question

Sounds more like a battery/BMS problem and/or a few settings are wrong not a problem with the Victron system.

If there is a low battery alarm the system forces a charging to the configured sustain voltage to protect the battery.

Thanks Mattias yes, unfortunately being away from home I'm unable to connect to the BMS to see what it's doing or how it's set. The behaviour certainly is as you describe. Now, for example it's using the grid (at high prices) when it should be using the battery, the battery is slowly being charged by solar, but ESS charge schedule is 'inactive'. The thing is, the low battery alarm is coming from the Multiplus not the BMS as far as I can see..... there are certainly no alarms shown in the BMS section of the 'Devices' menu, only the Multiplus. What I can do remotely (with a little help from a friend) is change the battery BMS protocol setting from 'Victron' to Pylontech. I might see if that syncs a bit better.

These are the Cerbo settings:

And these are the Ve.Config settings:

Hi Slartybart

as said by Matthias, first of all there is a problem with displayed SOC as with LFP cells at 3.27V you are more likely around 40% but certainly far from 100%.

BMS has been calibrated? parameterized?

Strange your "forced off" status

I don't have such option (only have the slider button to toggle between ON and OFF)

but SCS should also be off

Also strange that it doesn't follow the BMS informations?

In the ESS assistant in your ve.config there is a dynamic voltage. If your defaults are like mine, they are too high. Lower these as they seem to override the ones in all the screenshots in the above answers

Thanks all. I reverted the BMS Protocol setting back to Victron, so the DVCC settings are normal again, and everything is off. Ironically the Pylontech setting started flagging High Voltage warnings! Having played a bit more…. I think the issue is simply this: for some reason the charge voltage is never allowed to get above 53.8. When it reaches this the multiplus ramps down to zero, then moments later back up to trying to inject 5000w etc. so while it’s almost certainly a BMS issue, as jeanmarie pointed out, the issue isn’t that the multiplus isn’t decharging to its limit, it is in fact it’s never filling up in the first place, so the sustain mode cut off kicks in. I’ve emailed the battery supplier and shall see what they say. Thanks again for everyone’s help.

In addition to whatever BMS issues you may be having, verify what the ESS assistant dynamic cutoff values are. Those are very often preventing people from discharging to close to 0% while using ESS.

Thanks all. I thought the charge parameters in VE.Config were overridden by the BMS, but in case I'm wrong on that I've upped the float voltage to 55.2 as per battery instructions. It was previously set to 54... which is roundabout where, when charging, it keeps cutting out. The battery manual doesn't have an absorption setting so I've left the default 56.8 (it never reached anything like that voltage either!). While I'd have expected the Multiplus to continue charging until the BMS tells it the battery is full, if this setting is what the issue is, then at least now it shouldn't stop charging until it reaches 55.2v, which has got to be closer to full than 53.8 where it was stopping thus far...... It'll potentially need as much as 7kWh's so I'll wait until the price drops later on (saving me a potential 70p!) Let's hope it doesn't explode when I give it a go later on....

Jalle19.... I've actually upped the cut-off level from 37.2 to the manual's 43.2. I'm confident it's not reached either of those limits, but time will tell.

Thanks all for your help.

Turns out the battery was faulty, or at least one of the cells. Everything working now as it should, finally! Phew!