Has anyone else had a problem with the cells of these not being top balanced? I have had four in service for approximately three weeks and all four have a top balancing issue. Have only been able to charge to around 54.4V without tripping the OVP of the BMS. Each battery has a cell that will exceed the 3700mV and trip the BMS if charged to a higher voltage. As of yet the BMS has not made any noticeable difference to the balance. The delta between the highest and lowest cell voltage is 330mv (3700mV highest to 3370mV lowest). I have another four batteries yet to install and I'm not overly excited by the prospect of having to disassemble the eight packs and do a manual top balance, assuming the remaining four have the same issue. Curious if others have had a similar experience?
SOK 48V 100Ah top balance issue
- Thread starter Dan H
- Start date
My issue is documented here. https://diysolarforum.com/threads/disappointing-sok-rack-balance-issue.47789/#post-607488
I see some improvement but your observation about the BMS not doing much to balance is accurate. Can you go slow and charge to 54v and hold the voltage for a long time because the BMS requires to be charging for the balancing to happen.
@goldserve Thank you for the link to your thread.
I am aware that relying on the BMS for balancing is potentially a very slow process. I have dialled down the charge voltage (54.2V) and current (10A) in a hope that the charge cycle will go as long as possible and enable the maximum amount of balancing from the BMS. I am only guessing however if and when the BMS is balancing, and from my observations my settings are having no observable impact on the balance.
I am aware that relying on the BMS for balancing is potentially a very slow process. I have dialled down the charge voltage (54.2V) and current (10A) in a hope that the charge cycle will go as long as possible and enable the maximum amount of balancing from the BMS. I am only guessing however if and when the BMS is balancing, and from my observations my settings are having no observable impact on the balance.
Will do
@HighTechLab
Hi Dexter,
I'm hoping you might be able to give me some insight into how to resolve this problem. For context I am in Australia and bought my batteries from SOK Australia, so this is not your problem to resolve, however the team at SOK Australia whilst showing a keen interest to help are starting from a low base on their knowledge of these batteries and so we are working together to try and learn what to do to fix this issue. I suspect that you probably have the answers and I would be very grateful if you have the capacity and willingness to help.
I am charging the batteries using an MPP Solar HV2-5048, which does not have RS485 comms. Hence I only have the ability to manipulate the charge voltage, float voltage and charge current. I can not change the absorption time or tail current etc. I have tried to look to purchase (or make) the appropriate RS232 cable to enable me to see more detail on what the BMS is doing, however SOK Aus do not supply the cables and they are telling me that a standard RS232 cable purchased from another third party will work. However, from the Current Connected website it clearly states that the RS232 cable you sell is specific to the SOK. Hence I have tried to find out what the pin configuration is so that I could look to make the appropriate cable, but to no avail thus far.
From what I have read from some of your other posts, I suspect that the BMS is not currently configured to work optimally with my "no comms" system. Hence I need to try and figure out what those setting are and then to obtain the ability to make the appropriate setting changes. I understand that the BMS settings are "locked" and for good reason, so this is an obstacle I need to overcome.
No doubt there is lots more information you would need to be able to help and I am will and able to be as patient as necessary to resolve this issue.
I hope you are able and willing to help and I appreciate your time.
Hi Dexter,
I'm hoping you might be able to give me some insight into how to resolve this problem. For context I am in Australia and bought my batteries from SOK Australia, so this is not your problem to resolve, however the team at SOK Australia whilst showing a keen interest to help are starting from a low base on their knowledge of these batteries and so we are working together to try and learn what to do to fix this issue. I suspect that you probably have the answers and I would be very grateful if you have the capacity and willingness to help.
I am charging the batteries using an MPP Solar HV2-5048, which does not have RS485 comms. Hence I only have the ability to manipulate the charge voltage, float voltage and charge current. I can not change the absorption time or tail current etc. I have tried to look to purchase (or make) the appropriate RS232 cable to enable me to see more detail on what the BMS is doing, however SOK Aus do not supply the cables and they are telling me that a standard RS232 cable purchased from another third party will work. However, from the Current Connected website it clearly states that the RS232 cable you sell is specific to the SOK. Hence I have tried to find out what the pin configuration is so that I could look to make the appropriate cable, but to no avail thus far.
