dead group in battery? 57volt on single cell?!

[maarten_almighty]

My E-bike just stopped working whilst driving along. The BMS's low voltage cutoff is set at 56volt (I have a 12p, 20s setup so 72v nominal). The bike had just been charged to approximately 65volt so the BMS's low voltage cutoff shouldn't be the culprit.

When I got home I did some measurements. The total battery voltage appeared to be approx 49volt which is very weird seeing as it was 65volt just after charging and I only rode for 5 minutes afterward so normally the battery voltage after such a distance might have been 64,5 or similar..but definitely not 49volt.
I suspected something was wrong with the BMS so I proceeded to measure battery voltage (directly on the battery plus and minus wire so 'before' the BMS, which gave me the same voltage (49v). This voltage also seemed to drop slightly when connecting the multimeter which is quite weird...

My BMS' sense wires (21 pieces total) are divided over 2 connectors (1 big connector with 16 pins and 1 small connector with 5 pins,), both connectors are inserted into the BMS side by side, the connectors with the wires labeled can be seen in the image below:

Here is a schematic of how the BMS is connected:

I initially tried connecting my charger (1Amp) because I thought the low battery voltage might be at fault.. but unfortunately, the charger did not want to work (it gave a green light indicating it was on but no red light indicating it was charging). The charger is not broken, it works on my other bike just fine (have tested before and after). Mind you this is with the BMS in between battery and charger currently.. however, the weird thing is that, with the charger connected and the controller turned on, when you apply throttle the motor turns and the light on the charger turns red (indicating it is charging, for a brief duration (the red light on the charger turns off as soon as the throttle is released).. not sure what to think of this... I could perhaps try charging the battery once to a somewhat higher voltage (above BMS' low voltage cutoff voltage) with the charger connected directly to the battery (cutting out the middlemen, the BMS in this case) but with the weird voltages I'm getting from the BMS' sense wires I am not sure if this is a wise approach...

The cells I am using: Samsung ICR18650-22P (rated for 10A continuous, I'm currently using approx 3kw nominal and I think 5kw max peak so that would be approx 70Amp at nominal pack voltage (72) which the batteries should very easily be able to handle (12p, 10A each so 120A max continuous for the pack in theory).

I measured the voltages on the bms wires (the voltages of the different cell group and all appear to be approx 3.7volt apart from 2 exceptions:
B1 3.69V (first group connected to B- on one side)
B2 3.7V
B3 3.7V
B4 3.7V
B5 0.00V <-- probably dead? or perhaps there is something wrong with the bms wires for this cell group..(less likely)
B6 3.76V
B7 3.7V
B8 3.7V
B9 3.7V
B10 3.7V
B11 3.7V
B12 3.6V
B13 3.6V
B14 57,4V <-- how can this be so high, how has it not exploded yet?!
B15 3.6V
B16 3.6V
B17 3.6V
B18 3.5V
B19 3.6V
B20 3.6V

I considered that maybe there could be a short between two BMS wires which could somehow result in the insanely high reading of 57,4V for B14... but if that were the case I would expect the wires to get hot/start smoking/having melted away by now..which has not happened (wires aren't hot or even warm (at the ends that is, near the BMS connector, I can't currently access the part of the BMS sense wires where they run inside the battery housing/compartment)...

I will try with a different multi-meter asap (when I get my hands on one) but I don't think the multi-meter being wrong is likely since all other values appear to be in the correct range (3,6..3,7-ish), nonetheless, I will remeasure with a different meter...

Unfortunately, it is quite difficult to reach the cells (i tried to make the casing waterproof inside the bicycle frame which required lots of glue/caulk but I will probably open it up soon to check if the cells themselves(when measured directly on their terminals) give the same weird readings...

what could cause these weird symptoms? Should I worry about batteries exploding? ?

 

[goatman]

im confused by where your probes are, i cant see the black/negative wire

youre just jumping your way up instead of neg probe on black wire where voltage goes up accumulatively, 3,6,9,12,15,18

at b14 you have 57.4 or 4.1v@14s.

has b13 wire shorted to ground giving the accumulated voltage? somethings definitely wonky

 

[maarten_almighty]

im confused by where your probes are, i cant see the black/negative wire

youre just jumping your way up instead of neg probe on black wire where voltage goes up accumulatively, 3,6,9,12,15,18

at b14 you have 57.4 or 4.1v@14s.

has b13 wire shorted to ground giving the accumulated voltage? somethings definitely wonky

I have added a better image of the connectors with the wires labeled
I will measure again the way you suggested tomorrow and post results... that measurement should also clarify if b13 has indeed shorted to ground...

 

[qwerkus]

Could be a simple short to main. Check bms balance wires for defects. If all are fine and soldered to the correct P group, than the bms is probably defective.