[Greenworks 80V Battery Repair]

hey morning did you ever figured out what the problem was on the bms boards?  now kobalt, greenworks and briggs & stratton are basicly the same.  i'm working on a kobalt 80v and i swap a good bms with what i thought was a bad bms turned out the bms wasn't the problem.  its the back board which connects to your tool or charger. i think i found the problem in the  TVS3 # PK708K NYK.  not getting any reading on the multimeter either way.  i made sure the solder connection were cut and resoldered and still nothing.  i will try to replaced it but hard to do with 1 half-axx hand and the other blowing in the wind.  in other words disabled.  i hope i'm right.  we'll see in about a month from now.  

[Greenworks 80V Battery Repair]

On 6/17/2020 at 2:56 PM, ryan.bunce said:

Hello all - first post!

 

I've been learning all about how these tool batteries are constructed and I've been learning how to repair them using multiple techniques.

 

I've fixed a few of these 80V Greenworks batteries by either bringing the voltage back up by jumping to another battery or by opening the pack and charging each individual cell with a hobby charger.

 

The packs I have are the 2Ah packs which are 20 18650 cells in series yielding ~80V (72v nominal).

 

I have one pack that I can charge up with the hobby charger and it works fine in the tool but when I go to charge it on the Greenworks charger it thinks the pack is bad (blinking red LED on charger).

 

If you're familiar at all with the internals of this pack it has BMS that's looks like it's split between two PCB boards - the main part of the BMS is where the charge indicator lights are.  Like most BMSes its covered in resistors that are used to discharge overcharged cells to bring the groups into balance.  The main BMS is then connected to the other end of the battery where the main discharge and charge terminals are.  On that PCB there are two MOSFETs, a couple of resistors, and some voltage regulators.

 

I have swapped the main BMS from another battery known to be good and the behavior remained the same.  I therefore suspect that something on the terminal PCB, likely one of the MOSFETs is bad.  I've tested it as best I know how with my current limited knowledge set.

 

Anyone out there have an electronics degree and can help me troubleshoot?

Did anyone reply with the remedy?  I have similar issue with kobalt 80v batteries all same they all look good charged up to 80volts put into tool and starts 1 second then dies.  I think its in the main chip not letting it discharge.  Let me know please