‘LOAD’ OF THESE TYPES OF LIGHTS IS THE PRIMARY WINDING OF THE
BALLAST ( TRANSFORMER ), AS DISCUSSED ABOVE.
SO, OF COURSE, THEY WOULD BE ‘INDUCTIVE’ LOADS.
THE SYMBOL FOR A LIGHT BULB ( FIXTURE ) :
THE SYMBOL SHOWS
LINES EMITTING FROM
THE CIRCLE,
INDICATING LIGHT
EMITTING FROM THE
CIRCLE
R
THE ‘R’
INDICATES THE
COLOR OFTHE
BULB.
MOST SYMBOLS WILL NOT SHOW THE FILAMENT, ONLY THE CIRCLE WITH THE
LINES EMITTING FROM THE CIRCLE, WITH MAYBE A COLOR INDICATED.
3) SOLENOIDS:
ONE OF THE MOST COMMON ‘LOADS’ THAT ARE USED IN BOTH ELECTRICAL &
HVACR IS THE SOLENOID.
A SOLENOID CHANGES ELECTRICAL ENERGY INTO MECHANICAL ENERGY.
A SOLENOID IS, SIMPLY, AN INDUCTOR, WHICH IS USED AS AN ELECTROMAGNET,
WITH ITS SOLE PURPOSE TO ATTRACT METAL.
A SOLENOID IS A ‘COIL’ OF WIRE, WRAPPED AROUND A ‘CORE’ THAT PRODUCES A
MAGNET, WHEN CURRENT FLOWS THROUGH IT, WHICH WILL THEN CAUSE THE
ATTRACTION OF ( MAYBE REPULSION OF ) & THE MOVEMENT OF, A PIECE OF
METAL.
THE ‘KEY’ TO A SOLENOID IS THAT WE CAN ATTACH ANYTHING TO THE ‘PIECE OF
METAL’ THAT WE MIGHT NEED TO MOVE, SUCH AS A SWITCH.
THE ‘COIL’ OF A CONTACTOR, MAGNETIC STARTER OR RELAY IS A SOLENOID.
WHEN SUPPLIED WITH THE PROPER VOLTAGE, IT WILL ‘DRAW’ THE CURRENT
NECESSARY TO ATTRACT A PIECE OF METAL, ON WHICH CONTACTS ARE
ATTACHED. THE MOVEMENT OF THE METAL CHANGES THE POSITION OF THE
CONTACT(S).
HVACR ELECTRICAL COMPONENTS
PG 57 OF
LOADS – SOLENOIDS CONTINUED:
SOLENOIDS ARE ALSO USED TO CONTROL THE MOVEMENT OF ‘FLUIDS’
( AIR, REFRIGERANT, WATER, OR ANY TYPE OF LIQUID ).
WE USE A SOLENOID, TO OPEN OR CLOSE A ‘VALVE’ INSIDE THE FLUID PIPING.
WE CAN ENERGIZE A SOLENOID TO OPEN A ‘VALVE’ & ALLOW THE FLUID TO FLOW
THROUGH, OR WE CAN ENERGIZE THE SOLENOID TO STOP THE FLOW OF THE
FLUID.
THE SOLENOID DEVICE WILL BE SPRING-LOADED, WHICH MEANS THAT A SPRING
WILL CAUSE THE DEVICE TO RETURN TO ITS ‘NORMAL’ POSITION, ONCE THE
SOLENOID IS DEENERGIZED. ( JUST AS THE CONTACTS OF A RELAY OR CONTACTOR,
ARE SPRING-LOADED )
THE SYMBOL FOR A SOLENOID:
CR
DESIGNATOR
NOTICE: THE SYMBOL FOR A SOLENOID IS THE EXACT SAME SYMBOL FOR THE
‘COIL’ OF A RELAY OR CONTACTOR ( OR MAGNETIC STARTER ).
IF LOOKING AT THE SYMBOL ON AN ELECTRICAL DIAGRAM ( SCHEMATIC
DIAGRAM ), A TECHNICIAN CANNOT TELL IF THE SOLENOID IS USED AS A
‘COIL’ OF A RELAY, ETC, OR USED AS A VALVE TO STOP OR ALLOW THE
MOVEMENT OF A FLUID.
IMPORTANT: WHICH IS WHY, ON AN ELECTRICAL DIAGRAM ( SCHEMATIC
DIAGRAM ), THE SYMBOL WILL ALWAYS BE ACCOMPANIED BY A ‘DESIGNATOR’,
WHICH IS A LETTER & / OR NUMBER COMBINATION TO INDICATE ITS USE IN THE
ELECTRICAL CIRCUIT.
ON A SCHEMATIC DIAGRAM, THERE WILL BE A ‘LEGEND’ WHICH WILL EXPLAIN
ALL ‘DESIGNATORS’ LISTED ON THE DIAGRAM.
REMINDER: SINCE THE SOLENOID IS AN ‘INDUCTOR’, THEN THE SOLENOID WILL
PRODUCE INDUCTIVE REACTANCE ( DUE TO ‘CEMF’ ) AS ITS MAIN ‘RESISTANCE TO
THE FLOW OF CURRENT’.
THE ‘DC RESISTANCE’ ( RESISTANCE, AS MEASURED WITH AN OHMMETER ) OF THE
‘COIL’ WILL BE VERY SMALL, BUT ONCE CURRENT BEGINS TO FLOW, THE
IMPEDANCE ( DC RESISTANCE & INDUCTIVE REACTANCE = TOTAL RESISTANCE )
WILL BE HIGH, REDUCING THE CURRENT FLOW.
HVACR ELECTRICAL COMPONENTS
PG 58 OF
LOADS – MOTORS:
A MOTOR IS A DEVICE THAT CHANGES ELECTRICAL ENERGY INTO ‘ROTATING’,
MECHANICAL ENERGY.
A MOTOR USES INDUCTORS &THE PRINCIPLE OF INDUCTANCE TO CREATE
ELECTROMAGNETS THAT ATTRACT , VIA, THE ‘LAW OF CHARGES’, A MOVEABLE
‘PIECE OF METAL’, CAUSING THIS ‘METAL’ TO ROTATE IN A CIRCLE.
THE ‘SHAFT’ OF THE MOTOR IS ATTACHED TO THE MOVING ‘PIECE OF METAL’.
AN AC MOTOR HAS 2 ‘BASIC’ PARTS:
1) STATOR: THE STATOR IS THE STATIONARY PART OF THE MOTOR. THE STATOR
CONTAINS THE ‘INDUCTORS’ ( WINDINGS ) THAT ARE USED TO CREATE
THE ELECTROMAGNETS.
2) ROTOR: THE ROTOR IS THE ROTATING PART OF THE MOTOR ( THE ‘PIECE OF
METAL’ ). THE ROTOR WILL HAVE A ‘SHAFT’ ATTACHED TO IT, WHICH
WILL THEN BE ATTACHED TO THE MECHANICAL DEVICE THAT NEEDS
TO BE ROTATED.
LETS REVIEW THE ‘RULES’ OF INDUCTANCE’ THAT ARE USED, BY THE AC
‘INDUCTION’ MOTOR.
1) WINDING A CONDUCTOR INTO A ‘COIL’, PRODUCES AN
‘ELECTROMAGNET.
2) THE ELECTROMAGNET WILL HAVE THE SAME PROPERTIES AS A
PERMANENT MAGNET.
A) IT WILL PRODUCE A NORTH OR A SOUTH POLE, DEPENDING ON THE
DIRECTION OF CURRENT FLOW THROUGH THE WINDING.
B) IT WILL ATTRACT METALS.
3) THE STRENGTH OF THE ELECTROMAGNET ( HOW STRONG A MAGNET
IS PRODUCED ) IS A RESULT OF SEVERAL FACTOR.
A) THE AMOUNT OF CURRENT THAT FLOWS THROUGH THE ‘WINDING’.
THE GREATER THE CURRENT FLOW, THE STRONGER THE MAGNET.
B) THE NUMBER OF TURNS OF THE CONDUCTOR, IN THE ‘WINDING’.
THE MORE TURNS, THE STRONGER THE MAGNMET.
C) THE ‘CORE’ MATERIAL. A MOTORS ‘WINDING’ IS WRAPPED AROUND AN IRON
CORE, WHICH MAKES FOR A STRONGER MAGNET.
NOW LETS SEE HOW WE USE THESE ‘RULES OF INDUCTANCE’ TO MAKE A ‘SHAFT’
ROTATE BY USING A MAGNET TO ATTRACT THE PIECE OF METAL ( ROTOR ).
THE FIRST 2 ‘RULES’ FROM ABOVE, WINDING THE CONDUCTOR INTO A COIL,
THE ELECTROMAGNET PRODUCING A NORTH OR A SOUTH POLE, & THE ABILITY OF
THE ELCTROMAGNET TO ATTRACT METALS, ARE THE ‘RULES’ USED TO PRODUCE
MOVEMENT OF THE ROTOR ( PIECE OF METAL ) BY THE MOTOR.
HVACR ELECTRICAL COMPONENTS
PG 59 OF
LOADS – MOTORS CONTINUED:
THE LAST ‘RULE’, ABOUT THE STRENGTH OF THE ELECTROMAGNET, IS USED
TO DETERMINE HOW BIG THE ELECTROMAGNETIC WILL HAVE TO
BE TO MOVE A PARTICULAR SIZE DEVICE & HOW FAST THE DEVICE WILL MOVE.
VERY IMPORTANT TO UNDERSTAND: THE PART OF THE ‘RULES OF
INDUCTANCE’ THAT STATE THAT AN ELECTROMAGNET ( THE WINDING IN A
MOTOR ), WILL PRODUCE EITHER A NORTH OR A SOUTH POLE,
DEPENDING UPON THE DIRECTION OF CURRENT FLOW THROUGH THE
WINDING.
SINCE A NORTH POLE IS THE OPPOSITE OF THE SOUTH POLE & THE MAGNETIC
FIELDS PRODUCED BY EACH POLE MOVE IN OPPOSITE DIRECTIONS, THEN,
WHETHER AN ELECTROMAGNET WILL BE A ‘NORTH POLE’ OR A ‘SOUTH
POLE’ IS SOLELY DEPENDANT UPON THE DIRECTION OF CURRENT FLOW
THROUGH THE INDUCTOR.
THERE IS A ‘LEFT-HANDED’ RULE TO DETERMINE WHICH END OF AN
ELECTROMAGNET ( WINDING ) IS THE NORTH POLE.
WRAP YOUR LEFT-HAND FINGERS, IN THE DIRECTION THAT CURRENT FLOWS IN
THE ‘COIL’ & YOUR THUMB WILL POINT TO THE ‘NORTH POLE’ OF THE ‘COIL’.
SO, IF CURRENT CHANGES TO THE OPPOSITE DIRECTION, THE LEFT-HAND WOULD
HAVE TO BE TURNED OVER & THE THUMB WOULD POINT IN THE OPPOSITE
DIRECTION.
SOUTH
POLE
NORTH
POLE
CORE
CORE
NORTH
POLE
INDUCTOR:
CONDUCTOR WRAPPED
IN CLOCK-WISE
DIRECTION
( CW )
SOUTH
POLE
INDUCTOR:
CONDUCTOR WRAPPED IN
COUNTER-CLOCK-WISE
DIRECTION
( CCW )
AS THE PICTURES ABOVE INDICATE, BY WINDING THE CONDUCTOR IS OPPOSITE
DIRECTIONS, THE ‘POLES’ OF EACH ELECTROMAGNET WILL BE IN THE
OPPOSITE DIRECTION.
THIS IS THE MAIN ‘PRINCIPLE’ AS TO HOW A MOTOR WORKS.
HVACR ELECTRICAL COMPONENTS
PG 60 OF
LOADS – MOTORS CONTINUED:
IN ACTUALITY, IN AN AC INDUCTION MOTOR, ONE WINDING IS ‘SPLIT’ INTO 2 PARTS,
BY WINDING ONE PART OF THE WINDING IN ONE DIRECTION & WINDING
THE OTHER PART OF THE SAME WINDING IS THE OPPOSITE DIRECTION.
THIS CAUSES DIFFERENT ‘POLES’ ( NORTH OR SOUTH ) TO BE DEVELOPED ON EACH
‘END’ OF THE WINDING ( REMEMBER, SAME WINDING ).
NOW, LETS SEE IF WE CAN USE THE ABOVE PRINCIPLES & CAUSE THE MOVEMENT
OF A PERMANENT MAGNET, BY MEANS OF THE ATTRACTION & REPULSION OF
DC MAGNETIC FIELDS. ( LAW OF CHARGES ).
MAGNET
S
N
A
S
N
S
S
N
B
N
HVACR ELECTRICAL COMPONENTS
PG 61 OF
LOADS – MOTORS CONTINUED:
S
N
S
S
N
N
C
IN DRAWING ‘A’ ABOVE, WE HAVE ONE COIL OF WIRE ‘SPLIT’ INTO 2 PARTS.
EACH ‘PART’ IS WOUND AROUND AN IRON CORE.
WE PLACE A MAGNET IN THE MIDDLE, BETWEEN THE 2 ‘PARTS’ OF THE SINGLE
INDUCTOR.
( THE MAGNET IS ‘FIXED’ IN THE MIDDLE, SO IT CAN ROTATE )
IN DRAWING ‘B’, WE CLOSE THE SWITCH, ALLOWING CURRENT TO FLOW THROUGH
THE INDUCTOR, WHICH CAUSES MAGNETIC ‘POLES’ TO BE FORMED IN EACH ‘PART’
OF THE ELECTROMAGNET.
THE ELECTROMAGNET ‘POLES’, THROUGH THE ‘LAW OF CHARGES’, WILL ATTRACT
& REPEL THE PERMANENT MAGNET ‘POLES’, CAUSING THE MAGNET TO MOVE.
THE ‘NORTH POLE’ OF THE ELECTROMAGNET WILL ATTRACT THE ‘SOUTH POLE’
OF THE PERMANENT MAGNET, & VISE-VERSA, WHILE, AT THE SAME TIME,
THE ‘SOUTH POLE’ OF THE ELECTROMAGNET, WILL REPEL THE ‘SOUTH POLE’ OF
THE PERMANENT MAGNET, & VISE-VERSA.
THE MAGNET TURNS IN THE INDICATED DIRECTION.
IN DRAWING ‘C’, THE PERMANENT MAGNET HAS TURNED 90 DEGREES, & NOW THE
SOUTH POLE OF THE PERMANENT MAGNET IS DIRECTLY BY THE NORTH POLE OF
THE ELECTROMAGNET & THE NORTH POLE OF THE PERMANENT MAGNET IS
DIRECTLY BY THE SOUTH POLE OF THE ELECTROMAGNET.
THE CENTRIFUGAL FORCE WOULD ACTUALLY CAUSE THE PERMANENT MAGNET TO
TURN JUST PAST THE ELECTROMAGNET POLE, FOR AN INSTANT, &THEN IT WOULD
TURN ‘BACK’ TO LINE UP WITH THE ELECTROMAGNETS ‘POLE’.
BUT, THIS WOULD BE AS FAR AS THE PERMANENT MAGNET WOULD TURN, UNLESS
WE COULD DO SOMETHING DIFFERENT, LIKE....
TURN THE DC POWER SOURCE AROUND OR REVERSE THE DC SOURCE.
HVACR ELECTRICAL COMPONENTS
PG 62 OF
LOADS – MOTORS CONTINUED:
CENTRIFUGAL FORCE ALLOWS
MAGNET TO TURN PAST ‘POLE’
N
S
N
S
S
N
D
BATTERY REVERSED
IN DIAGRAM ‘D’, WHEN THE BATTERY IS REVERSED, THE DIRECTION OF CURRENT
FLOW THROUGH THE ELECTROMAGNET REVERSES.
WHICH CAUSES THE ‘POLES’ OF THE ELECTROMAGNET TO REVERSE,
NOW, THE ‘SOUTH POLE’ OF THE ELECTROMAGNET IS NEXT TO THE ‘SOUTH POLE’
OF THE PERMANENET MAGNET & THE ‘NORTH POLE’ OF THE ELECTROMAGNET
IS NEXT TO THE ‘NORTH POLE’ OF THE PERMANENT MAGNET.
SINCE, WE UNDERSTAND THE ‘LAW OF CHARGES’, WE KNOW THAT THE ‘SOUTH
POLE’ OF THE ELECTROMAGNET WILL REPULSE THE ‘SOUTH POLE’ OF THE
PERMANENT MAGNET & THE ‘NORTH POLE’ OF THE ELECTROMAGNET WILL
REPULSE THE ‘NORTH POLE’ OF THE PERMANENT MAGNET.
THIS REPULSION CAUSES THE PERMANENT MAGNET TO CONTINUE TO ROTATE.
( IN THE SAME DIRECTION AS BEFORE )
IN DIAGRAM ‘E’, BELOW, THE MAGNET CONTINUES TO ROTATE, FORCED BY THE
REPULSION & ATTRACTION OF THE DIFFERENT ‘POLES’ OF EACH MAGNET
( PERMANENT & ELECTRO ), SINCE THE VOLTAGE SOURCE HAS BEEN REVERSED.
IN DIAGRAM ‘F’, THE MAGNET WILL CONTINUE TO TURN UNTIL THE SOUTH POLE
OF THE PERMANENT MAGNET ALIGNS WITH THE NORTH POLE OF THE
ELECTROMAGNET, AT WHICH TIME, THE ROTATION WILL STOP.
THIS COMPLETES ONE REVOLUTION OF THE PERMANENT MAGNET.
HVACR ELECTRICAL COMPONENTS
PG 63 OF
LOADS – MOTORS CONTINUED:
N
S
N
S
N
S
E
BATTERY REVERSED
N
S
N
N
S
S
F
BATTERY REVERSED
VERY IMPORTANT: IN DIAGRAMS ‘A’ THROUGH ‘F’, THE PERMANENT MAGNET
ROTATED 360 DEGREES ( A FULL CIRCLE ), & ENDED WHERE IT BEGAN
( SOUTH POLE ON RIGHT & NORTH POLE ON LEFT ).
THE DIRECTION OF CURRENT FLOW THROUGH THE ELECTROMAGNETS
REVERSED ITS DIRECTION ONE TIME, TO COMPLETE THE ENTIRE CYCLE.
( WHEN THE BATTERY WAS TURNED AROUND )
HVACR ELECTRICAL COMPONENTS
PG 64 OF
LOADS – MOTORS CONTINUED:
SO, TO COMPLETE ONE COMPLETE CYCLE OF ROTATION OF THE PERMANENT
MAGNET, THE DIRECTION OF CURRENT FLOW THROUGH THE ELECTROMAGNET
HAD TO REVERSE....ONE TIME.
THE ‘MOTOR’ FROM ‘A’ THROUGH ‘F’ ABOVE, IS HOW A DC ( DIRECT CURRENT )
MOTOR OPERATES.
AS STATED PREVIOUSLY, A MOTOR HAS 2 PARTS, THE STATOR &THE ROTOR.
IN OUR EXAMPLE FROM ABOVE, THE ELECTROMAGNETS ARE WOUND AROUND
THE ‘STATOR’ (STATIONARY PART ), WHILE THE PERMANENT MAGNET IS THE
‘ROTOR’. ( ROTATING PART )
AN AC ( ALTERNATING CURRENT ) MOTOR OPERATES BY THE EXACT SAME
PRINCIPLE – THE ‘LAW OF CHARGES’.
CHANGING THE NORTH & SOUTH POLES OF AN ELECTROMAGNET TO ATTRACT OR
REPULSE THE ‘POLE’ OF THE ROTATING PART OF THE MOTOR.
HOWEVER, IN AN AC INDUCTION MOTOR, THERE ARE A FEW
DIFFERENCES.
1) THE ROTOR IS NOT A PERMANENT MAGNET, BUT AN
ELECTROMAGNET
THE AC INDUCTION MOTOR ALSO USES THE PRINCIPLE OF INDUCTION TO INDUCE A
VOLTAGE & A CURRENT INTO THE ROTOR, FROM THE STATOR WINDING.
2) WITH AN AC INDUCTION MOTOR, THE CURRENT FLOW THROUGH THE
WINDING IS NOT AT THE SAME ‘STRENGTH’ ALL THE TIME.
( AS IT IS IN THE DC MOTOR FROM THE ABOVE EXAMPLE )
REMEMBER: DC CURRENT FLOWS AT A STEADY VALUE & IN THE SAME DIRECTION,
AT ALL TIMES.
AN AC CURRENT IS CONSTANTLTY CHANGING IN VALUE & DIRECTION.
THE FOLLOWING DIAGRAM SHOWS THE ‘STRENGTH’ OF THE MAGNETIC FIELD,
PRODUCED BY THE CURRENT FLOW THROUGH THE INDUCTOR ( MOTOR WINDING ),
AT DIFFERENT POINTS ( MOMENTS OF TIME ) WITHIN ONE CYCLE OF THE AC
( ALTERNATING CURRENT ) ‘SINE WAVE’.
AT POINT # 1, THERE IS NO CURRENT FLOW SO THERE IS NO MAGNETIC FIELD
GENERATED BY THE ‘INDUCTOR’.
AT POINT # 2, THE CURRENT STARTS TO FLOW, IN A ‘POSITIVE’ DIRECTION,
WHICH CAUSES THE ‘INDUCTOR’ TO PRODUCE A MAGNETIC FIELD, WHOSE
‘STRENGTH’ IS A DIRECT RESULT OF THE AMOUNT OF CURRENT FLOWING
THROUGH IT. ( THE NUMBER OF TURNS, IN THE ‘COIL’ ARE ‘SET’. )
NOTICE: THE ‘POLES’ ON THE ‘INDUCTOR’. THE ‘POLES’ ARE DETERMINED BY THE
DIRECTION OF CURRENT FLOW THROUGH THE INDUCTOR.
AT POINT # 2 – THE NORTH POLE IS AT THE BOTTOM OF THE INDUCTOR.
WITH THE SOUTH POLE AT THE TOP.
HVACR ELECTRICAL COMPONENTS
PG 65 OF
LOADS – MOTORS CONTINUED:
AT POINT # 3, THE CURRENT IS AT A ‘POSITIVE’ MAXIMUM VALUE, SO THE
CURRENT FLOW THROUGH THE INDUCTOR IS MAXIMUM, SO THE RESULTING
MAGNETIC FIELD STRENGTH IS AT MAXIMUM.
( THE STRONGEST FORCE OF ATTRACTION OR REPLUSION )
NOTICE: THE ‘POLES’ REMAIN THE SAME ( NORTH ON BOTTOM ) BECAUSE THE
CURRENT FLOW IS STILL IN A POSITIVE DIRECTION.
AT POINT # 4, THE CURRENT FLOW STARTS TO DECREASE, CAUSING A SIMILAR
DECREASE IN THE STRENGTH OF THE MAGNETIC FIELD PRODUCED BY THE
INDUCTOR.
( THE FORCE OF ATTRACTION & REPULSION IS LESS )
BUT AGAIN NOTICE: THE ‘POLES’ REMAIN THE SAME, BECAUSE THE CURRENT
FLOW IS STILL IN A ‘POSITIVE’ DIRECTION.
AT POINT # 5, THE CURRENT FLOW DROPS BACK TO ZERO, SO THE MAGNETIC
FIELD PRODUCED BY THE CURRENT FLOWS IS ALSO ZERO.
OF COURSE, THE ATTRACTION & REPULSION ‘FORCE’ WILL ALSO BE ZERO.
HVACR ELECTRICAL COMPONENTS
PG 66 OF
LOADS – MOTORS CONTINUED:
AT POINT # 6, THE CURRENT, THROUGH THE INDUCTOR, STARTS TO INCREASE,
AGAIN. BUT THIS TIME THE CURRENT FLOW IS IN THE OPPOSITE DIRECTION
THAN IT WAS IN POINTS 2 THROUGH 4, ABOVE. NOW, IT IS IN A NEGATIVE
DIRECTION.
