Battery Charging from camper plug?

[BMWGSer]

In the bed of my truck I have a large, round plug in that was previously used for a slide in camper. I know that the camper batteries would charge while I was going down the road, and I had heavy wire run to this plug when it was installed. My truck has dual 160 amp alternators.

I would like to install a battery or two in the bed of my truck for some trips, I will probably fab up a custom box. The batteries will be to run an Engle fridge and some 12v lights for the tent. I would like to be able to plug the batteries into the plug to charge them. What alternatives do I have? I assume I should get some type of charger, but am unsure what type to get? I believe the chargers in RV's are typically a charger/converter, and I just need a way to charge the batteries from a 12v source. I would think I could hook up the ground and positive from the batteries to the plug, but am unsure if that would be the best way to go?

I have seen battery isolators that have posts to hook an alternator output to, and posts to hook batteries to. This would keep the load from drawing down my truck batteries if the aux batteries ever died, and says it allows charging. The largest ones I could find at Camping World were rated for 125 amp alternators, so am not sure if that wold work.

Any thoughts or advice would be very much appreciated.

 

[iigs]

In order to be safe, it will be important to find out what gauge wire is backing the heavy duty plug you refer to. Once you know that number, make sure that there is a fuse or circuit breaker between the engine bay and that wire to ensure that it does not end up bearing the full cranking capacity of the batteries and catch fire. A battery isolator for at least this leg would be well advised. If the breaker is below the rating of the isolator failure should not be a concern.

So long as you connect it properly (check voltage and polarity to be sure) you should be safe connecting the batteries straight to the plug in the bed. If the batteries are too low in charge, it's possible they will attempt to draw a lot of power to recharge and the amp rating of the breaker will be exceeded when first connecting them. I don't know of a clean solution for fixing that if it should happen, but I suspect there are DC-DC chargers that can do current limiting.

Good luck!

 

[ntsqd]

Dual 160 amp alternators?
What are they currently connected to? One to the truck's starting battery, but the other?

Picture of the plug? I'm guessing that it is an RV 7 pin electrical plug since the camper likely obscured the truck's tail lights and had it's own tail lights. In those plugs there is the provision for a trailer/camper battery charge wire.

Batteries are not an electrical current black hole. They do have some internal resistance so charge current is self-limiting. Whether or not all of the components in the system are up to that max is another story. Even if the entire system can handle 160 amps charge current you don't want the battery(ies) accepting a charge at that high of a rate. Battery life would be really short.

Going on the assumption that all electrical within the camper worked as intended and desired I would suggest simply finding the match to the existing socket and wiring according to how that plug is set-up. Knowing the charge wire size on the bed side of the of the socket will allow you to use the same size or bigger wire (if it will fit into the plug) on the plug side. If nothing else has changed the new auxiliary batteries will be charged the same way that the camper batteries were.
The converter/inverter in RV's makes 110 VAC from the 12 VDC batteries when not connected to shore power, and charges the house batteries when connected to shore power. The alternator(s) will charge the battery(ies) directly. No need for any conversion/inversion electronics.