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delt127 avatar image

Battery Reads 24.65V, but Battery Monitor states only 65% ... why?

BMV 712, CCGX, Multiplus, and my personal multimeter all have the Tesla battery at 24.65V. Yet the BMV 712, CCGX, and Multiplus all report the battery at 65-68%. Why?


Note: Happens both in solar charging and in grid charging. I have the Multiplus Absorption=24.6V, Float=24.5V, Charge Current=70A, Repeated Absorption Time=0.25hr, Repeated Absorption Interval=45 days, Max Absorption Time=1hr.

batterySOCvoltagebattery capacity
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2 Answers
Mark avatar image

For the BMV to function effectively it needs to be setup to;

1- Monitor and report the SOC% as accurately as possible (in relation to the true SOC%)

2- Synchronize regularly to reset to a known/true 100% SOC baseline

If you are confident that your battery is really fully charged, but the BMV is indicating ~65% SOC then I would work on tuning the sync parameters - 'charged voltage', 'tail current' and 'detection time'.

I would also conduct another full charge cycle while carefully monitoring the charge current at the end of the absorption phase just before switching to float phase and comparing this to the current BMV 'tail current' setting. If it is not dropping below the trigger threshold then it won't synchronize.

The issue/complication that I see with your current charging parameters is that absorption and float voltage are almost identical, so this may be difficult to work with for BMV synchronization.

For solar applications you typically set the 'charged voltage' to a little under the charger 'absorption voltage' and the 'tail current' to ~2% - that way when the battery voltage is over the 'charged voltage' AND the charge current drops below the 'tail current' and this is maintained for the 'detection time' it will automatically synchronize to 100% SOC.

Further info & reading;

BMV Manual;

https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE-PT-IT.pdf

BMV Setup Videos;

How to optimise the BMV-700 series sync parameters

https://www.youtube.com/watch?v=4ReljfO3k6M

Sync settings for Lithium batteries

https://www.youtube.com/watch?v=yMJ_vzB2avE

Introduction to the BMV 712-smart

https://www.youtube.com/watch?v=2vA-EjSSBVA

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delt127 avatar image

Just accomplished the above, works great. Thanks @Mark!

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No problem, I'm glad to hear that. Thanks for reporting back.