AS WE SHOULD HAVE ALREADY LEARNED, IF THE DIRECTION OF CURRENT FLOW,
IN AN INDUCTOR, IS REVERSED, THEN THE MAGNETIC FIELD PRODUCED BY
THAT CURRENT FLOW WILL ALSO REVERSE.
IF THE CURRENT FLOW & THE DIRECTION OF THE MAGNETIC FIELD ARE
REVERSED, THEN THE ‘POLES’ ON EACH END OF THE INDUCTOR WILL BE REVERSED.
SO, NOW, THE INDUCTOR POLES, PICTURED ABOVE, WILL REVERSE.
THE ‘NORTH POLE’ IS NOW AT THE TOP OF THE INDUCTOR, WITH THE ‘SOUTH POLE’
AT THE BOTTOM.
( IT WAS THE OPPOSITE IN POINTS 2 THROUGH 4, ABOVE ) )
AT POINT # 7, THE CURRENT FLOW, THROUGH THE INDUCTOR, IS MAXIMUM.
THE MAGNETIC FIELD GENERATED BY THE CURRENT FLOW THROUGH THE
INDUCTOR IS AT ITS MAXIMUM STRENGTH, & THE ‘NORTH POLE’ IS AT THE
TOP OF THE INDUCTOR.
AT POINT # 8, AGAIN, THE CURRENT FLOW, THROUGH THE INDUCTOR, IS
DECREASING, SO THE MAGNETIC FIELD STRENGTH IS REDUCED, BUT
SINCE THE CURRENT FLOW IS STILL IN THE SAME DIRECTION, THE ‘NORTH POLE’ IS
STILL AT THE TOP OF THE INDUCTOR, WITH THE SOUTH POLE AT THE BOTTOM.
AT POINT # 9, THE CURRENT FLOW IS ZERO, SO THE MAGNETIC FIELD STRENGTH
IS ZERO, & NO ‘POLES’ ARE DEVELOPED BY THE INDUCTOR.
THE INDUCTOR HAS COMPLETED A 360 DEGREE CIRCLE, & IS RIGHT BACK WHERE
IT STARTED.
AN IMPORTANT POINT TO UNDERSTAND: ABOUT THE DC ‘MOTOR’ AS
DESCRIBED PREVIOUSLY, & THE MOVEMENT OF THE AC SINE WAVE
AS DESCRIBED ABOVE.
REMEMBER THAT, IN THE DC ‘MOTOR’, WE HAD TO REVERSE THE DIRECTION OF
THE BATTERY ( & THEREFORE THE CURRENT GENERATED BY THE BATTERY )
TO REVERSE THE ‘POLES’ OF THE ELECTROMAGNET, TO COMPLETE ONE
REVOLUTION OF THE PERMANENT MAGNET.
( IN A REAL DC MOTOR, THIS ACTION IS ACCOMPLISHED BY USE OF ‘BRUSHES’
& A DEVICE CALLED A ‘COMMUTATOR’, WHICH IS A WAY THE ROTOR IS MADE. )
IN THE AC ‘MOTOR’ ACTION, FROM ABOVE, THE AC ( ALTERNATING CURRENT ),
AUTOMATICALLY, REVERSES ITS DIRECTION TO COMPLETE ONE CYCLE.
( IN A REAL AC MOTOR, THIS ACTION IS AUTOMATICALLY ACCOMPLISHED BY THE
CONSTANTLY ‘ALTERNATING’ CURRENT WAVE FORM. )
HVACR ELECTRICAL COMPONENTS
PG 67 OF
LOADS – AC INDUCTION MOTORS:
LETS SEE HOW AN ‘AC INDUCTION MOTOR’ WORKS:
THE STATOR: THE STATOR OF THE MOTOR IS WHERE THE INDUCTOR(S)
( WINDINGS ) ARE WOUND.
THE AC INDUCTION MOTOR HAS ONE ‘MAIN’ WINDING:
IT IS SOMETIMES CALLED A ‘RUN’ WINDING. THIS INDUCTOR ( WINDING ) IS
SEPERATED INTO 2 OR MORE ‘PARTS’.
EACH ‘PART’ OF THE MAIN WINDING IS CALLED A ‘POLE’.
S
N
THE ENTIRE WINDING , CALLED A ‘MAIN’ OR ‘RUN’ WINDING
( IN THIS CASE – 20 TURNS OF WIRE )
N
S
S
N
SAME WINDING AS ABOVE, JUST SEPERATED INTO 2 ‘PARTS’.
EACH ‘PART’ IS CALLED A ‘POLE’.
THERE ARE 10 ‘TURNS’ IN EACH ‘POLE’ OF THE WINDING.
THIS IS A 2-POLE WINDING ( 2-POLE MOTOR )
S
N
S
N
S
N
S
N
AGAIN, THE SAME WINDING IS USED HERE, AS IT WAS ABOVE.
AGAIN, EACH ‘PART’ OF THE WINDING IS A ‘POLE’ OF THE WINDING
OR MOTOR.
EACH ‘POLE’ OF THE WINDING WOULD HAVE 5 ‘TURNS’.
THIS WOULD BE A 4-POLE MOTOR WINDING.
AC INDUCTION MOTORS COME IN 2-POLE, 4-POLE, 6-POLE, OR 8-POLE STYLES.
( SOME MOTORS MAY EVEN HAVE MORE POLES )
NOTICE THAT THERE IS ALWAYS A EVEN NUMBER OF ‘POLES’.
IF YOU CONSIDER THAT EACH ‘PART’ OF THE WINDING IS ONE ‘MAGNETIC POLE’,
NORTH OR SOUTH, THEN IT IS EASY TO UNDERSTAND WHY THERE MUST BE AN EVEN
NUMBER OF ‘POLES’ IN A MOTOR.
( EACH ‘POLE’ WOULD EITHER BE NORTH OR SOUTH, SO IT TAKES 2 ‘POLES’ TO
MAKE A COMPLETE MAGNET )
HVACR ELECTRICAL COMPONENTS
PG 68 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
THE ‘NUMBER OF POLES’ THAT A MOTOR HAS IS RELATIVE TO THE ‘SPEED’ AT
WHICH THE SHAFT WILL ROTATE.
THE SMALLED THE ‘NUMBER OF POLES’, THE FASTER THE SPEED OF THE SHAFT.
SPEED OF AN AC INDUCTION MOTOR:
SHAFT RPM = FREQUENCY ( OF POWER SOURCE ) X ( TIMES ) 120 ( CONSTANT )
NUMBER OF POLES
SO, HOW FAST THE SHAFT WILL ROTATE, IN REVOLUTIONS PER MINUTE, IS
DIRECTLY RELATED TO THE FREQUENCY OF THE POWER SOURCE TIMES THE
‘CONSTANT’ OF 120, & INVERSELY RELATED TO THE NUMBER OF POLES
THAT THE MOTOR HAS.
SIMPLY STATED – THE GREATER THE NUMBER OF POLES THAT A MOTOR HAS,
THE LESS ITS SPEED WILL BE.
SINCE WE ARE IN THE UNITED STATES & THE FREQUENCY OF ALL OUR POWER
SOURCES IS 60 HERTZ, THEN THE FORMULA FOR THE SPEED OF A MOTOR CAN BE
WRITTEN AS:
7200
SPEED ( IN RPM’S ) = NUMBER OF POLES
THE ROTOR, OF AN AC INDUCTION MOTOR: A SERIES OF METAL BARS
CONNECTED AT EACH END, WHICH FORMS A COMPLETE ELECTRICAL CIRCUIT.
( TO ALLOW CURRENT TO FLOW, WHEN POWER IS INDUCED INTO IT )
A VERY SIMPLFIED EXPLANATION OF HOW A 2-POLE AC INDUCTION MOTOR
OPERATES.
THE MOTOR WILL HAVE ONE ‘MAIN’ ( OR ‘RUN’ ) WINDING, WHICH IS WRAPPED
AROUND THE STATOR. THE WINDING IS DIVIDED INTO 2 ‘PARTS’, EACH ‘PART’ WILL
BE LOCATED ON OPPOSITE SIDES OF THE ‘CIRCLE’ ( 180 DEGREES APART ) THAT
MAKES UP THE STATOR. EACH ‘PART’ OF THE WINDING IS CALLED A ‘POLE’ OF THE
MOTOR.
THE ‘ROTOR’ OF THE MOTOR IS LOCATED ‘INSIDE’ THE ‘STATOR’, SO A MAGNETIC
FIELD THAT IS PRODUCED AS CURRENT FLOWS THROUGH THE WINDING, WILL
CROSS ( CUT ) THE ‘BARS’ OF THE ROTOR, CREATING A VOLTAGE
& A CURRENT WITHIN THE ROTOR.
THE ROTOR ACTS LIKE A WINDING, IN THAT, THE CURRENT FLOW IN THE WINDING
WILL ALSO MAKE THE ROTOR INTO AN ELECTROMAGNET, WITH A NORTH & A
SOUTH POLE. ( JUST LIKE THE PERMANENT MAGNET FROM OUR PREVIOUS
EXPLANATION OF A DC MOTOR ).
AS CURRENT FLOWS IN THE MAIN WINDING, THE ‘POLES’ OF THE MOTOR WILL
ESTABLISH NORTH & SOUTH POLES, WHICH WILL ATTRACT & REPEL THE
‘POLES’ OF THE ROTOR, CAUSING MOVEMENT OF THE ROTOR.
OF COURSE, THE SHAFT OF THE MOTOR IS ATTACHED TO THE ROTOR.
HVACR ELECTRICAL COMPONENTS
PG 69 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
2-POLE AC INDUCTION MOTOR:
POWER
SOURCE
ROTOR
STATOR
‘POLE’
STATOR
‘POLE’
‘MAIN’ OR ‘RUN’ WINDING
240
VAC
S
N
STATOR
‘POLE’
STATOR
‘POLE’
MAGNETIC FIELDS ‘CUTTING’ ROTOR
WHEN THE SWITCH IS CLOSED, & CURRENT FLOWS THROUGH THE ‘MAIN’
WINDING, THE MAGNETIC FIELD PRODUCED BY THE CURRENT FLOW, EXPANDS &
CONTRACTS ACROSS THE ROTOR, CUTTING THE CONDUCTORS IN THE ROTOR, &
INDUCING A VOLTAGE & A CURRENT INTO THE ROTOR.
THIS VOLTAGE & CURRENT ( POWER ) INDUCED INTO THE ROTOR, CAUSES
NORTH & SOUTH ‘POLES’ TO BE DEVELOPED IN THE ROTOR.
HVACR ELECTRICAL COMPONENTS
PG 70 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
2-POLE AC INDUCTION MOTOR CONTINUED:
240
VAC
S
N
S
N
A
AC CURRENT
IN DIAGRAM ‘A’, ABOVE, AS THE AC CURRENT STARTS TO FLOW THROUGH THE
WINDING, MAGNETIC FIELDS START TO BUILD UP FROM EACH ‘PART’ OF THE
WINDING, CREATING MAGNETIC ‘POLES’ IN EACH OF THE ‘STATOR POLES’.
THE MAGNETIC FIELDS ‘CUT’ ACROSS THE ROTOR, INDUCING POWER ( VOLTAGE &
CURRENT ) INTO THE ROTOR, ESTABLISHING A NORTH & SOUTH ‘POLE’ INTO THE
ROTOR. DUE TO THE ‘LAW OF CHARGES’, THE ‘POLES’ OF THE ROTOR WILL BE
EITHER ATTRACTED TO OR REPULSED FROM THE ‘MAIN’ WINDING ‘POLES’.
THIS ‘PHYSICAL’ ACTION BETWEEN THE ‘POLES’ WILL CAUSE MOVEMENT OF THE
ROTOR. IN THE CASE OF THE DIAGRAM ABOVE, THE ROTOR WILL START TO
ROTATE IN A CCW ( COUNTER-CLOCKWISE ) DIRECTION.
NOTICE FROM THE CURRENT SINE WAVE, THAT AT THIS TIME, THE CURRENT HAS
NOT REACHED ITS ‘PEAK’ VALUE, SO THE STRENGTH OF THE MAGNETIC FIELD
( THE STRENGTH OF THE ATTRACTION & REPULSION ) HAS NOT REACHED ITS
MAXIMUM STRENGTH.
BECAUSE THE AC CURRENT IS A ‘POSITIVE’ VALUE ( AS SHOWN BY THE SINE WAVE ),
THE CURRENT FLOWS IN THE DIRECTION INDICATED.
ALSO REALIZE THAT SINCE THE WINDING IS AN INDUCTOR, INDUCTIVE
REACTANCE, IS BEING CREATED BY THE MOVEMENT OF THE MAGNETIC FIELD
ACROSS THE WINDING ITSELF, REDUCING THE AMOUNT OF CURRENT THAT CAN
FLOW THROUGH THE WINDING.
HVACR ELECTRICAL COMPONENTS
PG 71 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
2-POLE AC INDUCTION MOTOR CONTINUED:
240
VAC
S
N
N
B
S
AC CURRENT
IN DIAGRAM ‘B’, ABOVE, THE CURRENT HAS REACHED ITS ‘POSITIVE PEAK’ VALUE.
THE STRENGTH OF THE MAGNETIC FIELD IS MAXIMUM & THE ROTOR HAS
MOVED ¼ OF THE WAY ( 90 DEGREES ) AROUND ITS ‘CIRCLE’ ( 360 DEGREES ).
240
VAC
S
N
N
S
C
AC CURRENT
IN DIAGRAM ‘C’, ABOVE, THE CURRENT DROPS BACK TOWARDS ZERO, STILL IN A
POSITIVE DIRECTION, SO THE CURRENT STILL FLOWS IN THE SAME DIRECTION &
THE ROTOR CONTINUES TO ROTATE CCW. ( NOW AT 180 DEGREES )
BUT, NOW THE NORTH POLE OF THE ROTOR IS NEXT TO THE SOUTH POLE OF THE
STATOR WINDING, & THE SOUTH POLE OF THE ROTOR IS NEXT TO THE NORTH POLE
OF THE STATOR WINDING.
THE ROTATION OF THE ROTOR WOULD STOP, UNLESS WE REVERSE THE POWER
SOURCE, AS WE DID IN THE DC MOTOR EXAMPLE PREVIOUSLY.
BUT LOOK, THE ALTERNATING CURRENT ( AC ) IS AUTOMATICALLY GOING TO
REVERSE ITS DIRECTION. ( SEE THE CURRENT SINE WAVE )
HVACR ELECTRICAL COMPONENTS
PG 72 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
2-POLE AC INDUCTION MOTOR CONTINUED:
240
VAC
N
S
S
D
N
AC CURRENT
IN DIAGRAM ‘D’ ABOVE, THE CURRENT FLOW THROUGH THE ‘MAIN’ WINDING
HAS REVERSED ITS DIRECTION. IT IS NOW INCREASING IN A NEGATIVE DIRECTION.
THE REVERSING OF THE CURRENT FLOW, REVERSES THE DIRECTION THAT THE
MAGNETIC FIELD IS MOVING, WHICH REVERSES THE MAGNETIC ‘POLES’ OF THE
STATOR ( MAIN ) WINDING.
SO, NOW, THE STATOR ‘POLE ON THE RIGHT IS A SOUTH POLE ( IT WAS A NORTH
POLE ), & THE STATOR ‘POLE’ ON THE LEFT IS NOW A NORTH POLE ( IT WAS A
SOUTH POLE ).
NOW THE NORTH POLE OF THE STATOR WINDING WILL REPULSE THE NORTH POLE
OF THE ROTOR, AS THE SOUTH POLE OF THE STATOR WILL REPULSE THE SOUTH
POLE OF THE ROTOR.
THE ROTOR HAS NOW ROTATED APPROXIMATELY 270 DEGREES.
240
VAC
N
S
N
S
AC CURRENT
E
HVACR ELECTRICAL COMPONENTS
PG 73 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
2-POLE AC INDUCTION MOTOR CONTINUED:
IN DIAGRAM ‘E’, THE CURRENT HAS PEAKED & STARTED FALLING BACK TOWARDS
ZERO, IN THE NEGATIVE DIRECTION.
THE ROTOR HAS ROTATED A COMPLETE 360 DEGREES.
( IT IS BACK WHERE IT STARTED )
THE CURRENT, OF COURSE, WOULD CONTINUE ON ITS NEXT ‘CYCLE’ & THE ENTIRE
PROCESS ( DIAGRAMS ‘A’ THROUGH ‘E’ ) WOULD REPEAT CONTINUOUSLY, UNTIL
THE CURRENT STOPS. THE MOTOR WOULD BE ROTATING.
IMPORTANT NOTE: IT TOOK ONE COMPLETE CYCLE OF THE AC CURRENT TO MAKE
THE ROTOR ROTATE 360 DEGREES, OR ONE FULL ROTATION.
SINCE THE FREQUENCY OF THE AC POWER, IN OUR COUNTRY, IS 60 HERTZ
( OR 60 CYCLES PER SECOND ), THEN AT THAT RATE, THE ROTOR WOULD TURN
60 COMPLETE ROTATIONS ( 360 DEGREES EACH ) IN EACH SECOND.
LETS SEE: 60 ROTATIONS PER SECOND & 60 SECONDS PER MINUTE, SO THE
AMOUNT OF ROTATIONS COMPLETED IN 1 MINUTE = 60 x 60 OR 3600.
SINCE THE SPEED OF A MOTOR IS A RATING OF REVOLUTIONS PER MINUTE
( RPM’S ), THEN THIS 2-POLE MOTOR WILL ROTATE AT 3600 RPM’S.
FREQ x 120
USING OUR SPEED FORMULA: RPM = NUMBER OF POLES
THEN 60 HERTZ TIMES 120 = 7200 & 7200 DIVIDED BY 2 ( POLES ) = 3600 RPM
AT THIS POINT, THERE ARE 2 IMPORTANT ISSUES THAT WE NEED TO DISCUSS:
1) HOW MUCH CURRENT WILL A MOTOR ‘DRAW’ FOR ITS OPERATION:
THIS IS A EFFECT OF THE COUNTER-EMF ( REACTANCE ) OF THE ‘MAIN’ WINDING
BUT ALSO, THE EFFECTS OF THE MAGNETIC FIELD PRODUCED BY THE CURRENT
FLOW IN THE ROTOR.
2) HOW DO WE KNOW WHICH DIRECTION THE ROTOR WILL TURN
WHEN POWER IS APPLIED TO THE MOTOR:
WHEN APPLYING A MOTOR TO A PARTICULAR APPLICATION, WE NEED TO KNOW
WHICH DIRECTION THE MOTOR IS GOING TO ROTATE. ( CW OR CCW )
BEFORE DISCUSSING HOW MUCH CURRENT A MOTOR WILL DRAW, THERE IS
ANOTHER ‘TERM’ THAT WE MUST BECOME FAMILIAR WITH: TORQUE
TORGUE: THE STRENGTH OF THE ROTOR WHILE IT IS TURNING.
IN OTHER WORDS, HOW DIFFICULT WOULD IT BE TO STOP THE MOTOR SHAFT
FROM TURNING. ( THINK ABOUT GRABBING A ROTATING MOTOR’S SHAFT, WITH
YOUR HAND, WHILE IT IS TURNING. )
TORQUE IS A RESULT OF THE STRENGTH OF THE MAGNETIC ‘POLES’ OF THE MOTORS
WINDING & THE STRENGTH OF THE FORCE OF ATTRACTION & REPULSION ( PUSHPULL FORCE ) BETWEEN THE ‘MAIN POLES’ &THE ‘ROTOR POLES’.
THE AMOUNT OF CURRENT FLOW DETERMINES THESE ‘STRENGTHS’.
HVACR ELECTRICAL COMPONENTS
PG 74 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: CURRENT DRAW:
THERE ARE 2 AMOUNTS OF CURRENT FLOW THAT A MOTOR ‘DRAWS’
FROM ITS SOURCE.
1) LOCKED-ROTOR CURRENT: THIS IS THE AMOUNT OF CURRENT THAT A
MOTOR WILL ‘DRAW’( FROM THE SOURCE ) TO GET THE ROTOR TO START
TURNING. LOCKED-ROTOR CURRENT WILL BE 4 TO 6 TIMES GREATER THAN
THE ‘NORMAL RUNNING CURRENT’ THAT A MOTOR WILL ‘DRAW’ AFTER THE
ROTOR IS ALREADY TURNING.
THE RESISTANCE ( IMPEDANCE ) THAT A MOTOR HAS TO OPPOSE ( REDUCE ) THE
MOVEMENT OF CURRENT IS AN ALGEBRAIC SUM OF THE DC RESISTANCE OF THE
WINDING, & THE COUNTER-EMF ( REACTANCE ) PRODUCED AS THE MAGNETIC
FIELD CUTS THE ‘COILS’ OF THE WINDING ( SELF-INDUCTANCE ).
EG: THE DC RESISTANCE OF A ‘MAIN WINDING’ MAY ONLY BE 2 OR 3 OHMS.
IF 240 VAC IS APPLIED TO THAT RESISTANCE, SAY 2 OHMS, THEN 120 AMPS OF
CURRENT WOULD FLOW ( OHMS LAW ). BUT, SINCE, THERE IS ALSO THE REACTANCE
( COUNTER-EMF ) OF THE WINDING, THE CURRENT WOULD THEN DROP TO, MAYBE,
50 OR 60 AMPS.
SO, THIS MOTOR WOULD ‘DRAW’ 50 TO 60 AMPS OF CURRENT FROM THE SOURCE,
BEFORE THE ROTOR BEGINS TO TURN.
ONE MORE, VERY IMPORTANT, CONCEPT THAT WE MUST LEARN:
WHAT EFFECT DOES THE ROTOR TURNING HAVE, ON THE MOTOR.
AS STATED BEFORE, WHEN CURRENT FLOWS THROUGH THE ‘MAIN WINDING’, THE
MAGNETIC FIELD PRODUCED BY THAT CURRENT FLOW, ‘CUTS’ THROUGH THE
ROTOR, & ‘INDUCES’ A VOLTAGE & A CURRENT INTO THE ROTOR.
ALSO, AS WE SHOULD KNOW, BY NOW, ANY CURRENT FLOW PRODUCES A
MAGNETIC FIELD. SO THE ROTOR PRODUCES ITS OWN MAGNETIC FIELD THAT WILL
THEN ‘CUT’ THE ‘COILS’ OF THE MAIN WINDING.
THIS PRODUCES A ‘COUNTER-EMF’ IN THE MAIN WINDING THAT WILL OPPOSE THE
VOLTAGE ACROSS THE MAIN WINDING.
THIS ‘COUNTER-EMF’ WILL FURTHER INCREASE THE IMPEDANCE OF THE MOTOR &
THEREFORE FURTHER REDUCE THE AMOUNT OF CURRENT DRAWN BY THE MOTOR.
WE SHOULD ALSO REMEMBER THAT THE MORE ‘LINES OF FORCE’ THAT ARE
CUT, THE GREATER THE ‘INDUCED’ POWER ( VOLTAGE & CURRENT ) WILL BE.
SO, WE CAN PRODUCE A GREATER ‘COUNTER-EMF’ & DRAW LESS CURRENT, IF WE
CAN MAKE THE ROTORS MAGNETIC FIELD ‘CUT’ ACROSS THE MAIN WINDING ‘COIL’
MORE OFTEN.
WELL, WHAT DO YOU THINK HAPPENS AS THE ROTOR BEGINS TO TURN????
HVACR ELECTRICAL COMPONENTS
PG 75 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: CURRENT DRAW CONTINUED:
REMEMBER THAT THE MAGNETIC FIELD, OF THE AC CURRENT IN THE ROTOR, IS
BUILDING UP & COLLAPSING AT A RATE OF 120 TIMES A SECOND ( 60 CYCLE PER
SECOND & CHANGES DIRECTION TWICE EACH CYCLE )
NOW, BY ROTATING THE ROTOR, MANY MORE ‘LINES OF FORCE’ FROM THE
ROTORS MAGNETIC FIELD CAN ‘CUT’ ACROSS THE MAIN WINDING, THUS
INCREASING THE STRENGTH OF THE ROTORS MAGNETIC FIELD.
