Goals
 This module is to introduce basic electrical concepts as
they apply to power systems. Volts, Amps, Ohms,
Watts are discussed. Ohms Law is introduced and
different types of power sources are also introduced.
Objectives
Upon completion of this module, the student should be able to:
 Describe the safety hazards with power sources.
 Perform simple Ohms Law calculations.
 Select the proper meter for voltage and amperage
measurements and connect it properly in the circuit.
 Fabricate industry standard wire splices that are properly
soldered and insulated. (not sure this should be here and
not in controls)
Objectives (cont.)
 Determine the appropriate type, size and capacity of
battery or batteries for the ROV and their appropriate
placement on the surface.
 Estimate the total amount of energy and the maximum
instantaneous power that your vehicle will require to
complete its mission
 Select over current protection as dictated by the device
being powered.
High Voltage Electricity and Water are a Dangerous
Combination and is one of the greatest hazards students will
encounter in these projects, therefore, this section should be
thoroughly taught, tested , and constantly reiterated.
AC versus DC
AC (Alternating Current)
DC (Direct Current)
 Alternates its current in a sine
 The current travels the same
wave pattern
 Typically osculates between
50 and 60 HZ
 Typically found in all
building wiring.
 Typically above 100V (varies
from country to country)
direction and the voltage is
constant
 Most commonly comes in the
form of Batteries and Power
Adapters or Inverters that
change AC to DC
 Typically low in voltage (1.5V
– 32V
 Can be deadly!
 Can be deadly!
http://www.kropla.com/electric2.htm
http://phet.colorado.edu/en/simulation/circu
it-construction-kit-ac
A/C Electrical Power Safety
 115 Volts AC can and does kill roughly 100 people each
year
 Working around water GREATLY increases the risk of
serious physical injury
 Although it is common for many commercial ROVs to
use very high voltages, the people designing and
operating them are trained and certified professionals
– you are not!
 Therefore:
 A/C Power should never enter water at any time
and
 Working with A/C power near water should be done
minimally and with the highest regard of safety
If you must…
…work with A/C Power around water, commit the
following to memory or retype and post near outlets in
the room as a reminder to all.
 NEVER touch a device that is plugged in if either
you or the device is in contact with the water
CERTIFY
 that any device plugged into a wall socket around water is
plugged into a working GFI Outlet
GFI and GFCI are the highest rated quickest to respond to any short circuit
The cord on the right uses an in-line circuit breaker, and should only be used in
conjunction with a GFI wall outlet
NEVER
 Work on any electrical system while it
is plugged in (this includes small DC
wall adapters and Batteries of all
types)
Let your body become the electrical pathway
to the ground
ALWAYS
 Have a responsible person with you
(preferably trained in CPR and First Aid)
 Work in a dry uncluttered place
 Use tools with insulated handles
 Check and Double-check that everything is
unplugged before working with hands or
tools
 Ensure that there is no latent charge in
components that may have stored voltage
after the device has been unplugged
Energy
 Energy is the ability or capacity something has to affect
change in another thing
Forms of Energy
 heat
 electromagnetic radiation (light, radio waves etc)
 energy stored in chemical bonds
 mechanical energy (potential and kinetic)
 electrical
 mass
Quantifying Energy
 The Unit of Energy is the joule (J) One joule is roughly
the amount of energy needed to lift one apple one
meter from the floor
 It is the amount of energy it takes to lift an object one
meter using one Newton of force.
 Sometimes it is expressed as Newton Meters where
1 joule = 1 Nm or Newton-meter
Quantifying Energy – Watt Hour
Watt hours (Wh)
Are very useful to use when calculating the amount of
Energy each of the systems in our vehicles are each
going to need and how much the entire vehicle will
need. Therefore Watt Hours will be the most
commonly used unit of Energy
1Wh = 3600 joules
(an easy way to remember this is that an hour has 60 x 60 seconds and therefore 3600
seconds, why this is relevant will become clear when we talk about Units of Power)
Quantifying Energy –
Other common units
 Kilowatt hours (KWh) 1kWh = 1000 Wh = 3.6 million joules
Kilowatt hours are typically how building electricity usage is measured
when purchased from a power plant
 ft-lbs is the imperial equivalent 1 ft-lb = 1.356 joules
Notice how the ft-lb is a combination of distance and force, just like the
Newton-meter
 calorie
The amount of energy required to raise the temperature of one milliliter
of water one degree Celsius
 BTU
The standard by which natural gas is measured
Power
The rate at which electrical energy is transferred in an
electronic ciruit
 Notice that the power is a rate, which means that it forms a ratio over
time therefore the formula for power is:
Energy
Power = =
Power
Time
Energy and Power: What’s the
difference?
