AC/DC
ELECTRICAL SYSTEMS
HANDS-ON SKILLS FOR LEARNING ACTIVITY PACKET 6:
TRANSFORMERS
ITEMS NEEDED FOR HANDS-ON SKILLS
Amatrol Supplied
1
T7017 AC/DC Electrical Learning System
FIRST EDITION, LAP 6, REV. A
Amatrol, AMNET, CIMSOFT, MCL, MINI-CIM, IST, ITC, VEST, and Technovate are trademarks or registered trademarks of Amatrol,
Inc. All other brand and product names are trademarks or registered trademarks of their respective companies.
Copyright © 2014 by AMATROL, INC.
All rights Reserved. No part of this publication may be reproduced, translated, or transmitted in any form or by any means, electronic,
optical, mechanical, or magnetic, including but not limited to photographing, photocopying, recording or any information storage and
retrieval system, without written permission of the copyright owner.
Amatrol, Inc., 2400 Centennial Blvd., Jeffersonville, IN 47130 USA, Ph 812-288-8285, FAX 812-283-1584 www.amatrol.com
BB227-BC06UEN-E1 REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
SKILL 1
CONNECT AND OPERATE A TRANSFORMER
Procedure Overview
In this procedure, you will connect and operate a transformer. Then you
will use a DMM to show that a voltage is induced in the secondary.

1. Perform the following substeps to connect and supply power to the
transformer.
A. Connect the transformer to the power supply as shown in figures 1-1 and
1-2.
This transformer has two primaries and two secondaries. In this
application, you will connect the two primary windings in parallel (the
different connection possibilities will be covered later in this LAP).
B. Place the AC/DC selector switch in the AC position.
C. Turn on the T7017 power supply.
PRIMARY 1
SOURCE SELECT
PRIMARY 2
AC
DC
24V
12V
12V
TRANSFORMER
MODULE
SECONDARY 1
Figure 1-1.
SECONDARY 2
Operating a Transformer
BB227-BC06UEN-E1-S01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S01-1
SKILL 1 CONNECT AND OPERATE A TRANSFORMER
PRIMARY
1
SECONDARY
1
24 VAC
PRIMARY
2
Figure 1-2.

SECONDARY
2
Schematic of Transformer Connections
2. Set the DMM to measure AC volts and measure the voltage across the
primary, as shown in figure 1-3.
30XR
AC
VOLTS
SOURCE SELECT
NON
CONTACT
VOLTAGE
MIN MAX
V
AC
DC
200
HOLD
600 OFF 600
V
200
20
20
2
200m
2
200m
200
24V
12V
2m
20M
2M
12V
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
PRIMARY
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
SECONDARY
TRANSFORMER
MODULE
Figure 1-3.
Measurement of Primary Voltage
Primary voltage = ________________________________________ (VAC)

It should be approximately 26.5 VAC.
BB227-BC06UEN-E1-S01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S01-2
SKILL 1 CONNECT AND OPERATE A TRANSFORMER

3. Now measure the voltage across one of the secondaries, as shown in figure
1-4.
Secondary voltage = ______________________________________ (VAC)

The secondary voltage should be approximately 17.5 VAC. This voltage
is being induced in the secondary winding by the magnetic field from the
primary.
30XR
AC
VOLTS
SOURCE SELECT
NON
CONTACT
VOLTAGE
MIN MAX
V
AC
DC
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
24V
12V
2m
20M
2M
12V
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
PRIMARY
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
SECONDARY
TRANSFORMER
MODULE
Figure 1-4.

Measurement of Secondary Voltage
4. Measure the voltage across the other secondary.
Secondary voltage = ______________________________________ (VAC)

It should be similar to the value in step 3. You will learn later why this is so.

5. Turn off the power supply.

6. Disconnect the circuit.

7. Store all components.
BB227-BC06UEN-E1-S01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S01-3
SKILL 2
CALCULATE THE SECONDARY COIL VOLTAGE
OF A TRANSFORMER
Procedure Overview
In this procedure, you will determine the voltage output of each secondary
coil given the number of turns of the primary, the number of turns of each
secondary and the primary coil voltage.

1. Perform the following substeps to determine the secondary voltage of the
transformer shown in figure 2-1.
A. First, calculate the turns ratio of the transformer.
TR = ______________________________________________________
PRIMARY
120 VAC
Figure 2-1.
100
TURNS
SECONDARY
50
TURNS
V
VS
Calculating Secondary Voltage
The solution is as follows:
TR =
NP / N S
TR =
(100 / 50)
The turns ratio is 2/1.
This ratio is usually written as 2:1.
BB227-BC06UEN-E1-S02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S02-1
SKILL 2 CALCULATE THE SECONDARY COIL VOLTAGE OF A TRANSFORMER
B. Next, calculate the secondary voltage of the transformer.
The schematic shows that the input voltage is 120 VAC.
VS _______________________________________________________________________________________(VAC)
The solution is as follows:
VS =
VP
TR
VS = 120 / 2

The secondary voltage should be 60 VAC.