From what I have read from some of your other posts, I suspect that the BMS is not currently configured to work optimally with my "no comms" system. Hence I need to try and figure out what those setting are and then to obtain the ability to make the appropriate setting changes. I understand that the BMS settings are "locked" and for good reason, so this is an obstacle I need to overcome.
No doubt there is lots more information you would need to be able to help and I am will and able to be as patient as necessary to resolve this issue.
I hope you are able and willing to help and I appreciate your time.
Last edited:
@goldserve from what I can decipher from your thread, it looks as though I will need to talk to SOK/CC about reprogramming the BMS to work with the non-RS485 system that I have, ie balancing all of the time (not just whilst charging) and start balancing at a lower cell voltage, but lets see what Dexter has to offer.
Hello Dan
I have a similar problem with mine (I am also in Australia). There are two cells (11 and 12) that seem to be 200mA below the rest when getting close to a 100% state of charge. I have a cable that I made based off the Current Connected schematics, and that sets the charge voltage to 57.6v. In doing this, I get OVP on these cells about 55% of the time. I removed the cable, and manually set the charge parameters in the Growatt SPF3500, and the same results occur. I then lowered the charge voltage to 56.0v, and that avoided all OVP triggers. After that, I slowly increased the charge voltage by 200mA each week, until it started tripping OVP again. This tripping occurred at 57.0v, but only about 15% of the time now.
My understanding is that 56v should be ample to charge, but the SOK docs recommend 57.6v, and if using the comms cable, I don't think this value can be changed. My battery has gone through 40+ charge cycles, as I only use about 35% per day, and in that time, it's tripped OVP on a cell(s) 39 times.
I have a similar problem with mine (I am also in Australia). There are two cells (11 and 12) that seem to be 200mA below the rest when getting close to a 100% state of charge. I have a cable that I made based off the Current Connected schematics, and that sets the charge voltage to 57.6v. In doing this, I get OVP on these cells about 55% of the time. I removed the cable, and manually set the charge parameters in the Growatt SPF3500, and the same results occur. I then lowered the charge voltage to 56.0v, and that avoided all OVP triggers. After that, I slowly increased the charge voltage by 200mA each week, until it started tripping OVP again. This tripping occurred at 57.0v, but only about 15% of the time now.
My understanding is that 56v should be ample to charge, but the SOK docs recommend 57.6v, and if using the comms cable, I don't think this value can be changed. My battery has gone through 40+ charge cycles, as I only use about 35% per day, and in that time, it's tripped OVP on a cell(s) 39 times.
@HighTechLab
Still hitting some cell ovps while cell 2 is consistently weak. Should I consider taking the pack apart and balancing manually? I have the skills power supply and torque wrench… how hard would this be while trying not to disassemble the pack too much
Still hitting some cell ovps while cell 2 is consistently weak. Should I consider taking the pack apart and balancing manually? I have the skills power supply and torque wrench… how hard would this be while trying not to disassemble the pack too much
Lt.Dan
Solar Wizard
You shouldn't have to disassembled the entire pack. Just open the case and balance them with the cells still inside the case
Is there a procedure and do you mean I should top balance them one at a time to 3.6v?
Lt.Dan
Solar Wizard
I'm not sure if there is a walk through on opening the case. But just set your power supply to 3.6v and slowly bring up any low cells until they are about even with the rest. Once they are close enough, the BMS should be able to maintain a good balance with ease.
Do I need to disconnect the main negative lead from the bms and should I remove the balance leads since there will be a voltage into the bms but it’s not powered on.
Lt.Dan
Solar Wizard
It would be smart to decommission the battery. Disconnecting the BMS balance leads at the BMS will shut it off.
HighTechLab
AKA Dexter - CTO of Current Connected, LLC
- Joined
- Sep 23, 2019
- Messages
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This is not "horrible" balance as you said in the other thread. It's well within less than 1% and your pack will still easily pull rated capacity with flying colors. Sure, you can take it into your own hands and try to push it closer to satisfy yourself, but the BMS will do that for you in time anyway, as it already has done on the other 15 cells. As the screenshot shows, the BMS is running the balancers properly and the balance is even within acceptable tolerance despite calling it "horrible".
Please tell me if this battery fails to meet any rated spec, and we'll be 100% on top of resolving the problem.
