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bertschb avatar image
bertschb asked

Need help connecting negative battery cables to BMV-712 shunt with two 12v RV batteries in parallel.

I'm installing a BMV-712 in my RV. I have two 12v batteries connected in parallel. I was going to connect both battery negative wires to the "Battery" post on the Victron shunt. But, the quick start guide shows the negative wires from each battery going to opposite sides of the shunt. The quick start guide referred to the second battery as a starter or auxiliary battery. In my case, it's neither of these. My question is do I connect both negative battery cables to the "battery" side of the shunt or one on each side of the shunt?

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2 Answers
Paul B avatar image
Paul B answered ·

Both neg wire to the battery side of the shunt is correct all other Neg wires NO matter what to the load side of the shunt.


If you need any further help please post a diagram of the setup

Thanks



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donaldn01 avatar image donaldn01 commented ·

I am considering a similar set up with two 100Ah batteries in parallel. Do I set the battery parameters as 100Ah or 200Ah because each one is 100Ah.

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JohnC avatar image JohnC ♦ donaldn01 commented ·

In parallel, add them, so 200Ah

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donaldn01 avatar image donaldn01 JohnC ♦ commented ·

Thanks JohnC, that was what I was thinking. I also noticed on the manufacturers website for my battery it says it is an 81Ah. I was told by the RV dealer it was a 100Ah battery. I wonder if it is customary to round up.


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rft avatar image rft commented ·

@Paul B I have the same question as OP but I am a little confused about both Neg wires going to to shunt as in your reply. Here is a diagram from AM solar. Batteries are wired in Parallel and shows only one Negative cable to battery side of shunt. IS the better option to run two Negative to shunt or wire as in diagram?

Thanks.

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40-liexbmv240.png (177.2 KiB)
JohnC avatar image JohnC ♦ rft commented ·

The diagram is the correct way. In the case there battery balance is being considered too. And both -ve's make it to the shunt.

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rft avatar image rft JohnC ♦ commented ·

Perfect. Thanks.

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gavcol avatar image gavcol JohnC ♦ commented ·

Hi, I have almost identical setup but I have the 2nd positive supply cable (+B2) going to the + terminal on the battery on the right.

Is this ok or should I use only 1 (+B1) when running in parallel like the above diagram ?

Also, is there a way for the BMV-712 to be able to read individual voltage/capacity of both batteries individually when setup in parallel like @RFT's AM solar diagram above ?

And is there any difference or benefit of having both neg run straight to the shunt as opposed to having the jumper between batteries and single neg cable to the shunt like the AM solar diagram ??

Thanks

Gav



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jveiga avatar image jveiga commented ·

Hi there, wondering how I do this. Below is my setup as it stands. Having a hard time figuring out where I'd place the shunt. My Group 1 is basically all over the place. Where would I place the shunt to monitor that group? (the black and red big dots are basically busses)

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lklmenterprises avatar image lklmenterprises jveiga commented ·

Shunts always go as the Very last thing before the Negative terminal of a Battery or Battery group, and from there it is in between the Battery(group) and anything which that source powers. The idea is it measures the current going through it, so anywhere else and it won't accurately measure. It also requires a Positive power source to run, and that same Positive source needs to also be on a Common bus to your Negative. It is common enough to just make sure it is connected to the Positive bus of the same Battery(group.)


The Problem you appear to have is Multiple Battery sets within your group, where you have created a common ground. However that Common ground is also used by Group 2.

What you need to do is put the Shunt in between Group 1 and Group 2 then Bus bar from there to the rest of your Common ground circuit - so in below adjusted image, the Line from Group 2 is cut to the Common Bus Bar, Shunt goes in, and Group 2 Negative goes to the Load side of the Shunt, but the Battery side.

This will mean Group 2 is Unmeasured, but still free to travel to the rest of the circuit, and Everything from Group 1 will have to travel through the Shunt to get to the rest of the circuit.


You obviously have a signficiante amount of Battery power of course, so make sure you size your Shunt accordingly.

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jveiga avatar image jveiga lklmenterprises commented ·

Thanks so much. I suspected it would be somewhere around these lines. This helps a lot though since I was not sure what to do with the negative for group 2.

That said, no clue if the 712 Monitor comes with a shunt and which it might be. But I just ordered one. From the packaging seems it comes with one. I don't know what shunt I should get but from what I gather from the fusing on the system it should be anything that handles 40A...?

If you allow me, one more question. To monitor bank 2 with the 712, do I just need to get an extra shunt and put it between that bank's negative and the rest?

Thanks so much!

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jveiga avatar image jveiga lklmenterprises commented ·

Btw, just got my package. It comes with a 500A/50mv smart shunt. I'm hoping that's good enough.
Also here is a new diagram based on my understanding of what you told me plus the diagram of Victron's how-to. Does this make sense?


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escapade-nawlins avatar image
escapade-nawlins answered ·

Not an answer just a question...Is group 27 really an 800A battery? Do you mean cranking amps and not AH correct

?

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