I was thinking of this wrong. See post number
7 and 10 from tennmogger
#7
This question has come up for use on 24v Unimogs. The answer is...maybe you can run the 12v winch motor on 24 v but seldom will the control relays handle twice the current. At 24 v the 12v motor will draw much more current and turn faster, of course. Lots of older tractor owners run their 6 volt starters on 12v and get by with it for years, but those usually don't have relays (manual switching).
Why not put a 12v battery on the trailer along with the winch. This solves two problems, it gets 12v power close to the winch and eliminates the need to run long cables (with connectors) from the truck battery.
Then trickle charge the 12v battery off the truck system through a 24 to 12v converter.
If usage is short term, the 12v battery might get the job done without connection to the truck, then charge it when you get to shore power.
A short term charge can be done by running the 24v from the truck through a headlight bulb in series, to the 12v battery. Don't leave it like that or the battery will cook eventually.
Bob
and #10
You guys are thinking constant Wattage.
For achieving the same "Wattage", the current at 24v will be half that at 12v. (Watts = volts x amps). You can't make the motor draw less wattage at higher voltage!!
That DC motor is a big honking resistance. As voltage doubles across a resistance, the current doubles.
I = E/R, and R is constant (for all practical calculations) so as E doubles to 24v, I (amps) does too.
If you want to try that winch on 24v, you can put resistors in series with the relay coils to limit the current to the coils. That will make your relay pack survive. The motor will still be a 'maybe' if you load it down.
As for doubling the load capability of the winch, it's mechanical system would not handle twice the load. (If the mechanicals could handle twice the load, the marketing geniuses would have called it a bigger winch. They already stretch the truth.)
Also consider that the Wattage dissipated in the motor, at 24v instead of 12v, will quadruple!! That sucker is going to heat up fast.
Watts = volts x amps, and both volts and amps are doubling (with resistance constant).
Now, in reality, the commutator in the motor cannot transfer all that power as well at much faster speed. The brushes will arc more and heat more, and that will limit current somewhat....for a short time.
Another option is to buy a 24v motor for your winch. You might need one anyway if you hook the 12 v winch to 24 v
Bob