Please help: Cell Over Voltage Problem

[candersen]

Hello everyone ! Greetings from South America ???

I built a 150Ah battery 1 year ago using a BMS and installed it in my camper van with a Renogy DC to DC 50amp charger yesterday (solar mppt + alternator charger). When I started my van for the first time I noticed in the app that one of the cells triggers the "cell over voltage" protection from the BMS as seen in this video:

I did not balance the cells when I assembled the battery because to my knowledge the BMS could handle that ? is this the proper way the battery is supposed to be charged and is it safe and healthy? Should I disassembly and top balance the cells? ? I’m really worried because I should start my long awaited trip from a 2 year van build in 2 more days

Separate question: when I started the van with the battery connected for the first time you can see in the photos attached that in the app it says is at 8% charge, but magically 2 minutes later it’s at 100% and the cell over voltage is kicking in.
Solutions are much appreciated! Thanks for the feedback and help ??

 

[time2roll]

Two days to fix will be tough. First I would set the over-volt to be 3.650 as I see some spikes in the 3.7-3.8 range. Considering how unbalanced the cells seem I recommend changing the balance to always on with 3.2 start voltage to get maximum time balancing. If there is a power supply to hold the voltage steady at 13.8-14.2 volts it might come in line sooner. Balancing through the BMS can take a long time.

Do you have a smaller charger to run the voltage up a bit slower? Hard to tell but seems like the voltage is bouncing around a lot. I would want to verify the BMS cell voltage displayed is close to an actual voltmeter measurement direct on the cell. The way it seems to bounce around there could be some connection issues to resolve that are giving a false reading.

If there was more time I recommend ordering an active balancer.

I assume the 8% to 100% is again due to a bad connection and the BMS is jumping the % based on incorrect voltage.

 

[candersen]

Two days to fix will be tough. First I would set the over-volt to be 3.650 as I see some spikes in the 3.7-3.8 range. Considering how unbalanced the cells seem I recommend changing the balance to always on with 3.2 start voltage to get maximum time balancing. If there is a power supply to hold the voltage steady at 13.8-14.2 volts it might come in line sooner. Balancing through the BMS can take a long time.

Do you have a smaller charger to run the voltage up a bit slower? Hard to tell but seems like the voltage is bouncing around a lot. I would want to verify the BMS cell voltage displayed is close to an actual voltmeter measurement direct on the cell. The way it seems to bounce around there could be some connection issues to resolve that are giving a false reading.

If there was more time I recommend ordering an active balancer.

I assume the 8% to 100% is again due to a bad connection and the BMS is jumping the % based on incorrect voltage.

Hi there! Thank you so much for the response and help, much appreciated.

I have never balance a cell before, should I just top balance them like in this Will’s video?

If so, when I take the battery out, I will check for bad connections from the BMS. After this I should dissasembly the battery, connect the cells in pararell and buy a power supply (the only one available here in Chile is for 2A / 15v output) such as Will’s video and charge it to 3.65v right? Should I discharge the battery before doing this and if so, what’s the best way you recommend of doing it?

Also, how should I “change the balance to always on with a 3.2 start voltage”? Should I do this in the battery app? I only have the free version so I assume I should buy the pro version in order to be able to configure it and do this right?

As for the voltage balancing a lot, I think is mainly due to the engine running in iddle, the van is a 1985 VW Westfalia so I think when I will be going in the freeway the voltage should be more steady, but again this is just my assumption ?

Thanks for the help again!

 

[candersen]

Another thing I noticed is that the battery in the app says 100ah when my battery is 150ah. I checked my BMS order, and realized its a 100-120ah BMS… would this affect the battery in anyway or it would just read 100ah as it’s maximum capacity?

 

[time2roll]

Yes the cells need to be balanced. If you have the equipment and time the parallel to charge to 3.650 volts works well.

 

[TomC4306]

I have never balance a cell before, should I just top balance them like in this Will’s video?

Yes

 

[TacomaJoe]

Battery capacity is a user programmed value in the app. Change it to 150Ah. The BMS can handle a little balancing but not to your level of imbalance. The BMS will take a couple of cycles to sync up to the battery.

 

[candersen]

Yes

Perfect! I think I’m understanding how to do it now. Last question is if I need to discharge the battery for this? Or is it possible with it’s current state of charge (or maybe at 95-98% charge) I can balance the cells to 3.65v as on Will’s video?

Battery capacity is a user programmed value in the app. Change it to 150Ah. The BMS can handle a little balancing but not to your level of imbalance. The BMS will take a couple of cycles to sync up to the battery.

Awesome! I noticed that is on the premium version of the app, I will get it now. Thank you!

 

[candersen]

Yes the cells need to be balanced. If you have the equipment and time the parallel to charge to 3.650 volts works well.

That’s great news, I think I’m going to go that way, even if takes a little longer. The last thing I don’t understand if I need to drain the battery fully to do it or can I do it with it’s current state of charge? I remember that when I assembled the battery the cells where around 3.2volts each, so can I just top balance it to 3.65 connecting them in parallel just like the video without draining the battery?

