E=IR. What this means is that the more current that is flowing the higher the voltage drop will be. When you first start to charge a discharged battery there will be significant current flow and the voltage drop will also be significant. However, as the battery voltage climbs the current will drop, and with it, the voltage drop will drop. So depending upon how long you drive it may or may not make much of a difference on how high your battery will get charged when using a wire that is, to one degree or another, undersized.
If you start out with 12 gauge wire, a twenty foot run, nominal voltage of 12 volts, and 20 amp current you get a voltage drop of 1.27 volts, 10.58%, and end up with 10.73 volts. That is significant.
I've never seen a battery take that much current for more than a few moments when connected to any battery charger I've ever had.
If you get the battery charged up a bit and the current drops down to one amp the voltage drop drops to 0.064 volts, 0.53%, and you end up with 11.936 volts. Hardly what one would consider significant.
The voltage drop for a 16 gauge conductor running 12 volts at one amp for twenty feet at one amp is .16 volts, 1.33%, and you end up with 11.84 volts. Again, IMHO, an insignificant voltage drop.
See:
http://www.calculator.net/voltage-drop- ... &x=64&y=14It's kinda like the wire is a voltage regulator which will allow the charging voltage to climb as the battery becomes more and more charged. Yup an undersized wire may slow things down a bit but I don't think the effect is nearly as important as some folks do. As as the battery voltage increases the charging current is gonna drop more because of the batteries state of charge and the maximum voltage of your tow vehicle's alternator/regulator than because of the voltage drop in the wires used to charge the battery.
You gotta remember that the battery in your tow vehicle doesn't normally require a lot of voltage to drive a high charging current because is isn't designed to be discharged more than small amount when starting the engine. My vehicles usually start with about one second of cranking time. If you assume yer starter draws 200 amps that works out to be 0.055 amp hours. That means at even one amp your battery will require about three minutes to replace the juice you used to start the car. Yup you have a 60, 80, 120, or whatever amp alternator but that current is never directed at the battery but to the electrical loads of your vehicle. The current the battery receives is typically a small fraction of your alternator's capacity even when the battery voltage is really low.
I kinda think one ought to have a good quality dedicated 120 volt charger for one's trailer. When you leave home your battery ought to be fully charged. Relying on your tow vehicle as your only means of charging when camping seems a bit inefficient and less than optimum to me. Better to have some method of charging your battery properly over the course of the day (not exceeding a current that is 10% of your battery's amp hour capacity). The best alternatives, IMHO, are shore power and solar power. A generator or tow vehicle will require a lot more run time than is, again IMHO, cost effective, convenient, and easy on the ears.
Just my two scents.
Cheers,
Gus
The opinions in this post are my own. My comments are directed to those that might like an alternative approach to those already espoused.There is the right way,the wrong way,the USMC way, your way, my way, and the highway.
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