12 V Battery Connection

[chideock]

I am asking which of the diagrams below is the correct way to connect two 12volt batteries in my motorhome? Or does it matter?

First diagram shows how the batteries in the old motorhome were connected.

Second shows how my new motorhome batteries are connected.

[fonzie]

#2 is best

[SeaDog]

X2 with #2

[boondocking]

x3 for second connection.

[Kenny kustom]

First connection will draw equally though both batteries.

Both will work. First one works better.

2016 Sabre 36QBOK
2015 Ram 3500 CUMMINS

[BandJCarm]

Well, I flunked the Smarty Pants thread...........so I probably will expose more ignorance here.......

But, other than the pictures and the batteries are turned 90 degrees from each other, what is the difference? Both are wired in parallel. The only true difference I see is that in #1 the neg goes to neg on the source, and in #2, the neg goes to a ground.

?????

[raspivey]

Honestly, you shouldn't see any difference at all. You're not really "pulling" through one battery into another as you would with a series connection. You're just tying posts together and drawing from both at the same time. One battery may be slightly less efficient, but that will be due to the resistance in the wire between the two, which will be negligible.

[Kenny kustom]

Basically the batteries are joined.
Pos is hooked to one battery, neg to the other. That way current is drawn through both.

It matters more during high current/load situations, but if you can do it correctly, why not?


2016 Sabre 36QBOK
2015 Ram 3500 CUMMINS

[Kenny kustom]

If you want to get really fancy.

This one goes as far as equal length cables.

Even on my two battery setup, I tried to be as equal length as possible.


2016 Sabre 36QBOK
2015 Ram 3500 CUMMINS

[Flybob]

Slightly OT, but more important than which method you choose is that the batteries be of same type, equal capacity and very close in age.

[raspivey]

Originally Posted by BandJCarm

Well, I flunked the Smarty Pants thread...........so I probably will expose more ignorance here.......

But, other than the pictures and the batteries are turned 90 degrees from each other, what is the difference? Both are wired in parallel. The only true difference I see is that in #1 the neg goes to neg on the source, and in #2, the neg goes to a ground.

?????

I had to look twice. The only difference is whether the wires are connected to the same battery or pos to one battery and neg to the other. Before I went to 6V, I tied my 12's together pos on one, neg on the other...mainly because that's what matched up to my cable lengths the easiest. Out of habit, I charge mine like that. I really don't think it makes much difference unless we're talking a LARGE battery bank. In that case, in would probably be best to wire them on opposite corners.

[BandJCarm]

Ah.

I had to look three times.

But again.........I flunked the Smarty Pants thread........so......................

[Kenny kustom]

Originally Posted by Flybob

Slightly OT, but more important than which method you choose is that the batteries be of same type, equal capacity and very close in age.

Correct! Down to the same lot number!


2016 Sabre 36QBOK
2015 Ram 3500 CUMMINS

[chideock]

Thanks for the answers. The two sets of batteries were/are matched pairs. Fancy is interesting but I was just interested to know if one way is better than the other. It seems from the responses that there is no better one way or the other. The batteries are in parallel and that is what matters.

Thanks all

[Kenny kustom]

Originally Posted by chideock

. Fancy is interesting but I was just interested to know if one way is better than the other. It seems from the responses that there is no better one way or the other. The batteries are in parallel and that is what matters.

Thanks all

Well, technically one way is better than the other.
Will you ever notice? Nope.



2016 Sabre 36QBOK
2015 Ram 3500 CUMMINS

[jjuscg]

ELectrically, they are identical, no difference in current or draw. Whichever is easier to wire for your rig. Batteries should be same age and amperage, as stated above.

[Wolverine 1945]

I am guessing to truly test each battery,,, I must remove both crossovers ???

[pmsherman]

Electrically, the two hookup schemes appear identical but aren't. The difference is the resistance of the wires connecting the two batteries together in your first hookup picture. When supplying current to loads, the battery furthest away from the load wires will supply less of the current than the one nearer to the load wires. The same logic applies to charging with the batteries closest to the load wires getting charged first.

The larger the wires between the batteries, the smaller this effect will be. The smaller the load or charging current on the batteries, the smaller the effect will be. If the load wires are hooked up as shown in your second picture, the cable lengths to both batteries will be equal and the batteries will always be drawn on and charged equally.

The only thing in an RV that would make the battery hookup configuration critical is an inverter. Newer RVs with a residential fridge will have one of these which will place a large enough draw on the batteries to make having the optimum hookup a more important factor for full battery life.

As an FYI, my knowledge in this area comes from research and installation of a 10KW battery bank to run an off-grid solar/wind powered observatory.

Phil

[waiter21]

I'm not sure I see any difference?????

Either connection will be acceptable...

[5picker]

Originally Posted by raspivey

Honestly, you shouldn't see any difference at all. You're not really "pulling" through one battery into another as you would with a series connection. You're just tying posts together and drawing from both at the same time. One battery may be slightly less efficient, but that will be due to the resistance in the wire between the two, which will be negligible.

Bingo!
If all wires are of similar gauge and length, in a TWO battery, parallel set-up, you will see a negligible difference between the two proposed connections. This is of course, dependent on the two batteries sitting next to each other. If one is at one end of the rig and one at the other... all bets are off on either one of the connections.