48V 23,2Ah pack: voltage instant drop

[Souvlucky]

Hi everyone,
Although an amateur with batteries and electronics, I have been reading your forum with much interest lately.
I have an issue with a brand new e-scooter whose battery is likely problematic.
The battery is an "48V 14S 23,3Ah" and most likely from my reading includes 14 LiFePO4 18650 cells, however I still don't know of model or brand exactly. Apologies for this lack of info.

The situation is as follows:
-The e-scooter and its LCD can only light up when the unit is charging
-When the unit is charging and can be turned on, both its motors are in functioning state when the throttle level is pulled, and pulling the brake levers activates as it should an indicator on the LCD. This makes me think the problem is not cables, pin adaptors, the LCD, but has to do with the battery
-The charger when connected to the socket outputs 58,7-58,8V (tested on multimeter)
-The battery when charging displays 58,7-58,8V (green-red-green-red blinking of the charger, which from what other users of this specific e-scooter tell me usually means battery is ready/charged)
-It seems the battery does not want to hold a charge above ~56,7-57,1V, although the voltage is 58,7-58,8V when it is being "charged"
-Once the scooter's charger is unplugged, the multimeter shows the battery's voltage drop (from 58,7-58,8V which is the voltage when charging to 56,8-57,0V - the voltage stays there afterwards)
-When I try to turn the scooter ON (while it is not charging), the LCD and unit will not switch ON and the multimeter will show a battery voltage drop/freefalling from the levels it was* almost instanteously down to less than 14-12V (*again the maximum voltage reached by the battery so far has been ~57,0V, even after 2 days of continuous charging)


Right now I am thinking:
1) A BMS cut-off due to a possibly undercharged cell/-s (Low Voltage Protection) ?
2) A fuse burnt on the BMS (need to change whole BMS ?)
3) A cell or two having activated their Short-Circuit Protection (need to find someone who can individually dissassembe the pack and its plastic and test each cell?)

(Note the unit has a DC-DC converter for its LED lights and they are not lighting up, so perhaps this has something to do with the whole problem ?
Also the cables are HOT and not fused. This leaves the BMS fuses as the first guard of defense of the cells in case of sur-tension or anything, perhaps from the DC-DC converter)

Any help would be highly appreciated

Edit: I have tried leaving the charger over ~2 days on the unit to try and balance any possibly under-charged cell in the pack, unfortunately that did no help the situation (the battery's voltage was still 57,0V-57,1V max.)

 

[amberwolf]

It's unlikely the cells have individual protection, the BMS is there to do that.


Probably it's a bad cell or cell group triggering BMS shutoff, or a connection from the BMS to a cell group is bad, so it doesn't know there's a problem, or thinks there is one when there isn't.


FWIW, a badly-unbalanced pack could take weeks to charge correctly.

If it's LiFePO4, then each cell should be around 3.6-3.7v during balancing, when charger is at peak voltage. If that's 14s, then that would only be about 51-52v or so, and your charger would not need to be anywhere near as high a voltage as it is set for.

So it's unlikely to be LiFePO4, and would probably be some other chemistry with a higher voltage (most commonly around 4.2v/cell when full/balancing). For those, 14s would mean 58.8v, which would be what your charger is setup for, and so is probably what you have.

56V or so if all cells were equal would be about 4v/cell, which should have plenty of energy left, so if it doesnt' operate at that voltage then a cell/etc would probably be not charged, for whatever reason (or just bad).


You'd have to open the pack and measure group voltages. For the general method, just look up some of the many other battery troubleshooting threads.