Location: Choosing Cords and Wire Sizes

Wire Resistance Affects Chargers Hook Ups at RV Parks

Wire, being not quite a perfect conductor, loses some of the energy we are trying to pass over it. Wire, being not quite a perfect conductor, loses some of the energy we are trying to pass over it. When connected to a battery charger, from the power grid, the wire loss should both be accounted for, and mitigated. Failure to properly size the wires to and from your battery charger can result in heat, melted, wire casings, and even fires. Improperly sized wires cost you money every time you use them as you throw power into the trash can. Properly sized wires actually transfer the power to where you need it, when you need it, without losing much. For these reasons, we think you should take care to select the proper wires. Here is the why and how.

Simply put, the loss in a conductor has a correlation to the length of the conductor, the size of the conductor, and the amount of current (amps) being pushed through the conductor or wire. The longer the wire, the more voltage is lost in the distance. The less metal in a conductor (size of the wire), the higher the power loss as there isn't adequate metal. And finally, if you try to push too much power through a cord, you lose it to heat anyway.

What is the point of paying for 1000kw of power at the campsite, to see only 640kw go into your camper?
Fairly counterproductive wouldn't you say?
Here is how it could happen...
Bad Wire Install
150' cord aluminum 22 AWG extension cord to charger.
40 amp DC charger at 12 volts pulling rougly 500 AC watts at 120VAC or 4.5 amps
Based on calculations here, you net only 63% of the power

Worse yet, the voltage at the end of the extension cord would only be 76.34 volts, which could damage your charger. The answer is properly sized wires, that aren't too long, too skinny, or trying to pass too much power. To show you how, let's fix the improper install above first, and size the wires accordingly..

Good Wire Install with Aluminum
150' cord aluminum 12 AWG extension cord to charger.
40 amp DC charger at 12 volts pulling rougly 500 AC watts at 120VAC or 4.5 amps
Based on calculations here, you net only 97% of the power


Good Wire Install with Copper
150' cord copper 14 AWG extension cord to charger.
40 amp DC charger at 12 volts pulling rougly 500 AC watts at 120VAC or 4.5 amps
Based on calculations here, you net only 96% of the power


Conclusions:
Generally you want to calculate your loss at under 5%, by doing so you avoid heat, fire, etc.. In addition, this is in spec with NEC (North American Electrical Code), DOT (Department of Transportation), OSHA, etc..

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