 When applied non-scientifically, these words seem to
have similar meaning, but they have a constituent
relationship, they are part of one another.
 One way to imagine the difference is in a car.
 The Energy of the car is represented by the amount of
fuel in the car.
 The Power of the car is the ability of its engine to convert
the fuel into movement. How well it does this
determines how powerful is it.
Quantifying Power
Watt - The watt is the most often encountered metric
unit of power 1 Watt = 1 joule/second.
(remember that power is a rate of energy consumed over
time, joule is a unit for energy and second is obviously
a unit of time)
Kilowatt – A higher order unit of power 1 kW = 1000 W
Horsepower - An often used imperial unit of power.
1 Horespower = 746 Watts
Criteria for determining a
power system
What are the considerations that we need to make when
deciding which kind of Power
To understand how all of this is going to work together,
we need to know a little bit about how we talk, think
and work with electronics
This section is to provide only general , practical introduction to
electrical theory . Circuit design and system specific
electronics will be considered in another module. The focus of
this module is Supplying the appropriate amount of power and
delivering that power to the systems of the ROV
The Basic terminology
 Charged particles – elements (usually protons and
electrons) that have electrical attraction or repulsion
 Current – the flow of electrons from one location to
another (represented with the letter “I”)
 Voltage – the energy per unit charged in or repulsion
of charged particles (represented with the letter “V” or
“E”) (joules per coulomb)
 Resistance – a friction like property within a wire or a
component that generates a transfer of energy like
heat and other forms of energy (represented with the
letter “R”)
The relationship between voltage,
current and resistance
Since Electricity is invisible, we often
use analogies to help us understand
the different interactions that occur in
a circuit
Voltage is the amount of “pressure” needed
to “push” the current along, measured in volts
(V)
Current is the “rate” at which the charged
particles are moving through a substance,
measured in amperes (“amps” or A)
Resistance is the electronic “friction”
restricting the movement of the current:
measured in ohms (Ω)
So what? What is a circuit?
A circuit is a configuration usually comprised of a power source, a
conductor and something resistant
This is the schematic
Kahn Academy
http://www.youtube.com/watch?v=3o8_EA
RoMtg&feature=relmfu
CU Physics simulations
http://phet.colorado.edu/en/simul
ation/circuit-construction-kit-dc
Ohm’s Law
 The interaction between the constituent parts of
electrical power form a mathematical relationship
famously defined as Ohm’s Law, the most famous law
in all of electronics
V=IxR
(or E = I x R)
Using Ohm’s Law
This configuration, sometimes called Ohm’s triangle
is a useful way of remembering how to find one
element when you know the other two
Examples: …
http://phet.colorado.edu/sims/ohmslaw/ohms-law_en.html
Let’s practice seeing how this works in
our own circuits
http://phet.colorado.edu/en/simulation/circu
it-construction-kit-dc
What about Power and Energy?
Power is directly proportionate to Voltage and Current,
in other words we have another formula
P=VxI
(or P = E x I)
Remember that power is the Rate at which Energy is
put to use or used up, therefore it makes sense that as
the “pressure” or voltage increases and the “rate” of
the movement of the current increases, then the rate
of consumption must also increase
Again a triangle is useful to help us derive what
we want to know from two things that we know
The Wheel
If we substitute the constituent parts between the two
triangles mathematically we come up with an entire
array of different formulas
This looks really complicated, but if you
can simply remember the relationships
represented in the triangles, memorizing
this is not all that important.
It is useful however to see all of the
possible mathematical possibilities
between the four properties of electricity
and to realize that if any two properties
are known, than the other two properties
can be derived
Testing connections for proper voltage and current
Measuring Voltage, current and
resistance
 Generally we use a multi-meter to measure the
properties of a circuits.
