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kiackerdog avatar image
kiackerdog asked

Batteries in parallel with dual charger - where to put BMW-702 shunt?

My camper has two 100AH 12v batteries wired in parallel and charged with a ProSport 12 amp dual battery smart charger. The charger charges each battery separately instead of as a bank. It is wired like in the diagram below. Positive wire to fuse box/load comes off the (+) post of Bat 1 and negative to ground bus bar comes off the (-) post of Bat 2. I'm wanting to add a Victron BMW-702 battery monitor, but am unsure where to mount the shunt to the batteries. I understand from the directions (and other community posts) that both negatives from the batteries should be mounted to the battery side of the shunt instead of using the black jumper as in the diagram and the load side wired to the ground bus. But where do I put the negatives from the battery charger (cable 1 & 2) since there is one for each battery - do they each stay on the negative battery post as they are currently or will one (or both) cable negatives need to be moved to the load side of the shunt?

Thanks in advance!!

BMV Battery Monitor
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @kiackerdog

Your charger negs must both go to the LOAD side of the shunt. Same point as your load negs. Or a neg bus, whatever's convenient.

Your batt negs must remain connected to each other of course, and both those batt negs should be the only thing with continuity to the shunt's BATT side.

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caryboe avatar image caryboe commented ·
Hi JohnC,

I've got a very similar issue, however my batteries are wired in series. Same charger, similar batteries, same shunt. This makes things a bit tricky. I can't get an answer anywhere, and I've tried many different forums. Any advice would be greatly appreciated!

Thanks, Carrie

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JohnC avatar image JohnC ♦ caryboe commented ·

@caryboe

In a series string there's only one true negative, and that's the one to use. The intermediate neg(s) (joined to another pos) isn't at 'zero' volts, so is irrelevant. Is that what you mean?

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caryboe avatar image caryboe JohnC ♦ commented ·
Hi John,

Thanks for the reply. Agreed that in a series there's only one true negative, but the charger mfg. says to attach each set of leads to each 12v battery regardless of being wired in series or parallel. So how do I then accomplish this AND feed them through the shunt simultaneously as in the diagram at http://www.100cpsolutions.com ? That's my puzzle and no one can seem to help. If this was wired in parallel or if I had a 24v charger, this would be a non-issue.

Thanks again,

Carrie

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kiackerdog avatar image
kiackerdog answered ·

Thank you so much @JohnC ! I would have messed up by not keeping the battery negatives connected to each other. Thanks again!

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