Originally Posted by MedSailor
Could that be safely done for as long as it takes to power a windlass. Any idea how that would be wired?
way to achieve this is to use two '1-off-2' battery changeover switches (not
the normal 'off-1-2' ones) - the traditional system actually used two knife switches
- but you do need to know what you're doing to operate it.
Basically, you connect two batteries in series (24VDC) - one positive terminal to one negative - and wire the "1" position of each switch to the batteries negatives and the "2" position to the positives. Putting both switches in the "1" position or the "2" position gives you 12VDC from either Batt#1 or Batt#2 respectively and "1"&"2" either gives you 24VDC or nothing.
Supposedly one upside to this is that if your batteries are dead flat, switching the system to 24V might allow you to start the engine (or fry your starter if you judged it wrong), so.. is it safe?? Hmmm..
Anyway, if I was in your position, I'd be installing a completely separate
12VDC "winch battery" with the negative connected to the bus side of your Main Switch and the positive going directly to the winch breaker. For better usage, you could call it your "reserve battery" and wire the bilge pump, etc. off it without needing a whole extra breaker panel.
EDIT: Was typing this when CChaos responded above. I think we're saying the same thing, just this system is manual, his is automatic.. not sure... but my recommendation still holds.