question

sirisophie avatar image
sirisophie asked

Victron BMV 700 SOC inaccurate since I switched to a new battery. Help!

I previously had a 200 Ah AGM battery in my van with a Renogy solar controller and BMV 700. The SOC always seemed to give fairly stable & accurate readings. I recently installed a 200 Ah lithium battery and replaced my solar controller with a new Renogy MPPT with 50A DC-DC charger. All other connections remain the same. I updated my BMV settings to reflect recommendations for lithium batteries, but now it gives very inconsistent readings.


A few examples:

- The voltage is often above the charged voltage for many hours and the SOC does not increase. Right now I've had 13.5V for over 4 hours but no update to SOC.

- The SOC no longer shows incremental increases. It only goes down, then jumps back to 100%. With my AGM battery it would show incremental increases when my solar was charging or the battery was charging off the starter battery

- The SOC doesn't seem to reflect reality either. Just the other night, it read 60% battery, but then my inverter's low voltage alarm rang and I had to unplug everything.


Here are the settings I have:

- Battery capacity: 200Ah

- Charged voltage: 13.2V (as recommended by Renogy w/ the MPPT I have)

- Tail current: 4%

- Charged detection time: 03

- Peukert Exponent: 1.05

- Charge efficiency factor: 97% (as recommended by Renogy w/ the MPPT I have)

- Current threshold: 0.10

Can anyone recommend a settings change to help me get more accurate readings?

battery chargingBMV Battery MonitorLithium BatterySOC
2 |3000

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1 Answer
kevgermany avatar image
kevgermany answered ·

You're using solar to charge.

Sounds as if charge detection isn't set up correctly.

Suggest you

reduce tail current to 2% or lower (experiment...)

Set charged voltage to just below the recommended absorption voltage, somewhere closer to 14V.

Increase charge detection time to 10mins, maybe more.

However, a jump from 60% to full also isn't right. Did you reset the battery capacity correctly to match the new battery? (Typo possible)

And the million dollar question... Do you have anything except the shunt connected to the negative terminal of the new battery? Like the new MPPT? If so, move all these connections to the load side of the shunt.



1 comment
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sirisophie avatar image sirisophie commented ·
This solved it! The MPPT wasn’t connected to the shunt. It was on the battery. Moved it over to the shunt and now I can see proper charging on the BMV. Thank you so much!
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