roman & Gareth
I guess that's true. From what I can make out a 12v electric winch draws around 100 to 200 amps under load, but what does a hydraulic one draw? It could be a lot less if you accept a slower winching speed.
My batteries are each 80 AmpHours, which must be typical, so if you are pulling 100 amps you have probably got half an hour of active winching before you are getting into "can't restart" territory. I suppose it depends on what you intend to use the winch for.
[snip]
Thanks for all the replies. I'm sure there is a way that this can be done. Christopher Bell seems to be thinking along
the same lines as me. Somehow I need to "mimic" the starter by substituting the pump motor. I have a 12 / 24 switch
unit made by monark diesel -
www.monarkdiesel.co.uk possibly this may do the job. Incidentally suitably located diodes
would protect the 12v system from frying in the event of a short ?? Regards Gareth Jones.
Gareth, I don't know the switchover unit - but if it is designed to handle starter current it should be up to the job.
Diodes would theoretically suffice, but they would have to be seriously heavy duty. I've just had a look in the RS catalogue and the biggest rectifier I can find is 130A, and costs about ?70 (I couldn't find any individual diodes). Also bear in mind that:
(a) A silicon diode has a minimum forwards voltage drop of about 0.2v. At 100 Amps that means 20 watts or more of heat to dissipate, as well as the voltage loss.
(b) Diodes can fail.
(c) If they do fail .....
I'd use a switch!
Christopher Bell