bonsys avatar image
bonsys asked

Unexplained voltage drop on VE.Bus - MultiPlus-II 12/3000/120-50


MultiPlus-II 12/3000/120-50 (Firmware 497) powered by shore-power AC as the only energy source. There is a constant AC load about 1.3KW, absolutely no load on DC bus, two battery banks are completely OFF (battery switches are in OFF position and disconnected from VE.Bus). Which means that the MultiPlus-II is the only DC source on VE.Bus.

What can cause the voltage drops as per above screenshot? I only noticed it because from time to time it drops below configured "DC input low shut-down" of 12.4V triggering Low Battery Alarm.

How to approach and troubleshoot this?

Thank you!

1673236289925.png (332.4 KiB)
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1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

All Victron devices are designed to always have a battery connected. Running the system without a battery is not supported and can/will cause problems.

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bonsys avatar image bonsys commented ·
Thank you Matthias, do you mean incorrect system experience or potential Multiplus damage?
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kevgermany avatar image kevgermany ♦♦ bonsys commented ·
The battery acts as a buffer/stabiliser. These spikes you're seeing are very low current, looks to me as if the multi is trying to charge, but can't because the batteries are off. DC voltage here is low enough to tell the multi to charge. Net result is this spikey graph.

Will it cause damage? Maybe, it's cycling/switching very frequently, and the voltage spikes may well be higher than on the graph. If you have LiFePO4 batteries, the internal balancing won't be working and this can cause batteries to shut down prematurely.

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