Solar & Alternator Power


New member
your not really going to get much of a charge, little more than a trickle all the way back there.. but just go hot back to the battery, nice and simple.. your trailer battery also needs to be able to provide braking power in a break away situation. A charge controller would really only be recommended if your doing a dedicated line and planning on using your tow vehicle as a primary charge source.
I’m not ready to run dedicated power. We’re only out for a few days at most and the power is mostly to run a pump for a shower and maybe charging gadgets occasionally. We’re in RTT’s and typically camp where there’s lots of sun. When we arrive, we’ll setup a panel, and the trailer stays parked for the most part.

there’s no brakes on the trailer yet. It’s a m101-a2, and as much as I’d like to put electric brakes on it, I don’t think there’s anything that will work with the axle. (It was hydraulic/surge style)

I figure it’d be good to have the truck put something in the battery as we drive...if it needs it, but have never wired anything like that. I thought I might need a controller that can manage the different inputs. (Solar/alternator)
I’m planning to run a group 31 lead/acid battery.


Well-known member
If you have solar your golden, that will gladly get the battery back to full.. despite any voltage drop on the standard trailer harness.. Sounds like your not running a DC fridge or anything, you'll be fine, dont over complicate it.

When you get back home after an outing, let the solar put the battery back @ 100% state of charge or use a shore charger.. just so its not sitting for long time at partial charge.


Expedition Leader
smd3, you can connect a lead from your factory charging system to your trailer battery thru either a thicker cable of the puny 7pin hot and have your solar charge controller likewise connected to the trailer battery at the same time. No need for a switch, neither system cares that the other is there, the charging systems just see a sink on the line that needs filling. If the trailer battery is low it takes power from either or both. dwh or verkstad can wax poetic about potentiality and how many ergs can dance on the head of a pin, but in the basics, you can hook both to the same battery post. And in fact with your always hot 7-pin connected your trailer-mounted solar could even backfeed your primary battery.
Just unplug the 7 pin when you are in a camp situation to put all the trailer loads on the trailer battery and isolate your vehicle / starting battery from any camping drains. No switches or solenoids needed.
It would be better to at least run a heavier gauge wire (pair) thru a rear bumper coupling parallel to the 7pin, with an isolator / solenoid such that you can put a better charge on the trailer battery when the vehicle is running and have the trailer battery isolated from the vehicle battery when the key is off, thus requiring no other action by you. And do away with using the small always hot 7pin to feed the trailer battery.
It's the requirement for manual action, connecting or disconnecting or throwing a switch that will screw you up some time in the future. Typical 'human factors' problem. Try to engineer that out of the equation. It can be done pretty inexpensively (<$100) in its most basic arrangements.


Just replace the hydraulic backing plates with electric ones, lock out the plunger action on the tongue and you've got electric brakes, no need to build a hybrid system.