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maccos avatar image

Connecting Charge Controller to batteries question

I have 2 batteries in parallel. I have a victron battery monitor to measure the charge/discharge rate, Voltage, etc. I just added a victron solar charger to the system and wired it up as shown below.

With this setup, when monitoring the battery monitor, it is showing negative current going into the battery when the solar is connected (no loads on the battery). I assume this is because I dont have the negative lead from the solar controller going thru the shunt (its bypassing it). So I assume I need to wire it as shown below.

My 2nd question is, does it matter if I leave the positive wire on the battery to the left as shown in the above image, or do I need to move it to the battery on the right. I'd prefer to leave it as shown above since I am out of room on the battery terminal on the right battery. My thought is that all the red cables are essentially the same point of contact so it doesnt make a difference, but I wanted to check.


Thanks in advance.

charging batterySolar Panelmonitoring
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solar-changed.png (40.6 KiB)
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4 Answers
Paul B avatar image

we are advising the best case, its not something that has to be done NOW.

you really only have to extend the black one to be the same length as the red.


and as mark has suggested put a terminal block or joiner in and just buy a short cable to extend the neg cable to the same length as the red

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maccos avatar image

Thanks for drawing it up! I will have to order some new cables and reconfigure it.


So to confirm, the 2 cables that I've hi-lighted below are the ones that need to be the same length/gauge? Right now both are 0 Ga. The red cable is 28" long and the black is 10". Will that make that significant of a difference that requires ordering a new 28" black cable? Other option is to spin the left battery 180 degrees and re-order a red cable that is about 20" and a black cable that is 20". These cables aren't cheap!


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Paul B avatar image

Hi I have attached the modified drawing of yours with the suggested changes (easier to understand than words sometimes)


Mark is correct in what he says and there is no harm in any of his suggestions AT ALL and I would recommend you do these


Keeping the battery interconnecting cables as short as possible and as large AS POSSIBLE IS THE key, AND clean TERMINALS, Volt drop is the issue if the cables are to long or to small




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Mark avatar image

It will 'work' if you leave it (per your 2nd proposal) BUT you should NOT leave it that way because cable resistance between the two batteries will be uneven - causing an imbalance during charge & discharge.

As a result the battery with the 'direct' pos & neg connections will be doing all the work. Accordingly it will age & die much sooner than the other - So no a good thing..

To ensure that everything is equal you make only ONE 'main' connection per battery (all pos on one batt & all neg on the other batt).

Also the pos & neg 'link' cables need to be identical in length & gauge (so that the resistance & accordingly losses are the same)

If your having trouble with physically making all the connections at the battery terminals then the other option is to use a set of bus bars & make all connections on them.

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