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pekkaj asked

Strange voltage curve on battery

pow2.jpgpow1.jpg


First graph is from MPPT and second from monitor. MPPT curve looks normal till float state after battery gets full, but then some weird rise in voltage. Battery load was off the whole time, so only mppt working. Second curve is even weirder, should it be the same as with MPPT? I just installed BMV-712 so maybe it's still calibrating? But what could explain battery voltage rise after float state?

battery chargingbattery system voltage
pow2.jpg (269.9 KiB)
pow1.jpg (307.3 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·
any chance of getting screenshots with the same time range?

is this the first charge for the battery?


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klim8skeptic avatar image klim8skeptic ♦ klim8skeptic ♦ commented ·
Also add the current to screen shots.
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pekkaj avatar image pekkaj klim8skeptic ♦ commented ·

Sorry that's all I have, but time period is the same. I have been using the system without monitor for a week. Before that the battery (200ah lifepo4) was unused for six months and I was a bit worried that it might no like it. I haven't tested full 200ah capacity yet.

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4 Answers
pekkaj avatar image
pekkaj answered ·

Today curves match and no strange behaviour, so maybe this was some calibration thing.

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pekkaj avatar image
pekkaj answered ·

Related to this BMV-712 display says battery charge is ~25% but Android app says charge level is 62%. Maybe another "bug" related to initial calibration.

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kevgermany avatar image kevgermany ♦♦ commented ·
The BMV charge level is only meaningful after the first automatic synchronisation to 100%.

And this assumes that your battery and synchronization parameters are correct.


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pekkaj answered ·

screenshot-20230430-095439.jpg


So I think both the display and app show now same but wrong levels?


screenshot-20230430-095439.jpg (319.2 KiB)
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

That picture doesn't really help figuring out your issue...

But it shows another thing:
It seems did configured the BMV incorrect or not at all.
That jump from ~50% straight up to 100% shows that.

Make a screenshot of your settings. What kind of battery do you have exactly?

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pekkaj avatar image pekkaj Matthias Lange - DE ♦ commented ·

Just found a video explaining params. So I raised charged voltage from 13.2 to 14.4 (mppt is set to 14.5) and discharge floor from 50 to 5%. Battery is lifepo4. Should have read a bit more than first topic on the forum :)

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pekkaj answered ·

BTW manual was useless, all it says about lifepo4 is to set peukert value to 1.05. Unacceptable for crazy expensive voltage meter...

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christern avatar image christern commented ·
Just to make sure. BMV is NOT a voltage meter. It's an amperage meter. A h_ll of a difference.
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