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Twin Battery Wiring

Old 05-14-2008, 09:29 AM
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jxg
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Default Twin Battery Wiring

I did a search, didn't see anything similar to this.

Lets start out by saying i am an idiot for not labeling the wires.

I have a small CC with twin batteries and a Guest (i think) Battery Switch. My question is in regards to the way it was wired. I know that there were 2 POS leads, one from each battery to the switch. No problem there. There are 2 NEG wires that come up from the console floor, going back toward the engine (yam F115). well they are both long enough to attach to the farthest away battery (and it looks like that is how they were, but I can't be sure), and then there is another NEG lead that I know was connecting the 2 NEG terminals of the batteries. My question is, should the 2 long leads go to the one battery, or should one go to one, and the other to the other? Does it make a difference, since they are both connected by that one small NEG cable (NEG of one battery to NEG of the other).

next winter i WILL label these when i take them off....

TIA
Old 05-14-2008, 09:40 AM
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Default RE: Twin Battery Wiring

I would go and get a neg bus and connect all the neg on that. Get some neg battery cable and connect both batteries to that neg bus. As long as all the neg are connected, it should be good.
Old 05-14-2008, 11:01 AM
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jxg
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Default Re: Twin Battery Wiring

thanks for the input. i just went back out there, and I am not as big an idiot as i thought (but close). I wrote on the cables themselves, a 1 or 2, and marked the batteries 1 and 2. Not sure why the original owner has the 2 batteries connected though with the neg cable. i found the wiring diagram on the Guest website, and it doesn't show that.
Old 05-14-2008, 12:53 PM
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Default Re: Twin Battery Wiring

In a lot of cases the grounds are connected between batteries. Mine are connected to a negative bus bar, all grounds terminate at one place.
Old 05-14-2008, 04:51 PM
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Default Re: Twin Battery Wiring

The negative battery terminals are connected so there is a ground to either battery with the switch in 1 or 2.
Old 05-14-2008, 06:27 PM
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Default Re: Twin Battery Wiring

There is nothing wrong with connecting the two batteries together with a thick ground cable. That saves you running heavy gauge cable all over the place and lets you reduce the total # of connections you have floating around.
Old 05-14-2008, 07:10 PM
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jxg
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Default Re: Twin Battery Wiring

Curmudgeon - 5/14/2008 7:51 PM

The negative battery terminals are connected so there is a ground to either battery with the switch in 1 or 2.
but i guess the question is if there is already a ground from each battery to the bus bar, then why are the 2 batterys connected together with a ground?
Old 05-14-2008, 08:33 PM
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Default Re: Twin Battery Wiring

jxg - 5/14/2008 10:10 PM
but i guess the question is if there is already a ground from each battery to the bus bar, then why are the 2 batterys connected together with a ground?
The connection to the bus bar is the redundant one.

Think of it this way - if one battery is DEAD and the other is at 100%, and you flip the battery switch to "ALL" - what is the path that 100 amps of current is going to go through?

It's going to go through the switch and whatever ground is bonding the two batteries together. I would not want that to be two small 16 ga bus bar hookup. Ditto with starting the engine.

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