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ken-field asked

BMV-712 Setup Configuration for dual 12V and 24V AGM Battery Banks

I have a Roadtrek Adventurous CS with an unusual battery bank setup. There are two banks of 6V AGM batteries, one set up for 24V and the other as 12V. They each have a separate solar charge controller and they are linked through a Cooper Bussmann battery balancer/equalizer.

Do I need two BMV-712 monitors (one for each bank)? Or can I set up one as the main monitor and the other as a second battery? As they are connected through the battery balancer, will that confuse the capacity calculation?

If I set it up as a second battery, where in the parallel series of batteries does the secondary monitor connect? (I'm guessing to the most positive battery end of the parallel series.) And is there a preference to use the 24V (which powers the AC) or 12V (which powers the all the other accessories) as the primary battery?

I'm attaching an image that was shown as an answer to another question because it shows both systems that are present (although I think that there are 6 batteries in the 12V bank).3665-bmv-batteryconnection.png

Thanks for any advice you can provide!

BMV Battery Monitor
3665-bmv-batteryconnection.png (298.5 KiB)
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ken-field avatar image ken-field commented ·

I've done a little more investigating and I've determined that there are 8 batteries in the 24 volt bank (two series of 4 x 6V) and 2 batteries in the 12 volt bank (one series of 2 x 6V).

Why they would hook it up this way is a mystery to me, but I would still like to be able to monitor both banks.

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3 Answers
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ecowhale answered ·

Two BMVs will be needed since you can't mix the voltage safely. Ideally you would have only one battery bank, 24V being superior. Are there two banks due to one running out of space? If so, ideally get rid of all batteries and get two 12V lithium batteries in series for 24V.

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ken-field answered ·

Space is not really the issue. They have the 12V batteries running all of the house and the 24V just for the AC. Given how little I expect to use the AC, this seems like a total waste and I really like the idea of ditching the 12V altogether, in the long run. I will probably wait until there is a need to replace the older AGMs and then switch over to LiFePO4 batteries.

In the meantime, it sounds like I might want to just set it up to monitor one of the two banks.

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Trina answered ·

I would rewire the 12v bank for 24v and replace anything that needs it (what really?). It won't hurt anything and you can keep the existing 12v wires and dual-monitor the both banks with your BMV!

The price of a good dc-dc buck (for any strictly 12v needs) is far less than a 2nd BMV + you have a simpler, more efficient system that also has some redundancy and flexibility for recharging!

Yeah?

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