Since the secondary voltage is less than the primary voltage, the transformer
is called a step-down transformer.

2. Calculate the turns ratio and the secondary voltage of the transformer shown
in figure 2-2.
TR = ________________________________________________________
VS = ___________________________________________________ (VAC)

The secondary voltage in this case is 360 VAC, which is 3 times higher than
the primary voltage. When a transformer has a higher secondary voltage than
the primary voltage, it is called a step-up transformer.
PRIMARY
120 VAC
Figure 2-2.

60
TURNS
SECONDARY
180
TURNS
V
VS
Transformer Circuit
3. Calculate the turns ratio and the secondary voltage for the circuit shown in
figure 11 if the primary has 400 turns and the secondary has 100 turns.
TR = ________________________________________________________
VS = _________________________________________________________

The turns ration is 4:1 and the secondary voltage is 30 VAC.
BB227-BC06UEN-E1-S02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S02-2
SKILL 2 CALCULATE THE SECONDARY COIL VOLTAGE OF A TRANSFORMER

4. Calculate the secondary voltage for the circuit shown in figure 2-2 and
described in step 3 if the input voltage is 480 VAC.
VS ____________________________________________________________________________________________________

The secondary voltage is 120 VAC.

A transformer can also have more than one secondary coil, as shown in figure
2-3. The amount of voltage induced in each secondary is calculated using the
same formula used for a transformer with a single secondary.
PRIMARY
300
TURNS
SECONDARY
150
TURNS
V
100
TURNS
V SECONDARY 2
30
TURNS
V
VS2
120 VAC
Figure 2-3.

SECONDARY 1
VS1
SECONDARY 3
VS3
A Step-Down Transformer
5. Perform the following substeps to calculate the voltage output of each
secondary in figure 2-3.
A. Calculate the turns ratio for each secondary.
TR S1 = ___________________________________________________
TR S2 = ___________________________________________________
TR S3 = ___________________________________________________
The turns ratio for the secondary 1 is 2:1. The turns ratio for secondary 2
is 3:1. The turns ratio for secondary 3 is 10:1.
B. Calculate the voltages for each secondary.
VS1 = _______________________________________________ (VAC)
VS2 = _______________________________________________ (VAC)
VS3 = _______________________________________________ (VAC)
The voltage of secondary 1 should be 60 VAC. The voltage of secondary
2 should be 40 VAC. The voltage of secondary 3 should be 12 VAC.
BB227-BC06UEN-E1-S02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S02-3
SKILL 2 CALCULATE THE SECONDARY COIL VOLTAGE OF A TRANSFORMER

6. Perform the following substeps to calculate the voltage output of each
secondary in figure 2-4.
A. Calculate the turns ratio for each secondary.
TR S1 = ___________________________________________________
TR S2 = ___________________________________________________
TR S3 = ___________________________________________________
TR S4 = ___________________________________________________
The turns ratio for secondary 1 is 10:1, secondary 2 is 5:1, secondary 3 is
2:1 and secondary 4 is 100:1.
B. Calculate the voltage of each secondary.
VS1 = ________________________________________________ (VAC)
VS2 = ________________________________________________ (VAC)
VS3 = ________________________________________________ (VAC)
VS4 = ________________________________________________ (VAC)
The voltage of secondary 1 is 24 VAC, secondary 2 is 48 VAC,
secondary 3 is 120 VAC and secondary 4 is 2.4 VAC.
500
TURNS
240 VAC
50
TURNS
SECONDARY 1
100
TURNS
SECONDARY 2
250
TURNS
SECONDARY 3
5
TURNS
Figure 2-4.
SECONDARY 4
Voltage Output of Each Secondary Calculation
BB227-BC06UEN-E1-S02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S02-4
SKILL 3
TROUBLESHOOT A TRANSFORMER BY MEASURING CONTINUITY
Procedure Overview
In this procedure, you will troubleshoot a transformer for opens and shorts
on the primary and secondary to determine if it is good.

