question

mondeoman avatar image
mondeoman asked

Multiplus Battery cutoff while charging

I'm setting up a UPS (grid backup) system, no PV, no other energy sources.

I'm waiting delivery of a Multiplus Compact C 24 / 1600VA.

I also bought two 12.8V LiFePo4 "drop-ins" that have a built-in BMS. The BMS cuts off the battery in case of cell undervoltage / overvoltage.

I understand that the Multi is actually a bidirectional DC/AC converter and the control logic is powered from the DC bus where the battery is also connected.

I was wondering: what would happen if the BMS would cut off the battery while the Multi is powered from the grid via ACin and charging the batteries?

Would that damage the Multiplus? Does the 5 year warranty cover such an incident?

MultiPlus Quattro Inverter ChargerLithium Battery
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2 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @MondeoMan

That is no problem for the inverters, under normal use the inverter should shut down long before the batteries disconnect anyway.

But please check if your batteries are suitable for series connection to 24 V, most 'drop in replacement' batteries are not (but maybe these ones are)

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mondeoman avatar image
mondeoman answered ·

Thank you for the answer.

Yes, the batts can be connected in series (up to 4 units).

But I am not sure I explained the question clearly enough. My concern is about cut-off while charging. Let's say the Multiplus is Bulk Charging at 30A. There is no reason for it to shutdown. One of the cells is bad and shoots above 3.75 V. As per the datasheet, the BMS will cut off the battery. The Multiplus is in AC->DC conversion mode and the control logic circuits are powered from the DC bus. Now the DC bus is suddenly left without a 30 A load. I would guess this would cause a voltage spike on the DC bus.

Did you test whether your equipment can handle this spike without breaking?


Thank you!


PS: The existence of this community with Victron staff involvement was the deciding factor for me to go with Victron equipment.

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi @MondeoMan

That also is no problem for the Victron equipment, actually, batteries like BYD and Pylontech also disconnect when there is a cell-overvoltage.

On new batteries this is quite normal to happen, as the batteries have to do their initial balancing.

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mondeoman avatar image mondeoman Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Thank you, your answer is very helpful!

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