Electric wiring 12 volt stuff misc.

[Craig Weis]

My friend wants to add radar to his C-P 19. Already he has a radio for communication, a radio/CD/ for dancing, st'd lights, an extra lamp, mast head lamp for anchor [led] and a DVD player. Two 12 volt wet cell batteries and no charging system. Two things about this. One is a brown out and damage to the radar and other electronic stuff. The second is battery life. Will they be sucked down in a few short hours? I think maybe but I have not surveyed his ship for consumption

How much juice are you using? And how much do you need?

Really one should take the time to do an accurate wire digram to estimate the lengths of the wires. Count both ways, in and out for load calculations.

By taking the wattage and dividing it by the voltage, the amperage in each circuit can be determined. This figure is used to select a suitable breaker for that circuit. Sizes usually are 10, 15, 20, or 30 amps. Select a breaker about 10% larger then calculated.

Wire size...all wire [12 volt to 440 volt] needs to be for 600 volts, and 16 ga AWG minimum, determine watts, length of run, and wire dia. [per each circuit development] The thinner the wire [bigger AWG number] the greater the voltage drop along the wire...

To find the voltage drop or find the resistance of the wire's cross-sectional area.
Area of a circle is Pi  x  [R squared]. Resistance is Rv = p x L x [Pi x R squared]
Where Rv = resistance in ohms. p = Specific resistance of wire. L = Length of wire. So...

V = I x R
W = V x I
W = 12 x R
For example, a wire leading to a 30 watt light 30 foot from the panel on a 12 volt system W = V x I
I = W = 60/12 = 5 amps.

Take a 10 gauge wire with a resistance of 1.02 ohms per 1000 foot [Find p from a wire table for R]

1.02 x 60/1000 = 0.0612

If there are 5 amps flowing along the wire, the voltage drop is 5 x 0.0612 = 0.3 volts. So the voltage at the light is 12 - 0.3 = 11.7 volts, which is less than 2.5 % and is acceptable. Looking on a st'd table we should use 15 gauge wire. Good luck don't set the boat afire or blow up a battery. skip.