 

[TacomaJoe]

Check out the Overkill Solar app. It lets you make the changes and you don't need to buy the PRO version.

 

[candersen]

Check out the Overkill Solar app. It lets you make the changes and you don't need to buy the PRO version.

Thank you! Just a little late, just bought thw PRO version… either way I already took the battery out from the van!



I noticed that now on the app it says is 0% charge which is very strange. My guess is that everything is desconfigured and I should just start the process of balancing the cells and after that the BMS will be better configured? Here’s a screenshot of the app.

 

[TomC4306]

You do not need to discharge the battery. Just reconfigure in parallel, set the power supply to 3.65 volts, and connect to the battery. Do not touch the voltage setting on the power supply after connecting to the battery.
It will go faster if you do not use the alligator clip leads that came with the power supply. Make your own with ring terminals and heavier wire.

 

[candersen]

You do not need to discharge the battery. Just reconfigure in parallel, set the power supply to 3.65 volts, and connect to the battery. Do not touch the voltage setting on the power supply after connecting to the battery.
It will go faster if you do not use the alligator clip leads that came with the power supply. Make your own with ring terminals and heavier wire.

Great tips! Currently doing everything right now.

I disconnected the BMS and checked the voltage on the 4 cells and its weird because they seem very similar…

Cell 1: 3.217v
Cell 2: 3.216v
Cell 3: 3.236v
Cell 4: 3.236v

In the meantime while they’re balancing, I will remake the connectors from the BMS just to make sure.

 

[mikefitz]

The cell volts shown in the video reached over 3.7 volts without the BMS entering protection mode. This suggests the cell and perhaps back protection values in the BMS are incorrect. The settings for the BMS are shown on the Overkill site.
It's very possible a 50 amp B to B charger is too much for your alternator. Unless you have changed to a higher power alternator the stock unit could be overloaded. This may be the cause of the rapid change of voltage shown in the video..( the rapid charge may be due to the recording, its not in real time)
The low cost breakers shown are not very reliable.
It could be you have cell or balance lead termination poor contact, that is causing the voltage issues, the crimp on the balance lead looks suspect .
When carrying out the top balance set the charger to 3.65 volts, confirmed with a meter, before connecting to the cells. Do not readjust .

 

[candersen]

Hey everyone! After 5 days of charging, I just “finished” top balancing the cells. The cells though would not go over 3.34v… I waited a lot and it just got stuck in that number. I connected the BMS today and I just want to make sure if the parameters and settings in the BMS (through the app) are ok or if I must set anything else before installing.

I was also wondering if should just tell the bms that the 100% charge is 3.34v and just use the battery to its 75%? Appreciate the help!

 

[time2roll]

OK to put in service but leave the settings as is. Charge at 14.2-14.4 and see where the cell balance falls out.

 

[Bob B]

Hey everyone! After 5 days of charging, I just “finished” top balancing the cells. The cells though would not go over 3.34v… I waited a lot and it just got stuck in that number. I connected the BMS today and I just want to make sure if the parameters and settings in the BMS (through the app) are ok or if I must set anything else before installing.

I was also wondering if should just tell the bms that the 100% charge is 3.34v and just use the battery to its 75%? Appreciate the help!

If you only got the cells to 3.34 .... you didn't get them top balanced. Were they still taking current?

Depending on the charge rate, it can take longer than you think to charge them.

 

[TomC4306]

I just “finished” top balancing the cells.

No you didn't.
You haven't even charged it to 80%.
If you were only charging with four or five amps,
this process can take an extraordinarily long time. The voltage of these cells across the charge curve is very flat.
Bulk charge as a 12 volt battery until the BMS shuts off for a high cell and then disassemble and connect in parallel to actually perform the top balance.
Replace the alligator clip leads that came with your power supply with ring terminals and a heavier wire. That will vastly improve the speed at which your power supply can work.

 

[mikefitz]

The BMS settings could be more ideal.
Charge under temp could be in the range 0 Deg C to 4 deg C, must be lower than recovery value.
You need voltages for 100% SOC estimation, use 3.40 volts
Note these are used by the BMS to compute an approximate SOC, when cycled a more accurate value will determined.
The cycle capacity setting is either the actual battery capacity or the required cycle capacity, typically this would be 80% of specified capacity, 120Ah.

Your display of cell volts, 3.341 to 3.344 indicates a SOC of 80 to 90%. Whilst its possible the cells are not completely balanced the battery is usuable. I suggest putting into to service and hope the BMS improves balance overtime.
If the BMS reports cell overvolts, reduce the charge voltage to lower than 14.4 .

Mike

 

[Browneye]

For 100A cells, if they started with the battery at 12.2, then it was nearly empty, maybe 5 or 10%. So then putting into parallel, you now have 400 amp hours of charging to do. If you're using 10 amps that's 40 hours, five amps would take more than 80 hours - beyond 3-4 days.

BMS balancing is a very small amount of current, like half an amp or something. It can take many charge cycles to make even a little difference. Hence the need to get them as close as possible at full charge voltage. Waiting for near zero current in parallel does this, but they can still need some fine tuning at high knee. I had to bleed high cells down on my 230A to get them to match, even after top balancing.