THIS ALSO CREATES A STRONGER ‘COUNTER-EMF’ ( MORE COUNTER-VOLTAGE ),
IN THE MAIN WINDING, INCREASING THE REACTANCE PRODUCED BY THE
‘COUNTER-EMF’, & THEREFORE REDUCING THE CURRENT FLOW EVEN FURTHER.
VERY IMPORTANT POINT:
AS THE ROTORS SPEED INCREASES, THE COUNTER-EMF INCREASES. THE
‘REACTANCE’ INCREASES SO THE IMPEDANCE INCREASES.
IF THE IMPEDANCE INCREASES - THE CURRENT FLOW DECREASES.
SO, AS THE SPEED OF THE ROTOR INCREASES, THE CURRENT ‘DRAWN’ BY
THE ‘MAIN’ WINDING OF THE MOTOR DECREASES.
WHEN THE ROTOR REACHES ITS FULL SPEED ( BASED ON THE NUMBER OF POLES ),
THE CURRENT DROPS TO ITS LOWEST VALUE, WHICH IS REFERRED TO AS:
THE SECOND AMOUNT OF CURRENT DRAWN BY A MOTOR IS:
2) THE FULL-LOAD AMPS ( FLA ) OF THE MOTOR
THE FULL-LOAD AMP DRAW OF THE MOTOR IS WHAT THE MOTOR WILL ‘DRAW’,
FROM THE SOURCE, WHEN THE ROTOR IS ROTATING AT ITS MAXIMUM SPEED.
THE FULL-LOAD AMP ( FLA ) OF A MOTOR WILL BE PRINTED ON THE MOTOR’S
‘NAMEPLATE’, WHICH IS A ‘TAG’ APPLIED TO ALL EQUIPMENT SHOWING THE
‘VOLTAGE & NORMAL CURRENT DRAW ( FLA )’ OF THE EQUIPMENT, ALONG WITH
OTHER PERTINENT INFORMATION.
EVERY MOTOR WILL DRAW LOCKED-ROTOR CURRENT AT THE 1ST INSTANT
THAT POWER IS APPLIED, AND...
AS THE ROTOR GETS UP TO ITS FULL SPEED, THE CURRENT WILL DECREASE TO ITS
FULL-LOAD ( FLA ) VALUE.
BECAUSE A MOTOR MAY NOT BE FULLY LOADED WHEN IT OPERATES, IT MAY NOT
DRAW ALL OF ITS FULL-LOAD AMPERAGE ( FLA ). THE ACTUAL CURRENT DRAW OF
ANY MOTOR MAY BE SLIGHTLY LESS ITS FULL-LOAD AMPERAGE.
HOWEVER, A MOTOR SHOULD NEVER DRAW MORE THAN ITS FULL-LOAD AMPERAGE
( FLA ) , ONCE THE MOTOR HAS REACHED FULL SPEED.
IF IT DRAWS MORE THAN FULL-LOAD AMPERAGE, THERE IS A PROBLEM
WITH THE MOTOR OR THE DEVICE THE MOTOR IS TURNING.
HVACR ELECTRICAL COMPONENTS
PG 76 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION:
FOR A MOTOR TO OPERATE A MECHANICAL DEVICE PROPERLY, THE MOTOR MUST
ROTATE IN THE CORRECT DIRECTION, EITHER CW OR CCW.
LOOKING AT THE DIAGRAM OF THE 2-POLE INDUCTION MOTOR, BELOW, HOW DO
WE KNOW WHICH DIRECTION THE MOTOR WILL ROTATE, WHEN POWER IS 1ST
APPLIED TO THE MOTOR?
240
VAC
S
N
S
N
IN THIS CASE, THE MOTOR COULD ROTATE IN EITHER DIRECTION, BECAUSE THERE
IS NOTHING TO ‘FORCE’ THE ROTOR TO MOVE IN EITHER DIRECTION.
THE ‘START’ WINDING:
A SECOND
WINDING
CALLED A
‘START’ WINDING
‘MAIN’ OR
‘RUN’
WINDING
ROTOR
HVACR ELECTRICAL COMPONENTS
PG 77 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
IN THE ABOVE DIAGRAM, WE HAVE ADDED AN ADDITIONAL WINDING, CALLED
A START WINDING.
BY ADDING THE ‘START WINDING’, WE CAN CONTROL THE DIRECTION THAT THE
MOTOR STARTS, PLUS, PROVIDE ADDITIONAL STARTING TORQUE TO THE MOTOR.
UNDERSTAND: IT TAKES MORE ‘FORCE’ ( TORQUE ) TO GET THE MOTOR TO
START TURNING ( FROM A DEAD STOP ) THAN IT DOES TO KEEP IT TURNING, ONCE
IT IS MOVING.
TORQUE IS A RESULT OF THE STRENGTHS OF THE MAGNETIC ‘POLES’ OF THE
WINDINGS, WHICH CAUSE A ‘FORCE’ TO ATTRACT OR REPEL THE ROTOR.
THE STRONGER THE ‘FORCE OF ATTRACTION OR REPULSION ( THE SRENGTH OF
THE MAGNETIC ‘POLE’ ), THE MORE TORQUE THAT THE MOTOR PRODUCES TO
CAUSE THE ROTATION OF THE ROTOR.
THE MAIN FACTOR IN PRODUCING STRENGTH, IN THE WINDING INDUCTOR, IS THE
AMOUNT OF CURRENT FLOW THROUGH THE WINDING ( POLE ).
( SINCE THE NUMBER OF TURNS & THE CORE MATERIAL ARE ‘SET’ BY THE
MANUFACTURER )
ACTUALLY, IT IS THE ‘POWER’ THAT THE WINDING INDUCTOR PRODUCES THAT
MATTERS, BUT SINCE THE VOLTAGE IS ALREADY DETERMINED BY THE SOURCE,
THE ONLY FACTOR THAT CAN BE CHANGED TO PRODUCE MORE OR LESS POWER IS
THE AMOUNT OF CURRENT FLOW, THAT THE WINDING ‘DRAWS’.
THERE ARE 2 DIFFERENT ‘TORQUES’ PRODUCED BY A MOTOR:
1) STARTING TORQUE: THE ‘FORCE’ NECESSARY TO CAUSE THE ROTOR TO
BEGIN TO ROTATE, FROM ITS ‘DEAD STOPPED’ POSITION.
THE MOTOR HAS TO APPLY THE GREASTEST ‘TORQUE’, TO GET THE ROTOR TO JUST
BEGIN TO TURN.
2) RUNNING TORQUE: THE AMOUNT OF TORQUE NECESSARY TO KEEP A ROTOR
TURNING, ONCE IT HAS ALREADY BEGUN TO TURN.
THIS IS THE LEAST AMOUNT OF TORQUE PRODUCED BY THE MOTOR.
TO UNDERSTAND HOW A START WINDING, CAUSES MORE TORQUE TO BE
PRODUCED, & CAUSES THE ROTOR TO TURN IN A PARTICULAR DIRECTION,
WE MUST UNDERSTAND ANOTHER ASPECT OF INDUCTANCE.
INDUCTANCE CAUSES A ‘PHASE’ SHIFT BETWEEN THE VOLTAGE, APPLIED
TO THE INDUCTOR ( WINDING ) & THE CURRENT THAT IS ‘DRAWN’ BY THE
INDUCTOR ( WINDING ).
IN OTHER WORDS, THE CURRENT DOESN’T START TO FLOW AT THE SAME TIME
THAT THE VOLTAGE IS APPLIED TO THE INDUCTOR ( LIKE IT WOULD IN A RESISTIVE
CIRCUIT ).
THE VOLTAGE IS APPLIED TO THE INDUCTOR & SOME ‘TIME’ LATER, THE CURRENT
STARTS TO FLOW.
HVACR ELECTRICAL COMPONENTS
PG 78 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
THE ‘TIME’ THAT ELAPSES BETWEEN THE VOLTAGE BEING APPLIED TO THE
INDUCTOR & THE CURRENT STARTING TO FLOW IS A DIRECT RELATIONSHIP OF
THE AMOUNT OF INDUCTANCE THAT THE INDUCTOR HAS.
THE GREATER THE INDUCTANCE, THE GREATER THE AMOUNT OF TIME IT TAKES
FOR THE CURRENT TO FLOW AFTER THE VOLTAGE IS APPLIED.
THIS CAN BE ILLUSTRATED BY THE FOLLOWING GRAPH OF THE VOLTAGE &
CURRENT, IN AN INDUCTOR.
ZERO
AMOUNT &
TIME
‘TIME’
LINE
LINE
SHOWING
AMOUNT
NOTICE THE DIFFERENCE IN THE
‘TIME’ THAT THE CURRENT
‘LAGGED’ BEHIND THE VOLTAGE
NOTICE, IN THE GRAPH ON THE LEFT, THAT THE VOLTAGE IS APPLIED AT THE
‘ZERO POINT’ ON THE GRAPH, BUT THE CURRENT DIDN’T START TO FLOW UNTIL
LATER. WE SAY THAT THE CURRENT ‘LAGS’ THE VOLTAGE, OR THE VOLTAGE ‘LEADS’
THE CURRENT. [ ELI – VOLTAGE ( E ) LEADS ( L ) CURRENT ( I ) ]
THE GRAPH, ON THE RIGHT, SHOWS A GREATER ‘TIME’ DIFFERENCE BETWEEN
WHEN THE VOLTAGE STARTED & WHEN THE CURRENT STARTED.
THIS IS DUE TO A GREATER AMOUNT OF INDUCTANCE IN THE INDUCTOR
( WINDING ) ON THE RIGHT.
SO, AN INDUCTOR CAUSES THE VOLTAGE & THE CURRENT TO BE OUT-OF-PHASE,
WITH EACH OTHER.
( OUT-OF-PHASE SIMPLY MEANS ‘OCCURRING AT DIFFERENT TIMES’ )
BUT, WHAT GOOD DOES ALL THIS DO FOR OUR MOTOR ???
TO UNDERSTAND THIS QUESTION, WE MUST BEGIN BY UNDERSTANDING THAT A
‘START’ WINDING IS MADE WITH A DIFFERENT AMOUNT OF INDUCTANCE THAN THE
‘MAIN’ OR RUN WINDING HAS.
SO, THE CURRENTS FLOWING THROUGH THE START & RUN WINDINGS WILL BE
OUT-OF-PHASE WITH EACH OTHER.
IN OTHER WORDS, THE CURRENTS WILL NOT START, PEAK, OR FALL BACK TO ZERO
AT THE SAME TIME.
HVACR ELECTRICAL COMPONENTS
PG 79 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
ONE MORE ‘POINT’ TO UNDERSTAND:
THE ‘MAIN’ OR RUN WINDING &THE ‘START’ WINDING ARE CONNECTED IN
PARALLEL WITH EACH OTHER, SO THAT THEY RECEIVE THE SAME SOURCE
VOLTAGE.
‘MAIN’ WINDING
‘SCHEMATIC’
DIAGRAM OF
MOTOR
‘START’ WINDING
NOTICE: THE ‘START’ WINDING HAS MORE TURNS OF WIRE THAN THE ‘MAIN’
WINDING. THIS MEANS THAT THE ‘START’ WINDING WILL HAVE MORE INDUCTANCE
THAN THE ‘MAIN’ WINDING ( AS WELL AS MORE DC RESISTANCE – DUE TO SMALLER
WIRE USED FOR THE ‘START’ WINDING & MORE WIRE USED, DUE TO MORE TURNS
OF WIRE ).
THE VOLTAGE IS APPLIED TO THE ‘MAIN’ & ‘START’ WINDINGS AT THE SAME
‘TIME’, BUT DUE TO THE DIFFERENCE IN THE INDUCTANCE OF EACH WINDING, THE
CURRENTS, IN EACH WINDING, WILL START AT DIFFERENT TIMES.
THIS IS ILLUSTRATED BY THE GRAPH BELOW:
NOTICE; THE ‘START’ TIME OF THE
VOLTAGE & THE CURRENTS
THE VOLTAGE ( BLACK )
STARTS AT THE ZERO POINT.
BUT, THE CURRENT OF THE ‘MAIN’
WINDING ( GREEN )
DOESN’T START UNTIL SOME ‘TIME’
LATER.
AND SINCE THE INDUCTANCE OF
THE ‘START’ WINDING ( BLUE )
IS GREATER THAN THE ‘MAIN;
WINDING, THE CURRENT, IN THE
START WINDING IS ‘DELAYED’ EVEN
FURTHER
THE PURPOSE OF THE OUT-OF-PHASE CONDITION, BETWEEN THE WINDING
CURRENTS IS TO APPLY DIFFERENT STRENGTHS TO THE MAGNETIC ‘POLES’ OF THE
MOTOR AT DIFFERENT TIMES, TO CREATE GREATER ‘TORQUE’
( STRENGTH OF ATTRACTION OR REPLUSION ), ON THE ROTOR.
HVACR ELECTRICAL COMPONENTS
PG 80 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
NOW, LETS GO BACK TO OUR 2-POLE AC INDUCTION MOTOR DIAGRAM & SEE IF WE
CAN RELATE WHAT WE HAVE JUST LEARNED TO THE OPERATION OF THE MOTOR.
‘START’
WINDING
‘MAIN’ OR
‘RUN’
WINDING
ROTOR
IMPORTANT POINT: ONLY THE ‘MAIN’ OR ‘RUN’ WINDING ‘POLES ARE
CONSIDERED WHEN DETERMINING THE ‘SPEED’ OF AN AC INDUCTION MOTOR. THE
‘START’ WINDING ‘POLES’ ARE NOT CONSIDERED AS A ‘POLE’ OF THE MOTOR.
THE MOTOR PICTURED ABOVE, HAS 2 ‘MAIN’ WINDINGS, SO IT IS A 2-POLE MOTOR.
BUT, IT ALSO HAS 2, ‘START’ WINDING ‘POLES’ WHICH ARE 90 DEGREES APART
FROM THE ‘MAIN’ WINDING ‘POLES’.
NOTICE THAT BOTH WINDINGS ARE PARALLEL TO THE SOURCE.
WE SHOULD UNDERSTAND, BY NOW, THAT THE ENTIRE IDEA BEHIND ‘CAUSING THE
ROTOR TO ROTATE’ IS SIMPLY THE PRINCIPLE OF THE ‘LAW OF CHARGES’,
WHICH MEANS THAT THE WINDING ‘POLES’ MUST EITHER ATTRACT OR REPEL
THE ROTOR TO PRODUCE MOVEMENT OF THE ROTOR.
THIS SAME ATTRACTION & REPULSION IS USED BY THE ‘START’ WINDING TO CAUSE
THE ROTOR TO ROTATE IN THE DESIRED DIRECTION.
HVACR ELECTRICAL COMPONENTS
PG 81 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
N
S
N
S
S
N
N
S
N
S
LOOKING AT THE DIAGRAM ABOVE, WHICH DIRECTION WOULD THE ROTOR
MOVE??
IF WE UNDERSTAND THE ‘LAW OF CHARGES’, THE ROTOR WOULD MOVE IN A
COUNTER-CLOCKWISE ( CCW ) DIRECTION.
THE ‘NORTH POLE’ OF THE ROTOR WOULD ROTATE UPWARDS, BEING ATTRACTED
TOWARDS THE ‘SOUTH POLE’ OF THE ‘START WINDING’.
IT WOULD BE REPULSED BY THE ‘NORTH POLE’ OF THE ‘MAIN WINDING’
& ALSO BY THE ‘NORTH POLE’ OF THE ‘START WINDING’ ( AT THE BOTTOM ).
SO, THE DIRECTION OF THIS MOTOR WOULD BE COUNTER-CLOCKWISE ( CCW ).
THE ‘TORQUE’ OF THIS MOTOR WOULD THEN BE DEPENDANT UPON HOW STRONG
THE FORCE , OF THE ATTRACTION ( TO THE SOUTH POLE OF THE START WINDING )
WOULD BE, & HOW STRONG THE FORCE, OF THE REPLUSION ( FROM BOTH
NORTH POLES ), WOULD BE.
HVACR ELECTRICAL COMPONENTS
PG 82 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
THE STRENGTH OF THE ATTRACTION & REPULSION IS A DIRECT RESULT OF THE
POWER USED BY EACH WINDING ‘POLE’.
AS WE ARE AWARE, THE POWER USED BY EACH WINDING ( OR POLE OF EACH
WINDING ) IS A DIRECT RESULT OF THE VOLTAGE & THE CURRENT FLOW THROUGH
EACH WINDING. ( P = E x I )
SO, THE START WINDING ACCOMPLISHES 2 THINGS:
1) IT PROVIDES FOR A SPECIFIC DIRECTION OF ROTATION.
2) IT PROVIDES ADDITIONAL TORQUE.
TORQUE IS IMPORTANT IN THAT EVERY DEVICE OPERATED BY A MOTOR WILL
HAVE DIFFERENT ‘RESISTANCES’ TO MOVEMENT.
SO, DIFFERENT DEVICES WILL NEED DIFFERENT AMOUNTS OF MOTOR TORQUE
TO CAUSE THEIR PROPER OPERATION.
EG: SUCH AS A FAN OR A WATER PUMP. IT WILL TAKE MUCH MORE MOTOR
TORQUE TO MAKE THE PUMP OPERATE THAN IT DOES TO JUST MAKE A FAN TURN.
ALSO A LARGE FAN NEEDS MORE MOTOR TORQUE TO MAKE IT MOVE THAN A
SMALL FAN NEEDS.
SINCE TORQUE IS A RELATION TO ‘POWER’ – A MOTORS TORQUE IS REFERENCED
BY THE MOTORS RATINGS.
A MOTOR IS RATED FOR HOW MANY HORSEPOWER IT CAN PRODUCE.
AS WELL AS THE VOLTAGE THAT THE MOTOR OPERATES ON.
ONE HORSEPOWER ( MOTOR POWER ) = 746 WATTS ( ELECTRICAL POWER )
NOW, IF THE ABOVE DIAGRAMMED MOTOR TURNS IN THE COUNTER-CLOCKWISE
( CCW ) DIRECTION, THEN HOW CAN WE CHANGE ITS DIRECTION TO A CLOCK-WISE
( CW ) DIRECTION, IF NEEDED ?
THE ONLY WAY TO PROPERLY CHANGE THE DIRECTION OF A SINGLEPHASE AC INDUCTION MOTOR IS TO:
REVERSE THE DIRECTION THAT THE CURRENT FLOWS THROUGH THE
START WINDING.
THIS IS THE ONLY WAY TO REVERSE THE DIRECTION OF THE MOTOR & HAVE IT
OPERATE PROPERLY.
THE DIRECTION OF THE CURRENT THROUGH THE START WINDING IS IN RELATION
TO THE DIRECTION OF CURRENT FLOW THROUGH THE ‘MAIN’ ( OR ‘RUN ) WINDING,
AT A SPECIFIC MOMENT IN TIME.
WHEN TALKING ABOUT ALTERNATING CURRENTS ( AC ), WE MUST ALWAYS REFER
TO A SPECIFIC ‘MOMENT IN TIME’, AS THE AC IS CONSTANTLY CHANGING &
REVERSING.
HVACR ELECTRICAL COMPONENTS
PG 83 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
THE DIAGRAM, BELOW, IS THE SAME MOTOR THAT WE HAD PREVIOUSLY
DISCUSSED, WHICH WOULD ROTATE IN A COUNTER-CLOCKWISE ( CCW )
DIRECTION.
BY, SIMPLY, REVERSING THE WAY THE START WINDING IS CONNECTED ( BOLD RED
LINES ) TO THE SOURCE, WE CAN REVERSE THE DIRECTION THAT THE MOTOR WILL
ROTATE.
NOTICE THAT THE ‘MAIN’ ( OR ‘RUN’ ) WINDING IS STILL CONNECTED IN THE SAME
MANNER AS IT WAS IN THE PREVIOUS DIAGRAM.
S
N
N
S
S
N
N
S
S
N
NOW, IN THIS DIAGRAM, THE DIRECTION OF THE CURRENT FLOW THROUGH THE
‘START WINDING’ HAS BEEN REVERSED ( GOING IN THE OPPOSITE DIRECTION ),
AS COMPARED TO THE DIRECTION OF CURRENT FLOW IN THE ‘MAIN’ WINDING.
REVERSING THE CURRENT FLOW, REVERSES WHICH END OF EACH
‘START WINDING POLE’ IS A ‘NORTH POLE’ OR A ‘SOUTH POLE’.
LOOKING AT THE ‘POLES’ ( MAIN & START ), WHICH DIRECTION WILL THE MOTOR
ROTATE NOW ??
THAT’S RIGHT……CLOCK-WISE !
HVACR ELECTRICAL COMPONENTS
PG 84 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DIRECTION OF ROTATION CONTINUED:
WE CHANGED THE DIRECTION OF THE MOTORS ROTATION, SIMPLY, BY REVERSING
THE DIRECTION THAT THE CURRENT FLOWS IN THE ‘START WINDING’.
( IN REFERENCE TO THE DIRECTION OF CURRENT FLOW , IN THE MAIN WINDING )
REPEAT: THIS IS THE ONLY WAY TO PROPERLY CHANGE THE DIRECTION OF
ROTATION OF A SINGLE-PHASE AC INDUCTION MOTOR.
NOW, LETS LOOK AT THE DIAGRAM FOR A 4-POLE AC INDUCTION MOTOR.
‘MAIN’
WINDING
‘POLES
‘START’
WINDING
‘POLES
A 4-POLE MOTOR WOULD HAVE A ‘SPEED’ OF: 1800 RPMS
RPMS = FREQ x 120 = 7200
# OF POLES
4
= 1800 RPMS
THE SCHEMATIC DIAGRAM FOR THIS 4-POLE MOTOR WOULD LOOK, EXACTLY,
THE SAME AS A 2-POLE MOTOR DIAGRAM.
THE START WINDING
NOTICE:
USES SMALLER WIRE
THE
START
WINDING
SO IT HAS MORE DC
HAS
MORE
TURNS
RESISTANCE THAN
THAN THE MAIN
THE MAIN WINDING
WINDING
HVACR ELECTRICAL COMPONENTS
PG 85 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TYPES OF MOTORS:
THERE ARE 6 TYPES OF AC INDUCTION MOTORS:
LISTED ACCORDING TO THE AMOUNT OF ‘TORQUE’ THAT IS PRODUCED BY THE
MOTOR.
1) SHADED-POLE: HAS ONLY A ‘MAIN’ ( ‘RUN’ ) WINDING.
( NO START WINDING USED ).
HAS VERY LITTLE STARTING & RUNNING TORQUE.
USED TO OPERATE SMALL DEVICES THAT NEED VERY LITTLE TORQUE.
EG: FAN MOTORS ON REFRIGERATORS OR FREEZERS.
SYMBOL:
THE SHADED-POLE MOTOR CAN HAVE AS MANY ‘MAIN WINDING POLES’ AS
ANY OTHER TYPE OF MOTOR ( & THEREFORE THE SAME SPEEDS ).
THE DIRECTION OF ROTATION OF A SHADED-POLE MOTOR IS DETERMINED BY
A ‘RING’ OF WIRE ATTACHED TO ONE END OF ONE ‘MAIN POLE’.
TO REVERSE THE DIRECTION OF A SHADED-POLE MOTOR, THE ‘RING’ MUST BE
TURNED AROUND, WHERE IT FACES THE OTHER SIDE OF THE ROTOR.
THE MOTOR WILL
ROTATE IN THE
DIRECTION OF THE
‘SHADED’ POLE
( THE POLE WITH
THE ‘RING’ ON
IT )
ROTOR
THE PLACEMENT
OF THE ‘RING’
DETERMINES
THE DIRECTION
THAT THIS
MOTOR WILL
ROTATE
ROTOR
HVACR ELECTRICAL COMPONENTS
PG 86 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TYPES OF MOTORS:
2) SPLIT-PHASE MOTOR: A SPLIT-PHASE MOTOR HAS BETTER STARTING &
RUNNING TORQUE THAN THE SHADED-POLE MOTOR DOES.
