On Sun, 14 Apr 2013 08:37:44 -0500, Ignoramus25056
wrote:

On 2013-04-14, J.B.Slocomb wrote:
On Sat, 13 Apr 2013 23:03:57 -0500, Ignoramus17560
wrote:

I need to install a 12v winch and a battery next to it, on a trailer.
This winch may need a huge amount of current.

I hope that this auxiliary battery will provide the power needed to
run the winch, however, I want it to be charged from the vehicle's
auxiliary 12v supply.

What concerns me is that when the winch is working, the battery may
demand a lot of current from the vehicle, and blow a fuse. At the same
time, after use, it may also require a lot of current with the same
result.

Ideally, I would like a current limiting device, of some kind, between
the vehicle and the wnich battery, that would limit current to some
low value, like 15 amps, happily supplying any amps under 15, but
automatically limiting the current to 15 amps only.

Is there anything of the sort, that I can purchase off-the-shelf?

I do realize that I can just wire a resistor in series, and I do have
a 1.4 ohm, 290 watt resistor and some others, but I was hoping for
something more elegant.

Thanks

i

I don't know about your vehicle winch but boats with an electric
anchor winch don't seem to have a problem. Example:
100 lb capacity @62'/min = 25A
400 Lb @ 62'/min = 35A
900 lb @ 80'/min = 70A

Most boats, if they use a winch battery, just have it connected in
parallel to the main house bank and don't run the winch unless the
main engine or the generator is running.

As for restricting battery charging to 15 amps, I would think that
your alternator would likely be capable of producing 60 - 70 amps, and
maybe more, why would you restrict charging to such a low level?

For a semi truck use, and 400A demanded by the winch, it means that I
will need a 40 foot two conductor welding cable, at least 1/0. And the
number one concern is that it will be eventually stolen. I would
rather slowly recharge.

i

Ah well, if you are using a winch that requires 400 amps than you will
have a significantly big battery bank to support it. But still that is
no larger than many cruising yachts use for a "house bank". A "battery
combiner" isn't going to work as it simply isolates the batterys in
discharge mode and not in charge.

The problem is that an alternator putting out say 14 volts, is going
to pump a lot of amps into a mostly discharged 400+ amp battery bank.
I suspect that the easy way is a large resister in the charge line to
the winch batteries. Another alternative might be to build a pulse
width controller but that seems like a lot of work for little benefit.

My limited experience with truck winches is oil field trucks - 50 ton
truck, flat bed, load by winching load up over a tail roller - and
these all had mechanical winches driven off a power take-off, but I
would think that an electric winch drawing 400 amps would be a pretty
large device. A quick look at the catalog shows a 1260 lb. capacity
winch drawing 85 amps so a 400 amp winch may well be a 4 ton winch.

--
Cheers,

John B.