1. Place the transformer module from the T7017 on the work surface of the
trainer.

2. Set the DMM to measure resistance.

3. Check the primary coils for an open by measuring the resistance across each
as shown in figure 3-1. If the ohmmeter reads infinite resistance, the coil is
open and the transformer is bad. Record the resistance of the primary coils
below.
Primary 1_______________________________________________ (ohms)
Primary 2_______________________________________________ (ohms)

You should find that both primaries have resistance. This is the DC resistance
of the wire used for the primary coil. The transformer module used on the
T7017 should display a resistance of approximately 80 to 110 ohms. Larger
control transformers may only read a fraction of an ohm to a few ohms.
PRIMARY 1
30XR
PRIMARY 2
OHMS
NON
CONTACT
VOLTAGE
MIN MAX
PRIMARY
TERMINALS
V
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
200m
20k
2k
200
1.5V 9V
SECONDARY
TERMINALS
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
SECONDARY 1
10A
CAT
CAT
V
COM
TRANSFORMER
MODULE
Figure 3-1.
10 A
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
SECONDARY 2
Measuring Resistance Across the Primary
BB227-BC06UEN-E1-S03, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S03-1
SKILL 3 TROUBLESHOOT A TRANSFORMER BY MEASURING CONTINUITY

4. Check the secondary coils for an open by measuring the resistance across
each. If the ohmmeter reads infinite resistance, the coil is open and the
transformer is bad. Record the resistance of the secondary coils below.
Secondary 1_____________________________________________ (ohms)
Secondary 2_____________________________________________ (ohms)

You should find that both secondaries have resistance. This is the DC
resistance of the wire used for the secondary coil. The transformer module
used on the T7017 should display a resistance of approximately 30 to 50
ohms. Larger control transformers may only read a fraction of an ohm to a
few ohms.

In the next 5 steps, you will be checking for shorts between the coils of the
transformer. It does not matter from which side of the coils you take these
measurements since anything other than infinite resistance between the coils
indicates a bad transformer.

5. Connect one lead from your ohmmeter to one terminal of the Primary 1 coil.

6. Touch the second lead of your ohmmeter to one terminal of the other primary
coil. Observe the reading on the ohmmeter.
Resistance ______________________________________________ (ohms)


If the reading on the ohmmeter is anything other than infinite resistance, the
transformer is bad and should not be used.
7. Move the second lead of the ohmmeter to one terminal of each of the
secondary coils. Record the resistance for each measurement.
Resistance ______________________________________________ (ohms)
Resistance ______________________________________________ (ohms)
Both measurements should be infinite if the transformer is good.

8. Connect one lead from your ohmmeter to the Primary 2 coil.

9. Repeat step 7 with the second lead of the ohmmeter connected to one terminal
of each of the secondary coils.
Resistance ______________________________________________ (ohms)
Resistance ______________________________________________ (ohms)


Again, the resistances should both be infinite if the transformer is good.
10. Now place one lead of the ohmmeter on each secondary coil and record the
resistance below.
Resistance ______________________________________________ (ohms)

Again, the resistance should be infinite if the transformer is good.
BB227-BC06UEN-E1-S03, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S03-2
SKILL 3 TROUBLESHOOT A TRANSFORMER BY MEASURING CONTINUITY

You have now verified that no shorts exist between any of the transformer
coils.

In the next step, you will test for any shorts between the coils of the
transformer and the core of the transformer. The core of the transformer is
normally connected to earth ground. This is done to ensure that the core is
never above ground potential and will not expose people to a shock hazard if
they come in contact with the transformer core.
NOTE
The transformer used on the T7017 is a small circuit board mount unit
which when used with the 24VAC on the trainer does not present a shock
hazard. If this transformer were larger or being used with higher voltages, the
core would need to be grounded.
NOTE
The core of the transformer on the T7017 has a coating of shellac to protect
it from oxidizing. To make contact with the core itself you will need to place
the leads of the ohmmeter inside the tapped holes of the transformer core.

11. Place the leads of the ohmmeter inside the two tapped holes of the transformer
core as shown in figure 3-2. This allows you to make contact with the core
itself.
30XR
PRIMARY
OHMS
NON
CONTACT
VOLTAGE
MIN MAX
V
200
HOLD
600 OFF 600
200
20
V
20
2
200m
2
200m
200
2m
20M
2M
20m
200k
STANCOR
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
10A
CAT
CAT
A
600V
300V
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
SECONDARY
Figure 3-2.
Tapped Holes in Core for Ohmmeter Lead Placement
BB227-BC06UEN-E1-S03, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S03-3
SKILL 3 TROUBLESHOOT A TRANSFORMER BY MEASURING CONTINUITY

12. Press the leads of the ohmmeter against the sides of the tapped holes and
observe the ohmmeter. You should be reading a very low resistance (less than
2 ohms). If the ohmmeter does not indicate a connection, use the leads of the
ohmmeter to scrape any shellac off the inside of the tapped holes until the
ohmmeter shows a connection.
Resistance ______________________________________________ (ohms)

13. Now, leave one lead in contact with the core and use the second lead to touch
one terminal of each of the transformer coils. The ohmmeter should indicate
infinite resistance between the core and all coils. If it does not, the transformer
is bad and should not be used.
Resistance ______________________________________________ (ohms)


You have now verified that none of the transformer coils are shorted to the
transformer core.
14. Store all components.
BB227-BC06UEN-E1-S03, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S03-4
SKILL 4
SIZE A TRANSFORMER
Procedure Overview
In this procedure, you will use the table in figure 16 to size a transformer
for several applications. This is a typical catalog specification.