THE SPLIT-PHASE MOTOR USES A START WINDING:
WHICH IS WHY IT IS CALLED A SPLIT-PHASE MOTOR – THE MAIN & START WINDING
ARE OUT-OF-PHASE WITH EACH OTHER – IN OTHER WORDS, THE PHASE OF THE
SOURCE IS SPLIT DIFFERENTLY BETWEEN THE MAIN & START WINDINGS.
BESIDES ITS PHYSICAL APPEARANCE, THE SPLIT-PHASE MOTOR HAS ONE
CHARACTERISTIC THAT NO OTHER MOTOR HAS.
A CENTRIFUGAL SWITCH
A CENTRIFUGAL SWITCH IS A SWITCH, INSIDE THE MOTOR, THAT IS USED TO REMOVE
THE START WINDING AFTER THE MOTOR HAS REACHED APPROXIMATELY 75-80 %
OF ITS FULL SPEED.
ANOTHER IMPORTANT ‘BIT’ OF INFORMATION:
THE START WINDINGS, IN THE SPLIT-PHASE MOTOR ARE MADE OF VERY SMALL
WIRE ( MUCH SMALLER THAN MAIN WINDING ).
THEY CAN NOT HANDLE THE HEAT, CAUSED BY THE CURRENT FLOW,
FOR TOO LONG, OR THEY WILL BURN UP.
THE START WINDING ( SPLIT-PHASE MOTOR ) MUST BE REMOVED FROM THE
CIRCUIT BEFORE THE ROTOR REACHES FULL SPEED.
IMPORTANT TO KNOW:
THE CURRENT FLOW THROUGH THE START WINDING INCREASES AS THE SPEED OF
THE ROTOR INCREASES.
THIS IS OPPOSITE TO THE MAIN WINDING, WHOSE CURRENT FLOW DECREASES AS THE
ROTOR SPEED INCREASE.
SO, THE MAXIMUM CURRENT FLOW ( & MAXIMUM HEAT ) THROUGH THE START
WINDING IS WHEN THE ROTOR REACHES FULL SPEED.
TO PROTECT THE START WINDING, IT MUST BE REMOVED FROM THE MOTOR
CIRCUIT BEFORE THE ROTOR REACHES FULL SPEED.
IN A SPLIT-PHASE MOTOR, THE CENTRIFUGAL SWITCH REMOVES THE START
WINDING AT 75-80 % OF FULL SPEED.
THE CENTRIFUGAL SWITCH OPERATES ON THE ‘CENTRIFUGAL FORCE’, CREATED
BY THE ‘SPINNING’ ROTOR. AS THE ROTOR NEARS FULL SPEED, THE CENTRIFUGAL
SWITCH ‘POLE’ WILL ‘FLY OPEN’ DUE TO THE ‘CENTRIFUGAL FORCE’ OF THE
ROTORS MOVEMENT. ( THE SWITCH IS ATTACHED TO THE ROTOR )
HVACR ELECTRICAL COMPONENTS
PG 87 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: SPLIT-PHASE MOTOR CONTINUED:
VERY IMPORTANT POINT:
AS WAS MENTIONED ABOVE, THE START WINDING CURRENT INCREASES AS THE
SPEED OF THE ROTOR INCREASES. ( DIRECT CORRELATION )
IT WAS ALSO MENTIONED THAT THE MAIN WINDING CURRENT DECREASED AS THE
SPEED OF THE ROTOR INCREASED. ( INVERSE CORRELATION )
WE HAVE DISCUSSED THE COUNTER-EMF PRODUCED BY THE ROTOR, WHICH
COUNTERACTS THE VOLTAGE OF THE MAIN ( RUN ) WINDING ( REACTANCE ), THUS
REDUCING THE CURRENT FLOW, IN THE MAIN WINDING AS SPEED INCREASES.
( LOCKED-ROTOR CURRENT VS. FULL LOAD CURRENT )
HOWEVER, WE HAVE NOT DISCUSSED HOW THIS SAME COUNTER-EMF PRODUCED
BY THE ROTOR, EFFECTS A ‘START WINDING’.
THIS SAME COUNTER-EMF, PRODUCED BY THE SPEED OF THE TURNING ROTOR,
IS ALSO ‘FELT’ BY THE START WINDING.
ONLY, THE START WINDING, IS MADE UP OF MORE TURNS OF WIRE THAN THE MAIN
WINDING. IF YOU RECALL WHAT YOU LEARNED IN TRANSFORMERS, IF AN INDUCED
VOLTAGE IS TRANSFERRED INTO A CONDUCTOR WITH MORE TURNS THAN THE
WINDING THAT PRODUCED THE VOLTAGE ( ROTOR ), WHAT VOLTAGE WOULD BE
INDUCED INTO THE WINDING WITH MORE TURNS OF WIRE??
OF COURSE, A HIGHER VOLTAGE ( LIKE A STEP-UP TRANSFORMER ).
SO, SINCE THE START WINDING HAS MORE TURNS OF WIRE & THE ROTOR INDUCES
A VOLTAGE INTO THE START WINDING, THE VOLTAGE, FELT BY THE START
WINDING, WILL BE GREATER THAN THE VOLTAGE OF THE ROTOR.
IN OTHER WORDS, THE VOLTAGE ‘FELT’ BY THE START WINDING IS
GREATER THAN THE SUPPLY ( SOURCE ) VOLTAGE.
THIS VOLTAGE CAN BE MEASURED.
PER OHMS LAW, IF VOLTAGE IS INCREASED & THE RESISTANCE ( IMPEDANCE OF
THE WINDING ) STAYS THE SAME, THEN CURRENT FLOW INCREASES.
TO SUMMARIZE: THE ROTOR INDUCES A VOLTAGE INTO THE START WINDING,
BASED ON THE SPEED OF THE ROTOR. THE GREATER THE SPEED, THE GREATER THE
VOLTAGE INDUCED.
BECAUSE OF THE DIFFERENCE IN THE NUMBER OF TURNS,
THE VOLTAGE ACROSS THE START WINDING WILL BE GREATER THAN THE
‘SOURCE VOLTAGE’.
EG: THE SOURCE VOLTAGE IS 240 VAC, THE VOLTAGE READ WITH A VOLTMETER,
ACROSS THE START WINDING, COULD BE AS HIGH AS 450 VAC, WHEN THE ROTOR
REACHES FULL SPEED.
BEFORE THE ROTOR BEGINS TO TURN ( LOCKED-ROTOR), THE VOLTAGE ACROSS
THE START WINDING WOULD BE THE SAME 240 VAC AS THE SOURCE.
BUT, AS THE ROTOR BEGINS TO ROTATE, THE VOLTAGE ACROSS THE START
WINDING WILL INCREASE WITH THE SPEED OFTHE ROTOR.
HVACR ELECTRICAL COMPONENTS
PG 88 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: SPLIT-PHASE MOTOR CONTINUED:
NOW, LETS TAKE WHAT WE HAVE LEARNED & APPLY IT TO A SPLIT-PHASE MOTOR.
BECAUSE, THE VOLTAGE ACROSS THE START WINDING INCREASES, AS THE SPEED
OF THE ROTATING ROTOR INCREASES, THEN THE MAXIMUM VOLTAGE THAT
THE START WINDING WILL ‘FEEL’ IS WHEN THE ROTOR REACHES FULL SPEED.
AND SINCE, CURRENT FLOW IS A DIRECT RESULT OF THE APPLIED VOLTAGE, THEN
THE CURRENT FLOW THROUGH THE START WINDING WILL ALSO INCREASE AS
THE SPEED OF THE ROTOR INCREASES.
SO, THE MAXIMUM CURRENT FLOW, THROUGH THE START WINDING, OCCURS
WHEN THE ROTOR REACHES FULL SPEED.
BECAUSE OF THE WAY A MOTOR IS MADE, SMALLER WIRE IS USED FOR THE START
WINDING. SO, THE START WINDING MUST BE REMOVED FROM THE CIRCUIT,
BEFORE THE MAXIMUM CURRENT CAN FLOW THROUGH THE SMALL WIRE.
THE SPLIT-PHASE MOTOR USES THE CENTRIFUGAL SWITCH TO REMOVE THE START
WINDING FROM THE MOTORS ELECTRICAL CIRCUIT, BEFORE THE ROTOR
REACHES FULL SPEED.
THERE ARE 2 TYPES OF SPLIT-PHASE MOTORS:
( RECOGNIZED BY THE CENTRIFUGAL SWITCH )
A) RESISTANCE-START / INDUCTION-RUN ( RSIR ): A RESISTANCE-START /
INDUCTANCE-RUN SPLIT-PHASE MOTOR HAS A MAIN WINDING & A START WINDING.
THE START WINDING IS REMOVED BY THE USE OF A CENTRIFUGAL SWITCH, ONCE
THE ROTOR REACHES 75 – 80 % OF ITS FULL SPEED.
A RESISTANCE-START / INDUCTION-RUN MOTOR USES RESISTANCE ALONG WITH
THE INDUCTANCE OF THE WINDINGS TO CREATE A PHASE-SHIFT BETWEEN
THE MAIN & START WINDINGS. THIS PHASE SHIFT MUST BE ACCOMPLISHED TO
ALLOW THE MAIN & START WINDING ‘POLES’ TO CREATE THEIR ‘POLE’ STRENGTHS
AT DIFFERENT TIMES ( OF THE CURRENTS SINE WAVE )
THE SYMBOL FOR A ‘RESISTANCE-START / INDUCTION-RUN SPLITPHASE MOTOR:
MAIN
WINDING
OVERLOAD(OL)
‘START’
WINDING
CENTRIFUGAL
SWITCH (RED)
HVACR ELECTRICAL COMPONENTS
PG 89 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: SPLIT-PHASE MOTORS CONTINUED:
2ND TYPE OF SPLIT-PHASE MOTOR:
B) CAPACITOR-START / INDUCTION –RUN ( CSIR ): THE CAPACITOR-START /
INDUCTION-RUN SPLIT-PHASE MOTOR IS DESIGNED VERY SIMILAR TO THE ‘RSIR’
( RESISTANCE-START / INDUCTION-RUN ) MOTOR PREVIOUSY DESCRIBED.
THE MOTOR OPERATES ALMOST THE SAME AS THE RSIR MOTOR. THE ONLY
EXCEPTION BEING IS THAT THE CSIR ( CAPACITOR-START / INDUCTION-RUN )
SPLIT-PHASE MOTOR, USES A CAPACITOR, IN SERIES WITH THE START WINDING, TO
ADD ADDITIONAL STARTING TORQUE TO THE MOTOR.
THE MOTOR STILL USES A CENTRIFUGAL SWITCH TO TAKE THE START WINDING &,
NOW THE START CAPACITOR OUT OF THE CIRCUIT WHEN THE ROTOR SPEED
REACHES APPROXIMATELY 75-80 % OF FULL SPEED.
THE SYMBOL FOR A CAPACITOR-START / INDUCTION-RUN, ( CSIR )
SPLIT-PHASE MOTOR IS ALMOST THE SAME AS THE RSIR MOTOR, AGAIN,
WITH ONE EXCEPTION. THE CAPACITOR IS NOT INCLUDED IN THE
MOTOR DIAGRAM AS IT IS OUTSIDE THE MOTOR ITSELF.
TWO WIRES, FROM WITHIN THE MOTOR, ARE USED TO CONNECT
THE CAPACITOR INTO THE ELECTRICAL CIRCUIT.
MAIN
WINDING
START
CAPACITOR
OVERLOAD ( OL )
‘START’
WINDING
CENTRIFUGAL
SWITCH
THE CAPACITOR IS
CONNECTED
BETWEEN THE 2
BLUE WIRES
ON MOST CSIR, SPLIT-PHASE MOTORS, THE START CAPACITOR IS ATTACHED TO
THE OUTSIDE OF THE MOTOR.
THE ‘START CAPACITOR’ IS CONNECTED IN SERIES WITH THE START WINDING, AS
SHOWN IN THE SCHEMATIC DIAGRAM BELOW:
CENTRIFUGAL
MAIN WINDING
SWITCH
START WINDING
START
CAPACITOR
HVACR ELECTRICAL COMPONENTS
PG 90 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: START & RUN CAPACITORS:
A CAPACITOR IS INSTALLED, IN A MOTORS ELECTRICAL CIRCUIT, TO
PROVIDE ADDITIONAL MECHANICAL ‘TORQUE’.
AS PREVIOUSLY DISCUSSED: TORQUE IS A REFERENCE TO HOW ‘HARD’ THE
MOTORS ROTOR ( & SHAFT ) TURNS.
AS PREVIOUSLY DISCUSSED: THERE ARE 2 ‘TYPES’ OF TORQUE.
1) STARTING TORQUE: THE AMOUNT OF TORQUE NECESSARY TO GET THE
ROTOR STARTED TURNING, FROM A DEAD STOP.
2) RUNNING TORQUE: THE AMOUNT OF TORQUE THAT THE MOTOR WILL
MAINTAIN, AFTER IT IS OPERATING AT ITS FULL SPEED.
THERE ARE 2 TYPES OF CAPACITORS, USED WITH SINGLE-PHASE AC INDUCTION
MOTORS.
1) START CAPACITOR: TO PROVIDE ADDITIONAL TORQUE FOR THE MOTOR
TO USE IN GETTING THE ROTOR TO START ROTATING, FROM A DEAD STOP.
2) RUN CAPACITOR: TO PROVIDE ADDITIONAL TORQUE FOR THE MOTOR TO
USE IN KEEPING THE ROTOR ROTATING, UNDER ITS ‘LOAD’.
EITHER TYPE OF CAPACITOR IS ELECTRICALLY INSTALLED IN THE
SAME MANNER: IN SERIES WITH THE ‘START WINDING’.
AN AC INDUCTION MOTOR MAY USE EITHER OR BOTH TYPES OF CAPACITORS,
DEPENDING ON THE MOTORS ‘APPLICATION’ ( WHAT THE MOTOR ‘DRIVES ).
VERY SIMPLIFIED EXPLANATION OF THE USE OF A CAPACITOR, BY A MOTOR:
WE LEARNED PREVIOUSLY THAT INDUCTANCE CAUSES THE CURRENT TO ‘LAG’ THE
VOLTAGE. SO, IN A MOTORS WINDINGS, THE VOLTAGE IS APPLIED & SOMETIME
LATER, THE CURRENT STARTS TO FLOW.
A CAPACITOR, IS EXACTLY THE OPPOSITE. WITH A CAPACITIVE CIRCUIT, THE
CURRENT STARTS TO FLOW FIRST, AS THE CAPACITOR HAS TO CHARGE TO THE
SOURCE VOLTAGE. SO, IN A CAPACITOR CIRCUIT, THE CURRENT ‘LEADS’ THE
VOLTAGE ( OR THE VOLTAGE ‘LAGS’ THE CURRENT )
IN EFFECT, A CAPACITOR ‘CANCELS OUT’ SOME OF THE VOLTAGE & CURRENT
‘PHASE SHIFT’ CREATED BY THE INDUCTANCE.
THIS ACTION, BRINGS THE VOLTAGE & CURRENT CLOSER TOGETHER, IN PHASE,
THUS CREATING GREATER POWER.
SINCE POWER = TORQUE, THEN CREATING GREATER POWER ALSO CREATES
GREATER TORQUE.
HVACR ELECTRICAL COMPONENTS
PG 91 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: START & RUN CAPACITORS:
LETS LOOK AT A GRAPH OF THE PHASE SHIFT & GET A MENTAL PICTURE OF WHAT
HAPPENS WHEN A CAPACITOR IS ADDED TO AN INDUCTIVE DEVICE.
VOLTAGE
CURRENT
WITH AN INDUCTIVE
CIRCUIT,
‘ELI’
THE VOLTAGE ‘LEADS’ THE
CURRENT FLOW.
LINE ‘MARKS’ A
‘MOMENT IN
TIME’
WITH A CAPACITIVE
CIRCUIT,
‘ICE’
THE CURRENT ‘LEADS’
THE VOLTAGE
IN EITHER CASE, THE INDUCTIVE OR CAPACITIVE CIRCUIT, POWER IS STILL
RELATIVE TO VOLTAGE & CURRENT. ( P = E x I )
THE ORANGE LINE ABOVE, MARKS ONE MOMENT IN TIME, WHERE WE CAN COMPARE
THE VOLTAGE, AT THAT MOMENT, WITH THE CURRENT, AT THAT SAME MOMENT.
THEN WE CAN DETERMINE THE ‘POWER’ AT THAT MOMENT.
IN EITHER THE INDUCTIVE CIRCUIT ( ‘ELI’- THE VOLTAGE ‘LEADS’ THE
CURRENT ) OR THE CAPACITIVE CIRCUIT ( ‘ICE’ - THE CURRENT ‘LEADS’ THE
VOLTAGE ), THE AMOUNT OF POWER PRODUCED BY THE VOLTAGE x THE CURRENT
WILL BE LESS THAN IT WOULD BE IF IT WERE A ‘PURELY RESISTIVE’ CIRCUIT,
WHERE THE VOLTAGE & CURRENT ARE IN PHASE WITH EACH OTHER.
NOTICE THAT AT THE ‘POINTS’ SHOWN ABOVE ( ORANGE DOTTED LINE ), THE
VOLTAGES ARE NEAR THEIR ‘PEAKS’, BUT THE CURRENTS ARE LESS THAN THEIR
‘PEAKS’. MULTIPLIED TOGETHER, THE ‘POWER’ PRODUCED BY EACH ‘MOMENT’ OF
TIME IS MUCH LESS THAN IF THE ‘PEAK’ VOLTAGE OCCURRED AT THE SAME TIME
AS THE ‘PEAK’ CURRENT. ( AS IT DOES WITH A RESISTIVE CIRCUIT )
THEREFORE, AN INDUCTIVE OR CAPACITIVE CIRCUIT PROVIDES LESS POWER AT
ANY ‘MOMENT IN TIME’ THAN A ‘PURELY RESISTIVE’ CIRCUIT WOULD.
IN A MOTOR, THE INDUCTIVE CIRCUIT, CAUSES THE VOLTAGE & CURRENT TO BE
OUT-OF-PHASE WITH EACH OTHER, WITH THE VOLTAGE LEADING THE CURRENT.
BY INSTALLING A CAPACITOR, IN SERIES, WITH THE INDUCTIVE COMPONENT
( THE WINDING ), THE CAPACITOR, SIMPLY, CANCELS OUT SOME OF THE PHASE
SHIFT BETWEEN THE VOLTAGE & THE CURRENT.
HVACR ELECTRICAL COMPONENTS
PG 92 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: START & RUN CAPACITORS:
GRAPHICALLY, WE CAN ILLUSTRATE THIS:
WITH JUST THE WINDING, THE
VOLTAGE LEADS THE CURRENT
( EXAGERATED HERE )
BY SOME ‘TIME’.
THE RESULTING ‘POWER’ IS
REDUCED.
BY ADDING A CAPACITOR, THE
VOLTAGE & CURRENT MOVE
CLOSER TOGETHER, IN ‘TIME’.
THE RESULTING ‘POWER’ IS
INCREASED.
SO, BY ADDING A CAPACITOR, IN SERIES WITH THE START WINDING, THE START
WINDING ‘POLE’ PRODUCES MORE POWER, RESULTING IN A STRONGER MAGNETIC
FIELD PRODUCED BY THE ‘POLE’.
THIS STRONGER MAGNETIC FIELD PRODUCES A STRONGER ‘FORCE OF
ATTRACTION OR REPLUSION’, WHICH RESULTS IN A STRONGER MOVEMENT
OF THE ROTOR ( & SHAFT ) - MORE TORQUE.
VERY IMPORTANT: BECAUSE THE VOLTAGE ACROSS THE START WINDING IS A
RESULT OF THE EMF PRODUCED BY THE TURNING ROTOR & WILL BE GREATER
THAN THE APPLIED OR SOURCE VOLTAGE ( AT FULL SPEED ), AND THE INCREASED
POWER PRODUCED BY THE ADDITIONAL CAPACITOR, THE CURRENT FLOW
THROUGH THE START WINDING ( AT FULL SPEED ) WILL INCREASE AS THE
CAPACITANCE ( OF THE CAPACITOR ) INCREASES.
THE HEAT PRODUCED BY THE CURRENT FLOW ALSO INCREASES, WHICH MUST BE
ACCOUNTED FOR.
TOO MUCH CURRENT FLOW & TOO MUCH HEAT, FOR TOO LONG A PERIOD CAN
DAMAGE THE MOTOR ‘START WINDING’.
NOW WE NEED TO UNDERSTAND THAT:
THE GREATER THE CAPACITANCE THAT IS ADDED, THE CLOSER THE RESULTING
VOLTAGE & CURRENT BECOME & THE GREATER THE POWER PRODUCED.
IN OTHER WORDS, THE LARGER THE CAPACITOR USED, THE MORE TORQUE
PRODUCED.
IMPORTANT: A CAPACITOR IS ‘RATED’ FOR THE AMOUNT OF CAPACITANCE THAT
IT HAS & THE MAXIMUM VOLTAGE THAT CAN BE APPLIED TO IT. ( 370V OR 440V )
HVACR ELECTRICAL COMPONENTS
PG 93 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: START & RUN CAPACITORS:
LETS RECALL THE 2 TYPES OF CAPACITORS & SEE WHAT’S THE DIFFERENCE IN
EACH:
NOTE: CAPACITANCE VALUES ARE INDICATED BY HOW MANY ‘THOUSANDTHS
OF FARADS’ ( MICROFARADS - ‘UF’ ) THAT A CAPACITOR CONTAINS.
1) START CAPACITOR: USED TO ADD ‘STARTING TORQUE’ TO THE MOTOR.
CONTAINS HIGH VALES OF CAPACITANCE, 80 MICROFARAD ( UF ) & ABOVE.
( MORE THAN RUN CAPACITOR ).
‘START WINDINGS’ CANNOT HANDLE THE AMOUNT OF HEAT, PRODUCED BY THE
CURRENT FLOW CREATED BY THE START CAPACITOR, FOR VERY LONG.
THE START CAPACITOR MUST BE REMOVED FROM THE ELECTRICAL
CIRCUIT, BEFORE THE ROTOR REACHES FULL SPEED. ( OTHERWISE
DAMAGE FROM EXCESSIVE ‘HEAT’ ( FROM THE CURRENT FLOW ) CAN RESULT.
THE START CAPACITOR CAN BE REMOVED FROM A MOTORS ELECTRICAL CIRCUIT
BY SEVERAL METHODS.
THE SPLIT-PHASE MOTOR USES ITS INTERNAL CENTRIFUGAL SWITCH FOR THIS
PURPOSE, IF THE MOTOR ( CSIR ) USES A START CAPACITOR.
OTHER MOTORS USE DIFFERENT METHODS OF REMOVING THE START CAPACITOR
FROM THEIR CIRCUITS. THESE METHODS INVOLVE ADDITIONAL COMPONENTS
THAT ARE NOT PART OF THE MOTORS ELECTRICAL CIRCUITRY.
THESE WILL BE EXPLAINED LATER.
A ‘START CAPACITOR’ IS PAPER-FILLED & IS NOT ‘SEALED’.
2) RUN CAPACITOR: USED TO ADD ‘RUNNING TORQUE’ TO A MOTOR, DURING ITS
NORMAL OPERATION. ( AFTER REACHING FULL SPEED ).
MICROFARADS VALUE OF 3 TO 80 ( UF ) ( OR SLIGHTLY MORE ).
A RUN CAPACITOR CAN STAY IN THE ELECTRICAL CIRCUIT CONTINUOUSLY,
BECAUSE OF THE SMALL VALUE OF CAPACITANCE.
( SMALL ADDITIONAL CURRENT FLOW & SMALL ADDITIONAL HEAT )
A RUN CAPACITOR IS A ‘SEALED’ DEVICE, WITH OIL INSIDE TO DISIPATE THE HEAT
PRODUCED DUE TO THE CAPACITOR STAYING IN THE CIRCUIT AS LONG AS THE
MOTOR OPERATES. THE OIL IS USED TO KEEP THE CAPACITOR ‘COOLED DOWN’.
