question

markbuilt avatar image
markbuilt asked

BMV712 Smart reports higher SOC than LiFeBlue lithium batteries

I have 2 LiFeBlue LiFePo batteries (400Ah total). At night, batteries report same SOC as BMV712Smart: 82%. I awake to batteries reporting 74% SOC (which I believe is accurate), while BMV712 Smart reports 100% SOC (this can’t be accurate). I do have a SmartSolar 100/50 for my 500W of solar. But in January on a cloudy day, I believe the batteries are reporting correctly, NOT the BMV712 Smart. Please help me get an accurate SOC on the BMV712 Smart?

BMV Battery Monitor
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2 Answers
boekel avatar image
boekel answered ·

Also check the BMV settings: 'charged voltage' might be too low, causing a sync to 100% when voltage rises to this setting (at low current), like when a bit of sun hit's your PV panels.

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markbuilt avatar image markbuilt commented ·

Ok - increased Charged Voltage to 13.9V. Will see if this helps - many thanks!

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boekel avatar image boekel ♦ markbuilt commented ·

What charge voltages have you set in the MPPT? (smart solar)

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markbuilt avatar image markbuilt boekel ♦ commented ·

I’ve changed the MPPT charge voltages today, also. Absorb 14.4V, Float 13.7V. Max Absorb 2 min. Based on recommendation by AM Solar in AZ.

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boekel avatar image boekel ♦ markbuilt commented ·

ok. can be tricky to get it right than, after absorb batteries will go back to 13,7v so either they will synchronize while still charging (during low sun input), or they won't synchronize.

Another trick is to set 'charge efficiency' a little bit to high (like 98-99% for LiFePO4), this way the BMV will register a little bit too high, but you can see that as an 'alternative way to synchronize'

I assume you already have the 'peukert factor' set to 1.00?


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wkirby avatar image
wkirby answered ·

The most common cause foe SOC increasing during discharge (during the night time) is the shunt being wired back to front.

Please check the the battery negative is connected to the terminal marked "Battery Only" on the shunt PCB. The other terminal will be marked "Charger / Loads" or something like that.

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markbuilt avatar image markbuilt commented ·

Yep - shunt installed correctly. Thanks :)

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