1. Perform the following substeps to size a transformer for the following
application:
A machine needs a transformer to step down the line voltage from 240 VAC
to 120 VAC. The maximum in-rush current the machine’s motor draws is 4
amps.
A. Calculate the maximum in-rush VA that will be required.
Maximum in-rush VA = ___________________________________(VA)
This can be found by multiplying the maximum in-rush current by the
operating voltage of the machine.
Maximum in-rush VA should be 480 VA (120 V × 4A).
B. Choose a transformer from the table in figure 16 that has a greater
maximum in-rush VA rating than the machine requires.
Maximum In-rush VA Rating = _____________________________(VA)
In this case, the fourth transformer from the top with a maximum in-rush
VA of 660 VA would be the correct choice.
BB227-BC06UEN-E1-S04, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S04-1
SKILL 4 SIZE A TRANSFORMER

2. Select a transformer from the table in figure 4-1 given the following
information:

Maximum in-rush current drawn by the machine’s motor is 10A.

The line voltage is 240 VAC from a 25A circuit breaker.

The operating voltage of the machine is 120 VAC.
Maximum in-rush VA = _____________________________________(VA)
Maximum in-rush VA of selected transformer = __________________(VA)

The selection should be the transformer with a rating of 1360.
TRANSFORMER ELECTRICAL SPECIFICATIONS AND
ORDERING DATA (SUPPLY VOLTAGE 220 VAC)
VA
Max.
Inrush
VA†
50
75
100
150
250
500
1000
180
218
273
660
1360
1964
4014
Temp.
Rise
Dimensions
A
B
C
Model
636-
110-120 V Secondary Voltage Rating
55°C
55
55
55
55
115
115
3-5/16”
3-9/16”
3-3/4
4-5/16
5
5-1/2
6-3/4
3”
3-3/8
3-3/8
4-1/2
4-1/2
4-1/2
5-1/4
2-1/2
2-7/8
2-7/8
3-13/16
3-13/16
3-3/4
4-3/8
1111
1121
1131
1141
1161
1191
1211
2-1/2
2-7/8
3-13/16
1111824
1131824
1141824
22-24V Secondary Voltage Rating
50
100
150
180
273
660
55
55
55
3-5/16
3-3/4
4-5/16
3
3-3/8
4-1/2
(*) Terminal Type (†) Capability VA. Refers to maximum inrush VA after
calculations are made.
Figure 4-1.

Transformer Electrical Specifications
3. Select a transformer from the table in figure 4-1 given the following
information:

Maximum in-rush for the machine is 15A.

Operating voltage = 120 VAC.
Maximum in-rush VA = _____________________________________(VA)
Maximum in-rush VA of selected transformer = __________________(VA)

The transformer with a VA rating of 1964 should be selected.

This skill has taught how to select a transformer to operate at rated load and
voltage. A transformer can be operated at something other than rated load and
voltage. However, the efficiency will be lower. In the next objective, you will
learn more about this.
BB227-BC06UEN-E1-S04, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S04-2
Activity 1. Transformer Power Loss
Procedure Overview
In this procedure, you will load a transformer and take measurements
which will allow you to calculate the power in and out of the transformer.
You will then use these actual power values to calculate the efficiency of the
transformer. This will show that the transformer does in fact lose power.

1. Connect the circuit shown in figure 1-1. Set the DMM to measure AC current
(you will want to use the mA input jack).
This circuit uses the resistor module which has two 220 ohm resistors. These
resistors are connected in series to create a load of 440 ohms.