SO, A START CAPACITOR IS PAPER-FILLED, ( NO OIL ) INSIDE A DEVICE THAT IS NOT
‘SEALED’, & HAS LARGE AMOUNTS OF CAPACITANCE, WITH
USUALLY, A PHENOLIC ( HARD PLASTIC ) CASE, WITH ‘CARDBOARD’ ON THE END
WITH THE ELECTRICAL TERMINALS.
A RUN CAPACITOR IS IN A SEALED CONTAINER, TO HOLD THE OIL THAT IS USED TO
‘COOL’ THE CAPACITOR, HAS SMALL AMOUNTS OF CAPACITANCE, & IS
EITHER A METAL ‘CAN’ OR A HARD PLASTIC ‘CAN’.
THE ELECTRICAL TERMINALS ARE SEALED AROUND WHERE THEY EXIT FROM
WITHIN THE DEVICE.
NOTE THAT THE CAPACITORS ARE SIZED FOR THE MOTOR
HVACR ELECTRICAL COMPONENTS
PG 94 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: CAPACITOR-START MOTOR:
THE 3RD TYPE OF AC INDUCTION MOTOR:
3) CAPACITOR-START: THIS MOTOR IS SIMILAR TO THE SPLIT-PHASE MOTOR,
EXCEPT THAT THE DEVICE THAT REMOVES THE START CAPACITOR IS
EXTERNAL TO THE MOTOR. (A SEPERATE DEVICE )
A CSIR, ( CAPACITOR-START / INDUCTION-RUN ) MOTOR IS A CAPACITOR-START
MOTOR, BUT BECAUSE IT USES A CENTRIFUGAL SWITCH TO REMOVE THE START
CAPACITOR & START WINDING, IT IS CONSIDERED A SPLIT-PHASE MOTOR.
THE CAPACITOR-START MOTORS, AS REFERRED TO HERE, CAN HAVE DIFFERENT
NUMBER OF TURNS OF THE MAIN & START WINDINGS, AS WELL AS USING
DIFFERENT SIZES OF WIRE THAN A SPLIT-PHASE MOTOR USES.
THESE MOTORS STILL INCORPORATE A MAIN (RUN ) WINDING & A START WINDING.
EACH WINDING IS IN PARALLEL WITH THE OTHER.
THE START CAPACITOR ( EXTERNAL TO THE MOTOR ) IS THEN PLACED IN SERIES
WITH THE START WINDING.
A ‘CONTACT’ FROM THE DEVICE, THAT IS TO REMOVE THE START CAPACITOR &
THE START WINDING FROM THE CIRCUIT, IS PLACED IN SERIES WITH THE START
CAPACITOR &THE START WINDING.
C
‘OL’
R
S
THE SYMBOL FOR A CAPACITORSTART MOTOR IS THE SAME AS FOR
SEVERAL OF THE TYPES OF AC INDUCTION
MOTORS.
THE KEY TO KNOWING THAT IT IS A
CAPACITOR-START MOTOR IS THE
EXTERNAL ELECTRICAL COMPONENTS
THAT ARE CONNECTED TO IT.
THE ‘C’ TERMINAL, CALLED THE ‘COMMON’ TERMINAL, AS IT IS ‘COMMON’
TO BOTH THE MAIN & START WINDINGS.
ONE SIDE OF THE POWER SOURCE IS CONNECTED HERE.
THE ‘R’ TERMINAL, CALLED THE ‘RUN TERMINAL’, CONNECTS THE OTHER
SIDE OF THE POWER SOURCE TO THE RUN WINDING.
THE ‘S’ TERMINAL, CALLED THE ‘START TERMINAL’, IS THE CONNECTION TO
THE ‘START WINDING’. IT IS WHERE THE CAPACITOR & THE ‘CONTACT’ TO
REMOVE THE CAPACITOR & THE START WINDING ARE CONNECTED.
THE COMPLETE SYMBOL FOR A PARTICULAR MOTOR SHOULD INCLUDE ALL
NECESSARY COMPONENTS FOR THE MOTORS PROPER OPERATION, IN ANY GIVEN
CONDITION.
HVACR ELECTRICAL COMPONENTS
PG 95 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: CAPACITOR-START MOTOR CONTINUED:
THE COMPLETE SYMBOL FOR A CAPACITOR-START MOTOR:
SOURCE VOLTAGE
R
CONTACT FOR
REMOVING START
CAP & WINDING
START CAPACITOR
C
OVERLOAD ( OL )
S
FOR THE COMPLETE SYMBOL, ALL DEVICES, NEED FOR THE PROPER OPERATION OF
THE MOTOR, ARE SHOWN.
THE CAPACITOR-START MOTOR HAS GOOD STARTING TORQUE & POOR
RUNNING TORQUE. ( AS THERE IS NOT A RUN CAPACITOR USED FOR RUNNING
TORQUE ).
THIS MOTOR IS A CAPACITOR-START / INDUCTION-RUN MOTOR AS WAS THE CSIR
SPLIT-PHASE MOTOR. THE ONLY REAL DIFFERENCE IN THE TWO IS THE WAY THE
START CAPACITOR & START WINDING ARE REMOVED FROM THE ELECTRICAL
CIRCUIT.
A CAPACITOR START MOTOR DOES NOT HAVE A CENTRIFUGAL SWITCH.
THESE MOTORS ARE USED FOR OPERATING SMALL COMPRESSORS OR MEDIUM SIZE
‘LOADS’.
THE 3 METHODS OF REMOVING A START CAPACITOR &/OR A START WINDING FROM
A MOTORS ELECTRICAL CIRCUIT WILL BE EXPLAINED LATER.
THE 4TH TYPE OF AC INDUCTION MOTOR IS:
4) PERMANENT SPLIT-CAPACITOR ( PSC ): THIS TYPE OF MOTOR USES A
‘RUN’ CAPACITOR , NOT A START CAPACITOR.
THE PSC MOTOR HAS A SMALL STARTING TORQUE & GOOD RUNNING
TORQUE.
THE PSC ( PERMANENT SPLIT-CAPACITOR ) MOTOR HAS WINDINGS THAT CAN
WITHSTAND SOME HEAT, SO A ‘RUN’ CAPACITOR IS USED TO PROVIDE ADDITIONAL
RUNNING TORQUE. THE RUN CAPACITOR STAYS IN THE CIRCUIT, THE ENTIRE TIME
THAT THE MOTOR IS OPERATING.
HVACR ELECTRICAL COMPONENTS
PG 96 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: PERMANENT SPLIT-CAPACITOR ( PSC )
MOTOR CONTINUED:
COMPLETE SYMBOL FOR A PERMANENT SPLIT-CAPACITOR ( PSC ) MOTOR:
R
C
RUN
CAPACITOR
S
REVIEW: A RUN CAPACITOR HAS SMALL CAPACITANCE ( 3 TO 80 UF ).
MOST FAN MOTORS USE 3 TO 20 UF. COMPRESSOR MOTORS USE 20 TO 80 UF.
THE PSC ( PERMANENT SPLIT-CAPACITOR ) MOTOR IS THE MOST COMMON MOTOR
THAT HVACR TECHNICIANS WILL ENCOUNTER.
THE 5TH TYPE OF AC INDUCTION MOTOR:
5) CAPACITOR START & RUN ( CSR ): THIS TYPE OF MOTOR IS SIMPLY A PSC
MOTOR THAT WE HAVE ADDED A START CAPACITOR TO. BY ADDING A START
CAPACITOR, WE INCREASE THE STARTING TORQUE OF THE MOTOR, WHILE
KEEPING A GOOD RUNNING TORQUE ( WITH THE RUN CAPACITOR ).
THE START CAPACITOR IS ELECTRICALLY CONNECTED IN PARALLEL WITH THE RUN
CAPACITOR.
THE START CAPACITOR MUST BE REMOVED FROM THE MOTORS ELECTRICAL
CIRCUIT BEFORE THE ROTOR REACHES FULL SPEED.
SO, THERE MUST BE A CONTACT, IN SERIES WITH THE START CAPACITOR, TO
REMOVE THE CAPACITOR AT THE PROPER TIME.
THE CSR ( CAPACITOR START & RUN ) MOTOR HAS GOOD STARTING
TORQUE & GOOD RUNNING TORQUE.
THE CSR MOTOR HAS THE GREATEST AMOUNT OF STARTING TORQUE & RUNNING
TORQUE OF ANY OF THE SINGLE-PHASE MOTORS.
IT IS THE ‘STRONGEST’ SINGLE-PHASE MOTOR.
HVACR ELECTRICAL COMPONENTS
PG 97 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: CAPACITOR START & RUN ( CSR ) MOTOR:
THE BASIC SYMBOL FOR A CSR MOTOR:
R
RUN CAPACITOR
START CAPACITOR
C
CONTACT TO
REMOVE START
CAPACITOR
OVERLOAD (OL)
S
NOTICE THAT THE RUN & START CAPACITORS ARE IN PARALLEL WITH EACH
OTHER, BUT TOGETHER THEY ARE IN SERIES WITH THE START WINDING.
RUN CAPACITOR
START
CAPACITOR
‘CONTACT’ FOR REMOVING START
CAPACITOR
THE START CAPACITOR IS PLACED INTO THE CIRCUIT WHEN THE MOTOR NEEDS TO
BEGIN ROTATING, TO PROVIDE THE AMOUNT OF TORQUE NECESSARY TO MOVE
THE ROTOR UNDER A STRONG ‘LOAD’.
THE START CAPACITOR IS THEN REMOVED FROM THE CIRCUIT, BY THE CONTACT,
WHEN THE ROTOR REACHES 75-80 % OF THE ROTORS FULL SPEED.
( THE SAME AS THE SPLIT-PHASE CSIR & THE CAPACITOR-START/INDUCTION RUN
MOTORS )
MANY TIMES, IN THE HVACR FIELD, TECHNICIANS INSTALL A START CAPACITOR &
THE DEVICE TO REMOVE THE START CAPACITOR, ON A PSC MOTOR TO GET
ADDITIONAL STARTING TORQUE.
THIS IS USUALLY DONE WHEN A PSC MOTOR HAS TROUBLE STARTING.
THERE ARE DEVICES MADE TO BE ATTACHED TO THE RUN CAPACITOR TO ADD THE
START CAPACITOR TO THE CIRCUIT.
1) SUPERBOOST:
2) 3 IN 1 STARTER:
3) KICK-START:
HVACR ELECTRICAL COMPONENTS
PG 98 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MOTOR STARTING CIRCUITS:
THERE ARE 3 METHODS USED IN HVACR TO PROVIDE ADDITIONAL STARTING
TORQUE BY ADDING A START CAPACITOR TO A COMPRESSOR MOTORS ELECTRICAL
CIRCUIT & THEN REMOVING THE START CAPACITOR AT THE PROPER TIME.
1) POTENTIAL RELAY:
2) CURRENT RELAY:
3) SOLID-STATE RELAY:
ALL 3 METHODS INVOLVE, SOME MEANS OF SENSING THE SPEED OF THE ROTOR &
REMOVING THE START CAPACITOR AT THE PROPER TIME.
1) POTENTIAL RELAY: THIS DEVICE OPERATES BY SENSING THE VOLTAGE
ACROSS THE START WINDING ( WHICH WILL BE GREATER THAN THE
SOURCE VOLTAGE ).
AS WE SHOULD HAVE LEARNED, THE ROTOR INDUCES A VOLTAGE ACROSS THE
START WINDING. THE AMOUNT OF VOLTAGE IS DEPENDANT UPON THE SPEED OF
THE ROTOR. THE GREATER THE SPEED, THE GREATER THE VOLTAGE INDUCED
ACROSS THE START WINDING.
AT FULL SPEED, THIS VOLTAGE WILL BE GREATER THAN THE SUPPLY VOLTAGE.
SO, IF WE ( THE MANUFACTURER ) KNOW THE AMOUNT OF VOLTAGE THAT WILL BE
INDUCED ACROSS THE START WINDING, BY THE ROTOR, AT A CERTAIN SPEED
( 75 – 80 % OF FULL SPEED ), THEN WE CAN SENSE THIS VOLTAGE & CAUSE A
CONTACT TO OPEN, REMOVING THE START CAPACITOR.
THE POTENTIAL RELAY IS JUST WHAT IT SAYS – A RELAY.
THE RELAY HAS A ‘COIL’ & A ‘CONTACT’, JUST LIKE ALL RELAYS DO.
AND IF WE REMEMBER WHAT WE LEARNED ABOUT A RELAY, THE ‘COIL’ PRODUCES
AN ELECTROMAGNET, WHICH, WITH THE PROPER CURRENT FLOW THROUGH IT,
WILL PRODUCE A MAGNETIC FIELD THAT IS STRONG ENOUGH TO ATTRACT THE
‘METAL’ THAT THE CONTACT(S) ARE ATTACHED TO.
IN A POTENTIAL RELAY, THE RESISTANCE OF THE ‘COIL’ IS VERY HIGH, WHICH
MEANS THAT IT WILL TAKE A HIGH VOLTAGE TO CREATE ENOUGH CURRENT
TO FLOW THROUGH THE COIL TO CREATE A STRONG ENOUGH ELECTROMAGNET
TO ‘CHANGE THE POSITION OF THE CONTACT’. ( IN THIS CASE, MAKE A
NORMALLY-CLOSED CONTACT OPEN )
THE POTENTIAL RELAY USES A NORMALLY-CLOSED CONTACT ( INSTEAD OF THE
NORMALLY-OPEN CONTACT THAT HAS BEEN SHOWN ).
THE ‘COIL’ OF THE RELAY IS PLACED, IN THE ELECTRICAL CIRCUIT, IN PARALLEL
WITH THE START WINDING ( DIRECTLY ACROSS THE WINDING ), SO THAT IT CAN
RECEIVE THE SAME VOLTAGE THAT THE START WINDING RECEIVES FROM THE
ROTOR.
THE NORMALLY-CLOSED ‘CONTACT’ IS IN SERIES WITH THE START CAPACITOR.
( WHICH, OF COURSE, IS IN PARALLEL TO THE RUN CAPACITOR )
HVACR ELECTRICAL COMPONENTS
PG 99 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MOTOR STARTING CIRCUITS:
CSR MOTOR USING A POTENTIAL RELAY & CONTACT.
START CAPACITOR
NORMALLY-CLOSED
POTENTIAL RELAY
‘CONTACT’
POTENTIAL RELAY ‘COIL’
WHILE THE MOTOR IS DENERGIZED, THERE IS NO VOLTAGE ACROSS THE START
WINDING & SO NO VOLTAGE IS ACROSS THE POTENTIAL RELAY ‘COIL’.
THE POTENTIAL RELAY ‘CONTACT’ IS CLOSED. ( READY TO START )
AT THE INSTANT THE MOTOR IS ENERGIZED, THE ROTOR IS NOT MOVING.
THE VOLTAGE ACROSS THE START WINDING WILL BE ONLY FROM THE SOURCE
VOLTAGE, WHICH WILL NOT BE ENOUGH TO OVERCOME THE RESISTANCE OFTHE
‘COIL’ & ENERGIZE THE RELAY.
AS THE ROTOR BEGINS TO ROTATE, THE EMF, PRODUCED BY THE ROTOR WILL BE
‘FELT’ ACROSS THE START WINDING. THE FASTER THE ROTOR TURNS, THE MORE
EMF IS PRODUCED ACROSS THE START WINDING.
AS THE ROTOR NEARS FULL SPEED, THE VOLTAGE ACROSS THE START WINDING
( WHICH IS THE SAME ACROSS THE POTENTIAL RELAY ‘COIL’ ) INCREASES ENOUGH
TO CAUSE ENOUGH CURRENT IN THE RELAY ‘COIL’ TO PRODUCE A STRONG
ENOUGH MAGNET TO ‘CHANGE THE POSITION OF THE CONTACT’. THIS CAUSES THE
‘CONTACT’ TO OPEN & REMOVE THE START CAPACITOR FROM THE CIRCUIT.
WHEN THE MOTOR IS DENERGIZED ( TURNED OFF ), THE ROTOR SPEED WILL START
TO DECREASE, CAUSING A DECREASE IN THE EMF PRODUCED ACROSS THE START
WINDING & THE RELAY ‘COIL’. AT SOME POINT, THE SPEED OF THE ROTOR WILL BE
LOW ENOUGH TO CAUSE SUCH A DECREASE IN THE EMF, THAT THE POTENTIAL
RELAY ‘COIL’ WILL NOT HAVE ENOUGH CURRENT FLOW TO GENERATE ENOUGH
MAGNETIC ATTRACTION STRENGTH, TO KEEP THE CONTACT OPEN. THE CONTACT
WILL THEN RETURN TO ITS NORMALY-CLOSED POSITION, & BE READY FOR THE
NEXT TIME THAT THE MOTOR WOULD BE ENERGIZED
( TURNED ON ).
HVACR ELECTRICAL COMPONENTS
PG 100 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MOTOR STARTING CIRCUITS:
2) CURRENT RELAY: THIS DEVICE OPERATES BY SENSING THE ACTUAL
CURRENT DRAW OF THE ‘MAIN’ WINDING & USING THIS CURRENT TO CAUSE A
NORMALLY-OPEN CONTACT, IN SERIES WITH THE START CAPACITOR, TO CLOSE,
ENERGIZING THE ‘START CAPACITOR CIRCUIT’, TO PROVIDE THE STARTING
TORQUE.
REMEMBERING WHAT WE HAVE LEARNED:
AT THE MOMENT A MOTOR IS ENERGIZED ( POWER IS APPLIED ), THE ROTOR
IS NOT TURNING, SO THE MAIN WINDING DRAWS ‘LOCKED-ROTOR’ CURRENT FLOW,
WHICH IS 4 TO 6 TIMES GREATER THAN NORMAL FULL LOAD CURRENT.
THIS LARGE CURRENT FLOW IS ENOUGH THE ENERGIZE THE ‘CURRENT RELAY
COIL’, CAUSING THE NORMALLY-OPEN CONTACT ( IN SERIES WITH THE START
CAPACITOR ) TO CLOSE. THIS PLACES THE START CAPACITOR IN THE CIRCUIT,
PROVIDING THE TORQUE NEEDED TO GET THE ROTOR TO START TURNING.
AS THE ROTOR BEGINS TO TURN, THE COUNTER-EMF, CREATED BY THE ROTOR,
CREATES INDUCTIVE REACTANCE ( IMPEDANCE ) & THE CURRENT DRAWN BYTHE
MOTOR DECREASES. AS THE ROTOR NEARS FULL SPEED ( 75-80 % ), THE CURRENT
FLOW THROUGH THE ‘COIL’ OF THE RELAY DROPS TO A POINT THAT THE COIL
CANNOT MAINTAIN THE STRENGTH OF ITS MAGNETIC FIELD, SO THE RELAY
CONTACT OPENS , CUTTING THE START CAPACITOR & START WINDING, OUT OF THE
CIRCUIT. THIS LEAVES THE MOTOR TO ‘RUN’ ON ITS MAIN WINDING.
SINCE THE ‘RELAY COIL’ IS BASICALLY DEENERGIZED & THE ‘CONTACT’ IS OPEN,
AT THIS TIME, THE RELAY IS READY FOR THE NEXT START.
IN THIS CASE, THE SHUT DOWN OF THE MOTOR & THE RAMPING DOWN OF THE
ROTOR HAS NO EFFECT ON THE CURRENT RELAY ‘COIL’ OR ‘CONTACT’.
DIAGRAM OF A CAPACITOR-START MOTOR USING A CURRENT RELAY:
‘COIL’ OF CURRENT
RELAY
N/O CONTACT OF
CURRENT RELAY
START CAPACITOR
NOTICE, BY THE DIAGRAM, THAT THE MAIN WINDING CURRENT FLOWS THROUGH
THE ‘COIL’ OF THE RELAY, SO THE RELAY COIL MUST BE LARGE ENOUGH WIRE TO
HANDLE ‘LOCKED-ROTOR- CURRENT.
THIS IS WHY, THE CURRENT RELAY IS ONLY USED ON SMALLER
COMPRESSOR MOTORS OF, MAYBE 1HP OR LESS.
THESE WOULD BE FREEZER, COOLER, ICE MACHINE, WINDOW A/C UNITS, ETC.
HVACR ELECTRICAL COMPONENTS
PG 101 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MOTOR STARTING CIRCUITS:
3) SOLID-STATE RELAY: THIS DEVICE IS AN ELECTRONIC DEVICE.
( THE TERM ‘SOLID-STATE’ REFERS TO ELECTRONICS )
THIS SOLID-STATE DEVICE CONTAINS A MATERIAL WHOSE ‘RESISTANCE’
INCREASES AS ITS TEMPERATURE INCREASES. THIS MATERIAL IS CALLED:
A POSITIVE TEMPERATURE COEFFICIENT ( PTC ) MATERIAL.
SO, WITH A PTC DEVICE, THE RESISTANCE OF THE MATERIAL WILL INCREASE AS
THE TEMPERATURE OF THE MATERIAL ‘FEELS’ WARMER.
AS WE SHOULD HAVE LEARNED, THE CURRENT FLOW, IN THE START WINDING
CIRCUIT, IS MINIMUM AS THE MOTOR FIRST ENERGIZES, & AS THE ROTOR
INCREASES IN SPEED, THE EMF INDUCED BY THE ROTOR INTO THE START WINDING
INCREASES. THIS INCREASE IN VOLTAGE ACROSS THE START WINDING CAUSES AN
INCREASE IN THE CURRENT FLOW THROUGH THE START WINDING CIRCUIT.
WHEN THE ROTOR REACHES FULL SPEED, THE AMOUNT OF CURRENT, IN THE START
WINDING CIRCUIT, WILL BE ITS MAXIMUM VALUE.
SINCE ‘HEAT’ IS A BY-PRODUCT OF CURRENT FLOW, THEN THE LEAST AMOUNT OF
CURRENT FLOW THROUGH THE START WINDING CIRCUIT IS WHEN THE ROTOR IS
NOT MOVING ( LOCKED-ROTOR CONDITION ), THEN THE AMOUNT OF ‘HEAT’
PRODUCED BY THIS CURRENT FLOW IS AT ITS MINIMUM VALUE.
AS THE ROTOR BEGINS TO TURN, THE CURRENT IN THE START WINDING CIRCUIT
INCREASES, & SO DOES THE ‘HEAT’ PRODUCED BY THE CURRENT FLOW.
BY THE TIME THE ROTOR REACHES FULL SPEED, THE CURRENT & THE ‘HEAT’
PRODUCED BY THE START WINDING CIRCUIT WILL BE AT ITS MAXIMUM VALUE.
THE SOLID-STATE RELAY, WHOSE RESISTANCE INCREASES AS HEAT INCREASES
( PTC ) WILL HAVE A VERY LOW RESISTANCE WHEN THE ROTOR IS NOT TURNING,
( AT START-UP ) & AS THE ROTOR BEGINS TO TURN, THE RESISTANCE WILL
INCREASE, UNTIL IT REACHES A RESISTANCE HIGH ENOUGH ( AT ABOUT 75-80% OF
FULL SPEED ) TO EFFECTIVELY REMOVE THE CURRENT FROM FLOWING THROUGH
THE START CAPACITOR.
THE PTC DEVICE CAN BE USED ON, PRETTY MUCH, ANY SIZE & TYPE OF
COMPRESSOR MOTOR.
SOLID-STATE
( PTC ) DEVICE
START CAPACITOR
HVACR ELECTRICAL COMPONENTS
PG 102 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MOTOR STARTING CIRCUITS:
MOST SINGLE-PHASE COMPRESSOR MOTORS, IN HVACR, ARE PSC TYPE MOTORS.
THESE MOTORS, ORIGINALLY, DO NOT REQUIRE ‘START -ASSIST’.
START-ASSIST IS THE ADDITION OF STARTING DEVICES DESIGNED TO PROVIDE
ADDITIONAL STARTING TORQUE.
BUT, IN THE FIELD, TECHNICIANS FIND COMPRESSOR MOTORS THAT HAVE A HARD
TIME STARTING. THIS IS DUE TO AGE, SLIGHT BEARING PROBLEMS, ETC.
