PROBLEM WITH 36V DOLPHIN BATTERY

[2old]

Precipitously, my battery (10s,5p) didn't lose any charge when stored for two weeks, whereas usually it would require 15 - 30 minutes to top off before a ride. Also, the bike runs well at lower speeds (14 -16 mph), but cuts out when "opened up" and the King Meter goes from registering fully charged to "0". Turn the battery off, restart, same occurs.
The voltage shows 41.9 from the charger and the leads from the battery. Opened the case and nothing wrong inside. Don't have the values, but each of the contacts on the BMS was 4.2 V from the previous one.
BMS problem?

 

[wesnewell]

Bad connection somewhere.
One or more cells sagging below bms lvc under load.

 

[dogman dan]

Odd set of circumstances, that does tend to make the bms not working suspect. The lack of a very slight drain from the bms.

However, if the bms was not drawing any power at all, it would be stuck off, and not run, or stuck on, don't you think?

All I can think of to do, is test the battery the hard way. You need a 36v load, and a watt meter. Test the battery capacity through the bms first. Try to see if one cell group sags more than the others under load.

When recharging, look for a cell that fills suspiciously quicker than the others too.

And look very carefully again, for a bad connection, particularly to the bms on the small wires that could be mimicking a low cell.

Only as a last resort, test the battery under load without the bms.

 

[2old]

Thank you both very much.
Was hoping not to learn how to test a system under load, but hate to toss mostly good batteries (only 30 - 40 cycles).

 

[OldTimer]

I feel your pain. Having to dissect a battery pack is a daunting task. Luckily, it paid off for me and my battery is back functioning like it should. Listen to Dogman, his advice is golden. One thing I learned is the next battery I buy will be a lot easier to open up and work on. I'll go with one like this:
View attachment 1

Rather than one like this:


Easy access to the BMS for testing is a big plus in my book.
Good luck!

 

[sonnetg]

I dont use a builtin BMS, but I do monitor my 10S4P pack very closely. I have had a dud cell at 1P. I probably damaged it while soldering the power leads. The 1P never seems to stay in balance. If i had a BMS, it would have shutdown the whole pack.

You probably have a bad cell in there somewhere. See if you can open it up and perform a discharge test. Also use a volt meter to test all the cells connected in parallel. It may be off balance somewhere along the line.