Here is a good video illustrating the basic use of a multimeter
http://www.youtube.com/watch?v=BW3Wj7
UD-_s
And here is a virtual place to practice
http://phet.colorado.edu/en/simulation/circu
it-construction-kit-dc
Tips for checking voltage and
current
 Checking the voltage of a battery may give you a sense
of whether it is charged or not, but to be certain, it is
critical that either…
 A load is applied to the battery while it is being tested.
This is because the internal resistance of a battery
increases as it loses its charge, which may not be obvious
unless it is being discharged
 You use a car battery tester that has been designed to
apply a large enough load to do this without a circuit
 Remember when measuring current, the meter must
be placed “in-line” and the correct amperage port is
being used with the meter’s leads, ask for permission
to do this first, as it is common to blow the fuse if done
Soldering, crimping and an insulating
Proper soldering techniques
 Proper soldering is very important, a “cold”, a weekly
soldered connection, or a solder bridge can lead to a
lot of frustration and worse damaged equipment
 These films offer a great series on soldering techniques
which should be studied, practiced and strictly applied
 http://youtu.be/I_NU2ruzyc4
 http://www.makershed.com/product_p/mkel4.htm
 This you tube channel, the curious inventor, has dozens of excellent videos
that do a fantastic job of demonstrating and describing the proper way to
solder
Wire Gauges
 The thickness of a wire or its “gauge” is a standard unit
known as the AWG (American Wire Gauge)
 The wire gauge number INCREASES as the wire gets
smaller.
 Wires carry resistance: the thinner and longer the
wire, the more resistance it will have
 The method you choose to connect wires to other
wires, circuit boards and components will be
determined greatly by the wire’s gauge
Wire Gauges
 It is the amount of copper that determines the gauge of
the wire, not the insulation
Typically wires are stranded or solid.
When they are stranded, the total
combined width of the strands
determines the gauge
Using proper connections
 Special connectors have been designed for splicing
wires with other wires and components.
 Gauges of wire under #22 AGW can use crimp – on
terminal connecters as long as the correct size is used
and the connectors are not ever meant to come in
contact into contact with water
Other connectors
 For smaller wire, and other types of connections there
are literally hundreds of connectors that can be used,
depending on your application.
 A couple of resources that are good for finding the
right type of connector:
 http://www.mouser.com/
 http://www.digikey.com/
 http://www.mcmaster.com/
When choosing a power source there are multiple
considerations
• Safety
•Maximum Power Output
•Energy Capacity
•Size and Weight
•Depth of Discharge
•Type
•Cost
Battery Safety
 Any battery powerful enough to propel an underwater
vehicle is powerful enough to set a fire.
 When batteries are not in use, the leads should be
properly insulated
 The battery should always be stored in a place where it is
not going to tip, fall, or otherwise come into contact
with something that may cause a short
Content needed here
 NOTE to MATE: Jeremy and Scott recommended
adding content here about the following and
mentioned that they would contribute this content…I
have forwarded the file to them:
 Safely containing batteries in an enclosure (Scott)
 Sulfuric Acid Safety (Scott & Jeremy)
 Potential Off-Gassing (Scott & Jeremy)
 Baking soda (Scott & Jeremy)
 Video of melting metal with a battery (Jeremy)
Content needed here
 NOTE to MATE: Scott recommended adding content
here a direct power supply, I am going to defer to his
expertise in this matter since it is not discussed much
in the book:
Battery Safety continued
 Burns
 A short circuit can cause serious burns even if it doesn’t
cause fire
http://www.youtube.com/watch?v=2Tj9I6iP6Qg
 The chemicals in many batteries often include sulfuric
acid which will cause burns to the skin, so always use
gloves when dealing with any battery solution
 Poisonous Gasses
 Some batteries can give off gasses (even Sealed Lead
Acid batteries) that can either be poisonous or explosive
Maximum Power Output
 How much Power will you need?
