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lbj0611 avatar image
lbj0611 asked

Wiring batteries series parallel with midpoint monitoring

These two Victron wiring diagrams leave me confused whether one is wrong or both are correct, specifically with regard to whether to connect the positive or negative midpoints together. I assume they are both acceptable but seek confirmation before I pick one:

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stevesea answered ·

Somewhere in the wiring unlimited book they go more in depth into it. But the gist of it is that if you're not monitoring the midpoint, nor using a balancer, you *don't* connect the midpoints. The reason to connect the midpoint is to monitor it or balance them. If you do neither, and a cell goes bad, then your whole battery bank will go bad with it quickly.

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stevesea avatar image stevesea commented ·

The other point about connecting the battery bank midpoints (which they do have a snippet of it in the battery balancer datahsheet), is that the gauge of the connector should be able to handle the amperage if one battery has a open circuit--which works out to be 1/n the size of your main battery cables, n being the number of parallel strings.

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lbj0611 avatar image lbj0611 commented ·
I do want to monitor the midpoints, the question is do I connect the positive midpoints or the negative midpoints the two diagrams I posted are different in that regard.
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stevesea avatar image stevesea lbj0611 commented ·
My bad, misread your question. That's a good question, and something I didn't notice while doing it on my end even though I did see both images as well. I went with the diagram that came with the battery balancer (joining the negative terminals). But in practice, I don't think it would make much difference since the jumpers are usually very short (and thus a very low voltage drop). I guess the "perfect" way to do it is to also have a bus bar for the midpoints... but if they didn't bother with it on the Victron instructions, I guess the numbers/reasons come out in the wash.
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