AnswerID: 484529 Submitted: Sunday, Apr 29, 2012 at 12:13
This is a typical example of how limited the knoweledge of 12 volts electrics generally is and the preconcieved ideas people have.
It is indeed possible to charge a battery in a trailer thru the standard 7 pin flat or round plugs....in fact it is an application mentioned in the standards.....but there are limitations.
The pin for reversing lights is hardly ever used, so that is commonly used for battery charging.
the limitation is that the charging will be slow, but if properly done possibly not as slow as some would expect.
The rated current of the pins in the trailer plugs is arround 15 amps, it is certainly possible to connect cable capable of carrying 15 amps to a trailer plug.
By designing for specific voltage drop and not minimum voltage drop it is possible to select a wire that will self limit the charging current not unlike charging a battery thru a fixed resistor...of course appropriate fuses both ends.
So it is reasonable to have a nominal charging current of around 10+ amps delivered to the trailer battery thru the standard trailer plug.
If the battery in the trailer was only running some lights and the radio, this would be more than adequate particularly if the vehicle was driving 4 to 6 hours a day.
No dual battery controller required, very cheap and viable.
If you want to stop the car battery being drained at night pull the plug......but most of us would do that when we set up for the night anyway.
And if the trailer does not house a DC powred fridge or other heavy drain items, perfectly fine and reasonable...such as a traveler that uses ice like almost all of us once did, or someone who runs a fridge on LPG like untill quite recently was the norm.
OR for those who keep the fridge in the main vehicle and are simply towing a camper or small caravan a most eligant solution
Seriuolsy charging thru the standard trailer electrical connection should not be dismissed as rough or inadequate.
If however you have heavier drain items in that trailer or you require heavier chaging capacity, an heavier connection and wiring is necessary.
Reply 8 of 12
FollowupID: 759817 Submitted:
Sunday, Apr 29, 2012 at 12:18
The Bantam posted:
BTW...you should have both ends of the connecting cables fused near the batteries.
The battery in the trailer makes the connection on the drawbar live and a posible source of a short.
SO the cable from the trailer battery to the drawbar should have a fuese or a breaker in it as well asn the supply from the tow vehicle battery.
FollowUp 1 of 1