wiring switch to swap batteries for accesories

[shorty_f0rty]

Is there any major considerations i need to take if I want to add a switch to swap the main accessory circuit between crank and aux batteries?

The idea is so that when camped for a few days, flip the switch to aux to run radio, dash lighter socket, etc and maybe other accessories. I have a voltage monitor that i can use to keep an eye on things and with the switch I can monitor two batteries.

AFAIK there is a very slim likley hood of any damaging loads on that circuit that would stop me using a 20A switch and heavy duty auto cable from dse (#2027).

The dual battery setup to aux is not via the alternator but off the cranking battery so no major loads should be generated when starting and is isolated when starting

I guess the hardest thing would be figuring out how to isolate the power for the acc so i can setup the switch.. I have had all my electrics cut out in the middle of the night in the vic high country and she kept on goin (fubard +pos wiring) so i figured it this couldnt be too hard.

[Woop]

This is relatively easy to do. Its probably easier to have the entire electrical system change over to the aux battery (except the starter motor, but you could do this as well if you wanted to). You'll need to find the cable that feeds +12V from the main battery to all the various circuits in the fuse-box-this would probably be somewhere around the starter motor. You need to bring this to a suitably rated 2 position switch.
There are already heavy duty 3 position battery change-over switches around that will work well. Most of these switches have 3 battery sized contacts as well as 3 lower power contacts as well for accessory change-over.

Nick

[shorty_f0rty]

You dont mean those full on marine battery switches that take up half the dash?

I think I have a on/off/on Narva switch (Amperage rating 20A at 12V) which I plan to use and figured it would be able to handle the load.

[murcod]

What about using a relay that's wired to the ignition?

When the ignition's on the aux circuit is running off the main battery; turn the ignition off, the relay is de energised, and the second battery is switched in. No need for any switches on the dash then and you'll never forget to switch it over.

[Woop]

A switch with that rating should work fine, but it might be a bit difficult trying to isolate just the accessories feed. But i suppose if you located the cable from the ACC output of the IGN switch that goes to the fusebox, this would work ok if wired via a 2 way switch. Make sure second battery is earthed properly. A relay would work ok as well--you would just need to work out which battery to feed it coil from--it needs a small amount of current to keep it energized...

Nick

[chimpboy]

Have you considered running the starter (and coil?) off the new battery, and leaving all the other wiring in place? Then you use any of the typical isolating methods and you can run everything in the car except the starter until you hook them back together again.

This might be a lot simpler.

Jason