rainerb avatar image
rainerb asked

How to interpret VRM charged kWh and BMV SoC rising


I have a Multiplus 24/3000 (ESS) with 1,8kWp Fronius on ACout and a 1,1kWp Victron MPPT Smartsolar that are both charging a 24V battery bank (two rows of Sonnenschein A602/750Ah lead acid 12x2V cells). In the BMV712 I configured 1200Ah (C24) capacity for the battery bank.

Yesterday the SoC was at 90% in the morning and there was a very sunny winter day. According to VRM in sum 7,58 kWh pv energy were produced. 1,4kwh were directly used and 5,6kWh charged directly into the batteries. There was no discharge of the battery during this time period.

Now I am confused because with the 5,6kWh directly flowing into the batteries, the SoC was increased only from 90 to 98% during the whole day!

Without losses, 10% SoC of a 24V/1200Ah battery bank should be about ~3kWh, so what happened to the rest that was charged into the batteries?

The batteries are not getting warm at all.

The DC MPPT charger has a high efficiency, the Multi charger much less but I can’t believe there is about 50% charging loss???

After the sun was down, I switched to “Keep batteries charged” until the BMV sync point (100%) was reached. There was no big SoC jump so it seems to me to work quite good.

Any ideas where my battery kWhs are going? Should I increase/decrease the BMV712 capacity setting or charge efficiency?

Thank you and best regards...


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1 Answer
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @RainerB

As you've noticed, fully charging lead-acid batteries is not very efficient, the last 10-20% takes a lot of extra energy.

Also there are of course losses on charging equipment (say 10%?)

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