Charge line from the tow vehicle: Yes you can

[Jammer]

The charge line to my trailer has never worked right but I haven't really needed it until now so I hadn't investigated. Some poking around revealed that the mother ship didn't tighten a number of the nuts properly on the circuit breakers, junction points, and busswork under the gaucho, where the batteries, the converter, the breaker panel, and the traylah end of the umbilical all live. The charge line nut had come completely off the breaker stud and fallen on the carpet. Easily enough resolved.

The batteries were partially discharged so I put a magnetic ammeter on the charge line and started the truck. The ammeter recorded 45A of current at idle. Increasing the RPMs didn't change the current.

That's plenty to charge batteries.

I had modified the tow vehicle wiring last spring. My truck is older and the stock wiring had been carved up by a previous owner so I pulled new wires under the frame. I used 8 gauge wire for the charge line, which I connected through a circuit breaker to the auxiliary power lug on the power distribution panel Chevy installs inside the engine compartment on the left front fender. I used 8 gauge wire for the ground, which I ran to a bolt on the alternator frame.

I use a 6-way round trailer connector which I believe is an improvement over the 7-way RV type connector.

I use crimp-on connectors, which I install with a ratcheting-type crimper, which produces a much better crimp than the cheap ones. There is a soldered connection where I made a Y splice to serve a 6-way connector in the truck bed, which I put there for use with a future Avion C-10.

Other than these relatively minor modifications, the trailer and truck electrical systems are stock. No extra alternator, or fiddling with the voltage sense line, or reprogramming of the ECM.

So, yes, you can get reasonable charging performance from the tow vehicle, with minor modifications, care, and attention to detail.

I've thought about installing an ammeter in the tow vehicle's instrument panel wired to display the trailer charge current, since it's hard to know if something has gone wrong any other way.

[richinny]

jammer, is the charge line fused? if so where is it fused and what rating fuse? does that line need a different fuse for the 8 gauge run and the umbilical line?

it looks like you've got the best charge line on the forum!

[ventport]

This is what he said that answers your question. "I used 8 gauge wire for the charge line, which I connected through a circuit breaker to the auxiliary power lug on the power distribution panel Chevy installs inside the engine compartment on the left front fender."

[Jammer]

Ricky,

Building on what ventport said... there is a fuse in the power distribution panel that Chevy provides for each of the auxiliary outputs (there are two). As shipped, there is no fuse in the socket so it is up to whoever wires up the auxiliary outputs to select a fuse. I have a 70 amp fuse in there now but need to upsize it to 100 amps because it only protects the short piece of wire from the distribution panel to the place where I have my row of breakers on the firewall, and it feeds the brake controller and the running lights, as well as the charge line. If the fuse blows I would lose the trailer brakes so I want it to be large enough that the breakers will pop first.

The real overcurrent protection is provided by a self-resetting automotive type circuit breaker on the firewall. I have three of them, the other two being for the brake controller and the running light circuit, as noted above. I can't remember the ratings without looking but I believe I used a 50 amp one for the charge line.

Airstream also installs a breaker between the batteries in the traylah and the charge line. This is important since a fully charged traylah battery could otherwise turn the umbilical into a flaming, dripping mess of molten plastic in the event it got pinched under something, an all too common occurrence. I am uncertain of the rating of the breaker.

I believe there's another forum member who has wired up the charge line with its own separate alternator so I don't get the prize for the best setup in this area.

[Jammer]

Originally Posted by richinny

does that line need a different fuse for the 8 gauge run and the umbilical line

sorry for the serial post, but I missed that part...

The umbilical cable has 10 gauge wire. For home wiring in the USA it would, by code, have to be fused at 30 amps. Appropriate fusing in an automotive environment is subjective but usually higher. The 6-way round connectors are rated for 40 amps. The fact that the other conductors in the umbilical and the connector don't carry anything close to their rated loads, and are only used intermittently (except the tail/marker circuit), means that the rated capacity can be exceeded somewhat without overheating the assembly. I'd feel good about running 40 amps and recommending a 40 amp fuse. 50 amps is pushing it particularly since the ground wire is shared and could be carrying current from the tail/marker circuit.

The next step would be to run a separate umbilical for the charge line and ground. There are some higher current 2-conductor trailer connectors available that are used in commercial trucks for electric liftgates.

[ck21084]

Jammer,

You can also buy 9-wire cable. This comes with 8ga wire for the charging circuit. My trailer came with this from airstream and I just replaced it. I think that 10 ft cost me $46. If you only needed 6 wires you could just cap the other 3 and use them as backups if needed. This little project took only 4-5 hours and involved removing the couch.

I might have a few extra feet sitting around because the company sent me 40ft instead of 10ft and did not want to pay for the shipping back.

[richinny]

jammer, thanks for all the specifics. i'm sure it will be useful to a lot of people.

yes, i remember the dual alternator thread, that addresses the battery voltage averaging.

[Jammer]

Since I'm changing tow vehicles I'm going to have to do some rewiring. The new tow vehicle is a 2004 Suburban with the factory trailer wiring.

Last time I bought some automotive-grade wire and plastic loom, and fussed around for longer than I would like to admit getting 30' of wire inside 30' of loom.

This time I bought some marine wire that comes with a protective jacket, sort of like type UF house wire, only flexible. I'm going to secure that to the frame, and use it for the charge line and ground. It's 8 gauge, and I got some ring-type lugs since the local NAPA doesn't usually carry them.

[boondockdad]

That kind of current back to the trailer charger is outstanding.
I just found my next weekend project.

[ck21084]

Jammer,

Did you get a chance to complete this? I have 8ga in my umbilical and from the charging circuit to the plug. Its nice some times if i forget and leave the lights on in the van because the trailer will start the van if needed.

I put an amp probe on the positive and was getting 40amps charge from the van with weak batteries in the trailer.

Chris