Multiplus 12 800 35 Overcharging Lithium batteries and then tripping

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fkirsten asked Apr 8, '22

Multiplus 12 800 35 Overcharging Lithium batteries and then tripping

I have the 12 800 35 MultiPlus connected to AC in, some load on AC out and 2x100Ah 12V Lithium batteries. From AC to inverter mode it switches seamlessly. After an Inverter cycle it will charge the battery but the Voltage goes up and peaks over 16V. The protection in the battery trips and that trips the whole unit for about 30seconds to a minute. In that time the 220V Load is also switched off. Then the unit starts up and it charges up again till it trips again. This happens a few times and then the inverter goes into a mode that I assume is float charging. I have set the dip settings 2=on and 3=off with no improvement.

I do not have the USB cable and app to adjust.

I have taken the unit back to the supplier. They say they have re-programmed it but the problem persists and they have stopped responding to my emails.

As the situation stands now the system is of very limited/no use to me as UPS for critical equipment.

Multiplus-II Lithium Battery overvoltage

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Answer 1 · 2022-04-08T10:44:51Z

wkirby answered · Apr 08, 2022 at 10:44 AM

When you set the DIP switches 2 and 3 are you "storing" the setting with DIP switch 6 after?
So if you set 2=on and 3=off (for default LiFePO4 settings) you need to switch 6 on and then off again to store the setting. Of course the unit needs to be on to be able to store the setting.

It seems like the equalisation mode id set, that is the only way it can output 16V. That would be odd though because this option is disabled by factory default and can only be enabled with the VE.Configure software. What settings did your supplier say that they set?

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Answer 2 · 2022-04-09T10:25:06Z

fkirsten answered · Apr 09, 2022 at 10:25 AM

Yes, I switched 6 on and off again. There is currently a similar post to mine running but also not with a clear resolution yet.

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Answer 3 · 2022-04-09T13:42:09Z

snoobler answered · Apr 09, 2022 at 01:42 PM

Have you established cause/effect?

Is the MP going overvoltage causing the battery BMS to trip or is the battery imbalanced, the BMS tripping before absorption is reached and then the MP briefly going over-volt because of the sudden removal of the battery from the charging circuit?

Yes. Battery cell imbalance can happen with new, expensive LFP batteries.

What is odd is that most good BMSs don't cut the discharge when over-voltage protection occurs. They just cut the charge.

Lower absorption voltage to 14.2V and re-assess.

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Answer 4 · 2022-04-09T14:20:23Z

Trevor Bird answered · Apr 09, 2022 at 02:20 PM

As snoobler suggests you could lower the absorption voltage significantly and test. The aim is to make the battery BMS inactive when "fully" charged. The possible cause is the unintended consequence of the BMS providing instability of the terminal voltage of the battery bank causing the MP to shutdown based on what it perceives as excessive DC ripple.

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