 An inventory of all of your electrical systems provides
will give you this amount
 Use a spreadsheet to compose the inventory so that
changes can be easily made
Device
Thruster Motor
Video Light
Wireless Ethernet Switch
Network video camera
Camera tilt motor
Microcontroller
Lasers
Misc. Sensors and other electronics
Totals
Number
4
2
1
2
1
2
2
1
Current Total Maximum Maximum on Total Energy
(amps) Current (amps)
time
(amp-hrs)
3
12
1.5
18
2
4
1.5
6
0.5
0.5
2
1
0.1
0.2
2
0.4
0.75
0.75
0.5
0.375
0.05
0.1
2
0.2
0.1
0.2
1
0.2
1
1
2
2
17.75
25.8
Power Inventory
Device
Thruster Motor
Video Light
Wireless Ethernet Switch
Network video camera
Camera tilt motor
Microcontroller
Lasers
Misc. Sensors and other electronics
Totals
Number
4
2
1
2
1
2
2
1
Current Total Maximum Maximum on Total Energy
(amps) Current (amps)
time
(amp-hrs)
3
12
1.5
18
2
4
1.5
6
0.5
0.5
2
1
0.1
0.2
2
0.4
0.75
0.75
0.5
0.375
0.05
0.1
2
0.2
0.1
0.2
1
0.2
1
1
2
2
17.75
25.8
The power per device is derived by reading the rating of the device and if the
rating is in amps, multiply the amps and the volts to get the total power use
We do the reverse to determine how many amps we will need at total
Maximum power
Sizing the battery for the
machine
 Batteries are measured in Volts and amp hours which
gives you a broad sense of what you will need.
 Voltage is generally determined by the requirements of
your onboard electronics. Generally it is advisable to
choose a voltage that is as large or larger than the device
with the largest need
 Amp hours simply tells us that the battery is designed to
produce a certain level of current at its voltage for one
hour before losing significant voltage
Calculating the Maximum
power output of a battery
In this example the battery can provide 35
amps of current 12 Volts for 1 hour
If your system is drawing 7 amps of power
continuously, then the battery should
perform for five hours (5 x 7 = 35)
If it were to draw 70 Amps the battery will
only last 30 minutes
http://tinyurl.com/9ce9whc
These are not exactly precise because of various factors, but they give us a minimum threshold and put us in the
ballpark for what we need
So how much will we need?
Device
Thruster Motor
Video Light
Wireless Ethernet Switch
Network video camera
Camera tilt motor
Microcontroller
Lasers
Misc. Sensors and other electronics
Totals
Number
4
2
1
2
1
2
2
1
Current Total Maximum Maximum on Total Energy
(amps) Current (amps)
time
(amp-hrs)
3
12
1.5
18
2
4
1.5
6
0.5
0.5
2
1
0.1
0.2
2
0.4
0.75
0.75
0.5
0.375
0.05
0.1
2
0.2
0.1
0.2
1
0.2
1
1
2
2
17.75
25.8
Remember that Power = Volts x amps
The maximum power of the example above is 106 Watts.
Divide this by 12 and we should expect, that at a maximum, our system
will need 8.83 amps
The battery in our example provides 18 amp hours worth of energy so
18 ÷ 8.83 = 2.03. If everything were running continuously, we could
operate for 2.03 hours
So how much will we really
need?
 After we determine that we have more than enough amperage to power our
vehicle at its maximum, we can take a look at how much we will need for the
specific mission and see if our battery is sufficient
Device
Thruster Motor
Video Light
Wireless Ethernet Switch
Network video camera
Camera tilt motor
Microcontroller
Lasers
Misc. Sensors and other electronics
Totals
Number
4
2
1
2
1
2
2
1
Current Total Maximum Maximum on Total Energy
(amps) Current (amps)
time
(amp-hrs)
3
12
1.5
18
2
4
1.5
6
0.5
0.5
2
1
0.1
0.2
2
0.4
0.75
0.75
0.5
0.375
0.05
0.1
2
0.2
0.1
0.2
1
0.2
1
1
2
2
17.75
25.8
Notice the maximum on time for this 1.5 hour mission for some devices is 2 hours. Prior to actually beginning the mission
there may be a half hour spent testing equipment and that has been factored in
Now, taking the data from our battery: 12V x 18Ah = 216 Watt hours, which is half an
hour longer than is needed for our mission, therefore this battery is sufficient enough
for our needs
Devilish details
Data sheets for batteries tell us a little bit more about how we should
expect them to perform and before making a large investment, it is
critical to inspect these sheets to make sure that this is what we need
The “C” is the C-rate which is
essentially the factor of the
amperage we intend to use.
