I’ll drop it down back to 4.25
That is much too high. It ages the cells, increases the risks of problems from dendrites and lithium plating, and offers zero benefit beyond a few extra mAh.
You set it that high? Could you tell us why?
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That gives you no noticeable benefit and lots of damage to the cells. I recommend no higher than 4.20V if charging quickly and setting it lower if charging slower.
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I figured it was just reverse sag from charging, and it would bring up the low groups while the high ones would settle back down anyway/get balanced
You should drop it down to 4.2 . You’re going to age the cells prematurely. Very significantly so. 4.3 and 4.25 is too high.
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Ok after the 1st time this was said I dropped it down to 4.2
Are there any other settings I should adjust?
If you’re setting cell overvoltage (COV) to 4.25V but it allows them to get up to a touch over 4.30V then you’re got a crap BMS. It should hard shutoff at exactly 4.25V and then the cells settle.
But set it to 4.20V. If that allows cells to get to 4.25V then set it to 4.15V. Bottom line…no cell should exceed 4.20V and lower is better if you care about the life of that pack.
Your balance settings look okay but I recommend changing charge undertemp to 0°C and the release to 10°C. You should never charge a li-ion cell when under 0°C.
No idea why your BMS is failing to balance. Check your welds, connections, solder joints, etc., to make sure the pack and balance harness is okay. If they are then the BMS is not working properly IMO.
(Edit) didn’t catch your previous post in time
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This is exactly what it does
Have done this multiple times, visually and with a multimeter, and flicking nickel strips to make sure the welds are secure.
I feel like I should just go in there, drain high groups with some load resistors and charge low groups with a 1s BMS and get them as even as possible, then discharge a bit and charge through the BMS and see if there’s any issues then.
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Better to lower your charge current instead. It prevents the cell damage you’re getting now and allows the balancing to have a greater effect. If your BMS is working properly that is.
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It doesn’t really seem like it’s not working properly, but on the chance it’s bunk I do have a replacement I can use. Just gotta change over the JST
This BMS does seem to balance (groups it shows as balancing do drop in voltage), but it seems to only balance all odd groups or all even groups, not just the high group
You said a cell, or cells, peak at a touch over 4.30V. This is not a BMS shutoff at 4.25V. Settling after the BMS turns off has nothing to do with the BMS.
You can try that but it might takes a few cycles for the BMS to reveal its issues again.
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This is when it was set to 4.35V
This is how it was set 5 minutes ago. It’s now set to 4.2V
The charging shuts off at exactly the specified group voltage or pack voltage, whichever comes first
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Many BMS’ alternate between the odd and even cells as they balance. This keeps adjacent balancing load resistors from overheating but it does slow down the overall balancing.
A BMS with 50mA of balancing current will only drain the cells at an average 25mA rate at the most. It will be lower than this because a bit of time (with no balancing) is taken in order to measure the cell voltage.
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Which setting is balancing current?
That’s way too high.
That can’t be adjusted. It is determined by the value of the resistors they use to drain the cells when balancing.
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We’ve covered this, discussed it at length and already solved the issue. Thanks for your concern.
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Is this a spec I can look for when purchasing a BMS? Or is it a brand thing? How can I tell how fast/good balancing is on a BMS?
Can I balance faster with a heatsink and TIM?
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Many BMS spec sheets will list the balancing current but it might be the value going through the resistors and not the actual average current being drawn from the cells (as I describe above).
If you can get a good photo of the BMS balancing resistors you can check their value. For most China BMS you can then take about 40% of that number for your actual average balancing current if odd/even cells are being balanced.
If just one cell, or all odd or all even numbered cells, then your average will be about 90% of the current through the resistor because the BMS will not have to alternate channels for these situations.
How well the balancing is done is up to the specific design of the BMS and you probably won’t be able to tell by just looking at the PCB or the specs. You’d have to check around for feedback from other owners of that BMS.
Theoretically…yes, perhaps. But you’d have to replace the balancing load resistors and prevent their overheating and (possibly) the overheating of the FETs driving them. Lots of trouble for not a lot of return.
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