I have a F250 towing a Big trailer and the RV folks have told me that while the factory seven prong will supply power to the RV, it would take a days to charge the RV batteries. So...

1) Does the connector not really significantly charge the batteries?
2) Is there a faster way to charge the RV batteries while driving?
3) Would instructions something like I found at How to Charge Two 12 Volt Batteries on an RV Towed by a Ford F-150 | etrailer.com work?
4) Would #3 eventually tax my alternator so badly that I kill it?
5) Would #3 fry the electronics in the trailer?

I'm trying to charge 2 6-volt marine deep charge batteries in series.

Sorry if this is an old question, but I couldn't readily find an answer.

 

They are correct, your truck's system will keep the batteries "topped off", but there is only a 10 gauge wire going all the way back to the plug, and the trailer plug cannot handle but so much current anyway.

Their suggestion would cost a lot of money and be a significant load on your truck's charging system. If you read their response, they are suggesting putting a very very large wire to the rear and putting a new larger plug back there just for the large charging wire.

You could do the above, but I would double check the size of your alternator. I would feel better about it, if instead of using the truck's alternator you had another dedicated to the trailer only. Ford had dual alternator options for this purpose, they are mainly found in ambulance's. You then would not have to run the isolator. I am not sure how hard it would be to retrofit another alternator onto the truck.

I might be too conservative, your truck's alternator may handle it. Every once in awhile you will need to plug in and let the trailer's charger charge the batteries, with the isolator and the voltage drop through the cables and plugs, the batteries will be charged well enough, but need a high maintenance charge every once in awhile to keep them in good health.

 

Would a second alt. work on a gas engine?
My alt. is rated at 157 amps, I believe.

 

That is a very large alternator and should handle it. I thought they only came with 130amp units, but I get behind on the new stuff sometimes. A 130amp unit should handle it also.

 

Thanks for all your help on this.

Can I just run this from the 25 amp upfitter switch?

Thanks again.

 

The whole deal is what charging rate you want to use to charge the batteries. This will determine the circuit size(fuse ratings) and wire size. You can try the 25 amp circuit, but if it blows the fuse once in awhile, I would put a 15 or 20 amp self-resetting circuit breaker in the circuit somewhere. Sometimes if the batteries are really dead, they can demand a lot of current, and if the rest of the circuit is capable of supplying it, it can cause your fuse to blow. A circuit breaker will trip, cool off, and then reset. It can do this several times till the batteries can build back up a little bit and the charge current tapers off to a resonable level.

 

I did this in my expedition for towing and implements at the rear. Ran 0 wire to the back and used an industrial connector mounted to the rear (positive and negative two wire plug). Controlled power to it by a switch in the cab going to a relay.

 

I'd like to add that you need a battery (-) connection equal to the battery (+) connection in order to maintain a useful charge rate. Trailer hitch ball and a 16 gauge ground through the plug won't cut it. Also, don't forget that battery isolator. Make sure it disconnects while you are cranking the vehicle.

 

Why are the batteries so depleted? Are you dry camping? If you DO have a plug-in while camping, the in-trailer converter should charge the batteries while camping. If you are dry camping, I'd install a photo cell panel or two to keep the batteries charged.