30XR
AC
CURRENT
SOURCE SELECT
NON
CONTACT
VOLTAGE
MIN MAX
V
200
HOLD
600 OFF 600
200
20
AC
V
20
2
200m
DC
2
200m
200
2m
20M
2M
24V
12V
200m
20k
2k
200
12V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
V
COM
3
2
1
CAT
CAT
A
BATT 9V
7
6
5
R1
220
MAX
600V
600V
PRIMARY
TRANSFORMER
MODULE
8
5
600V
300V
200mA
MAX
FUSED
10A MAX
FUSED
4
1
10 A
1.5V 9V
10A
A
20m
200k
2
6
3
7
24
VAC
R2
220
SECONDARY
4
220
8
R1
220
R2
Figure 1-1.
TRANSFORMER LOAD
MODULE
Test Circuit for Activity 1

2. Place the AC/DC selector switch on the power supply in the AC position.

3. Turn on the power supply and record the reading displayed by the DMM in
the space provided. This is the transformer primary current.
Transformer primary current = _______________________________ (mA)

Primary current should be approximately 78mA.
BB227-BC06UEN-E1-A01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A01-1
ACTIVITY 1. TRANSFORMER POWER LOSS

4. Use the analog voltmeter on the T7017 to measure the voltage across the
primary and record this value below.
Transformer primary voltage = ______________________________ (VAC)
Primary voltage should be approximately 26.5 VAC.


5. Turn off the power supply.

6. Now move the DMM to measure the current in the secondary, as shown in
figure 1-2.
30XR
AC
CURRENT
SOURCE SELECT
NON
CONTACT
VOLTAGE
MIN MAX
V
200
HOLD
600 OFF 600
200
20
AC
V
20
2
200m
DC
2
200m
200
2m
20M
2M
24V
12V
200m
20k
2k
200
12V
1.5V 9V
200
BATT
10 A
200m
2m 20m
A
mA
2
A
600V
300V
PRIMARY
8
7
6
R1
220
MAX
600V
600V
1
TRANSFORMER
MODULE
A
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
3
CAT
CAT
V
COM
4
5
10 A
BATT 1.5V
10A
1
20m
200k
2
6
3
7
24
VAC
5
R2
220
SECONDARY
220
R1
4
8
220
R2
TRANSFORMER LOAD
MODULE
Figure 1-2.
Move the AC Ammeter to Measure the Secondary Current

7. Turn on the power supply and record the reading displayed by the DMM in
the space provided. This is the transformer secondary current.
Transformer secondary current =(mA)


Secondary current should be approximately 54mA.
8. Use the analog voltmeter on the T7017 to measure the voltage across the
secondary and record this value below.
Transformer secondary voltage = ____________________________ (VAC)


Since the transformer is connected in a 1:1 configuration this value should be
close to the value you recorded in step 4 (approximately 26.5VAC).
9. Turn off the power supply.
BB227-BC06UEN-E1-A01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A01-2
ACTIVITY 1. TRANSFORMER POWER LOSS

10. Use the data you obtained in steps 3 and 4 to calculate the power being used
by the primary.
Primary Power = _________________________________________ (Watts)



The solution is as follows:
P
=
I×E
P
=
78mA × 26.5V
P
=
2.06 Watts
The power used by the primary is approximately 2 Watts. Your computed
value may vary slightly depending on actual values obtained in steps 3 and 4.
11. Use the data you obtained in steps 7 and 8 to calculate the power being used
by the load on the secondary.
Secondary Power = _______________________________________ (Watts)



The solution is as follows:
P
=
I×E
P
=
54mA × 26.5V
P
=
1.43 Watts
Power used by the secondary is approximately 1.43 Watts, your computed
value may vary slightly depending on actual values obtained in steps 7 and 8.
12. Use the actual power values that you calculated in steps 10 and 11 to calculate
the efficiency of the transformer. Record your answer in the space provided.
Transformer Efficiency = ______________________________________ %

The solution is as follows:
Transformer Efficiency % =
Transformer Efficiency % =
Power Out
Power In
1.43
2.0
× 100
× 100
Transformer Efficiency % = 0.71 × 100
Transformer Efficiency % = 71%

The actual transformer efficiency is approximately 71%. Your computed value
may vary slightly depending on actual values obtained in steps 10 and 11.
NOTE
This efficiency is fairly low because of this transformer’s small size. Also
we are using it at a voltage other than that for which it was designed (24 volts
instead of 240 volts). A normally-loaded transformer usually has an efficiency
in the 90% range.
BB227-BC06UEN-E1-A01, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A01-3
SKILL 5
CALCULATE THE CURRENT LOAD ON A TRANSFORMER
Procedure Overview
In this procedure, you will use the information given to size a transformer
for the application. You will also determine if the machine will cause an
overload on the feed circuit.


