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wheeto avatar image
wheeto asked

Multiplus II charging when not commanded

Hello,

I have set up a MultiPlus II in ESS mode with an external current clamp, a Cerbo GX and SoK batteries connected to the Cerbo. There is a 3rd party solar inverter on the AC line, and I use an OpenEnergyMonitor to record power usage.


It was working fine for a couple of weeks, but would never discharge the battery bank below about 50%, as the voltages in the assistant were set too high.

Today I adjusted the voltages in the ESS assistant down to 46.1V and uploaded these to the MP2. Now the system keeps charging for short bursts even when the battery is above the Minimum SoC set-point (25%). Any ideas what's wrong?

Thanks for any help,




Present minimum SoC from Cerbo:

screenshot-2023-07-12-at-130739.png



Short bursts of charging the battery at full power as shown on the Cerbo:

screenshot-2023-07-12-at-130801.png



Short bursts of charging as shown on house energy monitor

screenshot-2023-07-12-at-130838.png


Multiplus-II
screenshot-2023-07-12-at-130801.png (160.2 KiB)
screenshot-2023-07-12-at-130739.png (166.8 KiB)
screenshot-2023-07-12-at-130838.png (262.9 KiB)
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6 Answers
Alexandra avatar image
Alexandra answered ·

@wheeto

What is the bms sending to the system?

If you switch to keep batteries charged does the behaviour change?

Also I see an entire 488w missing from the incoming reading between loads and battery charging (4560-544-3528) so maybe a battery or two or three are offline? It is most likely battery comms that is the issue there.

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wheeto avatar image
wheeto answered ·

Hello,


How do I get more information about what the BMS is sending?


I will try setting to "keep charged" for a while and report back.


I think the "missing " energy is just due to the event being so quick that not all of the counters have time to stabilize on the display before I did the screenshot. Both batteries are online and displaying identical pack voltages on their front screens.


Thanks so much for your thoughts.

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Alexandra avatar image Alexandra ♦ commented ·
The bms charge discharge values can be seen on the GX itself under the battery in the device list.


The other way is a widget in the advanced page on the vrm.


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wheeto avatar image wheeto Alexandra ♦ commented ·
I've not been able to switch pages on the Cerbo quickly enough when these brief chargings happen.
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derrick thomas avatar image
derrick thomas answered ·

What is the "sustain" voltage set to in the assistant?

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
There is an explanation for that in the ESS assistant, also see here:

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/controlling-depth-of-discharge.html#UUID-6b8f380a-3e19-c040-9dad-673577d775d5

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wheeto avatar image wheeto commented ·
46.2 - I set it deliberately low (just 0.2V above the BMS shutdown voltage) so way below the current voltage
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wheeto avatar image
wheeto answered ·

I still haven't really got to the bottom of this. Any more ideas?


I've set the min charge level to 5%


screenshot-2023-07-21-at-201945.png


But - with a fairly constant load of around 3KW - I'm still seeing behavior like this:


https://youtu.be/ZJ4lZOZOTvk


Where it's way above the 5% setpoint, and also constantly "bouncing"


screenshot-2023-07-21-at-201945.png (158.6 KiB)
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wheeto avatar image
wheeto answered ·

I also meant to say that if I set the minimum charge to 20% or higher, everything works entirely as expected.

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wheeto avatar image
wheeto answered ·

I've still not managed to get an answer to this - does anyone recognize what's going on?


This video shows the Cerbo screen when the "charge / discharge" bouncing is happening

https://youtu.be/YOO4xKwR5L4


This video shows the same event from the point of view of the battery's BMS:


https://youtu.be/nY_7iBpix3g


The two packs and the cells within them are well-balanced and seem to show an appropriate state of charge. I left this going overnight in case it sorted itself out after a few hours, but it didn't. The following screenshot shows the energy monitor until I raised the minimum SoC in the morning at 0630.



overnight.png


It seems a shame to just write off the lower 20% of my battery bank's capacity??


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