SO, TECHNICIANS CAN ADD A ‘START-ASSIST’ DEVICE TO THE PSC COMPRESSOR
MOTOR TO PROVIDE ADDITIONAL STARTING TORQUE, TO ALLOW THE MOTOR AN
EASIER TIME IN GETTING STARTED.
THE TECHNICIAN CAN INSTALL TWO OF THE THREE DEVICES JUST DESCRIBED,
1) A POTENTIAL RELAY & A SEPERATE START CAPACITOR.
2 ) SOLID-STATE RELAY & A SEPERATE START CAPACITOR
( A CURRENT RELAY & START CAPACITOR ARE NOT FIELD INSTALLED AS A
START-ASSIST DEVICE )
BUT, THERE ARE 3 TYPES OF DEVICES THAT ARE MANUFACTURED TO PROVIDE AN
EASY WAY TO PROVIDE A ‘START ASSIST’ TO THE MOTOR.
ALL 3 OF THESE DEVICES CONNECT ACROSS ( IN PARALLEL TO ) THE RUN
CAPACITOR.
1) SUPERBOOST: THIS DEVICE IS A SOLID-STATE RELAY & START CAPACITOR
CONTAINED WITHIN ONE DEVICE. THIS DEVICE WILL HAVE 2 WIRES ATTACHED TO
IT & IT IS CONNECTED ACROSS ( IN PARALLEL WITH ) THE RUN CAPACITOR.
2) 3 IN 1 STARTING DEVICE: THIS DEVICE, USUALLY, CONTAINS A POTENTIAL
RELAY ( 1 ), A START CAPACITOR ( 2 ), & AN OVERLOAD DEVICE ( 3 ).
THATS WHY ITS CALLED A 3-IN-1 DEVICE. THE OVERLOAD IS USED TO
PROTECT THE MOTOR IF IT STILL DOESN’T START EASILY.
THIS DEVICE ALSO CONNECTS ACROSS ( IN PARALLEL WITH ) THE RUN CAPACITOR.
3) KICK-START: THIS DEVICE IS A POTENTIAL RELAY & A START CAPACITOR
CONTAINED WITHIN ONE DEVICE. AS THE OTHER 2, IT CONNECTS ACROSS THE RUN
CAPACITOR.
CAPACITORS THAT ARE USED IN THE STARTING OR RUNNING OF A MOTOR ARE
‘RATED’ FOR THE AMOUNT OF CAPACITANCE THAT THEY CONTAIN, AS WELL AS
THE MAXIMUM VOLTAGE THAT THE DEVICE CAN WITHSTAND CONTINUOUSLY.
WHEN INSTALLING A CAPACITOR, RUN OR START, A TECHNICIAN MUST INSURE
THAT, IF REPLACING AN EXISTING CAPACITOR, THAT THE SAME CAPACITANCE IS
USED & THAT THE VOLTAGE RATING IS, AT LEAST, THE SAME ( OR GREATER ) THAN
THE ORIGINAL CAPACITOR RATING.
TOO MUCH CAPACITANCE CAN CAUSE THE START CIRCUIT TO DRAW TOO MUCH
CURRENT & TOO LITTLE CAPACITANCE CAN CAUSE THE MAIN WINDING TO DRAW
TOO LITTLE CURRENT – EITHER WAY, THE MOTOR CAN BE DAMAGED.
HVACR ELECTRICAL COMPONENTS
PG 103 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: AC INDUCTION MOTOR CONTINUED:
THE 6TH TYPE OF AC INDUCTION MOTOR:
6) 3-PHASE: THE 3-PHASE MOTOR WINDINGS ARE CONNECTED IN THE SAME
MANNER AS 3-PHASE POWER. THE MOTOR WINDINGS CAN BE CONNECTED
IN A ‘WYE’ OR A ‘DELTA’ CONFIGURATION.
THE 3-PHASE MOTOR HAS THE GREATEST STARTING & RUNNING
TORQUE OF ANY OF THE AC INDUCTION MOTORS.
THE 3-PHASE MOTOR DOES NOT, EVER, NEED ANY START-ASSIST.
SYMBOLS:
L1
L1
L2
L2
L3
L3
WYE
DELTA
REVERSING THE DIRECTION OF A 3-PHASE MOTOR:
TO REVERSE THE DIRECTION OF A 3-PHASE MOTOR, SIMPLY SWAP ANY
TWO OF THE THREE LEADS.
JUST AS IN A SINGLE-PHASE MOTOR, THE DIRECTION OF ROTATION DEPENDS ON
WHICH ‘POLE’ OF THE MOTOR RECIEVES THE HIGHEST STRENGTH AT THE MOMENT
OF STARTING.
BY SWAPPING ANY TWO LEADS, THE ‘TIME’ AT WHICH THE ‘POLES’ ARE AT
MAXIMUM STRENGTH CHANGES FROM ONE SIDE OF THE ROTOR TO THE OTHER
SIDE. THE MOTOR REVERSES ITS STARTING DIRECTION.
THE 2 LEADS CAN BE SWAPPED AT THE MOTOR, AT THE ‘CONTACTOR’, CONTROLLING
THE MOTOR, OR AT THE POWER SOURCE, WHERE THE EQUIPMENT
GETS ITS POWER.
HVACR ELECTRICAL COMPONENTS
PG 104 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: DC MOTORS ( ECM ):
THERE IS ONE OTHER TYPE OF MOTOR THAT HVACR TECHNICIANS HAVE TO BE
FAMILIAR WITH.
THE DC MOTOR – CALLED AN ‘ECM’ MOTOR.
‘ECM’ STANDS FOR ‘ELECTRICALLY COMMUTATED MOTOR’.
THE ‘ECM’ MOTOR HAS TO HAVE AN ELECTRONIC CONTROL BOARD , WHICH
CHANGES THE AC POWER, FROM THE SOURCE, TO A DC POWER, WHICH IS
USED TO CONTROL THE DC MOTOR.
THE ELECTRONIC CONTROL BOARDS ARE, USUALLY, ATTACHED TO THE END OF
THE MOTOR.
THE DC ‘ECM’ MOTOR DELIVERS THE SAME AMOUNT OF POWER AS A COMPARABLE
AC MOTOR WOULD, BUT THE ‘ECM’ MOTOR USES LESS CURRENT.
THIS MAKES THE DC ‘ECM’ MOTOR MORE EFFICIENT THAN THE
COMPARABLE SIZE AC MOTOR.
THERE ARE 2 TYPES OF DC ‘ECM’ MOTORS.
1) SINGLE-SPEED: THIS MOTOR, WHICH MAY HAVE MORE THAN ONE ‘SPEED
TAP’, OPERATES JUST LIKE AN AC MOTOR WOULD.
IT USES ONLY ONE SPEED, AT A TIME, FOR THE SYSTEM OPERATION.
2) VARIABLE-SPEED: THIS TYPE OF MOTOR CAN VARY ITS SPEED BASED ON THE
‘STATIC PRESURE’ ( EXPLAINED IN A LATER COURSE ) OF THE AIRFLOW, IN A
SYSTEM, OR IT CAN BE PROGRAMMED TO ALTER ITS SPEED BY VARIOUS OTHER
METHODS.
THE VARIABLE SPEED DC MOTORS WILL HAVE A SECOND ELECTRONIC CONTROL
BOARD TO PROVIDE PROGRAMMING CAPABILITIES.
( THEY STILL HAVE AN ELECTRONIC CONTROL BOARD ATTACHED TO THE MOTOR )
THE ‘ECM’ MOTOR IS WOUND SIMILAR TO A 3-PHASE MOTOR.
THE DC ‘ECM’ MOTOR DOES NOT USE ANY STARTING DEVICES OR ANY
START-ASSIST.
JUST FOR YOUR INFORMATION:
IN LARGE COMMERCIAL & INDUSTRIAL SYSTEMS, AN AC INDUCTION MOTOR
CAN BE USED AS A VARIABLE SPEED MOTOR.
REMEMBERING WHAT DETERMINES THE SPEED OF AN AC INDUCTION MOTOR:
FREQUENCY x 120
SPEED ( RPMS ) = NO. OF POLES
WE CAN VARY THE SPEED OF AN AC INDUCTION MOTOR BY VARYING THE
FREQUENCY OF THE POWER SUPPLIED TO THE MOTOR.
THIS IS CALLED A ‘VFD’ ( VARIABLE FREQ. DRIVE ) SYSTEM. IT USES ELECTRONIC
CONTROLS TO ALTER THE FREQUENCY OF THE POWER SUPPLIED TO THE MOTOR.
HVACR ELECTRICAL COMPONENTS
PG 105 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: ‘UNIVERSAL’ AC INDUCTION MOTOR:
A ‘UNIVERSAL’ AC INDUCTION MOTOR IS A REPLACEMENT MOTOR USED BY
TECHNICIANS TO REPLACE A NUMBER OF DIFFERENT MOTORS, IN DIFFERENT
APPLICATIONS.
ORIGINAL EQUIPMENT MOTORS ARE, USUALLY, NON-REVERSIBLE & MOST WILL
ONLY HAVE 3 LEADS EXTENDING FROM THE MOTOR.
A ‘COMMON’ LEAD, A ‘RUN WINDING’ LEAD & A ‘START WINDING’ LEAD.
THIS IS CALLED A 3-WIRE MOTOR:
L1
L2
C
R
S
RC
THE ‘RUN’
CAPACITOR MUST
HAVE A SEPERATE
WIRE TO CONNECT
IT TO THE ‘L2’ SIDE
OF THE POWER
SOURCE
ONLY 3 WIRES ( IN BLUE ) EXTEND FROM THE ‘ORIGINAL’ MOTOR.
IN ANY GIVEN MOTOR REPLACEMENT SITUATION, A TECHNICIAN WILL HAVE 2
OPTIONS:
1) REPLACE THE MOTOR WITH AN ORIGINAL DESIGNED MOTOR, FROM THE
EQUIPMENT MANUFACTURER.
THE ORIGINAL MOTOR MAY NOT BE READILY AVAILABLE OR MAY BE EXPENSIVE.
2) USE A ‘UNIVERSAL’ MOTOR, WHICH ARE USUALLY CHEAPER & EASIER TO
OBTAIN.
THE ‘UNIVERAL’ MOTOR WILL HAVE A MEANS TO REVERSE ITS DIRECTION, SO
THAT THE MOTOR CAN BE USED NO MATTER WHAT THE ORIGINAL DIRECTION OF
ROTATION IS.
THE ‘UNIVERSAL’ MOTOR WILL HAVE 2 WIRES, EXTENDING FROM THE MOTOR,
TO CONNECT TO THE ‘RUN CAPACITOR’.
A SINGLE-SPEED UNIVERSAL MOTOR WILL HAVE:
1) 3 WIRES TO CONNECT TO THE SAME 3 TERMINALS OF THE ORIGINAL MOTOR.
A ‘COMMON’ WIRE – CONNECTS TO THE COMMON TERMINAL
A ‘RUN’ WIRE – CONNECTS TO THE ‘RUN TERMINAL
A ‘START’ WIRE – CONNECTSTO THE ‘START TERMINAL
4 WIRES TO CHANGE THE DIRECTION OF ROTATION
AN ADDITIONAL WIRE TO CONNECT TO THE OTHER SIDE OF THE RUN CAPACITOR.
( THE START WINDING WIRE ALREADY CONNECTS TO ONE SIDE OF THE CAPACITOR)
HVACR ELECTRICAL COMPONENTS
NEED TO SHOWPG
4-WIRE
MOTOR DIAGRAM
106 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: ‘UNIVERSAL’ AC INDUCTION MOTOR:
THE DIAGRAM, FOR A SINGLE-SPEED’ UNIVERSAL PSC MOTOR IS AS FOLLOWS:
L1
L2
R
BROWN WITH WHITE STRIPE
C
S
BROWN
ALTERNATE
METHOD OF
CAPACITOR
CONNECTION
DIRECTION CONTROL WIRES
BY RECONNECTING THE START
WINDING, THE MOTOR CAN BE
REVERSED
NOTICE:
1) THERE ARE 2 WIRES, COMING OUT OF THE MOTOR FOR CONNECTION TO
THE RUN CAPACITOR.
THIS IS CALLED A 4-WIRE CONNECTION: 2 ‘SOURCE CONDUCTORS ( L1 & L2 ),’
& 2 CAPACITOR WIRES ( TOTAL OF 4 WIRES ).
2) THE BROWN-WITH-WHITE-STRIPE WIRE IS CONNECTED, INSIDE THE MOTOR,
TO THE EXACT SAME PLACE AS THE ‘RUN’ ( OR L2 ) WIRE.
THIS IS WHY A 4-WIRE MOTOR CAN BE CONNECTED AS A 3-WIRE MOTOR.
JUST CAP OR TAPE OFF THE BROWN-WITH-WHITE-STRIPE WIRE &
CONNECT MOTOR AS YOU WOULD A 3-WIRE MOTOR.
3) THE REVERSING CONNECTIONS: 4 WIRES ARE COMING OUT OF THE MOTOR
& HAVE CONNECTORS ON THEM, SO THAT THE ‘START WINDING’ CAN BE
‘TURNED OVER’ TO CHANGE THE DIRECTION OF THE MOTOR.
THE ONLY PROPER METHOD TO CHANGE THE DIRECTION OF ROTATION
OF AN AC INDUCTION MOTOR, IS TO CHANGE THE DIRECTION THAT THE
CURRENT FLOWS THROUGH THE START WINDING.
TURN THE START WINDING AROUND ( OR OVER ).
HVACR ELECTRICAL COMPONENTS
PG 107 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MULTI-SPEED AC INDUCTION MOTOR:
SOME MOTORS, USED IN HVACR, CAN SUPPLY MORE THAN ONE SPEED.
EACH ‘SPEED’ IS ABOUT 150 RPM DIFFERENT FROM THE NEXT ‘SPEED’
THERE ARE 5 POSSIBLE SPEED:
1) HIGH
2) MEDIUM HIGH
3) MEDIUM
4) MEDIUM LOW
5) LOW
MOST MOTORS WILL HAVE ONLY 2 OR 3 SPEEDS, BUT 5 SPEEDS ARE POSSIBLE IN
SOME MOTORS.
MULTI-SPEED MOTORS ARE GENERALLY USED, IN HVACR, FOR BLOWER MOTORS.
THE DIAGRAM FOR A MULTI-SPEED PSC MOTOR:
NOTICE: THE ‘RUN’ TERMINAL IS NOW
CALLED THE ‘COMMON’ TERMINAL
L1
L2
C
HI
MED
RUN
CAPACITOR
LO
CONNECT ‘L1’ TO
WHICHEVER SPEED IS
REQUIRED OR DESIRED
S
IN THE MULTI-SPEED MOTOR, AN ADDITIONAL WINDING IS ADDED, WHICH IS
REFERRED TO AS THE ‘SPEED WINDING’.
THE ‘SPEED WINDING’ IS EQUIVALENT TO ADDING ‘POLES’ TO A MOTOR.
SINCE THE SPEED OF A MOTOR IS EQUAL TO:
FREQUENCY x 120
NUMER OF POLES
THEN IF WE CHANGE THE NUMBER OF POLES, WE CHANGE THE SPEED.
BY ADDING THE ‘SPEED WINDING’, WE HAVE, IN EFFECT, ADDED A SMALL
‘POLE’ TO THE MOTOR, THEREBY REDUCING THE MOTORS SPEED.
HVACR ELECTRICAL COMPONENTS
PG 108 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: MULTI-SPEED AC INDUCTION MOTOR:
NOTICE, IN THE ABOVE DIAGRAM, THAT THE ‘HIGH SPEED’ WIRE IS CONNECTED TO
THE MOTOR AS IF IT DID NOT HAVE A ‘SPEED WINDING’.
( IT IS CONNECTED IN THE SAME MANNER AS A SINGLE-SPEED PSC MOTOR )
THE ‘SPEED WINDING’ IS ‘SHORTED-OUT’ BY THE HIGH SPEED CONNECTION
IN OTHER WORDS, CURRENT DOESN’T FLOW THROUGH THE SPEED WINDING
WHEN THE HIGH SPEED CONNECTION IS USED.
THE ‘MEDIUM SPEED’ CONNECTS TO THE MIDDLE OF THE ‘SPEED WINDING’, SO
IT ONLY USES PART OF THE SPEED WINDING.
THIS IS LIKE ADDING A ½ ‘POLE’ TO THE MOTOR.
THE SPEED OF THE MOTOR WILL BE REDUCED BY, APPROXIMATELY, 150 RPMS.
( CURRENT ONLY FLOWS THROUGH PART OF THE SPEED WINDING )
THE ‘LOW SPEED’ CONNECTS ALL OF THE ‘SPEED WINDING’ IN THE ELECTRICAL
CIRCUIT. THIS PLACES THE ENTIRE ‘SPEED WINDING’ INTO THE ELECTRICAL
CIRCUIT & CURRENT FLOWS THROUGH THE ENTIRE WINDING.
THIS IS LIKE ADDING 1 ADDITIONAL ‘POLE’ TO THE MOTOR.
THE SPEED OF THE MOTOR WOULD BE REDUCED BY ANOTHER 150 RPMS BELOW
THE SPEED OF THE MEDIUM SPEED CONNECTION & 300 RPMS BELOW THE
HIGH SPEED CONNECTION.
BELOW IS THE DIAGRAM FOR A MULTI-SPEED, UNIVERSAL, PSC MOTOR:
L1
L2
HI
BROWN W / WHITE STRIPE
MED
LO
BROWN
A UNIVERSAL, 3-SPEED PSC MOTOR WILL HAVE AS MANY AS 10 CONNECTIONS.
HVACR ELECTRICAL COMPONENTS
PG 109 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: AC INDUCTION MOTOR RATINGS:
ALL MOTORS WILL HAVE A ‘NAMEPLATE’ ATTACHED TO IT, SHOWING THE
INFORMATION NECESSARY TO INSURE THAT IT IS USED PROPERLY.
THE NAMEPLATE WILL SHOW WHAT THE MOTOR IS RATED FOR:
AS WELL AS OTHER, SOMETIMES USEFUL, INFORMATION.
AN AC INDUCTION MOTOR IS RATED FOR:
1) THE VOLTAGE THAT IS REQUIRED FOR IT TO PROPERLY OPERATE.
2) THE HORSEPOWER THAT IT CAN PRODUCE. THIS IS THE
SIZE OF THE MOTOR.
3) THE RPMS OR ‘SPEED’ THAT IT CAN PRODUCE.
THE NAMEPLATE WILL ALSO INDICATE: ( AMOUNG OTHER THINGS )
1) THE CURRENT DRAW OF THE MOTOR AT ‘FULL LOAD’ – MEANING THAT THE
MOTOR IS FULLY LOADED.
THIS WILL BE ABBREVIATED AS: FLA – FULL LOAD AMPERAGE, OR
RLA – RATED LOAD AMPERAGE ( TERM USED FOR COMPRESSOR MOTORS )
2) THE MODEL & SERIAL NUMBER FOR THE TYPE OF MOTOR THAT IT IS.
3) THE SIZE OF ‘RUN CAPACITOR’, IF USED
4) THE TYPE OF ‘FRAME’, WHICH IS RELEVANT TO – HOW IT MOUNTS.
5) THE WIRING DIAGRAM, SHOWING ALL WIRING CONNECTIONS
6) IF THE MOTOR OPERATES IN ONLY ONE DIRECTION, THE DIRECTION OF
ROTATION WILL BE INDICTAED BY AN ARROW SHOWING THE DIRECTION.
DETERMINING THE DIRECTION OF ROTATION:
A MOTOR HAS TWO ‘ENDS’: THE ‘SHAFT END’ ( SE ) & THE ‘LEAD END’ ( LE ).
THE ‘LEAD END’ IS THE END WHERE THE WIRES EXTEND FROM THE MOTOR.
THE DIRECTION OF ROTATION WILL DEPEND ON WHICH END OF THE MOTOR
THAT YOU ARE LOOKING ‘FROM’.
EG: IF LOOKING TOWARDS THE ‘SHAFT’ ( SE ), THE MOTOR MAY BE TURNING
CLOCKWISE ( CW ). IF YOU TURN THE MOTOR AROUND & LOOK FROM THE
‘LEAD END’ ( LE ), THE MOTOR WILL BE TURNING COUNTER-CLOCKWISE ( CCW ).
MANUFACTURERS OF MOTORS MAY USE EITHER END OF THE MOTOR FROM
WHICH TO DETERMINE THE DIRECTION OF ROTATION OF THEIR MOTORS.
A TECHNICIAN MUST INSURE THAT THE MOTOR IS ROTATING IN THE PROPER
DIRECTION.
HVACR ELECTRICAL COMPONENTS
PG 110 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER:
THE MOTOR WINDINGS CAN BE CHECKED, WITH AN OHMMETER, TO SEE IF:
1) THE WINDINGS ARE INTACT ( CONTINUITY ): EACH MOTOR WINDING
WILL HAVE A CERTAIN AMOUNT OF DC RESISTANCE. THIS DC RESISTANCE CAN
RANGE FROM 1 OHM TO 100 OHMS ( OR MORE ), DEPENDING ON THE MOTOR.
UNLESS THE TECHNICIAN KNOWS WHAT THE ACTUAL RESISTANCE OF THE
WINDING SHOULD BE, THEN ALL THE TECHNICIAN IS LOOKING FOR IS THE
‘CONTINUITY’ OF THE WINDING. ( IS THE WINDING INTACT ).
USE THE LOWEST ‘RANGE’ SETTING, ON THE OHMMETER, TO TEST FOR
‘CONTINUITY’.
TO UNDERSTAND HOW TO CONNECT THE OHMMETER & WHAT READING TO EXPECT,
THE TECHNICIAN SHOULD REFERENCE THE DIAGRAM OF THE PARTICULAR MOTOR
THAT THEY ARE TRYING TO TEST.
SHADED-POLE MOTOR:
A SHADEDPOLE MOTOR
ONLY HAS
ONE WINDING
THE OHMMETER WILL
READ A RESISTANCE IF
THE WINDING IS INTACT
IF THE WINDING IS NOT
INTACT, THE OHMMETER
WILL INDICATE
‘OVERLOAD’ OR OPEN
SPLIT-PHASE MOTOR:
A SPLIT-PHASE MOTOR IS A LITTLE TRICKY!!
THE SPLIT-PHASE
MOTOR HAS 2
WINDINGS.
‘START’ & ‘RUN’, & A
CENTRIFUGAL
SWITCH, WHICH WHEN
THE MOTOR IS NOT
TURNING, WILL BE
CLOSED
CENTRIFUGAL
SWITCH
THE OHMMETER
WILL READ THE
‘PARALLEL’
RESISTANCE OF
BOTH WINDINGS
TOGETHER.
IF ONE WINDING IS
‘OPEN’, IT WILL BE
DIFFICULT TO
RECOGNIZE.
HVACR ELECTRICAL COMPONENTS
PG 111 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER
CONTINUED:
PSC & CSR MOTORS:
THE ‘PSC’ & ‘CSR’ MOTORS ARE THE MOST COMMON MOTORS IN HVACR.
R
C
A
S
B
C
THERE ARE 3 DIFFERENT OHMMETER READINGS THAT CAN BE OBTAINED WITH A
‘PSC’ OR A ‘CSR’ MOTOR.
A) ‘COMMON’ TO ‘RUN’: IF AN OHMMETER IS CONNECTED BETWEEN THE
‘COMMON’ TERMINAL ( OR WIRE ) & THE ‘RUN’ TERMINAL ( OR WIRE ), ( OHMMETER
‘A’, ABOVE ), THEN THE OHMMETER ‘READS’ THE CONTINUITY OF THE ‘RUN’
WINDING ONLY.
B) ‘COMMON’ TO ‘START’: IF AN OHMMETER IS CONNECTED BETWEEN THE
‘COMMON’ TERMINAL ( OR WIRE ) & THE ‘START’ TERMINAL ( OR WIRE ),
( OHMMETER ‘B’, ABOVE ), THEN THE OHMMETER ‘READS’ THE CONTINUITY OF THE
‘START’ WINDING ONLY.
