Basic 12V DC Installations

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Basic 12V DC Installations
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Saftey

• Remove all Metal Jewelry
• Rings
• Watches
• Neck Chains
• CIRCUMFERENTIAL ELECTRIC BURNS OF THE RING FINGER

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OHMs Law

• Ohm's Law defines the relationships between (P)
  power, (E) voltage, (I) current, and (R)
  resistance. One ohm is the resistance value
  through which one volt will maintain a current of
  one ampere. ( I ) Current is what flows on a
  wire or conductor like water flowing down a
  river. Current flows from negative to positive on
  the surface of a conductor. Current is measured
  in (A) amperes or amps. ( E ) Voltage is the
  difference in electrical potential between two
  points in a circuit. It's the push or pressure
  behind current flow through a circuit, and is
  measured in (V) volts. ( R ) Resistance
  determines how much current will flow through a
  component. Resistors are used to control voltage
  and current levels. A very high resistance allows
  a small amount of current to flow. A very low
  resistance allows a large amount of current to
  flow. Resistance is measured in ohms. ( P )
  Power is the amount of current times the voltage
  level at a given point measured in wattage or
  watts.

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OHMs Law
E
Volts
I R
Ohms
Amps
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OHMs Law
P
Watts
I E
Volts
Amps
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Plumbing Analogy

• Battery Source of water at a certain Pressure
• Volts Pressure like PSI (Pounds per Square
  inch)
• Current Flow/ How much Water is actually moving
  GPH
• Resistance disruptions to the flow/ valves,
  reducers, motors, etc.

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Load
12V
Valve
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Series Circuit

12V
-
5W
5w/12v .416A
.416A
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Parallel Circuit

12V
-
5w
5w
5w
5w
.42 A
.84 A
1.26 A
1.68 A
.42 A
.42 A
.42 A
.42 A
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Electrical concerns for any installation on a
boat?

• What is the max rated current draw of the device?
  
• What is the round trip length for the wire run,
  from the batteries to the load and back?
• What amount of Voltage drop is acceptable?
• What gauge wire do I need?
• How big of a breaker do I need/want?

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AYBC Standards

• Properly sizing your wire or cable as suggested
  by the ABYC for the marine environment. These
  standards might be a bit more strict than those
  in the automotive environment however, they err
  on the side of caution and were developed with
  safety in mind.
• In the boating world it is suggested3 max
  voltage drop for conductors providing power to
  panels and switchboards, navigation lighting,
  bilge blowers, main DC feeders, and any other
  circuit where voltage drop should be kept to a
  minimum10 max voltage drop on conductors used
  for general lighting and other non-critical
  circuits
• The ampacity (amperage) tables help to choose the
  correct size cable to handle the power load for
  which you are trying to find the correct wiring.
  There are individual tables for single conductor
  and multiple conductor runs as current carrying
  conductors which are bundled together will
  transfer heat to each other in effect reducing
  their safe current handling capabilities.

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ABYC Standards

• After calculating the Circular Mil Area (CM), use
  Table B to determine the proper conductor size. 
  The National Fire Protection Agency and Coast
  Guard require that the next larger conductor be
  used when the calculated CM area falls between
  two conductor sizes.
• CMK x l x L / E
• CM Circular Mil area of Conductors
• K 10.75 (Constant representing the mil-foot
  resistance of copper)
• I Current - amps
• L Length - feet
• E Voltage drop at load (in volts)

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• For Example...
• Q.  A bilge pump draws 10 amps.  The positive run
  is 11 feet from the power panel, including the
  float switch.  The negative run is only 10 feet. 
  What size wire?
• A.  Use the following formula to reach the
  correct answer CM 10.75 x 10 (amps) x 21
  (total length of run) / 0.36 (3 of 12v) 6,271
• The table below shows that 12 AWG wire has a CM
  area of 6,500 and is the correct choice. However,
  SAE wire has a CM area of only 5,833.  Under NFPA
  and USCG regulations, 10 SAE wire must be used.
• CM 10.75 x 10 (amps) x 21 (total length of run)
  / 0.96 (3 of 32v) 2,352
• Ampacity is the ultimate safe current carrying
  capacity of the wire before damage occurs to the
  insulation, without regard to voltage drop!

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Circular Mils Chart
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Wire Sizer

• Go to WireSizer.xls

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Lofrans Progress 2
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Lighthouse 1501
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Assuming 60ft round trip and 100 amps at max
load. What gauge wire is necessary for 3 voltage
drop?
Method 1 Straight run of large cable from the
Batteries to the windlass and back.
Assuming The same run and load what gauge wire is
necessary for 5 voltage drop?
A. 2/0 AWG
A. 4/0 AWG
West Marine lists 4/0 red or black _at_ 17.99 per
foot.
West Marine lists 2/0 red or black _at_ 14.99 per
foot.
Polar Wire lists 4/0 red or black _at_ 5.95 per
foot.
Polar Wire lists 4/0 red or black _at_ 4.02 per
foot.
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• 3 drop 60ft of 4/0 _at_ 5.95 per foot 357
• 5 drop 60ft of 2/0 _at_ 4.02 per foot 241

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Assuming 40ft round trip to the Fwd battery and a
60amp max current through the ACR. What gauge
wire is necessary for 3 voltage drop?
Method 2 Install a dedicated battery for the
windlass as close as feasible to the windlass and
charge the battery using a Blue sea ACR.
Assuming 20ft round trip to the Windlass and a
100 amp max load. What gauge wire is necessary
for 3 voltage drop?
ACR
A. 2 AWG
A. 1 AWG
Polar Wire lists 2AWG red or black _at_ 2.12 per
foot.
Polar Wire lists 1/0 AWG red or black _at_ 3.12 per
foot. This would be 2.5 Voltage drop. They dont
list 1awg on the site. It would be less..
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Method 2 - 3

• 40ft 1/0 awg _at_ 3.12 125
• 20ft 2 awg _at_2.20 44
• Battery 100
• ACR 95

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Washdown Pump
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Washdown pump
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Washdown Pump

• Looking at the max distance of 100ft round trip
  and using 12.4 amps at max pressure this is a 20
  voltage drop or 9.6 volts using 12AWG at the
  Pump????? What crap! Use the charts!

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Trouble Shooting

12V
-
5W
5w/12v .416A
.416A