question

Geomz avatar image

Why is my Quattro sending 30.07 volts to my 24 v batteries???

I have a Quattro 24/5000/120 connected to a pair of 12V lithium batteries in series, with a BMV 712 monitoring them.

I usually don’t allow a full absorption cycle to run, but the last few days I’ve let it complete the cycle to resync everything. And I’ve actually left the system to manage the batteries as “normal” allowing it to keep them full. It’s been “short cycling” the recharge as the batteries are mostly full, but discharge slightly over float then restarts the bulk cycle.

Since then, I’ve noticed my battery BMS throwing a high voltage alarm and I traced it down to my Quattro sending over 30 volts to my batteries!!

How can this happen?

My absorption voltage is set to 28.4 and float is 27.2.

This appears to happen just as it’s switching from bulk to absorption. It happens pretty fast and sometimes VRM doesn’t even catch it. This time it did.

Is this normal?

This is quite concerning since that voltage is way too high for these batteries.



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

Hi @Geomz

Your BMS disconnected at 28.2 volt, causing a voltage spike on the DC bus.

28.4 volt is quite high for lithium (LFP) batteries, so probably a cell got too high and the battery disconnected itself. The battery thus never had this voltage over the cells.

I'd set the maximum charge voltage a bit lower (28 volt?) to prevent this from happening.

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Actually my batteries absorption range is from 14.2 to 14.6 (each). So in series I have it set at the lowest end of that scale.

So it appears to me that my batteries are seeing the high voltage and then they’re kicking out well after the voltage spikes this high.

You don't mention what brand battery, or ah capacity.

Well your charger is never reaching your specified absorption voltage. I tend to agree that a BMS is taking a battery briefly out of circuit. Or something else weird like that.

What battery?