Battery not charging

val4o

1 µW
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Sep 21, 2022
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It was very cold here in CO, so I haven't used the bike for a month. Finally it warmed up a bit abd I went to check it out, bms was off, so I plugged in the charger and the BMS started, but it won't charge the battery.
Battery is 72v, build with EVE 25P 18650 2500mAh 20A, bms is ANT BMS. Temperature is over the minimum setting for charging.Screenshot_2023-02-05-12-41-42-84_425154530a3df2b6520d5742e232d9aa.jpg
 
val4o said:
It was very cold here in CO, so I haven't used the bike for a month. Finally it warmed up a bit abd I went to check it out, bms was off, so I plugged in the charger and the BMS started, but it won't charge the battery.
Battery is 72v, build with EVE 25P 18650 2500mAh 20A, bms is ANT BMS. Temperature is over the minimum setting for charging.Screenshot_2023-02-05-12-41-42-84_425154530a3df2b6520d5742e232d9aa.jpg
The screenshot shows what appear to be error logs at the bottom showing undervoltage in two separate errors in the protect section, and also in the warning section as well as one for what looks like charger current, and SOC low errors.

If those are not error conditions presently applied, I don't know why it would show them...so I would check the ohter screens to see what the cell voltages are vs the limits set in the BMS. My guess is the cell group at 2.5v is below the recharge-allowed limit. (generally, that should be the case; about 2.8v is probably a good lower limit, depends on the specific brand and model of cell, which you can use to look up the cell datasheet).

Note as well the >0.6v difference between cells--AFAICR this BMS has a setting for how different they can be to still allow charge, and the one I recall was set to a tenth of a volt, which is enough to indicate a serious difference between cell groups (unmatched cells). Over half a volt difference indicates a definite problem with at least one cell group (any groups that are not approximately the same, within a few hundredths of each other, could be considered problematic).

FWIW, 53v for a 20s pack is VERY low--below normal LVC. Your controller should have shut it off well above that, usually above 60v, probably more like 64v. If the controller LVC is set too low, the BMS has to do all the protecting, and that's not how systems like this should work--it risks cells being pushed harder than they are meant for and can damage them--even if it doesn't it will wear them out faster, and with poorly matched cells like what your pack has been built with, they will beocme more and more unbalanced and take longer and longer to rebalance as they age faster and become more and more unmatched.

Based on your previous post here
https://endless-sphere.com/forums/viewtopic.php?f=49&t=117825&p=1740759#p1740761
your pack has been badly balanced (because it's built of poorly matched cells that do not all have the same characteristics, capacity, etc) at least since your report there.
 
Screenshot_2023-02-05-15-43-53-72_425154530a3df2b6520d5742e232d9aa.jpgScreenshot_2023-02-05-15-43-58-99_425154530a3df2b6520d5742e232d9aa.jpg
Battery was charging fine, It's brand new, barely 10miles on the bike. Cells were all within 0.1v apart. I haven't used it for about t month when the temperatures dropped below 0° for a while, battery was at 74v before that. So it dropped that much just from sitting in the cold? And if i change the low voltage parameters to 2.5v it should start charging then? There's one more error in warning info, "UnitTotalRelatedProtect" any idea what that's for?
 
val4o said:
Screenshot_2023-02-05-15-43-53-72_425154530a3df2b6520d5742e232d9aa.jpgScreenshot_2023-02-05-15-43-58-99_425154530a3df2b6520d5742e232d9aa.jpg
Battery was charging fine, It's brand new, barely 10miles on the bike. Cells were all within 0.1v apart.
Not according to your first screenshot--it says they are 0.614V difference from highest (3.125v) to lowest (2.511v). I don't see any screenshots of the actual cell group readouts, so I couldn't tell you what you've got at the moment, but that's what it was at the time the info displayed on that screenshot was logged (it does not say when).

But even if they were only 0.1v apart, that's a huge difference, indicating unmatched cells (which will only grow worse with time and usage). If the pack was built right of good well-matched cells, there would be a tenth of that difference, if any.

Unfortunately "brand new" doesn't mean anything regarding cell balance, condition, etc., because it's too common for packs to be built of completely unmatched cells that will never stay in balance, and that is probably what you have there. At best the pack builders may test them to be below some level of cell resistance, and above some level of capacity--neither of those does anything to match cells. They may also sort them by voltage (which means nothing regarding cell matching, that's just a safe pack building practice).

Some manufacturers (probably not yours) even use recycled garbage cells to build packs from....


I haven't used it for about t month when the temperatures dropped below 0° for a while, battery was at 74v before that. So it dropped that much just from sitting in the cold?
Probably not. It probably has either bad cells that have self-discahrged and drained the groups they are in, or the BMS itself drained the groups (or the whole pack), or more likely there was something on the bike (controller, display, etc) still connected to the pack and draining it while you weren't using it. Or some combination of these.

And if i change the low voltage parameters to 2.5v it should start charging then?
You'd want to check the cell-manufacturer datasheet (if available) for your specific cells to be sure that's a safe voltage to recharge from first.

Assuming the cells don't have any damage and that's a safe voltage to recover from, you'd need to change any parameters that the pack or cells are not within the limits of, including the difference between cells, so that the pack/cells are then within those limits. Be sure to note down anything you change so you can put it back.

And remember--the limits they put in there are generally there for safety--when the BMS disallows charging or discharging, it is trying to prevent cell damage that can lead to a fire. ;)

There's one more error in warning info, "UnitTotalRelatedProtect" any idea what that's for?
No, you'd have to see if it's in the BMS or app manual or help, or if anyone has posted that specific term here on ES for that brand of BMS / app.
 
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