Electric Winch Question

It's mounted on a flatbed car trailer. Have a 12v battery mounted on the trailer to run the winch.

The other day I was pulling a pretty big load with it and ran the battery down. Got a fresh battery, and also a neighbor loaned me a long set of jumper cables so I could hook them between the pickup battery and the winch battery.

Started pulling with the jumper cables hooked up(double-checked that positive went to positive and negative went to negative) and there was a shower of sparks and the winch cable(the one that pulls the car on the trailer) burnt in two. When I stepped on the trailer there were a bunch of sparks between the trailer hitch and the ball on the pickup when the trailer wiggled. Unhooked the jumper cables from the pickup to the winch battery and everything worked normal again(minus the broken winch cable which I tied together and finished the job with).

What's the deal here? Does the winch need a good ground strap to the trailer frame? Does the trailer need a good ground to the pickup frame? Both? Something messed up in the winch itself? Don't think it's the winch since it worked fine with just the one 12v battery. Why would hooking an additional battery in parallel with the winch battery cause this?

Anyway, any ideas would be great- don't wanna melt the new winch cable next time I use it!

The return path through the trailer frame, hitch, & pickup frame would have a lot less resistance than the path through the negative jumper cable, particularly if the jumper clamps weren't making super good contact. Therefore, most of the return current (several hundred amperes if you have a reasonable size winch under heavy load) flowed back through the winch cable to the trailer frame through the hitch ball to the pickup frame to the negative vehicle battery cable. Even if the winch wasn't running, its a good bet that most of the current flowing into the discharged trailer battery was also going back through this path.

Bet the winch cable burned in two where it rubbed on the trailer frame, or on the fairlead where it came out of the winch itself.

A couple solutions...1) get a bigger winch battery so you don't run it down as quickly & therefore don't have to jump it, 2)as others have said, disconnect the trailer from the tow vehicle, or 3) disconnect the tow vehicle battery negative lead from the tow vehicle before using it to jump the trailer battery (don't do this with the engine running!).

Be aware that if you disconnect the hitch, you also need to disconnect the connector for the lights & brakes, otherwise all the winch current will try to return via the ground wire in the trailer connect & you'll melt the whole thing.

Good luck,

Keith

Have your truck alternator tested
so you don't have any suprises later on.

I pulled a similar stunt once with
a PeterBuilt COE and a reefer trailor.
Was trying to jump start the reefer.
Should have unhooked the trailer first.

Pooh Bear

Unhooking the trailer would be the best bet, but it's a 16ft car trailer and if I unhooked it while loading the tounge would go 8 feet in the air, so unhooking is out.

The guy I borrowed the long jumper cables from said the reason he had them was to run a winch on his own trailer, but he just hooked the cables directly to the winch and didn't have a second battery on the trailer. Would that be the way to go on this deal? It'd save having an extra battery on the trailer..... .but I'd worry about voltage drop on such a long run of cable, even though they are nice big cables.

You could have also unhooked the battery cables
from the battery in your truck.
This unhooks the truck ground from the circuit.
But then you don't get the alternator output.

If I had to run cables from a remote battery
I would want VERY thick cables.
Losses are huge at 12 volts.

You can get alternators that charge
2 batteries at the same time.
Charge your truck battery and the trailer battery.

Pooh Bear

I'm kinda thinking just having a good battery on the trailer for the winch with good cables, and maybe a spare to replace it with, would work best to avoid the current drop of the long cables.