question

Topper asked Jan 19, '23

SOC drops fast while AC input is active

Hello, this morning the SOC value of my 2x Victron lithium batteries 25,6V/200Ah dropped from 78,5% to almost 0% out of the blue. See the following graphs;

For the last few weeks the system was running in ESS #1 and ESS #2 mode because off less sun shine. Is there some algorithm that forces the battery to discharge almost completely after some time when the battery is not enough recharged?

Thanks in advantage for answering.

ESS Lithium Battery SOC

soc-drop-1.jpg (23.2 KiB)

soc-drop-2.jpg (52.9 KiB)

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Alexandra ♦ commented · Jan 19, 2023 at 01:32 PM

More information please.

The dip looks like it happened when there was a sudden demand, so fails when power assist happened. So they possibly switched off then on again.

Check the cell balance.

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Topper Alexandra ♦ commented · Jan 19, 2023 at 01:46 PM

@Alexandra thanks for your answer, i cant see that there was a sudden demand for power on the AC-out, see the following graph;

The output power is constantly around the 550 W, the Victron Quattro is situated before all the connected users / devices.

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soc-drop-3.jpg (40.8 KiB)

Topper commented · Jan 19, 2023 at 04:08 PM

The DC voltage was also very low see graph;

Every night the DC voltage did get lower for the past 7 days..

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soc-drop-5.jpg (48.6 KiB)

Alexandra ♦ Topper commented · Jan 19, 2023 at 05:24 PM

You may need to set it to keep batteries charged for a bit.

Have you seen the system go into sustain at all?

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