Goals This module is to introduce basic electrical concepts as they apply to power systems. Volts,...
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Module 6 Power Systems: Supplies
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
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.
Slide 3
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)
Slide 4
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.
Slide 5
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.
Slide 6
AC versus DC AC (Alternating Current) DC (Direct Current)
Alternates its current in a sine wave pattern Typically osculates
between 50 and 60 HZ Typically found in all building wiring.
Typically above 100V (varies from country to country)(varies from
country to country Can be deadly! The current travels the same
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!
http://www.kropla.com/electric2.htm
http://phet.colorado.edu/en/simulation/circu
it-construction-kit-ac
Slide 7
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
Slide 8
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
Slide 9
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
Slide 10
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
Slide 11
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
Slide 12
Slide 13
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
Slide 14
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
Slide 15
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)
Slide 16
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 Quantifying Energy Other common
units
Slide 17
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:
Power = Power
Slide 18
Energy and Power: Whats 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.
Slide 19
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
Slide 20
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
Slide 21
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
Slide 22
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)
Slide 23
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 () 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
Slide 24
So what? What is a circuit? A circuit is a configuration
usually comprised of a power source, a conductor and something
resistant http://phet.colorado.edu/en/simul
ation/circuit-construction-kit-dc This is the schematic
http://www.youtube.com/watch?v=3o8_EA RoMtg&feature=relmfu Kahn
Academy CU Physics simulations
Slide 25
Ohms Law The interaction between the constituent parts of
electrical power form a mathematical relationship famously defined
as Ohms Law, the most famous law in all of electronics V = I x R
(or E = I x R)
Slide 26
Using Ohms Law This configuration, sometimes called Ohms
triangle is a useful way of remembering how to find one element
when you know the other two Examples: Lets practice seeing how this
works in our own circuits
http://phet.colorado.edu/en/simulation/circu it-construction-kit-dc
http://phet.colorado.edu/sims/ohms- law/ohms-law_en.html
Slide 27
What about Power and Energy? Power is directly proportionate to
Voltage and Current, in other words we have another formula P = V x
I (or P = E x I) Again a triangle is useful to help us derive what
we want to know from two things that we know 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
Slide 28
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
Slide 29
Testing connections for proper voltage and current
Slide 30
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 And here is a
virtual place to practice
http://phet.colorado.edu/en/simulation/circu it-construction-kit-dc
http://www.youtube.com/watch?v=BW3Wj7 UD-_s
Slide 31
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 meters leads, ask for permission to do this first, as it
is common to blow the fuse if done incorrectly
Slide 32
Soldering, crimping and an insulating
Slide 33
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
Slide 34
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 wires gauge
Slide 35
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
Slide 36
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
Slide 37
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/
Slide 38
When choosing a power source there are multiple considerations
Safety Maximum Power Output Energy Capacity Size and Weight Depth
of Discharge Type Cost
Slide 39
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
Slide 40
Content needed here NOTE to MATE: Jeremy and Scott recommended
adding content here about the following and mentioned that they
would contribute this contentI 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)
Slide 41
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:
Slide 42
Battery Safety continued Burns A short circuit can cause
serious burns even if it doesnt cause fire
http://www.youtube.com/watch?v=2Tj9I6iP6Qg
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
Slide 43
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 DeviceNumber Current (amps) Total Maximum
Current (amps) Maximum on time Total Energy (amp-hrs) Thruster
Motor43121.518 Video Light2241.56 Wireless Ethernet Switch10.5 21
Network video camera20.10.220.4 Camera tilt motor10.75 0.50.375
Microcontroller20.050.120.2 Lasers20.10.21 Misc. Sensors and other
electronics11122 Totals 17.75 25.8
Slide 44
Power Inventory 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
DeviceNumber Current (amps) Total Maximum Current (amps) Maximum on
time Total Energy (amp-hrs) Thruster Motor43121.518 Video
Light2241.56 Wireless Ethernet Switch10.5 21 Network video
camera20.10.220.4 Camera tilt motor10.75 0.50.375
Microcontroller20.050.120.2 Lasers20.10.21 Misc. Sensors and other
electronics11122 Totals 17.75 25.8
Slide 45
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
Slide 46
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 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
http://tinyurl.com/9ce9whc
Slide 47
So how much will we need? 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 DeviceNumber Current (amps) Total
Maximum Current (amps) Maximum on time Total Energy (amp-hrs)
Thruster Motor43121.518 Video Light2241.56 Wireless Ethernet
Switch10.5 21 Network video camera20.10.220.4 Camera tilt
motor10.75 0.50.375 Microcontroller20.050.120.2 Lasers20.10.21
Misc. Sensors and other electronics11122 Totals 17.75 25.8
Slide 48
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 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 DeviceNumber Current
(amps) Total Maximum Current (amps) Maximum on time Total Energy
(amp-hrs) Thruster Motor43121.518 Video Light2241.56 Wireless
Ethernet Switch10.5 21 Network video camera20.10.220.4 Camera tilt
motor10.75 0.50.375 Microcontroller20.050.120.2 Lasers20.10.21
Misc. Sensors and other electronics11122 Totals 17.75 25.8
Slide 49
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
Slide 50
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
Slide 51
Multiple Batteries Voltage can be increased by connecting
batteries in series Energy can be increased by connecting batteries
in parallel
Slide 52
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.
Slide 53
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
Slide 54
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 average car battery
Slide 55
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,
Slide 56
Battery Types continued Lead Acid Car Batteries Deep cycle
marine 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 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
Slide 57
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.
Slide 58
Slide 59
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