How can I charge my trailer battery, off of my vehicle battery charging system?

[Woods]

I'd like to run power wires from my vehicle battery, to my trailer, through my trailer lights wiring. I have two spare wires, through my trailer light wiring. These are 12 gauge wires and I'm sure that 12 gauge is not big enough to handle the load from the vehicle.

Any electrical engineers know how to run a charger through 12 gauge wire?


9/23 update - My Conclusion

Thanks to Red_5, for posting a great solution. This seems like a great product at a great price.

From my Conqueror build thread:

I had to build a wire harness for the truck with a 10ga power, 12ga brake control and an extra wire for a lighting relay to power the rear facing lights on the roof rack.(no factory brake control wiring or charge wiring for the trailer). I ran it through the firewall and parallel the truck's wire harness inside the pass compartment. All protected by circuit breakers @ the battery.

That was a real chore.

The 10ga is hot all the time, and I'm using a TOAD Charger installed at the rear of the truck (rather than on the trailer), taking power off the 10ga lead and protected by it's own 15A circuit breaker, from there to the 7-way trailer connector. I chose this option for two reasons A)It's automagic, sensing charging voltage on the vehicle side to turn it on B)It's deep cycle friendly, limiting charge current to 10A. On the trailer side, I installed a 2 wire harness directly to the battery.

This has been working great since I installed it. Zero issues.

http://www.lslproducts.com/ToadChargePage.html

 

[larcie]

Run extended Pos and Neg battery leads from your battery to the rear of the vehicle terminate in an Anderson plug.
Run extended leads from your trailer battery up your A-frame and terminate in an Anderson Plug.
Leave enough length for trailer movement and articulation and storage when not in use.
Anderson plugs should be readily available in electrical hardware outlets.

 

[Woods]

Anderson plugs are a great solution, but I'm trying to avoid running heavy gauge wire.

Run extended Pos and Neg battery leads from your battery to the rear of the vehicle terminate in an Anderson plug.
Run extended leads from your trailer battery up your A-frame and terminate in an Anderson Plug.
Leave enough length for trailer movement and articulation and storage when not in use.
Anderson plugs should be readily available in electrical hardware outlets.

 

[Mark Harley]

My GMC 2500HD was set up at the factory with a 7 pole trailer plug.
I wired the trailer with a eight foot 7 pole lead into a junction box on the trailer.
When I am ready to wire the trailer for a battery charger the wire is there.

 

[Woods]

That's how I'm looking to do it. Have you found a DC to DC charger yet? I've found a cool trickle charger HERE, but it's limited to 1.5 amps. I'd like to find something that will run up to 18 amps (that's what my 12 gauge wire will handle). Have been considering a solar charger. Not even sure if I need a charger. If there's a way to limit the amps to 18, then I would just do that and let the Jeep regulator handle everything else.

My GMC 2500HD was set up at the factory with a 7 pole trailer plug.
I wired the trailer with a eight foot 7 pole lead into a junction box on the trailer.
When I am ready to wire the trailer for a battery charger the wire is there.

 

[ThomD]

A quick google says that for a 12 gauge wire, 15 feet long, max amps is 10. At the very least you'll need a 10 amp fuse up front. (that's seems small and makes me think this may not be a good idea.) Something like a National Luna battery controller would be the "ideal" solution and they recommend 4 gauge. (16 square mm). My advice - Bite the bullet and run the heavy gauge. I did for my 2nd battery (it took all freakin' day), but it's done.

I just remember that I did wire up a 7 pin setup, but that was to power the brakes, not to charge a battery on the trailer. Even that wire is 10 gauge.

 

[Woods]

Yeah, I've heard what a hassle it is. I'm planning to sell my Jeep in 6 months, so I really don't want to run heavy wire. Would be curious to see where you found 12 Gauge, 10 amps, 15 feet. I figured I could run 12 gauge, 20 feet at 10 amps on the conservative side. Interesting how different data is on this topic.

