Possible to check individual cells while tab welded ???

[mxer125]

Father in laws 3yr old Cyclamatic is not very well...

24v battery dead according to the traffic light led's (nothing) charger just stays green when plugged in....

Anyway had it apart to check the cell voltages but all reading same voltage due to the cells tabbed 4v... So looked at the bms and disconnected the ballance plug, plugged it back in and it came back to life 27v live , Led's lighting up to full voltage and even plugged it in and it's was charging too ...

Over the weekend (without use) as he has not collected yet it's gone again

So i'm thinking a dodgy cell or two shutting down the BMS, So back on topic, Is there a way to check every cell on an individual basis without ripping all the tabs welds apart ?....Many Thanks in advance.....

 

[Deleted member 4366]

The BMS sees each string of five as a single cell. Maybe it was just a faulty connection that caused the BMS to shut down. Check all the solder joints on the balance wires because I've seen them come unsoldered before. You can't measure individual cells while they're welded, but I'd be surprised if one is faulty.

Also, theres two fuses in there. Maybe one was making a bad connection and you disturbed it during your investigation to bring it back to life.

 

[mxer125]

Ok Thanks d8veh great advice, I'll open it up again tommorrow and have another look, Two fuses has got me could only see one ? guessing there is one internally aswell ?.. Thank again!!!...

I'll report back my findings

 

[mxer125]

Ok, Can't get my head round this? one minute it's fine (bright LED's) after a strip down and check and reset BMS etc 28v. then after a while (hour or so, sitting) it's dead again 13.6v showing at terminals and have to strip and reset again (No LED's)?...It's almost like only half the battery is working ?...

When it is dead there is the 28v going into the BMS (direct) but only the 13.6 comming out, so somethings not right....

Any other checks i can make ? and is it possible to buy a new BMS (if it is the problem?) fuses checked (both) wires continuity between ballance connections etc, Now i'm lost ???...If the battery was dead (cells) then i could buy a new one but as all cells seam to be fine (28v) it's hard to part with the money...Thanks again all

 

[Deleted member 4366]

The BMS is probably shutting down because it has detected a problem. The 14v is what you measure, but you can't take any current from it. When you get 14v, what are the individual string voltages?

 

[mxer125]

when i have 14v complete pack at the terminals that connect to the bike, I open it up check the pack cells before it enters the bms and it is 27v going in and 14v comming out so lossing 14v in the bms somewhere ?....

I will check the individual cell voltages, but like i said there is always 27v comming from the pack before entering the bms, so it's the bms or a lose connection cutting the bms off....

I did notice a little browning on one of the tiny gauge wires that go to the led's to show battery level, so something may have shorted in the past ?.....The fun continues, Thanks again d8veh!!!...I will find the issue and will let you know the outcome, while i'm here is it possible to purchese a new bms here in the UK ?...

 

[mxer125]

Lol, he 's bought a new one now, So have a handfull of cells to play with , Trouble is i'm 48v so will have to find another one to benifit from them... Thanks again all