Trailer battery needs to be isolated from rig?

[e9999]

OK, frantically trying to rig up the wiring for a 7 pin trailer connector before I'm (trying to) leaving for Moab. Not looking good, timewise. Anyway.
Most of the stuff is straightforward, doing it from scratch.
One thing I'm wondering about though:
- In my 100 I ran into trouble cuz some idiot at Toy connected the trailer battery pin to the instrument cluster (more elsewhere). To avoid these issues in my 80 I was planning to run a heavy fused wire directly from my battery to the trailer connector pin feeding the trailer battery (to recharge the battery). If I had the time and energy I'd put a relay in that circuit to isolate the 2 batteries when the truck is off. But this is a pain cuz I gotta get another suitable power signal. In any case that would not solve my primary concern: If the 2 batteries are directly connected, wouldn't that mean that when I start my engine, there would be a big draw on the trailer battery too, through this (by starter standards very small wire)? IOW, would I need to isolate fully the 2 batteries to avoid problems?
waddaya think?
TIA

 

[Mike S]

You would be very smart to totally isolate the trailer battery from your vehicle battery. There are many reasons for this.

1. The trailer and start batteries are likely not the same type and age - basic inbalance problem in charging

2. You have no isolation (diode or manual) to preserve charge in the start battery. If not isolated, the trailer battery will pull down your start battery.

3. There is a long run from the start battery to the trailer battery, a lot of connections, and excellent probability of a circuit failure that could disable you.

Go to a marine store and buy a portable or on-board battery charger and use that to charge the trailer battery from a 120V source.

M

 

[photogod]

Cabela's has the Gorilla charger on sale now. It is a dedicated charger for boat and RV batteries. Seems to be what you are looking for. Don't know a lot about them but give it a look.

 

[Brentbba]

On your 80 you should be able to run the power thru the 7-pin connector. That's they way mine is set up and I just finished rewiring a new 7-pin connector along with the Kaymar bumper install. Fairly easy.

 

[dieseldog]

On my trailer, I have a 24 volt Warn military winch mounted. There is a battery box and two 12volt batteries hooked in series that power that baby. When not being used for winching, I unhook the series connection and have a solar trickle charger that I use to hook to the batteries in parallel and the one 12 volt charger charges both batteries. It's pretty simple and a no-brainer.

 

[e9999]

what kind of wire gauge would I need to use to run power back to the trailer to charge the battery?

odd thing is that I don't see evidence of an isolator on the OEM 7pin wiring system on the 100

 

[baloo]

The MAN at a local RV repair place told me to use a 100 amp solenoid to activate the trailer battery charging through a 10 ga. wire. The solenoid only charges when the engine is running, the 10ga. wire works like a trickle charger. I did this a year ago we have driven our camp trailer for 10 days on this system and it works like a charm.

 

[e9999]

10ga uh? seems like what I saw on the 100 and trailer wirings, so probably OK.
May try it and start with a small fuse and see if it pops...
and this solenoid is activated by what signal?
interestingly, I had to rig a relay system on the 100 to avoid having the trailer battery mess up the dashboard electronics when the ignition is turned off...

 

[baloo]

I just used a signal from an accessory that only operates with the engine running. I'll check my notes and post the answer.

 

[e9999]

anything more on any of this, anybody?
may need to rig something up soon...

 

[hammerhead]

I have run with a 10 Ga. wire fused at both ends for years without a bit of trouble. I unplug the trailer when I'm not on the road and the 2 systems are not affected by each other. When towing both batteries charge perfectly. If the trailer battery gets low while camping I can either back up to it and plug it in to charge it or I can use a generator. I've even used jumper cables on it when that was easier than trying to back in to hook it up.

 

[e9999]

I have run with a 10 Ga. wire fused at both ends for years without a bit of trouble. I unplug the trailer when I'm not on the road and the 2 systems are not affected by each other. When towing both batteries charge perfectly. If the trailer battery gets low while camping I can either back up to it and plug it in to charge it or I can use a generator. I've even used jumper cables on it when that was easier than trying to back in to hook it up.

dang, this 10ga wire thing is intriguing...
what size fuses are you using?
and no isolator on yours either then?

 

[e9999]

well, spent the evening pulling wires and all. I think I'm ganna try the 10 gauge trickler bit... We'll see how it goes...
I'm rigging a system to add a 7pin plug system with brake controller to a 4 pin system so I can switch from one to the other easily.

 

[Brentbba]

E - why don't you just purchase the adapter to plug into your 7 pin so you can use a 4 pin when you need to???

 

[e9999]

E - why don't you just purchase the adapter to plug into your 7 pin so you can use a 4 pin when you need to???

cleaner, less work, more out of the way, and cheaper this way; but thanks

 

[Mike S]

Not sure how you are setting up your trailer leads, but on a cruiser, the brake, directional signals, and rear running lights are separate, and you need a combiner to run them with a standard 4 plug set-up, so it might not be cheaper.

 

[e9999]

Wiring all done, nicely tucked under, fused up and all.
Now to try it! Yikes!

(there was a already a 4 pin plug on, so I imagine there is some sort of converter in there someplace)

 

[e9999]

OK, tried it out.
Seems to work just fine.
Used a 10 ga wire from main battery to trailer, with a 30A fuse for now.
When I turned the engine on, the main battery went right away to 14+ V whereas the trailer battery went slowly up from the 12.7V is showed when disconnected up to about 14V. Took a while (5 - 10 mins) even though I had partially (?) charged the trailer battery first to avoid causing a huge draw through the circuit.
Seems like it is a "trickle" kinda charging. Not sure why given that the 10 ga is a pretty hefty wire, I would assume it has a very low resistance.
And the 30A fuse held fine, so might be overkill, will try with smaller one. Although charging a completely dead trailer battery might draw more than that? Will do trial and error.
(Need to try and figure out how the ammeter function works on my multimeter.)

So for now, seems to be OK!