question

dangermouse avatar image

SOC Issue with BMV and CCGX

Hello,

I am building a 24v Victron system to go in an expedition vehicle.

Currently I have (For testing) 2 x 95ah 12v batteries lead acid type

CCGX

BMV712

Multiplus (Older chip updated to firmware with Assistants)


My question is - The voltage drop overnight with a 100ma load (BMV and CCGX) above is not reflected in the SOC. The capacity in the BMV is set to 85ah and all settings are correct for the battery type, all connections are checked. Shunt is correctly wired.

Why is the SOC not dropping in line with the voltage?

Many thanks

SOCbattery capacitybattery system voltage
vdrop-overnight.jpg (75.7 KiB)
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4 Answers
dangermouse avatar image
dangermouse answered ·

HI

Thanks for your reply

The big drop off in battery voltage was switching on the multiplus with no load connected so about a 1.0 amp draw.

Im guessing one of the (New) batteries is faulty.

Ill test them shortly and update the thread


Many thanks


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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Something doesn't look right with your batteries, but you haven't said what size the big load is that caused a voltage drop from 25.5 to 23.5 V in 2 hours from 7PM to 9PM. That must be much be MUCH larger than 0.1A on a 95Ah battery bank.

Forgetting about the BMV for a moment, and now thinking about the batteries. Are you able to do a discharge test with a known continuous load, eg 10A for 5 hours from a full battery to see what happens to the battery voltage?

Remember as a rule of thumb, a lead acid battery is only able to supply a continuous C10 load. In this case ~10A or 250W.

If you are trying to run bigger loads than that, you are asking too much of your relatively small batteries and you will see the voltage collapse.

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dangermouse avatar image
dangermouse answered ·

Hi


Thanks for the info

Will test tonight, however I get the same issue if i run the multiplus with a load on it cuts out at low voltage but im still seeing 85% SOC


Thanks

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jasontav avatar image
jasontav answered ·

The default current threshold setting on the BMV is set to 0.1A (100mA) and below this value the current is considered 0. Maybe this is the issue.

Try with this setting set to 0.0A and see what happens......


From the BMV manual:



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