Trevin Corkery avatar image
Trevin Corkery asked

BMV prematurely resets SOC to 100%

I have a 12v lead acid battery that I drained to 50% SOC but when the charge controller starts charging the battery it will increase the SOC normally until the charger makes the battery reach 13.20v while current is going into it, which makes the SOC jump to 100%. I know the battery isn't 100% SOC because its still undergoing the bulk charge and hasn't touched absorption/float as it normally does.

I assumed since the BMV does calculations with amperage for discharging to determine that actual SOC instead of relying on voltage, that it would do the same with charging.

Also I could have the BMV configured incorrectly so if there is something I should change in the settings let me know.

BMV Battery Monitor
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Mark avatar image Mark ♦♦ commented ·

To assist further could you provide some screen images of you current:

- Charger settings (I assume MPPT)

- BMV settings

- Battery capacity

- Confirmation that it is a premature synchronization that causes the SOC% to jump to 100% at one point during recharge, or if this happens gradually during recharge.

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Trevin Corkery avatar image Trevin Corkery Mark ♦♦ commented ·

I just watched an older video about syncing the BMV correctly so below are my new settings. (Haven't had the sun yet to test them)

Battery cap is 122AH (Deep cycle lead acid)

BMV settings:

Charged Voltage: 14.1v (Before it was 13.2v)

Tail Current: 4%

Charged detection time: 3m

Peukerk exponent: 1.25

Charge efficiency: 95%

Charge Controller Settings:

Absorption charge: 14.40v

Max absorption time: 6h

Float Voltage: 13.80v

Equalization Voltage: 16.80v

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1 Answer
Mark avatar image
Mark answered ·

You new settings look like a good start.

Providing that the battery does get fully recharged and the charge current drops off sufficiently at the end of absorption phase, you could go even lower with the tail current %, say ~2 or 2.5%.

You just need to be careful not to make the sync criteria too strict or you will have the opposite problem and it won't ever sync.

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