THE ‘START’ WINDING WILL HAVE MORE RESISTANCE THAN THE ‘RUN’
WINDING.
C) ‘RUN’ TO ‘START’: IF AN OHMMETER IS CONNECTED BETWEEN THE ‘RUN’
TERMINAL ( OR WIRE ) & THE ‘START’ TERMINAL ( OR WIRE ), ( OHMMETER
‘C’, ABOVE ), THEN THE OHMMETER ‘READS’ THE COMBINED RESISTANCE OF
‘RUN’ & ‘START’ WINDINGS, AS THEY WILL BE IN SERIES WITH EACH OTHER.
HVACR ELECTRICAL COMPONENTS
PG 112 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER
CONTINUED:
SO, IN TESTING THE ‘CONTIUITY’ OF A PSC OR CSR MOTOR:
A) ‘COMMON’ TO ‘RUN’ = THE LOWEST RESISTANCE
B) ‘COMMON’ TO ‘START’ = HIGHER RESISTANCE THAN ‘A’.
( START WINDING HAS MORE DC RESISTANCE )
C) ‘RUN’ TO ‘START’ = HIGHEST RESISTANCE.
( BOTH WINDINGS ARE IN SERIES )
3-PHASE MOTOR – DELTA OR WYE:
THE WINDINGS OF A 3-PHASE MOTOR ( 3 OF THEM ) ARE THE SAME, SO THEIR
DC RESISTANCES WILL BE THE SAME.
SO, THE RESISTANCE BETWEEN EACH ‘PHASE’ TERMINAL ( OR WIRE ) SHOULD BE
THE SAME.
A
A
B
C
B
C
IN THE ABOVE EXAMPLE, ALL THREE OHMMETERS WILL READ, APPROXIMATELY,
THE SAME RESISTANCE. ( IF ALL WINDINGS ARE INTACT )
IF ONE WINDING IS OPEN, TWO OF THE METERS WILL READ ‘OVERLOAD’, WHILE
ONE METER WILL READ THE WINDING RESISTANCE.
NOW THAT WE HAVE SEEN HOW TO OHM-OUT THE WINDING OF AN AC INDUCTION
MOTOR, THERE IS ONE MORE DEVICE, THAT IS A PART OF MOST MOTORS, THAT
CAN CAUSE A MOTOR TO OHM-OUT AS OPEN WINDINGS, WHEN THE MOTOR
WINDING IS STILL INTACT.
THE INTERNAL OVERLOAD:
HVACR ELECTRICAL COMPONENTS
PG 113 OF
LOADS – AC INDUCTION MOTORS CONTINUED:
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER
CONTINUED:
CONTINUITY TESTING OF A MOTOR WITH AN INTERNAL OVERLOAD:
AS YOU HAVE PROBABLY NOTICED, IN MOST OF THE MOTORS DRAWN, IN THIS
BOOK, A DEVICE HAS BEEN DRAWN INTO THE SINGLE-PHASE MOTORS ,
COMMON TERMINAL CIRCUIT. ( IN SERIES WITH THE ‘COMMON’ TERMINAL )
SYMBOL FOR
INTERNAL
THERMAL
OVERLOAD
MOST MOTORS HAVE A TEMPERATURE SENSING
SWITCH EMBEDDED INTO ITS ‘MAIN’ WINDING.
THIS TEMPERATURE SWITCH ( OVERLOAD )
SENSES THE TEMPERATURE OF THE WINDING,WHICH
IS A RESULT OF THE CURRENT FLOW THROUGH THE
WINDING.
THE SWITCH IS SET TO ‘OPEN’ IF THE TEMPERATURE
EXCEEDS A ‘HEAT’ VALUE THAT CORRESPONDS TO
THE MAXIMUM CURRENT THAT THE MOTOR CAN
SAFELY HANDLE
‘OVERLOAD’ IS A TERM, SIMPLY MEANT, TO INDICATE THAT A MOTOR IS
DRAWING TOO MUCH CURRENT FLOW....MORE THAN IT IS ‘RATED’ FOR.
WE MEASURE THIS CURRENT FLOW BY MEASURING THE AMOUNT OF ‘HEAT’ THAT
THE CURRENT FLOW PRODUCES.
JUST ABOUT ALL MOTORS, USED IN HVACR, WILL BE PROTECTED BY AN OVERLOAD.
MOST OVERLOADS ARE ‘INTERNAL’ BUT SOME ARE ‘EXTERNAL’, TO THE MOTOR.
IT IS ONLY THE INTERNAL OVERLOADS THAT MUST BE CONSIDERED WHEN
OHMMING-OUT ( CHECKING CONTINUITY ) A MOTORS WINDINGS.
THE ‘OVERLOAD’ WILL OPEN IF A MOTOR DRAWS TOO MUCH CURRENT OR GETS
TOO HOT.
SO, IF AN OVERLOAD OPERATES AS IT IS DESIGNED TO, THE MOTOR WILL BE ‘HOT
TO THE TOUCH’ WHEN THE OVERLOAD IS OPEN.
ONCE THE MOTOR ‘COOLS DOWN’, THE OVERLOAD WILL CLOSE ( RESET ),
& THE MOTOR WILL OPERATE OR TRY TO OPERATE AGAIN.
THIS ON-OFF OF THE MOTOR WILL, FINALLY, DAMAGE THE MOTOR, IF THE
PROBLEM OF WHY THE MOTOR IS GETTING ‘HOT’ IS NOT CORRECTED.
OCCASSIONALLY, THE OVERLOAD WILL NOT ‘RESET’ ( CLOSE AFTER COOLING
DOWN ), & THE MOTOR WILL HAVE TO BE REPLACED.
NOW LETS SEE HOW AN OPEN ‘OVERLOAD’ WILL AFFECT RESISTANCE
( CONTINUITY ) READINGS.
HVACR ELECTRICAL COMPONENTS
PG 114 OF
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER
CONTINUED:
SINGLE-PHASE MOTORS:
IN A SINGLE-PHASE MOTOR THE OVERLOAD IS, ELECTRICALLY CONNECTED, IN
SERIES WITH THE ‘COMMON’ TERMINAL.
THE ‘COMMON TERMINAL’ ( OR WIRE ) IS IN SERIES WITH THE PARALLEL
COMBINATION OF THE ‘RUN’ & ‘START’ WINDINGS.
THIS MEANS THAT, IF THE ‘OVERLOAD’ OPENS, THE FLOW OF CURRENT IS STOPPED
FROM GETTING THROUGH EITHER WINDING.
R
C
R
C
S
S
AS YOU CAN SEE, BY THE ABOVE ELECTRICAL DIAGRAMS OF A SINGLE-PHASE
MOTOR, THE OVERLOAD IS IN SERIES WITH BOTH WINDINGS.
SO, IF THE OVERLOAD IS OPEN, THEN A TECHNICIAN WOULD SEE THE FOLLOWING
RESISTANCES FROM AN OHMMETER.
A) ‘C’ TO ‘R’ = ‘OL’ ( METER OVERLOAD )
B) ‘C’ TO ‘S’ = ‘OL’ ( METER OVERLOAD )
C) ‘R’ TO ‘S’ = THE RESISTANCE OF THE 2 WINDINGS IN SERIES.
THE READING BETWEEN THE ‘RUN’ & ‘START’ WINDINGS ( ‘R’ TO ‘S’ ) LETS THE
TECHNICIAN KNOW THAT THE TWO WINDINGS ARE INTACT & HAVE CONTINUITY
THROUGH THEM. ( THE WINDINGS ARE ‘GOOD’ )
3-PHASE MOTORS:
SINCE MOST 3-PHASE MOTORS, USED IN HVACR, ARE WYE WOUND MOTORS,
THE OVERLOAD IS LOCATED, ELECTRICALLY, IN THE MIDDLE, WHERE ALL
3 WINDINGS CONNECT TOGETHER.
THE OVERLOAD DISCONNECTS ALL 3 WINDINGS FROM THE ELECTRICAL CIRCUIT.
SO, NO CONTINUITY CAN BE MEASURED BETWEEN ANY OF THE 3
WINDING TERMINALS ( OR WIRES ), IF THE OVERLOAD IS OPEN.
HVACR
ELECTRICAL
COMPONENTS
DRAW THE
DIAGRAM
OF THE 3-PHASE
MOTOR WITH OVERLOAD
PG 115 OF
AC INDUCTION MOTOR: TESTING A MOTOR WITH AN OHMMETER
CONTINUED:
A MOTORS WINDINGS CAN ALSO BE CHECKED TO DETERMINE IF:
2) THE WINDING(S) ARE ‘GROUNDED’:
WHEN CHECKING FOR A GROUNDED CIRCUIT, USE THE HIGHEST
‘RANGE’ OF THE OHMMETER.
ATTACH ONE LEAD OF THE OHMMETER TO THE ‘ELECTRICAL’ GROUND
CONNECTION, IN ONE OF 3 PLACES.
1) WHERE THE GROUND WIRE, FROM THE ELECTRICAL SOURCE, IS CONNECTED
TO THE PIECE OF EQUIPMENT.
2) THE METAL FRAME OF THE EQUIPMENT, IF THE FRAME IS GROUNDED.
MAKE SURE OF A SOLID CONNECTION.
3) TO THE COPPER SYSTEM PIPING. IF THE SYSTEM HAS A SOLID GROUND
CONNECTION, THE COPPER PIPING WILL ALSO BE GROUNDED.
ATTACH THE SECOND OHMMETER LEAD TO THE MOTOR TERMINAL(S).
ANY RESISTANCE TO GROUND ON A BLOWER, FAN, OR PUMP MOTOR IS AN
INDICATION OF A GROUNDED CONDUCTOR.
THE MOTOR SHOULD BE REPLACED.
ON COMPRESSOR MOTORS, ANY RESISTANCE UNDER 200,000 ( 2M ) OHMS,
INDICATES A ‘GROUNDED’ COMPRESSOR.
OHMMETER
GROUNDED
COMPRESSOR
WINDING
ELECTRICAL ‘PATH’ THROUGH
THE ‘GROUND’
EQUIPMENT
‘GROUND’
IF THE MOTOR WINDINGS ARE INTACT ( BUT GROUNDED ), ATTACHING THE
OHMMETER LEAD TO ANY 1 OF THE 3 TERMINALS ( OR WIRES ) WILL ‘FIND’
THE GROUND AT ANY POINT IN THE MOTOR.
HVACR ELECTRICAL COMPONENTS
PG 116 OF
GENERAL INFORMATION: CAPACITORS:
REMEMBERING OHMS LAW – RESISTANCES, IN SERIES, ADD UP FOR THE TOTAL
RESISTANCE & RESISTANCES, IN PARALLEL, MUST BE CALCULATED, WITH
THE TOTAL RESISTANCE EQUALING LESS THAN THE SMALLEST RESISTANCE.
CAPACITORS CAN ALSO BE CONNECTED IN EITHER A SERIES OR A PARALLEL
ARRANGEMENT.
BUT WITH CAPACITORS, THE TOTAL CAPACITANCE IS DETERMINED EXACTLY
OPPOSITE TO THE WAY WE CALCULATED RESISTANCE.
WITH CAPACITORS: PARALLEL CAPACITORS ARE ADDED TOGETHER TO FIND
THE ‘TOTAL CAPACITANCE.
SERIES CAPACITORS ARE CALCULATED, THE SAME AS RESISTANCES IN PARALLEL,
USING THE FORMULA - C1 x C2
C1 + C2
EG: IN A CSR MOTOR, THAT HAS A ‘RUN’ CAPACITOR & A ‘START’ CAPACITOR,
THESE CAPACITORS ARE CONNECTED IN PARALLEL WITH EACH OTHER.
THE TOTAL CAPACITANCE OF THE ELECTRICAL CIRCUIT IS THE SUM OF
THE ‘RUN’ & ‘START’ CAPACITORS CAPACITANCES.
THIS INFORMATION IS IMPORTANT WHEN A TECHNICIAN FINDS A BAD CAPACITOR,
BUT DOES NOT HAVE THE EXACT SAME CAPACITOR IN ‘STOCK’.
AS A TEMPORARY MEASURE, THE TECHNICIAN CAN COMBINE TWO OR MORE
CAPACITORS IN EITHER A SERIES, PARALLEL, OR COMBINATION CIRCUIT, TO
ACHIEVE THE DESIRED CAPACITANCE, UNTIL THE PROPER CAPACITOR CAN BE
OBTAINED & INSTALLED.
REMEMBER: IT IS VERY IMPORTANT TO REPLACE THE EXISTING CAPACITOR
WITH A CAPACITOR OF THE SAME ‘RATED’ VOLTAGE OR GREATER.
EG: A 370 VAC ‘RATED’ CAPACITOR CAN BE REPLACED WITH A 370V OR A 440 V
CAPACITOR, BUT A 440 V CAPACITOR CANNOT BE REPLACED WITH A 370 V
CAPACITOR.
EXAMPLE:
A TECHNICIAN FINDS A BAD COMPRESOR RUN CAPACITOR. THE SIZE OF THE
EXISTING CAPACITOR IS 50 UF @ 440V.
THE TECHNICIAN DOES NOT HAVE A 50 UF CAPACITOR ON HIS SERVICE VAN.
BUT HE DOES HAVE A 35 UF @ 440V, & A 15 UF @ 440V.
BY CONNECTING THESE 2 CAPACITORS IN PARALLEL, THE CAPACITANCE ADDS
TOGETHER. 35 + 15 = 50
SINCE THIS JOB IS IN THE COUNTRY & ITS FRIDAY EVENING, THE TECHNICIAN
CAN SUBSTITUTE BOTH CAPACITORS, IN PARALLEL, FOR THE EXISTING 50UF
CAPACITOR, UNTIL MONDAY, WHEN HE CAN OBTAIN THE CORRECT CAPACITOR,
RETURN & INSTALL IT.
HVACR ELECTRICAL COMPONENTS
PG 117 OF
GENERAL INFORMATION: THE TERM ‘COMMON’:
‘COMMON’ IS A TERM USED OFTEN, IN ELECTRICAL WORK.
THE TERM ‘COMMON’ IS USED TO DENOTE A WIRE, TERMINAL, OR CONNECTION
THAT CONNECTS TO ( IS ‘COMMON’ TO ) MORE THAN ONE PART OF AN
ELECTRICAL CIRCUIT.
THERE ARE 3, GENERALLY USED, APPLICATIONS FOR THE WORD ‘COMMON’.
1) TO DENOTE ONE SIDE OF A 120 VAC OR 24 VAC ELECTRICAL SUPPLY
( SOURCE ):
120 VAC SUPPLIED BY A FUSE OR CIRCUIT BREAKER PANEL HAS A
‘NEUTRAL’ CONDUCTOR, WHICH IS TIED TO THE EARTH GROUND AT
THE ELECTRICAL SERVICE ENTRANCE.
A 120 VAC OR 24 VAC SECONDARY OF A TRANSFORMER IS, USUALLY, GROUNDED
ON ONE SIDE OF THE SECONDARY WINDING.
THIS MEANS THAT THE ‘GROUNDED’ CONDUCTOR ( NEUTRAL ), IS ‘COMMON’ TO
BOTH (A) THE ELECTRICAL CIRCUIT & (B) THE GROUND. IT CONNECTS TO 2 POINTS.
IN OTHER WORDS, THE GROUNDED SIDE OF THE SOURCE OF POWER IS CONNECTED
TO BOTH THE SOURCE & TO THE GROUNDED CIRCUIT.
( IT IS ‘COMMON’ TO BOTH, THE POWER SOURCE & TO GROUND )
2) COMMON CONNECTION OF A RELAY:
IF A RELAY USES A SINGLE-POLE / DOUBLE-THROW CONTACT, THEN ONE SIDE
( INPUT ) OF THE SWITCH CONNECTES TO BOTH THE NORMALLY-CLOSED ‘OUTPUT’
& THE NORMALLY-OPEN ‘OUTPUT’ ( WHEN THE COIL IS ENERGIZED ).
SO, THE ‘INPUT’ TERMINAL ( OR WIRE ) IS ‘COMMON’ TO BOTH THE N/C & THE
N/O SIDES OF THE RELAY CONTACT.
3) ‘COMMON’ CONNECTION OF A MOTOR:
ON A SINGLE-PHASE AC INDUCTION MOTOR, THERE WILL BE A ‘COMMON’
TERMINAL ( OR WIRE ).
THIS ‘COMMON’ TERMINAL IS CONNECTED TO THE RUN WINDING & THE START
WINDING. SO, IT IS ‘COMMON’ TO BOTH WINDINGS.
BE SURE THAT YOU FULLY UNDERSTAND THE TERM ‘COMMON’, WHEN YOU
HEAR THE TERM, IN THE FIELD.
REALIZE WHAT COMPONENT IS BEING REFERRED TO & THEN REMEMBER:
WHAT IS COMMON’ TO MORE THAN 1 ‘THING’
HVACR ELECTRICAL COMPONENTS
PG 118 OF
REVIEW: LOADS:
A LOAD CHANGES ENERGY FROM ONE FORM TO ANOTHER.
LOADS CAN BE EITHER SINGLE-PHASE OR 3-PHASE.
LOADS CAN ALSO BE EITHER RESISTIVE OR INDUCTIVE.
( IF INDUCTIVE, THE LOAD WILL BE AN INDUCTOR )
HEATERS ARE THE ONLY TRULY RESISTIVE LOAD.
INDUCTIVE LOADS INCLUDE:
A) TRANSFORMERS
B) COILS OF RELAYS & CONTACTORS
C) SOLENOIDS
D) INCANDESCENT LIGHT BULBS
E) MOST ALL OTHER LIGHTING FIXTURES
THE PRIMARY WINDING OF A TRANSFORMER IS A ‘LOAD’ TO THE SOURCE
THAT PROVIDES THE POWER TO THE TRANSFORMER.
A TRANFORMER IS RATED FOR:
1) ITS VA ( POWER RATING ) ( ALSO ITS SIZE )
2) THE VOLTAGE REQURED BY THE PRIMARY WINDING
( TO PRODUCE THE CORRECT AMOUNT OF SECONDARY VOLTAGE ).
3) THE SECONDARY VOLTAGE
THE TOTAL OPPOSITION TO THE FLOW OF CURRENT PRODUCED BY AN INDUCTOR
IS CALLED IMPEDANCE.
IMPEDANCE IS THE ALGEBRAIC SUM OF THE DC RESISTANCE & THE INDUCTIVE
REACTANCE.
TRANSFORMER SYMBOL
MOST TYPES OF LIGHT FIXTURES USE A ‘BALLAST’ TO CAUSE THE LIGHT BULB
TO PRODUCE LIGHT.
THE ‘BALLAST’ IS JUST A STEP-UP TRANSFORMER.
( SEDCONDARY VOLTAGE IS GREATER THAN PRIMARY VOLTAGE )
FILAMENT
SYMBOL FOR INCANDESCENT LIGHT
BULB
SIMILAR SYMBOL USED FOR OTHER
TYPES OF LIGHTS
HVACR ELECTRICAL COMPONENTS
PG 119 OF
REVIEW: LOADS CONTINUED:
A SOLENOID IS AN INDUCTIVE LOAD THAT USES AN INDUCTOR TO PRODUCE AN
ELECTROMAGNET.
THE ELECTROMAGNET IS USED TO MOVE A SET(S) OF CONTACTS, OR TO OPEN OR
CLOSE A FLUID VALVE.
SINCE A SOLENOID IS AN INDUCTOR, ITS TOTAL RESISTANCE TO CURRENT FLOW
IS CALLED IMPEDANCE.
OR
SOLENOID SYMBOLS
A MOTOR IS A DEVICE THAT CHANGES ELECTRICAL ENERGY INTO
MECHANICAL ENERGY
A MOTOR CONSISTS OF AN INDUCTOR, CALLED, A WINDING, THAT, WHEN CURRENT
FLOWS THOUGH THE INDUCTOR, PRODUCES AN ELECTROMAGNET, WHOSE NORTH
& SOUTH ‘POLES ATTRACT OR REPULSE, A PIECE OF METAL, CALLED A ROTOR.
ATTACHED TO THE ROTOR IS A ‘SHAFT’ THAT IS USED TO CONNECT THE MOTOR
TO WHATEVER DEVICE THE MOTOR IS SUPPOSE TO OPERATE ( TURN ).
THERE ARE 2 MAIN PARTS TO A MOTOR:
1) STATOR: STATIONARY PART WHERE THE WINDINGS ARE WOUND.
2) ROTOR: ROTATING PART, THAT ATTACHES TO THE MOTOR SHAFT.
THE STRENGTH ( TORQUE OR POWER ) PRODUCED BY A MOTOR IS A DIRECT RESULT
OF THE STRENGTH OF THE ELECTROMAGNETS ‘POLES’.
THE STRENGTH OF THE ELECTROMAGNETIC ‘POLES’, OF A MOTOR, IS A DIRECT
RESULT OF THE AMOUNT OF CURRENT FLOW THROUGH THE INDUCTOR
( WINDING ).
( THE NUMBER OF TURNS & THE CORE MATERIAL ARE ALREADY ‘SET’ BY THE
MANUFACTURER )
REMEMBERING THAT AC CURRENT IS ALWAYS CHANGING, SO THE STRENGTH
OF THE ELECTROMAGNETIC ‘POLE’ OF THE MOTOR WILL ALSO ALWAYS CHANGE.
IN AN AC INDUCTION MOTOR, THE ROTOR BECOMES AN ELECTROMAGNET.
IN AN AC INDUCTION MOTOR, THE STRENGTH OF EACH MAGNETIC ‘POLE’ VARIES,
AS DOES THE SIGN WAVE OF THE AC CURRENT ( & VOLTAGE ).
HVACR ELECTRICAL COMPONENTS
PG 120 OF
REVIEW: LOADS CONTINUED:
AN AC INDUCTION MOTOR CONSISTS OF 2 POSSIBLE WINDINGS:
1) THE MAIN ( OR ‘RUN’ ) WINDING
2) THE START WINDING
THE SPEED OF AN AC INDUCTION MOTOR IS A DIRECT RESULT OF THE FREQUENCY
OF THE SOURCE TIMES 120 ( A CONSTANT ) & INVERSELY ITH THE ‘NUMBER OF
POLES’ OF THE ‘MAIN’ WINDING.
SPEED IN RPMS = FREQUENCY x 120
NUMBER OF POLES
THE ‘MAIN WINDING’,OF A MOTOR, IS DIVIDED INTO 2 TO 8 PARTS. EACH ‘PART’ OF
THE WINDING IS A ‘POLE’ OF THE MOTOR.
THERE ARE 2 CURRENT LEVELS THAT ARE OF IMPORTANCE IN MOTOR OPERATION
& IN TROUBLESHOOTING MOTORS.
1) LOCKED-ROTOR AMPERAGE ( LRA ): THE CURRENT DRAWN BY THE
MOTOR ( FOR LESS THAN A SECOND), BEFORE THE ROTOR BEGINS TO TURN.
THIS CURRENT WILL BE, FOR MOST MOTORS, 4 TO 6 TIMES THE CURRENT
THAT THE MOTOR WILL DRAW AFTER THE ROTOR ACHIEVES ITS FULL SPEED.
2) FULL LOAD AMPERAGE ( FLA OR RLA ): THE CURRENT DRAWN BY THE
MOTOR, AFTER THE ROTOR ACHIEVES FULL SPEED. THIS CURRENT IS BASED ON
THE MOTOR HAVING THE MAXIMUM ‘LOAD’ APPLIED TO IT.
MOTOR TORQUE: THE STRENGTH THAT THE ROTOR PRODUCES, WHILE
TURNING. IN OTHER WORDS, HOW ‘HARD’ THE ROTOR TURNS. HOW MUCH
STRENGTH WOULD IT TAKE TO ‘STOP’ THE ROTOR WHILE IT IS TURNING.
