Wiring battery on trailer to charge

I have a flat bed trailer that I haul my tractors with. Recently installed a winch and want to wire the battery into the harness so that it is kept charged by the truck. I know that many RV's have this setup. Would seem simple, just connect the battery to a constant hot wire on my seven pin plug, but I would want the battery isolated so that when the trailer is unhooked from the truck, there is no drain on the winch battery. I have searched online and have found a lot of useful information, just not anything on wiring in the battery. Anyone have a good link or have the information readily available? TIA

Those 7 pole RV Plugs n Connectors have a terminal labeled AUX that can be used to keep the trailer battery charged via the tow vehicles alternator while driving. Id use a 20 or 30 amp circuit breaker, depending upon wire sizes (Id likely run 10 gauge to the rear and use a 30 amp breaker), to protect that feed wire fuzed close to the tow vehicles battery, of course. When you disconenct the trailers plug youre disconencted from the tow vehicle (and its battery) of course which should suffice but if you want additional protection for the trailer battery you can install a disconenct right at its + terminal. You can disconenct the trailer plug from the truck when using the wench to prevent discharging the truck battery and/or plug back in n let the truck run to recharge the trailer battery, teh 30 amp breaker will provide some protection.

John T

Try This, works for me !
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my truck has 6 plug and the center pole is always hot. my trailer uses that wire to keep the small energency brake battery charged so when i put winch on the trailer i just hook the big batter to energency brake and the hot wire from truck keeps it charged.if the trailes is unhooked there is no draw down. i do unhook it when using the wench so it wont over heat the small wire from drawing to many amp. i ure the seven prong plug have a hot wire for doin the same thing

when I wired my tired old pickup to tow my tired old travel trailer, I added a relay to the charge line. It was set up so the circuit was dead unless the ignition switch was on the run position. If the key was off, it wouldn't drain the pickup battery when parked.

You need a battery isolator so the truck will charge the trailer battery, but when you hit the truck starter it will not try to pull current back from the trailer mounted battery. Then just wire it through the hot lead of the trailer plug. when the trailer is unplugged there is nothing to drain the battery.

My 01 F350 has the 7 pin plug with the aux terminal hot only when the ignition is on. It also has a fuse in the block under the hood for the circuit. You have to put a fuse in it as it does not come with it installed.

Sid

The RV folks have got'n away from battery isolators and gone to constant duty solenoids,,, I spec it was more a cost factor and that the voltage drop across a dio will not let the aux bat fully charge.

I had a RV that the coach bat would only last 2 years,,, ditched the isolator and went to a constant duty solenoid and the bat's ran a good life span.

A Battery isolator is the best way. I have a truck set-up with a battery isolator to keep the wench battery in the rear of the truck charge. I also made a connection through the trailer light connection to charge a battery on the trailer that powers the electric trailer tongue jack and also is the starter battery for the on-board generator.

Kent

Nearest RV store will have a battery isolation relay. It looks like a starter relay, but is designed for continuous operation rather than for short bursts like a starter.

It should come with a wiring diagram. If it doesn't, the small terminal goes to a source of 12 volt power that's only hot when the engine is running (or the key is on, if you can't find a source that operates from the engine itself). This ensures that the relay will disconnect the trailer battery from the tow vehicle battery when you shut the tow vehicle off.

There will be two larger terminals. One of these (either one on the units I've seen) goes to the hot side of the battery through a fuse or circuit breaker sized for the size of wire you're using. The other large terminal goes to the AUX connection on the trailer connector. # 10 or 12 wire with a 30 amp fuse/breaker is probably a good size for the interconnect wiring, as it will somewhat limit the maximum amount of current a dead trailer battery can draw.

What kind of a tow vehicle are you using? If you have a factory tow package, I would expect most newer vehicles to have a trailer battery charge circuit already in place. My '99 Ford does.

Keith

PS...if you have electric trailer brakes, you can also use the winch battery as the source for the breakaway brake switch rather than have a separate little battery.

Keith