BMV-712 Midpoint Voltage Deviation 99.8% on 12V 2 series 2 parallel Ampere Time battery

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takuma-hori asked May 26, '22

BMV-712 Midpoint Voltage Deviation 99.8% on 12V 2 series 2 parallel Ampere Time battery

First of all, for about a week, the BMV-712 display did not drop from 100%.

I thought it was because "Battery starts synchronized" was enabled, so I turned it off, but no matter how many times I changed the setting in "state of charge", it kept going back to 100%.

Two days ago, I heard a beep from BMV-712 and the midpoint voltage deviation was 99.4%.

I measured the voltage difference between each battery and found only a 0.01V difference.

The voltage flowing to the shunt was also the same as the batteries.

I also checked that the shunt was on backwards and there was no problem.

What are the possible causes?

BMV Battery Monitor voltage

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Answer 1 · 2022-05-26T19:12:43Z

kevgermany answered · May 26, 2022 at 07:12 PM

SOC - your battery voltage is higher than charged voltage setting, which looks to be set too low, hence the 100%.

Mid point. This is a little confusing. You have a shot showing Starter battery and another showing midpoint. The 712 can measure one or the other, but not both. Sounds like a wiring problem. It's supplied with two thin red wires with fuses. Check the manual for details, but one goes to battery positive and as you're seeing good voltage, that appears to be correctly wired. The other should be connected to the mid point of the battery bank for mid point as per the manual. Check that's true and also check the fuse hasn't blown.

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Answer 2 · 2022-05-27T03:34:51Z

takuma-hori answered · May 27, 2022 at 03:34 AM

Thank you for your response.

I changed to the proper charging voltage for Ampere Time and it seems to go to 100 percent with no problem.

However, the BMV-712 is still giving the Midpoint Voltage Deviation warning.

I checked the fuse and it is not blown.

Is this situation a safety issue?

Thank you

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kevgermany ♦♦ commented · May 27, 2022 at 03:52 AM

Please post a wiring diagram. What mid point voltage is the 712 showing?

Please also address/reply to my other points

Probably not a safety issue

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