A friend just installed 400 A/hr of Lithium battery into his trailer. It's actually 2 of the Victron 200 A/hr Lithium Superpack batteries. He pulls this with a new 2500 Chevy truck. I am concerned about the high charge current the batteries will accept damaging the truck's alternator or other inline components.

I have helped equip sailboats which make the transpacific cruise to Hawaii. Alternator output on those boats is controlled by programmable alternator regulators. I can't do that on this guys truck. I do know Victron Energy makes their Orion DC-DC battery charger which is also current limited. Is that the only option?

I'm thinking 30 Amps might be a reasonable limit for a 3/4 ton truck. then again, 20 amps may be more realistic, even less depending on circumstances. I've grown accustomed to expecting from 80 to 175 amps continuous from alternators. That 7-pin socket for the trailer plug shouldn't be able to carry much load. The ground pin on that socket also needs to carry about 10 amps or so for the trailer brakes alone. I would not like him to melt that socket and then lose his trailer brakes or some combination of problems.

Maybe just install the Orion DC-DC converter and live with the limitations?

The output through the trailer plug is already regulated.  I doubt if you get 10 amps.  They aren't going to let you melt the wire.

ETA: It's fused at 30 amps, so you're not going to damage anything but the fuse, in any case.

That’s my take, it will not be an issue.  My trucks have a decent size(10 ga) wire feeding that circuit, and I bet ske is right, the output is already regulated to give more of a trickle charge.

Etrailer site probably has a in depth answer, they are a good resource for all things towing.

It's a low-brow solution, but just hook it up and measure the unregulated current.  There may be so much voltage drop initially that it may self-regulate.  If not, you could wire a resistor inline to limit current.  


The better solution would probably be something like this:

Usually trailer power is fused at 30a but not otherwise regulated. I have a sealed lead acid battery in a trailer that has its own separate charge controller to limit current draw for this reason.

put an inverter in the truck and run ac to the trailer and a good charger, use a switch or ford relay to power the inverter while running.