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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) asked

MultiPlus 12/3000 and VE.Bus BMS/Smart Lithium jumping between bulk and absorption charging

Hi,
I installed a new system, mainly consisting of a MultiPlus 12/3000/120, VE.Bus BMS and 4 Smart Lithium 12.8/100 for a total of 400Ah.
Multi firmware is 2600430. Charger set for Lithium and Lithium Assistant is set up and started.

After letting it run for 24h discharging with small loads, today I connected shore power to see how the system is performing with AC In connected.

Charger went into Bulk, charging with 50A until after some time 14.2V was reached. Then it switched into Absorption as expected. Charging amps slowly decreased, which I think is ok. But then also the voltage started to drop until about 13.84V. Charger then switched into Bulk again, charging current starts to increase until 14.2V is reached. Then the whole process starts all over again, This all happens within minutes. See images attached.

I would expect the charger to stay in Absorption for 1h as it is set for with VE.configure.
So I feel there is something not working as expected.

Any help much appreciated.

Stefanie


edit: additional info - the moment absorption is reached, the BMS red LED comes on, which means either high voltage disconnect or temperature. Battery voltage is around 14.2V when this happens. None of the individual cells are anywhere near 4V nor is the temperature exceptionally high.

MultiPlus Quattro Inverter ChargerBMSVE.Bus
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2 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @Stefanie

It's probably still high cell voltage (above 3.7V I think)

I'd set charging current very low (like 2A per battery = 8A), it might be enough to set a low AC input current limit to lower the charge current.

After a day maximum the batteries should be balanced (if they can stay at 14V long enough)

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ commented ·

Thank you Daniel!

Yes, this is what I'm thinking now too after looking at the log files (looking good) and finally reading the battery manual (sorry...).
Until then I had no idea that the BTV is giving an over voltage alarm to be processed by the BMS. And yes, on two of the batteries there are two or three cells with 3.76V (somehow I had 4.2V in my mind). Out of balance.

I then decreased charge current to 7A (2 for the loads and 5 for the charge). But that seems not to be enough as the battery voltage increases only up to around 13.63V. Will change that tomorrow to what you suggested when back on the boat and report how it went.

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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @Daniël Boekel (Victron Energy Staff),

just to let you know that everything worked as suggested.
There was one troublemaker cell reaching 3.74V just seconds before absorption phase was reached and I expected the BMS to shut the Multi off, but magically the cell recovered pretty fast and within 20 minutes went down to an acceptable level while the system started to balance.

After about 1.5hours of absorption all cells were well balanced within 0.03V at around 3.55V.


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