12 Gauge, 20 feet, 10 amps

12 Gauge, 20 feet, 20 amps

12 Gauge, 20 feet, 24 amps

Honestly, 10 amps is more than enough to do what I need. I'm going to head down to my local electronics store and see if they can come up with something for me.

A quick google says that for a 12 gauge wire, 15 feet long, max amps is 10. At the very least you'll need a 10 amp fuse up front. (that's seems small and makes me think this may not be a good idea.) Something like a National Luna battery controller would be the "ideal" solution and they recommend 4 gauge. (16 square mm). My advice - Bite the bullet and run the heavy gauge. I did for my 2nd battery (it took all freakin' day), but it's done.

I just remember that I did wire up a 7 pin setup, but that was to power the brakes, not to charge a battery on the trailer. Even that wire is 10 gauge.

 

[ThomD]

That's funny. I found my info about the 15 feet bit in the same chart you linked too. I didn't think your jeep that was that long.

Somebody who actually knows what they are talking about will show up soon and correct me, but I thought the safety concern was "how much power will a dead trailer battery try to suck from my system?" There was a heated debate about that somewhere around, but I didn't care enough to pay attention to the "experts".

Put a small fuse on it and if it blows the fuse, you know you need heavier wire

 

[Woods]

I'm already thinking circuit breaker, as I think I'd go through a bunch of fuses.

That's funny. I found my info about the 15 feet bit in the same chart you linked too. I didn't think your jeep that was that long.

Somebody who actually knows what they are talking about will show up soon and correct me, but I thought the safety concern was "how much power will a dead trailer battery try to suck from my system?" There was a heated debate about that somewhere around, but I didn't care enough to pay attention to the "experts".

Put a small fuse on it and if it blows the fuse, you know you need heavier wire

 

[gonejeeping15]

I hope you get some good imput from this topic, I'm planning the same project for my MB-T RTT to a Jeep TJ.

Thanks

 

[McZippie]

Here you go:

http://www.expeditionportal.com/forum/threads/60703-Battery-set-up-question

 

[VanIsle_Greg]

Good info.

I had my Jeep Cherokee wired with a 7 pin setup when we bought our Tent Trailer a few years back. It has a solenoid and not an isolator for the charging circuit as this was what their installers recommended for trailer charging on the go. It has worked very well since install, and I am happy with the install job they did (nice and clean).

Anyhow... I have an M101 CDN2 1/4 ton that was switched to a flat 4 connector, and had the stock lights gutted and replaced with 12 volt lighting. I would like to install a battery in the trailer with some LED lighting and so on, and would like to be able to charge it with the Jeep on the go. I guess I will need a new 7 pin trailer side harness, an inverter/charger etc. Any suggestions where I can get a reasonable setup online? I have a 1000 Watt inverter (12 volt to 110) but nothing for the charge side of things?

Sorry to hijack, this was what I was looking for tonight! Thanks OP for asking and all for your input and the links.
Greg

 

[gonejeeping15]

I'm thinking it would be setup same as a dusl battery system with an isolator and all that stuff, only the second battery would be mounted in the trailer. So what ever guage wiring you need to carry required amps for that distance determines what type of trailer connector you need. Am I wrong in my thinking?

Doug

 

[UK4X4]

I have my trailer set up to charge from the vehicle

Just a 20amp fuse and 3mm sq cored cable roughly a 12guage wire

never had an issue with the charging- or surge in either directions

Wire is a quality high temp multistrand cable - not some cheap wally world wire- that disolves at 100oF

I ran it from the battery down into the frame to the rear of the vehicle, just fished it along hole to hole

 

[NeverEnough]

I'm thinking it would be setup same as a dusl battery system with an isolator and all that stuff, only the second battery would be mounted in the trailer. So what ever guage wiring you need to carry required amps for that distance determines what type of trailer connector you need. Am I wrong in my thinking?

Doug

No. A circuit is a circuit and all the rules apply. The fact that it's a trailer just means there's increased length to the runs, which is an issue for DC, and there's a coupler involved. An isolator is always a good idea in a auxilary battery installation. The thread referenced above has a ton of great info. Good luck!