ESS keeps failing to charge

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1

Hello everyone,

I’ve had an ESS with a MultiPlus II and a DIY battery with a REC BMS since around December last year.

It worked perfectly for many months. However, for some time now, it keeps happening that the ESS doesn’t charge even though there’s enough surplus PV power available. The next day, it may work perfectly again. Restarting my Ekrano has no effect. If I restart the BMS, it works again. I’ve also already received an update for the BMS from REC. It then worked normally for a few days, but the problems returned, although they seem to occur slightly less often.

Are there any ways to debug this? For example, can I see somewhere whether the BMS is limiting the charging current?

A few relevant settings:

  • ESS Optimised without Battery Life
  • Scheduled charging levels inactive
  • DVCC, STS and charge-current limitation enabled
  • REC BMS detected correctly and active as the controlling BMS
2

You could take a look at the battery monitor widget in VRM …

graphic
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3

Oh, I haven’t had a proper look at that yet. Cool stuff :stuck_out_tongue:

That’s what it looks like. Can anyone explain this? No errors on the system.

Screenshot 2026-07-14 at 21.31.57
Screenshot 2026-07-14 at 21.31.571059×918 97.3 KB

4

Where does your PV surplus come from—DC or AC side? AC in or out? Looks like around 6 kW are being fed into the grid…

5

The Victron is connected to the grid via AC In. It receives the data via Modbus TCP from the Fronius Smart Meter. The connection is stable.

6

So, does that mean you’re measuring the PV output separately and that the GX also “knows” about it? In other words, a PV meter on “AC In”?

The system will only use the power to charge the battery if it detects that you’re generating PV power. Simply displaying surplus on the Grid Meter doesn’t mean that the system is charging from the surplus.

You can also go back in the VRM overview to compare the data … and how did your system reach 80% SOC the previous day?

7

I’d say the BMS is limiting it to 52.7 V… But why? I’d check the BMS settings.

8

You’re completely wrong there, Steffen. The system absolutely doesn’t care where the surplus comes from.

9

… True … that would only be important for the visualisation … :upside_down_face:

10

Quite right, the voltage issue should have stood out.

Here are the last two days; yesterday was fine. So the settings should be correct too—I’d already sent them to REC before. In any case, I’m now seeing exactly what I wanted. I’ll send the screenshot to REC Support.

Screenshot 2026-07-14 at 22.02.58
Screenshot 2026-07-14 at 22.02.581054×910 111 KB

11

That looks good … you can post your VE-Configure configuration file here sometime … then we can have a look through it :face_with_monocle:

12

What do you mean? When it’s running, it looks good. But I still don’t have an explanation for why the BMS lowers CVL at 50% SoC, and does so irregularly.

13

The VE Configure part would only be interesting because the Multi acts as a charger … but as you can see, your BMS lowers the charging voltage and sets the current completely to 0 even though the SOC isn’t 100% … do you have temperature sensors on the BMS that could be responsible for this? …

14

Temperatures are usually between 30 and 35 degrees. It doesn’t correlate with the behaviour, and there’s no alarm showing on the BMS either—nothing in the logs, either.

15

Just wanted to give a quick update: after consulting REC, I changed the value for End of charge hysteresis per cell from 0.25 V to 0.18 V.

Everything has been fine since then!