RadioB Tech Xiaoxiang BMS discharge wont turn on cells out of balance
- Thread starter arcsum68i
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High cell seems kind of random. Why is the charging slider turned off in the third picture? I don't recall if my slider turns to the off position when not charging.
You are correct, it does seem random but usually ends up being #2 when its fully charged. I believe it turns off automatically when full, I would have to wait until I recharge it to confirm.
Really wonder if there is just a problem with the balancer on this BMS or other issues entirely. You can see in the 3rd pic that the B is on which I assume means it is balancing, but the voltage continued to go up multiple times.
If nobody can provide a solution I may just throw a balancer on there.
Really wonder if there is just a problem with the balancer on this BMS or other issues entirely. You can see in the 3rd pic that the B is on which I assume means it is balancing, but the voltage continued to go up multiple times.
If nobody can provide a solution I may just throw a balancer on there.
Only the third screenshot would have that "B" indicator since the voltage had not yet hit the 3.4 volt threshold for balancing in the second screenshot.
mikefitz
Solar Wizard
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The slider turns to the off position, opening the charge path, due to cell overvolts on cell 2. The pack at 14.0 volts. I guess the charger is set to something like 14.4 volts.
The BMS will balance under charging. If the charge voltage is reduced to lower than 14 volts, say 13.8, with a long absorbtion time, the balance may improve, as it will be able to balance for longer.
The general impression I get is that , a) the cells did not experience a correct top balance, near, but not 100%.
and b) there are conection issues at cell 1 and 2.
Note that the voltage detected at cell 1 is low with negative current and high with positive current, suggesting some resistance at buss bar to cell. Since the issue developed over time perhaps there is slight corrosion.
It may be Interconnection issues are having an adverse effect.
Mike
The BMS will balance under charging. If the charge voltage is reduced to lower than 14 volts, say 13.8, with a long absorbtion time, the balance may improve, as it will be able to balance for longer.
The general impression I get is that , a) the cells did not experience a correct top balance, near, but not 100%.
and b) there are conection issues at cell 1 and 2.
Note that the voltage detected at cell 1 is low with negative current and high with positive current, suggesting some resistance at buss bar to cell. Since the issue developed over time perhaps there is slight corrosion.
It may be Interconnection issues are having an adverse effect.
Mike
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Just to be clear, this pack was built in April of 2022 and was used two times before I started this thread, hard to believe age has any factor. I top balanced per instructions on this forum after those 2 trips and you are correct that the charger is set to 14.4 volts but this is not adjustable. This was a drop in replacement (Wf-8955Lis-Rep) converter for the factory charger/converter in my travel trailer, it is either on or or off, there are no settings to adjust. Considering the age (and pic) you can see there is zero visible corrosion though I highly doubt there is any at all considering the climate in Northern CA. I really do not believe this to be an issue related to corrosion of the buss bar, though I am willing to accept there may be an issue with the termination at the terminal to the BMS, I will say this is not my first wiring 'rodeo'.
FWIW - After letting the trailer run on batteries again and letting it charge and am balanced and have a voltage difference of 0.014v and a total voltage of 13.5v. I highly suspect that when I check this again in the morning things will be off.
FWIW - After letting the trailer run on batteries again and letting it charge and am balanced and have a voltage difference of 0.014v and a total voltage of 13.5v. I highly suspect that when I check this again in the morning things will be off.
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"Corrosion" could be an oxide layer between the cell terminal and the busbar. The usual corrosion that we think of with a lead acid battery is non-existent with LiFePO4 batteries. We have to deal with stealth corrosion because there is a lot of aluminum surfaces.
The oxide layer can be sneaky. My preferred way to clean the aluminum surface is with a Scotchbrite pad. Be gentle. Don't go all Rambo on it. No need to draw First Blood. Lightly buff the aluminum with the Scotchbrite pad, then clean residue from the the surface with a clean rag with denatured alcohol on it. Even more gently, do the same to the mating surface of the busbar. Tinned copper busbars shouldn't have much in the way of oxides on them. Do check the busbar for burs. The burs can prevent the busbar from making good contact with the cell terminal.
No go on the oxide layer idea, swapped out the busbar, drained down and recharged with the same exact results. This is annoying for a near new battery setup. I am not sure what the issue is, but it does not appear to be mechanical unless the busbars themselves are bad. Maybe the cells (docanpower) were not great, maybe its the charger configuration, maybe its the BMS.
You summarized the possible culprits quite well.
One test of a bad cell is to move it around in the battery pack. If the imbalance follows the cell, while keeping the balance leads in the same positions, then the cell is likely the problem. The other test of a cell is to measure the internal resistance. A special tool is required. I don't have one, nor have I ever used one.
One test of a bad cell is to move it around in the battery pack. If the imbalance follows the cell, while keeping the balance leads in the same positions, then the cell is likely the problem. The other test of a cell is to measure the internal resistance. A special tool is required. I don't have one, nor have I ever used one.
I compressed my cells per many instructions and read that I would lose any benefit from undoing that after initial charge. I may need to consider purchasing an active balancer, still need to do some research on that. I doubt I will get anywhere by reaching out to RadioB Tech.
When the cell is at a lower state of charge, say 40% to 60%, and has not been recently charged or discharged (heavily), you can take the cells out of the fixture. They shouldn't bloat at that state of charge and at rest.
Good to know, I also read the opposite somewhere... who knows
LiFePO4 cells are highly unlikely to spontaneously bloat without outside influence.
