Just a little warning about DIY using solenoids as suggested.
Having been making the Trollbridge24 for nearly 5 years now I warn against casual parallel/series switching wihout mechanical or electronic safety
interlocks. If you look at the schematic it only takes one relay to fail to operate, or stick shut and you have a dead short across the battery(ies). If you go this route
, please put a safety
fuse in each positive battery lead rated above the stall current
of the winch
and less than the worst case value of the CCA of the battery.
The Trollbridge24 not only has the safety interlocks but it detects when a load current
is drawn while the batteries are in parallel and switches automatically to 24 volts. This saves going to the winch
to switch to 24 volts or having to add cables
for a remote
control, the normal (remote if you have it) on/off will switch it to 24 volts.
Keep in mind that it was designed for trolling motors, not winches or bow thrusters and it can only handle motors up to 2 horsepower.