THERE ARE 2 DEGREES OF MOTOR TORQUE:
1) STARTING TORQUE: THE AMOUNT OF TORQUE ( POWER ) NEEDED TO START
THE ROTOR TURNING, FROM A DEAD STOP.
2) RUNNING TORQUE: THE AMOUNT OF TORQUE ( POWER ) NEEDED TO KEEP
THE ROTOR TURNING ONCE IT HAS ALREADY STARTED TURNING.
A MOTOR NEEDS MUCH MORE ‘STARTING TORQUE’ TO GET THE ROTOR TO BEGIN
TO TURN THAN IT NEEDS TO KEEP THE ROTOR TURNING ( RUNNING TORQUE ).
THE TORQUE, THAT A MOTOR PRODUCES, CAN BE INCREASED BY ADDING A SECOND
INDUCTOR ( WINDING ) CALLED A ‘START WINDING’.
THE ‘START WINDING’ IS SEPERATED INTO THE SAME NUMBER OF ‘PARTS’ AS THE
‘MAIN WINDING’.
THE ‘PARTS’ OF THE START WINDING ARE WOUND IN BETWEEN EACH ‘POLE’ OF
THE MAIN WINDING.
HVACR ELECTRICAL COMPONENTS
PG 121 OF
REVIEW: LOADS CONTINUED:
THERE ARE 2 REASONS FOR A MOTOR TO HAVE A START WINDING:
1) TO ADD STARTING OR RUNNING TORQUE.
2) TO CAUSE THE ROTOR TO TURN IN A CERTAIN DIRECTION ( CW OR CCW ).
THE DIRECTION OF ROTATION OF THE ROTOR ( & THE SHAFT ) IS SOLELY
DETERMINED BY THE DIRECTION THAT THE CURRENT FLOWS THROUGH THE
START WINDING, IN REFERENCE TO THE DIRECTION THAT THE CURRENT
IS FLOWING THROUGH THE MAIN WINDING.
TO REVERSE THE DIRECTION OF A SINGLE-PHASE AC INDUCTION MOTOR THAT
HAS A START WINDING:
SIMPLY TURN THE START WINDING OVER ( WHICH CHANGES THE DIRECTION
THAT THE CURRENT FLOWS THROUGH THE WINDING ).
THE 2ND METHOD FOR INCREASING THE TORQUE PRODUCED BY A MOTOR:
ADD A CAPACITOR IN SERIES WITH THE START WINDING.
THERE ARE 2 TYPES OF CAPACITORS USED TO ADD TORQUE TO A MOTOR:
1) START CAPACITOR:
A) HIGH CAPACITANCE VALUE { 80 + MICROFARADS (UF / MFD) }
B) PAPER-FILLED
C) MUST NOT BE LEFT IN CIRCUIT. IT MUST BE REMOVED WHEN THE ROTOR
REACHES 75-80% OF FULL SPEED.
2) RUN CAPACITOR:
A) LOW CAPACITANCE VALUE { 3 TO 80 MICROFARADS ( UF / MFD ) }
B) OIL-FILLED: TO DISSIPATE HEAT
C) RUN CAPACITOR WILL ALWAYS BE CONNECTED TO THE CIRCUIT.
( THE ENTIRE TIME THE MOTOR IS OPERATING )
A MOTOR MAY INDIVIDUALLY USE A START ( TO ADD STARTING TORQUE ) OR A RUN
CAPACITOR ( TO ADD RUNNING TORQUE ) FOR ITS OPERATION. OR IT MAY USE
BOTH CAPACITORS
THERE ARE 6 TYPES OF AC INDUCTION MOTORS THAT HVAC TECHNICIANS WILL
ENCOUNTER:
1) SHADED-POLE
2) SPLIT-PHASE
A) RSIR – RESISTANCE-START / INDUCTION-RUN
B) CSIR – CAPACITOR-START / INDUCTION RUN
3) CAPACITOR-START
4) PSC – PERMANENT SPLIT CAPACITOR
5) CSR – CAPACITOR START & RUN
6) 3-PHASE
HVACR ELECTRICAL COMPONENTS
PG 122 OF
REVIEW: LOADS CONTINUED:
SHADED-POLE INDUCTION MOTOR:
1) HAS ONLY ONE WINDING ( MAIN OR RUN )
2) USES A RING ON ONE END OF EACH ‘POLE’ OF THE MOTOR TO
DETERMINE DIRECTION OF ROTATION.
3) HAS POOR STARTING & POOR RUNNING TORQUE
SYMBOL FOR SHADED-POLE MOTOR
SPLIT-PHASE INDUCTION MOTOR:
THE SPLIT-PHASE MOTOR USES A CENTRIFUGAL SWITCH TO REMOVE THE START
WINDING & THE START CAPACITOR ( IF USED )
THERE ARE 2 TYPES OF SPLIT-PHASE MOTORS:
1) RSIR – RESISTANCE-START / INDUCTION-RUN
A) HAS A MAIN (RUN ) WINDING & A START WINDING.
B) THE START WINDING IS REMOVED FROM THE MOTORS
ELECTRICAL CIRCUIT BY A CENTRIFUGAL SWITCH.
( AT 75-80% OF FULL SPEED )
C) OPERATES ON THE MAIN WINDING ONLY, AFTER THE ROTOR
GETS UP TO SPEED.
D) POOR STARTING & POOR RUNNING TORQUE
‘MAIN’ ( RUN ) WINDING
MOTOR
OVERTEMPERATURE
SWITCH
( OVERLOAD )
SYMBOL FOR RSIR
SPLIT-PHASE MOTOR
‘START’
WINDING
CENTRIFUGAL SWITCH
HVACR ELECTRICAL COMPONENTS
PG 123 OF
REVIEW: LOADS CONTINUED:
2) CSIR – CAPACITOR-START / INDUCTION-RUN:
A) HAS A MAIN ( RUN ) WINDING & A START WINDING
B) USES A ‘START’ CAPACITOR TO ADD STARTING TORQUE.
C) THE START WINDING & THE START CAPACITOR ARE REMOVED
FROM THE MOTORS ELECTRICAL CIRCUIT
BY A CENTRIFUGAL SWITCH.
( AT 75-80% OF FULL SPEED )
D) OPERATES ON THE MAIN WINDING ONLY, AFTER THE ROTOR
GETS UP TO SPEED.
E) GOOD STARTING TORQUE & POOR RUNNING TORQUE
‘MAIN’ ( RUN ) WINDING
SYMBOL FOR CSIR
MOTOR
SPLIT-PHASE
MOTOR
OVERTEMPERATURE
SWITCH
( OVERLOAD )
THE ‘START CAPACITOR’
IS MOUNTED TO THE
MOTOR FRAME
‘START’
WINDING
CENTRIFUGAL SWITCH
THE CSIR ( SPLIT-PHASE ) MOTOR IS, BASICALLY, THE SAME MOTOR AS THE
RSIR ( SPLIT-PHASE ) MOTOR, WITH THE ADDITION OF A START CAPACITOR.
CAPACITOR-START INDUCTION MOTOR:
1) THIS MOTOR IS THE SAME AS THE CSIR ( SPLIT-PHASE ) MOTOR, EXCEPT
THE CAPACITOR-START MOTOR DOES NOT HAVE A CENTRIFUGAL
SWITCH TO REMOVE THE START CAPACITOR WHEN THE ROTOR
REACHES 75-80% OF FULL SPEED.
2) THE CAPACITOR-START MOTOR MUST USE AN EXTERNAL MEANS TO REMOVE
THE START CAPACITOR FROM THE CIRCUIT.
3) CAPACITOR-START MOTORS ARE USED IS SMALL COMPRESSORS, & NORMALLY
USE A CURRENT RELAY TO REMOVE THE START CAPACITOR & START
WINDING AT THE PROPER TIME ( 75-80% OF FULL SPEED )
4) GOOD STARTING TORQUE & POOR RUNNING TORQUE
HVACR ELECTRICAL COMPONENTS
PG 124 OF
REVIEW: LOADS CONTINUED:
CAPACITOR-START MOTOR CONTINUED:
‘MAIN’ ( RUN ) WINDING
SYMBOL FOR
CAPACITOR-START
MOTOR
MOTOR
OVERTEMPERATURE
SWITCH
( OVERLOAD )
‘START CAPACITOR’
EXTERNAL CONTACT FOR
REMOVING START
CAPACITOR & START
WINDING FROM THE
CIRCUIT
‘START’
WINDING
PERMANENT SPLIT CAPACITOR ( PSC ) INDUCTION MOTOR:
1) A PSC MOTOR USES A RUN CAPACITOR TO PROVIDE SOME ADDITIONAL
RUNNING TORQUE. ( IT ALSO ADDS A LITTLE EXTRA TORQUE FOR STARTING)
2) THE RUN CAPACITOR &THE START WINDING REMAIN IN THE MOTORS
ELECTRICAL CIRCUIT WHILE THE MOTOR IS OPERATING.
3) THE PSC MOTOR HAS A LITTLE EXTRA STARTING TORQUE & GOOD RUNNING
TORQUE.
‘MAIN’ ( RUN ) WINDING
MOTOR
OVERTEMPERATURE
SWITCH
( OVERLOAD )
‘START’
WINDING
SYMBOL FOR
PERMANENT SPLIT
CAPACITOR ( PSC ) MOTOR
‘RUN CAPACITOR’
HVACR ELECTRICAL COMPONENTS
PG 125 OF
REVIEW: LOADS CONTINUED:
CAPACITOR-START & RUN INDUCTION MOTOR:
1) THE CAPACITOR START & RUN MOTOR IS THE SAME MOTOR AS A PSC MOTOR,
BUT WITH A START CAPACITOR ADDED TO INCREASE THE STARTING TORQUE.
2) THE START CAPACITOR MUST BE REMOVED BY AN EXTERNAL MEANS BEFORE
THE ROTOR REACHES 75-80% OF FULL SPEED.
3) THE CSR MOTOR HAS THE HIGHEST STARTING TORQUE & RUNNING
TORQUE OF ANY OF THE SINGLE-PHASE AC INDUCTION MOTORS.
‘MAIN’ ( RUN ) WINDING
SYMBOL FOR
CAPACITOR START & RUN
( CSR ) MOTOR
MOTOR
OVERTEMPERATURE
SWITCH
( OVERLOAD )
START CAPACITOR
CONTACT TO
REMOVE START
CAPACITOR
‘START’
WINDING
RUN CAPACITOR
THREE-PHASE ( 3-PHASE ) INDUCTION MOTOR:
1) HAS THE HIGHEST STARTING & RUNNING TORQUE OF ANY AC INDUCTION
MOTOR.
( THE STARTING TORQUE & THE RUNNING TORQUE ARE THE SAME )
2) HAS 3 WINDINGS WHICH ARE SPREAD AROUND THE STATOR 120 DEGREES
APART FROM EACH OTHER.
3) 3-PHASE MOTORS NEVER NEED ANY TYPE OF START-ASSIST.
4) THE 3 WINDINGS MAY BE WOUND IN EITHER A WYE OR A DELTA
CONFIGURATION.
HVACR ELECTRICAL COMPONENTS
PG 126 OF
REVIEW: LOADS CONTINUED:
3-PHASE INDUCTION MOTORS CONTINUED:
SYMBOLS:
L1
L1
L2
L2
L3
L3
WYE
DELTA
EACH OF THE 3 WINDINGS USES THE SAME SIZE CONDUCTOR & THE SAME NUMBER
OF TURNS OF WIRE, SO THE DC RESISTANCE OF EACH WINDING SHOULD BE THE
SAME.
MOTOR TERMINAL DESIGNATIONS:
1) SHADED-POLE & SPLIT-PHASE MOTORS WILL ONLY HAVE 2 CONDUCTORS
( WIRES ) OR TERMINALS. THESE TWO WIRES OR TERMINALS MUST CONNECT
TO BOTH ‘SIDES’ OF THE POWER SOURCE.
2) CAPACITOR-START, PSC, & CSR MOTORS WILL HAVE 3 CONDUCTORS ( WIRES )
OR TERMINALS. TWO OF THESE WIRES ( TERMINALS ) CONNECT TO BOTH
‘SIDES’ OF THE POWER SOURCE & THE 3RD WIRE ( TERMINAL ) CONNECTS
TO THE RUN &/OR START CAPACITORS.
‘C’ =
‘COMMON’
TERMINAL
COMMON TO
BOTH RUN &
START
WINDINGS
R
C
S
‘R’
CONNECTS TO ‘RUN’
WINDING
‘S’
CONNECTS TO
‘START’ WINDING
HVACR ELECTRICAL COMPONENTS
PG 127 OF
REVIEW: LOADS CONTINUED:
MOTOR TERMINAL DESIGNATIONS CONTINUED:
3) 3-PHASE MOTORS WILL HAVE 3 CONDUCTORS ( TERMINALS ) THAT CONNECT
TO EACH OF THE 3 POWER WIRES FROM THE SOURCE.
THEY MAY BE LABELED ‘A’, ‘B’, & ‘C’ OR ‘T1’, ‘T2’, & ‘T3’.
FACTORY INSTALLED MOTOR START - ASSIST DEVICES:
THERE ARE 3 METHODS ( DEVICES ) USED TO REMOVE THE ‘START CAPACITOR’
FROM A MOTOR, WHEN THE ROTOR REACHES APPROXIMATELY 75-80% OF FULL
SPEED. ( CAPACITOR-START & CSR MOTORS )
1) POTENTIAL RELAY:
THE POTENTIAL RELAY OPERATES ON THE VOLTAGE DROPPEDACROSS THE
‘START’ WINDING.
A) THE RELAY ‘COIL’ IS CONNECTED IN PARALLEL WITH THE START WINDING.
B) USES A NORMALLY-CLOSED CONTACT, IN SERIES WITH THE START CAPACITOR
C) HAS 3 VOLTAGE RATINGS:
I) PICK-UP VOLTAGE: THE VOLTAGE NEEDED TO CAUSE
THE RELAY TO ENERGIZE & OPEN THE CONTACT
( TAKING OUT THE START CAPACITOR )
II) CONTINUOUS VOLTAGE: THE MAXIMUM VOLTAGE THAT THE ‘COIL’ MUST
WITHSTAND WHEN ROTOR IS TURNING FULL SPEED.
III) DROP-OUT VOLTAGE: THE VOLTAGE AT WHICH THE ‘COIL’ OF THE RELAY
WILL DEENERGIZE & CAUSE THE CONTACT TO CLOSE.
2) CURRENT RELAY:
A) THE CURRENT RELAY ‘COIL’ IS CONNECTED IN SERIES WITH THE ‘RUN’ WINDING.
THE COIL MUST BE ABLE TO HANDLE THE TOTAL FULL LOAD CURRENT DRAWN BY
THE COMPRESSOR MOTOR.
B) USES A NORMALLY-OPEN CONTACT IN SERIES WITH THE START CAPACITOR.
C) IS USED ON SMALL COMPRESSOR MOTORS, WITH SMALL FULL LOAD CURRENT.
3) SOLID-STATE RELAY:
A) USES A MATERIAL KNOWN AS A POSITIVE TEMPERATURE COEFFICIENT
MATERIAL ( PTC ) WHOSE RESISTANCE INCREASES AS ITS TEMPERATURE
INCREASES.
B) THE ENTIRE DEVICE IS CONNECTED IN SERIES WITH THE START CAPACITOR.
THE SOLID-STATE RELAY USES A VERY LOW RESISTANCE, WHEN IT IS COOL,
TO ACT LIKE A ‘CLOSED CONTACT’ & ALLOW CURRENT TO FLOW THROUGH
THE START CAPACITOR.
WHEN HEATED ( BY THE CURRENT FLOW ) THE RESISTANCE OF THE DEVICE,
INCREASE UNTIL IT GETS SO HIGH THAT IT ACTS LIKE A OPEN CONTACT
AND STOPS THE FLOW OF CURRENT THROUGH THE START CAPACITOR.
HVACR ELECTRICAL COMPONENTS
PG 128 OF
REVIEW: LOADS CONTINUED:
FIELD INSTALLED MOTOR START – ASSIST DEVICES:
THERE ARE 3 TYPES OF FIELD-INSTALLED START-ASSIST DEVICES THAT CAN
BE ADDED TO A PSC MOTOR TO TURN IT INTO A CSR MOTOR, OR THAT
CAN REPLACE THE FACTORY INSTALLED START-ASSIST DEVICES FROM
ABOVE.
1) SUPERBOOST: INCLUDES A SOLID-STATE RELAY & CAPACITOR
2) 3 IN 1 STARTING DEVICE: INCLUDES A POTENTIAL RELAY , A START
CAPACITOR, & AN OVERLOAD ( OVERTEMP SWITCH ).
3) KICK-START: CONTAINS A POTENTIAL RELAY & A START CAPACITOR
ALL 3 OF THE ABOVE FIELD-INSTALLED DEVICES SIMPLY CONNECT IN PARALLEL
TO THE RUN CAPACITOR.
( MOST CONNECT DIRECTLY TO THE RUN CAPACITORS TERMINALS )
DIRECTION OF MOTOR ROTATION:
1) SHADED-POLE MOTOR: MUST PHYSICALLY TAKE THE ROTOR OUT & TURN IT
OVER ( TO CHANGE POSITION OF SHADED-POLE )
2) SPLIT-PHASE, CAPACITOR-START, PSC & CSR MOTORS: REVERSE THE DIRECTION
THAT THE CURRENT FLOWS THROUGH THE START WINDING.
( TURN THE WINDING OVER )
3) 3-PHASE MOTOR: SWAP ANY TWO POWER WIRES FEEDING THE MOTOR
NOTE: DIFFERENT MANUFACTURERS USE DIFFERENT METHODS TO STATE THE
DIRECTION OF ROTATION OF THEIR MOTORS.
THERE IS ONLY 2 DIRECTIONS OF ROTATION:
1) CLOCK-WISE ( CW ) – SAME DIRECTION AS CLOCK TURNS
2) COUNTER CLOCK-WISE ( CCW )- OPPOSITE DIRECTION THAT CLOCK TURNS
THE QUESTION IS: FROM WHICH END OF THE MOTOR IS THE TECHNICIAN LOOKING
AT TO DETERMINE THE DIRECTION THE MOTOR IS TURNING OR NEEDS TO TURN.
THE TECHNICIAN MAY BE LOOKING AT THE MOTOR FROM THE SHAFT END ( SE ),
OR THE OTHER END OF THE MOTOR WHERE THE WIRES ( CALLED LEADS ) COME
OUT OF THE MOTOR – CALLED THE LEAD END ( LE ).
EACH MOTOR MANUFACTURER USES A DIFFERENT END FROM WHICH TO
DESIGNATE THE DIRECTION OF ROTATION, SO THE TECHNICIAN MUST
KNOW FROM WHICH END THE MANUFACTURER IS REFERRING WHEN
THEY INDICATE A DIRECTION OF ROTATION, SUCH AS CW OR CCW.
SOMETIMES THE MOTOR WILL STATE WHICH END TO USE, SUCH AS:
CWLE: CLOCK-WISE LEAD END
CCWLE: COUNTER-CLOCK-WISE LEAD END
CWSE: CLOCK-WISE SHAFT END
CCWSE: COUNTER CLOCK-WISE SHAFT END
HVACR ELECTRICAL COMPONENTS
PG 129 OF
REVIEW: LOADS CONTINUED:
ADDITIONAL TYPE OF MOTOR USED IN HVACR
DC ‘ELECTRICALLY COMMUTATED MOTOR’ ( ECM ): IS WOUND SIMILAR TO
A 3-PHASE AC MOTOR. HAS 3 WINDINGS.
ELECTRONIC CONTROL BOARD RECTIFIES ( CHANGES ) THE INCOMING ( SOURCE )
AC VOLTAGE INTO A 3-PHASE DC VOLTAGE, WHICH IS SENT TO THE MOTOR
WINDINGS.
THERE ARE 2 TYPES OF DC MOTORS USED:
1) SINGLE-SPEED ECM MOTOR
2) VARIABLE SPEED ECM MOTOR
THE VARIABLE SPEED MOTOR HAS A 2ND ELECRONIC CONTROL BOARD THAT
DETERMINES THE SPEEDS AT ANY GIVEN TIME OR CIRCUMSTANCE
THE DC MOTOR HAS VERY GOOD STARTING & RUNNING TORQUE.
BETTER THAN THE CSR AC INDUCTION MOTOR.
THE DC MOTOR USES LESS CURRENT TO PROVIDE THE SAME TORQUE ( AS
AN AC MOTOR OF THE SAME SIZE ),
WHICH MEANS THAT THE DC MOTOR IS MORE EFFICIENT THAN THE AC MOTOR.
IN REPLACING A MOTOR, A TECHNICIAN HAS 2 POSSIBILITIES:
1) USE THE SAME MOTOR, FROM THE EQUIPMENT MANUFACTURER,
CALLED AN OEM MOTOR. ( ORIGINAL EQUIPMENT MANUFACTURED )
2) USE A UNIVERSAL MOTOR.
A UNIVERSAL MOTOR WILL HAVE WIRES FOR THE NORMAL CONNECTIONS
OF THE MOTOR ( 3 ), PLUS WIRES FOR CHANGING THE DIRECTION OF THE MOTOR
( 4 ), PLUS WIRES FOR THE RUN CAPACITOR.
ANOTHER TYPE OF MOTOR USED IN HVACR IS THE MULTI-SPEED MOTOR:
THE MULTI-SPEED MOTOR USES A 3RD ( SMALL ) WINDING IN SERIES WITH THE
‘COMMON’ TERMINAL, CALLED A ‘SPEED’ WINDING.
RD
THIS 3 WINDING CAN HAVE AS MANY AS 5 SPEEDS ( USUALLY 2 OR 3 SPEEDS ).
EACH ‘SPEED’ CONNECTS TO A PORTION OF THE ‘SPEED’ WINDING, EXCEPT
THE HIGHEST SPEED, WHICH BYPASSES THE ‘SPEED’ WINDING.
THE ‘SPEED’ WINDING ACTS LIKE A SMALL ADDITIONAL ‘POLE’ OF THE MOTOR
THEREBY REDUCING THE MOTORS SPEED.
THE HIGHEST SPEED OF THE MOTOR, BYPASSES THE ‘SPEED’ WINDING & IS THE
MAXIMUM SPEED OF THE MOTOR.
THE LOWEST SPEED OF THE MOTOR USES THE ENTIRE ‘SPEED’ WINDING.
ALL OTHER SPEEDS, USE PART OF THE ‘SPEED’ WINDING.
HVACR ELECTRICAL COMPONENTS
PG 130 OF
REVIEW: LOADS CONTINUED:
MULTI-SPEED MOTOR CONTINUED:
C
MULTI-SPEED
OEM MOTORS
DESIGNATE THE
‘RUN’ TERMINAL AS
‘C’
HIGH
MED
LOW
SYMBOL FOR MULTISPEED AC MOTOR
S
AC INDUCTION MOTOR RATINGS:
AC INDUCTION MOTORS WILL HAVE A ‘NAMEPLATE’ ATTACHED TO THE MOTOR
WHICH WILL STATE AS MUCH INFORMATION ABOUT THE MOTOR AS POSSIBLE.
SUCH AS:
1) MOTOR HORSEPOWER: THIS IS THE SIZE OR STRENGTH OF THE MOTOR.
2) THE RPM’S: ( REVOLUTIONS PER MINUTE ) THAT THE SHAFT ROTATES.
3) VOLTAGE(S): THAT MUST BE PROVIDED TO THE MOTOR FOR OPERATION.
4) DIRECTION OF ROTATION: MAY OR MAY NOT BE SHOWN
5) FULL LOAD CURRENT: THE CURRENT THAT THE MOTOR WILL DRAW
UNDER FULL LOADED CONDICTIONS.
6) SIZE OF RUN CAPACITOR: IF A PSC MOTOR, THE RUN CAPACITOR SIZE WILL BE
LISTED.
7) A WIRING DIAGRAM: SHOWS THE PROPER CONNECTION OF THE MOTOR.
& OTHER PERTINENT INFORMATION.
USING AN OHMMETER TO TEST A MOTOR: