pack not charging fully


100 W
Nov 16, 2017
horncastle lincs uk
Hi all,i have a 13s pack,lithium ion not lifepo4 my charger is outputting 54.6v but the pack gets to 51v then the charger shuts off,any ideas?,thanks in advance also are the schematics for jbd smart bms's available anywhere?,i have a fried resistor on one and need its value to replace as its unreadable.
Sounds like the BMS is seeing a fault and triggering. Use a voltmeter and measure each cell group voltage. If one group is higher than the rest, it can trigger shutdown before full charge.
the battery is at 52.19v,heres the cell group voltages 1=4.105v 2= 4.015v 3=3.986v 4=4.050v 5= 3.990v 6=3.996v 7=4.201v 8=3.961v 9= 3.971v 10= 3.986v 11= 3.955v 12= 4.018v 13=3.967v,its been like this on charge overnight,my voltmeter on the bms output reads 54.56v with the charger on but goes to 51.67v when the charger is turned off .
this started after i had one cell group go to 0v,i replaced the cells and it was ok untill i went on a long ride to check it,it cut off at about half its normal range now it wont charge fully but all cell voltages look ok ish,also i have a screen via rs.485,it is new but shows connection error when plugged into the bms via rs.485, i took the bms apart and saw 2 resistors hod overheated with one end of both unsoldered from the pcb,i resoldered then but still have the issue not charging fully,should i get a new bms,this one works ok over bt but not with my 485 screen.
It is unbalanced. Bank #1 is at 4.100 volts, and bank #7 is at 4.200, while all the rest are around 4.00 volts. You say it;s been like that for a day? If the other banks are not increasing after another day, then your BT BMS isn't balancing. Might have to replace it.
It's pretty far out of balance.
Some BMS prevent charge if there is more than 0.1v difference between cells, and you have more than that.

This is because a pack with this much difference usually has a serious problem with the group(s) that are that different from the others, and is trying to prevent a problem that could lead to a fire in cases where it's because of a badly failed cell, wiring fault, etc.

If you are certain the groups that are different are ok (like if they are the ones you replaced so they're at a different state of charge), you can see if the BMS (if programmable) has a user-changeable setting for this difference shutoff, and *temporarily* change it to rebalance the pack and fully charge it. As soon as that is done, you should change it back to the original setting, so it can continue to protect you as designed.

If the problem then crops up again, you will need to deal with whatever group(s) are then causing the problem, replacing as needed.

Note that a pack cutting off at half the usual capacity probably means that one or more groups in there are seriously degraded and should be replaced, if the pack started out perfectly balanced when you began the ride. If you checked the cell voltages at the shutoff point, the ones that are lower than the others are the cause of that particular issue--they've run out of juice.

If they weren't all balanced at the beginning of the ride, then you'd have to test by first making sure they all are exactly the same to start with, at whatever SoC you start at, then ride and test and watch cell voltages--any that vary lower than others under load are degraded and are only going to get worse.
i pulled the pack apart,one nikel strip was corroded almost thru,anoyed as it was brought as pure nickel strip,anyway replaced it as matter of course,also ordered a new bms as mine had two resisters overheated with one side lifted from the pcb,i resolderd them but no difference,seems the rs485 port is dead as my new screen says communication error,funny but the bt works ok with my fone app,will try with a new bms.