micmak avatar image
micmak asked

Quattro/BYD/GX/Fronius - High Voltage Alarm when reaching 100% SoC


I got an AC coupled system installed about 3 weeks ago. Quatrro 8k, Fronius 8k, GX and BYD LVS Premium 24kwh. Grid is available between 0 and 6 hours a day, very random, and we could go 10 days with total grid outage. Configuration made by the installer is ESS with "keep batteries charged".

Things are running as expected, except that I am worried about two things that I think are related. High voltage alarm from BYD whenever it gets to 100% and the delta between cell min/max once the SoC is at 100%. Here's an example from today.

SoC reaching 100% at 9:11


Increase in min/max cell voltage, and the delta stays large as long as the batteries are not discharging:


And I also get the alarm (visible on the GX as well in the notifications):


Here's an example from yesterday showing the delta while SoC is 100% for a longer period. I reached 100% yesterday, through Grid in the early morning hours, then discharged a bit, then 100% again once the sun rose.


I don't mind sharing my exported config from vrm or any data that might help to understand what's happening. There are some days that I don't get the alarm, but the delta is always there. I read in different posts that this is normal for new installations, but I would assume after 3 weeks, I should be seeing some improvement?

I also read somewhere to keep the batteries at 100% for a week or so. Grid wise this is impossible. I could run a generator for that long but the cost would be very high.

MultiPlus Quattro Inverter Chargercerbo gxFroniusAC PV CouplingBYD
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3 Answers
micmak avatar image
micmak answered ·

I got a feedback from BYD on this, if anyone is having a similar issue:

Secondly, as mentioned you concern whether that will harm the battery. We can guarantee that these kinds of warnings won`t. That max cell voltage is still under control. If the voltage goes even higher, the battery will shut down automatically to protect itself.

Meanwhile, we are researching a better strategy to solve this issue perfectly. But that may take some time.

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nickdb avatar image
nickdb answered ·

Your install is new and cell imbalances are to be expected. With that differential, one of more cells will hit their warning threshold and the batteries internal protection may kick in.

This should sort itself out with time.

Differences are exaggerated at full charge because the voltages are higher. You have not provided enough data to see if your setup is configured correctly ie charging at the correct voltages.

You can run through the recommendations here to check:

If they are correct, you could tune them down a little to prevent the alarms.

In a properly configured and sized system, imbalances tend to resolve themselves with time.

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micmak avatar image
micmak answered ·

thanks @nickdb for your reply. The alarm itself doesn't bother me, I only want to make sure I am not doing anything that will harm the batteries. It seems the installer used the recommended values:

1651671418108.png1651671443939.png1651671460614.pngIn ESS configuration, the below values are set:

  • battery capacity 500ah
  • sustain voltage 54V
  • rest are related to cut-off and pv inverter, etc...

What I noticed that the BYD reports 468ah in the GX while it is configured as 500ah in ESS. Not sure if that's an issue"

1651671831006.pngFrom the GX, DVCC is forced on, SVS and STS are forced off. Battery monitor is set for BYD on CAN-bus. Latest alarms in notifications:


Anything suspicious in the configuration? or I should just be patient and give it few more weeks? This is my usual trend in days where the grid is non-existent:


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nickdb avatar image nickdb ♦ commented ·

Can you check the bms limits chart on VRM? Also available via the details tab on the GX under the BMS tab. Look for what the CVL is reported as, is it fixed or variable?

You seem to have hit 0.6V above absorption, so it would be interesting to see what the BMS is setting its limit to. This peak would be what pushes the cell difference into triggering the alert.

If it gets too high, the BMS will usually offline modules and drop the charge limits which DVCC enforces.

If the BMS reports 468AH, that is what you should be setting in the inverter/charger limits also, since all 6 modules seem to be online.

Also check on the GX -> settings -> system setup that the BMS is selected as the battery monitor.

What specific battery model do you have?

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micmak avatar image micmak nickdb ♦ commented ·

I have the BYD Premium LVS 24kwh (6 modules stacked, 4kwh each). I think the 500ah comes from 24000wh/48v. Here's the bms limits chart from VRM for today:


and the BMS is selected as the battery monitor:


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nickdb avatar image nickdb ♦ micmak commented ·

So, 500AH assumes 48V but the nominal voltage is 51.2V so actually 468AH.

The battery is requesting a much higher charge voltage and then clamping charge current to 0 and dropping the charge voltage. Thereafter it raises them again, rinse and repeat. Just appears like it is fully charged and trying to manage imbalanced cells.

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micmak avatar image micmak nickdb ♦ commented ·

Thanks again Nick. I assume that's the correct behavior and I just let it be as it is, wait for few more weeks to have it balanced?

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nickdb avatar image nickdb ♦ micmak commented ·

As long as all your settings stack up with the BYD setup docs, it all looks fine.

I don't know how proactive BYD is at balancing, some batteries can take ages to balance.

You can also try putting the system onto ESS keep charged for a few days, that can help.

Others suggest some deep discharge cycles can also assist.

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