1. Perform the following substeps to calculate the current load on a transformer.
The secondary voltage (VS) is 120 volts and secondary current (IS) is 3 amps.
The primary voltage (VP) is 240 volts.
A. Calculate the VA.
VA = _________________________________________________ (Amps)
The solution is as follows:
VA =
VS × IS
VA =
120 × 3
VA =
360
B. Select a transformer from the chart in figure 16.
Model No. _________________________________________________
You should pick one which has a VA larger than 360. This is model
636-1191.
C. Calculate the maximum current of the transformer.
Maximum Current ____________________________________ (Amps)
The solution is found by dividing the maximum VA of the transformer by
the primary voltage. This is:
IP =
500 ÷ 240
IP =
2.08 Amps
BB227-BC06UEN-E1-S05, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S05-1
SKILL 5 CALCULATE THE CURRENT LOAD ON A TRANSFORMER

2. Calculate the maximum current load of a transformer given the circuit in
figure 5-1. Then, select a transformer from the chart in figure 5-2.
Transformer Model _____________________________________________
Current load, IP =________________________________________ (Amps)

The answer is transformer 636-1161 and 1.0 amp.
IP
2 AMPS
240
VOLTS
Figure 5-1.
DEVICE
120
VOLTS
Minimum Current Load Calculation
TRANSFORMER ELECTRICAL SPECIFICATIONS AND
ORDERING DATA (SUPPLY VOLTAGE 220 VAC)
VA
Max.
Inrush
VA†
50
75
100
150
250
500
1000
180
218
273
660
1360
1964
4014
Temp.
Rise
Dimensions
A
B
C
Model
636-
110-120 V Secondary Voltage Rating
55°C
55
55
55
55
115
115
3-5/16”
3-9/16”
3-3/4
4-5/16
5
5-1/2
6-3/4
3”
3-3/8
3-3/8
4-1/2
4-1/2
4-1/2
5-1/4
2-1/2
2-7/8
2-7/8
3-13/16
3-13/16
3-3/4
4-3/8
1111
1121
1131
1141
1161
1191
1211
2-1/2
2-7/8
3-13/16
1111824
1131824
1141824
22-24V Secondary Voltage Rating
50
100
150
180
273
660
55
55
55
3-5/16
3-3/4
4-5/16
3
3-3/8
4-1/2
(*) Terminal Type (†) Capability VA. Refers to maximum inrush VA after
calculations are made.
Figure 5-2.
Transformer Electrical Specifications
BB227-BC06UEN-E1-S05, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S05-2
SKILL 5 CALCULATE THE CURRENT LOAD ON A TRANSFORMER

3. Calculate the maximum current load for the transformer in figure 5-3 given
the following information. Then, select a transformer from the chart in figure
5-2.
HINT
The wattage rating of the light bulb determines the VA of the secondary.
Transformer Model _____________________________________________
Current load, IP =_______________________________________________

The answer is transformer 636-1131 and .42 amps.
IP
240
VOLTS
Figure 5-3.

120 VOLTS
100 WATT
LIGHT BULB
Maximum Current Load Calculation
4. Determine if a new machine can be added to a circuit given the following
information:

Line voltage of 240 VAC is fed from a 30 A circuit breaker to three other
machines which are drawing a total of 25 A. You need to know whether or not
adding a fourth machine will overload the circuit.

The current required for the fourth machine is 4 A and its operating voltage is
120 VAC. Select the correct transformer from figure 5-2 and use its maximum
VA to calculate the current load.
Machine #4 Current Load, IP = _____________________________ (Amps)
Machine can be added ___________________________________ (Yes/No)

The current load is 2.08 Amps. The machine can be added to the existing
circuit.
BB227-BC06UEN-E1-S05, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S05-3
SKILL 6
DESIGN A CONTROL TRANSFORMER CIRCUIT TO PROVIDE
A GIVEN OUTPUT VOLTAGE
Procedure Overview
In this procedure, you will determine how the primaries of a control
transformer should be connected to produce a desired output given the line
voltage and number of turns of each coil. You will then connect a transformer
to deliver their desired output.

1. Redraw the control transformer schematic shown in figure 6-1 on a separate
piece of paper. Make the connections so that the output voltage is 120 VAC.
H1
H3
100
TURNS
X1
100
TURNS
240 VAC
H2
X2
100
TURNS
H4
Figure 6-1.
Control Transformer Schematic
BB227-BC06UEN-E1-S06, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S06-1
SKILL 6 DESIGN A CONTROL TRANSFORMER CIRCUIT TO PROVIDE A GIVEN OUTPUT VOLTAGE

2. Redraw the schematic shown in figure 6-2 with the transformer connected to
produce a turns ratio of 1:1. Use both primary and secondary coils.

Draw your circuit on a separate piece of paper.

