high voltage spike happened when lithium battery 100% SOC and reduced load, using Renology suitcase solar

[Jane Scott]

Hi, We started playing with lithium and solar just shy of one year ago.
All has gone well but then we got a high voltage alarm on our battery monitor (just above 17v).
Details:
200 AH (100 BMS) LiTime lithium battery,
Renogy Suitcase 200w solar, PWM controller, connected with alligator clips to battery.
Victron BMV712 bluetooth battery monitor.
Settings for the battery monitor were the standard ones for lithium and renolgy was set for lithium (I don't remember if we were able to put in exact settings).

No problems until about 2 days ago.
We had topped up the battery with the generator to 100%. We had about 6-7 amps load on the battery and we typically get somewhere between 2-4 amps from solar at that time (it was late morning), depending on sun strength.
About 10 minutes after we topped up the battery, I shut down starlink.
At that time were probably getting a positive charge from solar (1-2 amps above the load we were using).
About a minute after I turned off starling, we got an alarm from the battery monitor - it showed high voltage above 17 (17.1 or maybe 17.3). A steady alarm. We disconnected the solar and the alarm was sounding the entire time (maybe 20 seconds).
We don't have bluetooth access to the batteries BMS so we can't see the stats, but we had fans running and didn't notice any interruption of service (it is possible the BMS cut off the input).
The Victron still showed a SOC of 100%, and there was a small amount of current but I could not say if it was positive or negative (I didn't stop to take a picture I just figured what the alarm was and unhooked the solar to stop the situation).

Reading here in the forum, I saw other people who had an PWM controller and when they hit 100% it took a second or two for the PWM to recognize the battery was charged and to stop sending electricity to the battery.
The Renology suitcase specs say it prevents overcharging the battery.

I don't know if the victron battery monitor noticed a second long spike but kept the alarm on until I turned it off. After I pressed a key to stop the noise it still showed the high voltage reading.

I don't know if there is a problem with the controller (I have a case out with Renology, they are asking for pictures of all the controller screens).

I am sure we have hit the situation before where we charged the battery up to 100% and when we turned off the generator we had more electricity coming from the solar than we were using (we have been places where our solar kept things fully charged even when we were using all our electronic items). But the scenario of having the battery at 100% and then reducing the load so that the amps coming in were greater than the amps going out - we night not have had that situation (in that order) before.

I did set the Victron to shut off when voltage got to 14 (after reading other posts).

If anyone has any insights or knows this equipment and exactly what it would have done, I would appreciate it.
After we get the solar controller screen readings, we will try to reproduce the problem (battery charged up to 100% by generator, having a load on that will be more than the solar - easy to do at our current location, then take starlink off so that solar if putting out more than the resulting load). Of course I will need to set the Victron shutoff higher - Renogy agreed it was ok to put it at 15 (not 17) and we will be filming a multimeter being used while we lower the load. It will be a couple days before the sun is strong enough to try to reproduce it and by then Renogy might already have their solution (after viewing the screens).

TIA for any insights/knowledge you all have including how to determine exactly what happened (e.g best place to locate the multimeter).

 

[timselectric]

If I had to guess.
The BMS shut off charging, when the voltage reached over voltage protection. And this created the brief higher voltage, seen by the victron alarm.

 

[Jane Scott]

Timselectric, do you know if the Victron battery monitor does a long alarm once it detects just that short high voltage (e.g. the solar controller dropped sending electricity after it realized the battery was full but it took a second or so to do that?
Maybe we should try to reproduce the situation and see if the Victron keeps the alarm on but the Renogy dropped the voltage quickly.

 

[timselectric]

Maybe we should try to reproduce the situation and see if the Victron keeps the alarm on but the Renogy dropped the voltage quickly.

Agreed

 

[mikefitz]

My guess is the BMS shutdown the charge path due to cell overvolts, this is not uncommon and will occur with a near full charged battery where there is a a charger used with a high charge voltage. The primitive solar PWM controller had difficulty responding to this BMS shutdown and in effect connected the solar panel power to your system equipment.

did set the Victron to shut off when voltage got to 14

I assume this is the shunt alarm, changing the alarm setting won't solve the issue of overvolts.

Suggested solutions:
Adjust the charge voltage in the Renogy controller to a lower value if possible.
Replace the solar controller with a MPPT controller that allows user control of charge voltage.

The Renogy Voyager PWM controller does not allow user setting of charge voltage. The LFP setting is 14.4 charge volts, no float and a reboost at 13.5.. Changing to LTO setting, 14.0 volts would be an option .

Using the solar panels with a MPPT controller would be an ideal solution. Better control of charge perameters and less possible long term damage to battery and system electronics.

I don't hold much hope in Renogy being able to solve your issue. It could be the Voyager controller is malfunctioning , but even a replacement could still have issues.