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Battery isolator solution for dual battery setups (factory & aftermarket)

Discussion in 'GM Electrical Tech' started by dptyrob, Nov 28, 2010.

  1. dptyrob

    dptyrob Member

    I'm not an expert on anything (certainly not electrical issues), so I'm hoping that I don't make a complete idiot out of myself by sharing this with y'all. I've got a 98 Suburban with a dual battery setup from the factory. Recently I experienced the joy of having one of the batteries croak and then it sucked the life out of the other battery. By the time I figured out what had happened, the other battery was no longer capable of holding enough charge to start it on its own when it was cold. The simple solution to the immediate problem was, of course, 2 new batteries. I'm a little (ok, maybe alot) on the obsessive compulsive side though, and didn't want to experience this same problem again. That, and I also wanted to set this thing up to where if something happened to drain one battery, that I'd still have a way to start it with the other.

    In looking at battery isolators that you can buy from the auto parts store I ran into the decision of which kind of isolator you can use; the diode or the relay type. The drawback of the diode type is that it cuts down on the rate at which your alternator can charge the battery (or at least one of them). The drawbacks that they both had was the price of the isolator and the wiring necessary to install them (none of it is huge, but hey, I'm poor :) ).

    With my factory setup the hot cable runs from the PS battery back toward the firewall (I haven't traced it all of the way to see where all it goes). There's a second cable crimped into the same battery terminal that goes to the DS battery and another cable crimped into the hot terminal of that battery going to the fusebox under the hood. After thinking about it at some length I got to wondering what would be the problem with just installing a solenoid on the ground cable of one of the batteries. So I grabbed an internally insulated constant duty solenoid from the auto parts store for about $30.00 and a second ground strap/cable for another $5.00 and wired it up to the DS battery. Lo and behold it works. I have tested it to make sure that the solenoid is indeed killing that battery when it's off (to make 100% sure that it's not getting a ground through the solenoid) and it is. In addition to that, while I was testing everything out, I unhooked the ground from the PS battery to see if I could get the DS battery back on (to jump myself off) with just a short piece of wire as a jumper. I turned the ignition switch to the on position (so that the solenoid would get power if/when it came on), then I took a 4" piece of 14 ga wire and made a jumper from one side of the solenoid to the other. That was enough of a ground to power the ignition and turn on the solenoid and voila, that battery was on line and I can jump myself off. A couple of advantages that I see to having set it up this way are that 1) I don't have a bunch of extra hot contacts for stuff to short out against and 2) I'm not subjecting this solenoid to a lot of heat/current.

    I'm thinking that down the road a piece I may install a momentary switch to provide a ground to the DS battery so I can power the solenoid and jump myself off that way if needed and I may also install a disconnect to the PS battery so that if I have run it dead that I can take it off line while I'm jumping myself off.

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