ESS recharge battery instead of discharge

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question

tobuildings asked Jan 30, '24

ESS recharge battery instead of discharge

Hi,

I have a ESS with 3 Multiplus II 5000VA, Cerbo, MPPT, 50kWH Battery LiFePo

Today I updated the BMS and wanted to do a full battery cycle. Up to 100%, down to 0% and up again.
Loading was easy. I set "keep battery full".

Afterwards I set "Optimized without BatteryLife" min SoC 0%
After hitting 12% the ESS started charging with 50A. - cerbo did not show any BMS alarm like "low voltage"...

In VRM Portal it says "recharge"

Now it is at 31% and still wants to charge from grid, I set max. charge current to 1A for now.

I dont know how to stop the "recharge" - tried to switch trough different ESS modes, set min SoC to several different values - still no difference.

I want the battery to dicharge for know, but I dont know how to make it... AC loads I have, but battery charges with 1A from grid.

ESS SOC

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Answer 1 · 2024-01-31T11:19:55Z

matt1309 answered · Jan 31 at 11:19 AM

Hi @ToBuildings

My guess is the BMS is requesting the recharging. Any data/settings visible within the BMS that gives a hint?

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nickdb ♦♦ commented · Jan 31 at 11:27 AM

The BMS can't make the system charge the battery, it merely sets limits for charge/discharge and/or blocks the battery being used if it leaves its specs.

There are multiple settings that could cause a system to behave like this, ESS SOC minima is only one of them.

There are voltage limits in the inverter setup, cut-offs and other thresholds in the assistant.

Supported batteries take this into account in their config docs, most likely the peripheral settings around ESS are incorrect. If this is a non-supported battery, best to consult with the supplier for the config it requires.

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matt1309 nickdb ♦♦ commented · Jan 31 at 04:14 PM

@nickdb Under normal conditions yes, but if the BMS minimum limits change when already below said limit the victron system would charge the battery to that limit.

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nickdb ♦♦ matt1309 commented · Jan 31 at 05:26 PM

I suggest you re-read the original post.

It would not apply to that scenario, unless other thresholds are hit.

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matt1309 nickdb ♦♦ commented · Feb 01 at 09:10 AM

If BMS min voltage was hit, the victron system charges to sustain level doesn't it?

I assumed that would mean that BMS min voltage had changed as part of the update given no mention of any other settings being updated.

I see your point that maybe the sustain is set too high but root cause is surely BMS given no mention of any other changes before the behaviour occurred.

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Answer 2 · 2024-02-01T09:23:44Z

thanar answered · Feb 01 at 09:23 AM

Strange. Even if the battery had hit an inverter-set low-voltage limit and had to "sustain", you should definitely see some feedback in VRM / Console. Any chance your ESS assistant was setup with a different battery? Did you check the ESS settings, through VEconfigure?

Funny thing is I did the same to my battery today, because BMS-reported % was way off, and the procedure you mentioned worked as expected. Battery discharged down to 1%, stayed there for a few hours, and updated to 0% as soon as the BMS cut off. The inverter entered "sustain" mode, I limited the charge current through DVCC until it went out of sustain and adjusting minimum SoC since.

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