question

alexch avatar image
alexch asked

SOC and Voltage

i got a multiplus 5000 parallel to the grid, using a Li ion battery with JK BMS. 15s. 2.7 - 4.2V according to data sheet. No communication JK BMS <> MP 5000 established.

NO Shunt added.

Worked good the last months.

Recently i ran into a problem: in ESS, the SOC says its about 10% (and stops discharging cause of ESS Minimum SOC Setting at 10%), while voltage is about 52 volt.

In the past, the system worked until 45 volt which is my Cutoff Voltage in VEConfigure.

How to fix this? I read about other similar setups without a shunt running fine.



Multiplus-II
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5 Answers
kevgermany avatar image
kevgermany answered ·

SOC etc comes from the BMS. Time to talk to the BMS suppliers.

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alexch avatar image
alexch answered ·

I know. I even got the hardware for communication between bms and MP .

But I didn't set it up cause the system worked good for month. And now it is difficult to add cables etc in retrospect.

I would like to now why this now happened, and how to solve it. Cause other systems are setup without shunt and communication, too, and seem to work.

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pwfarnell avatar image
pwfarnell answered ·

Often the SOC can drift over time in most systems due to small inaccuracies and this is corrected when the battery is fully charged to 100%. If the battery does not get an occasional full charge then the SOC can accumulate large errors. Has your system been up to 100% over the months of use or has it been permanently at partial charge. In the short term, give it a full recharge to see if the SOC resets.

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alexch avatar image alexch commented ·
System has been recharged to 100 percent daily until the sunny hours decreased during the last week's.

Is there no option besides charging to 100 percent?

The system should prioritize voltages and not soc

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pwfarnell avatar image pwfarnell alexch commented ·
The answer is in your reply, the BMS SOC is drifting off because it is no longer seeing a full charge. Without BMS to Multiplus communication or a shunt the SOC in the Multiplus is only an estimate.
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alexch avatar image alexch pwfarnell commented ·
Any idea how often I need a full charge to prevent these problems? Than I would just charge the battery from grid to 100 % (if that's possible at all...).
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pwfarnell avatar image pwfarnell alexch commented ·
Not really, I think you will need to experiment with your usage pattern, give it a full charge then watch the SOC vs voltage for the next few days and see how they diverge until they get too far apart then recharge. Maybe you can go a week between full charges, but it depends on individual usage pattern.
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alexch avatar image alexch pwfarnell commented ·
How can I execute "start charging battery from grid NOW" or something similar? Can't find an answer online. Thank you.
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pwfarnell avatar image pwfarnell alexch commented ·

I do not know the detail.

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1234enough avatar image
1234enough answered ·

Its only one wire from bms to mp, guide https://github.com/Louisvdw/dbus-serialbattery.

Once this is up and running you can see loads of extra info in VRM from JK BMS anywhere in the world - examples belowscreenshot-20231116-190602-vrm.jpgscreenshot-20231116-190521-vrm.jpgscreenshot-20231116-190458-vrm.jpgscreenshot-20231116-190442-vrm.jpg


screenshot-20231116-190602-vrm.jpg (194.1 KiB)
screenshot-20231116-190521-vrm.jpg (189.2 KiB)
screenshot-20231116-190458-vrm.jpg (216.6 KiB)
screenshot-20231116-190442-vrm.jpg (180.2 KiB)
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alexch avatar image
alexch answered ·

I knew this, but min and max voltages are not suitable. And from the GitHub I couldn't see if I can change these. Its mentioned there, but contradictory overall.

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