This is the transformer on the T7017 transformer module. Notice that the
transformer has two primaries and two secondaries. Also, the primary coils
are not crossed.
1
5
SECONDARY
PRIMARY
100
TURNS
50
TURNS
2
6
3
7
100
TURNS
50
TURNS
8
4
Figure 6-2.
Transformer on the Transformer Module
NOTE
The number of turns listed for the transformer coils in figure 6-2 is used
simply to show the turns ratio concept. The actual number of turns in the coils
is proprietary information and not available from the manufacturer.

3. Connect the circuit you drew in step 2 on the T7017. Use the 24 VAC jacks to
supply power to the transformer.

4. Turn on the power supply and use the DMM to measure the input and output
voltages. Record these values below:
Input Voltage ____________________________________________ (VAC)
Output Voltage __________________________________________ (VAC)

You should find an input voltage of approximately 26.5 VAC and an output
voltage of approximately 35 VAC. The output voltage is actually greater than
the input voltage. This is because transformers of the size used on the T7017
are rated for the output voltage at a specific output current.
BB227-BC06UEN-E1-S06, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S06-2
SKILL 6 DESIGN A CONTROL TRANSFORMER CIRCUIT TO PROVIDE A GIVEN OUTPUT VOLTAGE

In the next four steps, you will add a load to the secondary of the transformer.
This load is sized to draw rated current from the transformer. You will then
re-check the input and output voltages.
NOTE
This is the same reason you actually read 26.5 VAC at the T7017 power
supply jacks. It is rated for 24 VAC at a specific load current.

5. Turn off the power supply.

6. Add a 440 ohm load to the secondary of the transformer, as shown in figure
6-3.
NOTE
The 440 ohm load is created by connecting the two 220 ohm resistors in
series.
5
TRANSFORMER
MODULE
5
8
SECONDARY
6
R1
220
7
R2
220
220
R1
220
R2
TRANSFORMER LOAD
MODULE
Figure 6-3.
8
Load for Transformer Secondary

7. Turn the power supply back on.

8. Use the DMM to measure the input and output voltages. Record these values
below:
Input Voltage ____________________________________________ (VAC)
Output Voltage __________________________________________ (VAC)

You should find that the input voltage is still approximately 26.5 VAC but the
output voltage is now also approximately 26.5. This is the 1:1 ratio when the
transformer is loaded.
BB227-BC06UEN-E1-S06, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S06-3
SKILL 6 DESIGN A CONTROL TRANSFORMER CIRCUIT TO PROVIDE A GIVEN OUTPUT VOLTAGE


9. Turn off the power supply.
10. Solve the following design problem.

With the primary connected in parallel, determine how the transformer
secondary should be connected to produce a turns ratio of 2:1.

Draw your circuit on a separate piece of paper.

11. Connect your circuit on the T7017.

12. Add a 110 ohm load to the secondary of the transformer, as shown in figure
6-4. This will properly load the transformer for this ratio.
NOTE
The 110 ohm load is attained by connecting the two 220 ohm resistors in
parallel.
5
TRANSFORMER
MODULE
5
8
SECONDARY
220
R1
6
R1
220
R2
220
7
220
R2
TRANSFORMER LOAD
MODULE
Figure 6-4.
8
Load for Transformer Secondary

13. Turn the power supply back on.

14. Use the DMM to measure the input and output voltages, record these values
below:
Input Voltage ____________________________________________ (VAC)
Output Voltage __________________________________________ (VAC)

You should find an input voltage is still approximately 26.5 VAC but the
output voltage is approximately 13.2. This is the 2:1 step down ratio.

15. Turn off the power supply.

16. Disconnect and store all components.
BB227-BC06UEN-E1-S06, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
S06-4
Activity 2. The Distribution Transformer
Procedure Overview
In this procedure, you will connect the transformer module on the T7017
in a configuration which will simulate a distribution transformer. You will then
take measurements to verify the available voltages and currents present in the
transformer. This will show you how important it is to have balanced loads on
a distribution transformer.


1. Connect the circuit shown in figure 2-1.
This circuit simulates a distribution transformer. Since each secondary has an
equal number of turns, the connection of the two secondaries is equivalent to
a center tap.
NOTE
The transformer is actually set up for a 1:1 ratio. In an actual distribution
transformer, this would be a much greater ratio. The secondary configuration
is what we will be testing in this procedure.
PRIMARY
SECONDARY
CENTER
TAP
24
VAC
220
220
Figure 2-1.
Distribution Transformer Configuration
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-1
ACTIVITY 2. THE DISTRIBUTION TRANSFORMER

2. Turn on the power supply.

3. Use the DMM to measure the voltage across the secondary as shown in figure
2-2. Record this reading below.
Voltage across secondary __________________________________ (VAC)

You should measure approximately 25 to 26 VAC. This is where the high
power requirement loads would be attached to the distribution transformer.
PRIMARY
24
VAC
SECONDARY
220
V
220
Figure 2-2.
Measuring the Secondary Voltage
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-2
ACTIVITY 2. THE DISTRIBUTION TRANSFORMER

4. Use the DMM to measure the voltage across each of the two loads.

Record below the voltage across load #1 and load #2 in the spaces provided.
Figure 2-3 shows the connection for measuring the voltage across load 1.

