common ground

[ALX357]

Batteries... that is. Is there any reason to not use a common ground for all the batteries; motor, cabin lights, other DC stuff, if the positive poles of the batteries are kept separate and isolated. ?

[Chip Hindes]

Unless you've got a pretty sophisticated switching apparatus, if you want to be able to charge all your batteries from a single alternator you have to use a common ground.

[Andy26M]

I can't quite figure out how you'd be able to make it work with multiple separate grounds...

- AndyS

[ALX357]

uh, ok, duh me ... was adding batteries and that is what i figured on doing, but thanks for the confirmation, seems pretty obvious, but i am adding that multiple stuff only just now, and previously had a real simple set-up with independant batteries, with no switches, combiners etc. Had to charge the house battery by moving the wire from one battery to the other, or manually connecting an AC charger to one and then then the other.

[Chip Hindes]

You could do the wire switching thing with two separate grounds as well, you'd just have to switch both wires.

Most manuals caution against disconnecting or switching off the battery with the motor running, as an alternator with no battery connected can fry itself. Usually they're talking about high output marine alternators on full size motors. Don't know if it's as much a problem with a small outboard alternator, but I wouldn't want to try it to find out.

[James V]

Yes, you only need to keep the positive seperate. There are switches where you can switch from one to the orther or use both or charge both at the same time. However, the lower battery will drag the other down quickly.
I suggest that you get a battery switch instead of moving the battery cables. If you twist the post to hard you can breaK the wires in the battery and will have to buy another one. Use a good compound on the terminals to keep them from going bad.