In our case we are using at most
8.83 Amps which is a little less than
half of the rated Amp hours of the
battery (18Ah), therefore to see how
this battery would perform at
maximum power we can follow the
line for 0.6 C and plan accordingly
Of course this is at Maximum Power so we could go back through the chart and estimate a more
realistic usage and then apply our chart. Notice how the bottom scale is logarithmic and a C rate of .25
actually triples our workable time
Other Electrical Considerations
 Deep Cycle batteries are designed to withstand severe
discharging and repeated recharging cycles.
 Marine batteries are often Deep cycle or hybrids
between deep cycle and standard auto batteries
 RV and Electric Car batteries are also of this type
 Maximum Charge Rate
 Batteries us the C-rate to inform what the maximum
charge rate is, therefore if our battery must be charged at
0.5 C than the most Amperage we should supply is 9
amps
Multiple Batteries
 Voltage can be
increased by
connecting batteries in
series
 Energy can be
increased by
connecting batteries in
parallel
Size
 Big batteries provide a lot of power, but if you have to
travel far, they may prove to be more of a burden then
they are worth
 Also, large batteries may be more expensive than
necessary, so it is best to choose a size that is
appropriate for your needs.
Battery Types
 Alkaline - typical drug store batteries, not rechargeable and
therefore not often considered for submersible vehicles
 Sealed Lead-Acid – Exact same chemistry of the traditional Car
battery, only sealed and therefore not vulnerable to spillage
 AGM – Essentially a Sealed Lead Acid, only the fluid has been
captured into an Absorbed Glass Mat, thereby making them very
durable and ideal for surface
 NiMH and Ni-Cad – Nickel based rechargeable batteries that have
become the standard replacement for the alkaline as a rechargeable
alternative, affordable and available, when stacked to create higher
voltages they can provide a good alternative to more expensive types
Battery Types continued
 Lead Acid Car Batteries
These are not ideal for many reasons:
 They leak if they are not handled properly
 They may not have the “depth” to provide constant
current and be very inefficient
vs.
 Deep cycle marine batteries
 Can often be purchased as AGM and therefore not prone
to mishandling
 Are meant to handle small amounts of current for longer
amounts of time and are thus much more ideal than the
Battery Types to avoid
 Lithium – Because of the volatility of lithium, especially in water,
Lithium is not recommended
 Automobile (Starter) batteries – Although very popular and
readily available, these are discouraged because of the lack of
containment of the battery fluid, Sealed Lead Acid and AGM should be
used as an alternative,
Battery Types continued
Lead Acid Car Batteries
These are not ideal for many
reasons:
 They leak if they are not
handled properly
 They may not have the
“depth” to provide constant
current and be very
inefficient
Deep cycle marine
batteries
Are suggested as an
alternatives to Car
batteries because they:
 Can often be purchased as
AGM and therefore not as
prone to mishandling
 Are meant to handle small
amounts of current for longer
amounts of time and are thus
much more ideal than the
average car battery
Charging batteries
 With Sealed Lead Acid, Lead Acid and AGM
 Consult the manufacturer about what charging
amperages will work most effectively. This is a
consideration that should occur as decisions are made
about the battery, as batteries will be charged a lot!
 Nickel based batteries – Investing in a “Smart” charger
will preserve the life of the battery and ensure that
batteries are fully charged each time they are used.
Fusing
 In line fuses placed as close to the positive lead of the
power supply must be present to prevent short
circuiting
 The voltage must be higher than the voltage of your
system, and can be as high as you wish
 The current rating must be chosen carefully, the
standard is 1.25 times the maximum current your
system will draw
 “Slow blow” fuses are recommended to accommodate
quick surges in the circuit, but still provide safety if the
high current persists
References
 http://www.allaboutcircuits.com/
 https://6002x.mitx.mit.edu/courseware/
 http://ocw.mit.edu/index.htm
 http://phet.colorado.edu/en/simulations/category/ph
ysics