The two 220 ohm resistors represent the 120 VAC loads that would be
balanced across the secondary of the transformer.
Voltage across load #1 = _____________________________________ VAC
Voltage across load #2 = _____________________________________ VAC

You should measure approximately 12.5 to 13 VAC across the loads. This is
how the user accessible outlets and lighting circuits would be attached to the
distribution transformer.
PRIMARY
SECONDARY
220
V
24
VAC
220
Figure 2-3.
Measuring the Voltage Across the Loads
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-3
ACTIVITY 2. THE DISTRIBUTION TRANSFORMER

5. Perform the following substeps to measure the current flowing through load
#1.
A. Turn off the power supply.
B. Configure the DMM to measure AC current, use the mA input jack.
C. Place the meter in series with load #1 as shown in figure 2-4.
SECONDARY
TRANSFORMER
MODULE
8
7
6
5
A
5
30XR
AC
CURRENT
NON
CONTACT
VOLTAGE
MIN MAX
R1
220
HOLD
LOAD #1
V
200
600 OFF 600
200
20
6
V
20
2
200m
220
2
200m
200
2m
20M
R1
2M
20m
200k
200m
20k
2k
200
10 A
1.5V 9V
220
200
BATT
BATT 1.5V
A
mA
R2
10 A
200m
2m 20m
LOAD #2
CAT
CAT
V
COM
10A
600V
300V
R2
220
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
MAX
600V
600V
TRANSFORMER LOAD
MODULE
Figure 2-4.
7
A
8
Measuring Load #1 Current
D. Turn on the power supply.

6. Record below the current flowing through load #1.
Load #1 current = _________________________________________ (mA)


You should measure approximately 55 to 65 mA of current through load #1.
7. Repeat step 5 to obtain the current through load #2. Record this value below.
Load #2 current = _________________________________________ (mA)

You should measure approximately 55 to 65 mA of current through load #2.

In the next steps, you will calculate the unbalanced current that should be
flowing in the common conductor. You will then measure the common current
to verify that only the unbalanced current is flowing in the common.
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-4
ACTIVITY 2. THE DISTRIBUTION TRANSFORMER

8. Subtract the lower of the two values you recorded in steps 6 and 7 from
the higher of the two values. This gives you the approximate current that is
flowing in the common conductor. Record this value below.
Unbalanced current = ______________________________________ (mA)
Typical values will range from 2 to 7 mA.

NOTE
It is possible to have these two exactly equal each other. If they match
exactly, you should read zero current in the common line. However, actual
values will usually not match exactly and will leave a small amount of
unbalanced current.

9. Move the DMM to now measure current in the common as shown in figure
2-5.
SECONDARY
TRANSFORMER
MODULE
5
8
7
6
5
30XR
R1
220
AC
CURRENT
NON
CONTACT
VOLTAGE
MIN MAX
HOLD
LOAD #1
V
200
600 OFF 600
200
20
A
20
2
200m
2
200m
220
200
R1
2m
20M
2M
20m
200k
7
200m
20k
2k
200
10 A
1.5V 9V
200
BATT
BATT 1.5V
10 A
200m
2m 20m
A
mA
CAT
CAT
V
COM
10A
6
V
A
R2
220
220
600V
300V
R2
BATT 9V
200mA
MAX
FUSED
10A MAX
FUSED
LOAD #2
MAX
600V
600V
TRANSFORMER LOAD
MODULE
Figure 2-5.
8
Measuring Current in the Common

10. Turn on the power supply and record below the current flowing in the
common.
Current in the common = ___________________________________ (mA)

Typical values will range from 2 to 7 mA depending on actual resistance and
voltage values.
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-5
ACTIVITY 2. THE DISTRIBUTION TRANSFORMER

11. Compare the value you measured in step 10 with the value you calculated in
step 8.
Are they close? ________________________________________ (Yes/No)

You should find that these values match exactly, any differences will be in the
meter or reading accuracy.

As you can see, if the loads on a distribution transformer are balanced, the
common current is almost zero.

12. Turn off the power supply.

13. Disconnect and store all components.
BB227-BC06UEN-E1-A02, REV. A TRANSFORMERS
Copyright © 2014 Amatrol, Inc.
A02-6