80v Kobalt battery pack for mowing machine

Thread Starter

Florian Siegrist

Joined Apr 25, 2023
3
Hey there

I do have some problems with two 80v kobalt battery-packs. the batterys are used for mowing machines. both of them are well treaten and almost new. i gues one has arround 1000 cycles and the secound probably 500. what happened:

The mowing machine everytime died after 5min work. i disambled the two batterypacks and found some dead kobalt cells. i replaced the cells and charged every cell to exactly the same voltage. sadly when i put the battery in to the mower it again died after 5min. i guess the bms cutts off to early. could there be some remembering function that didnt reset to the new capacity and still stays in "batterie dead" mode ? are there any possibilities to reset or fix a bms like this? i really hard tried to find out something about it but hadnt success so far.

I would be really really gratefull if you guys could give me some help! tanks

Salutations Flo
 

Attachments

crutschow

Joined Mar 14, 2008
34,285
What is the battery voltage of all the individual cells when initially charged and when the mower quits?
Likely it stops when the battery is below the battery monitor programmed cutoff voltage to keep from damaging the cells.

You may have more bad or marginal cells.
 

Thread Starter

Florian Siegrist

Joined Apr 25, 2023
3
Hey Dodgydave
Do you have tutorial or sth. for altering or reset? Your posted link is just the data-sheet right? Thanks for your reply anyway!

Hey crutschow
The cells are really totaly ok now! seems to be sth. different. Thanks for your help!

Cheers
 

Dodgydave

Joined Jun 22, 2012
11,285
I don't have any knowledge of this chip only the datasheet, but there are two calibration pins on the pcb for something, so see what the voltage is at these points..
 

Thread Starter

Florian Siegrist

Joined Apr 25, 2023
3
Hey Dodgydave

Thanks für your reply! What does the voltage at the calibration pins say? can i read sth. out of it? sorry, im beginner... :)

I wrote the whole datasheet and saw, that the reset could be initialised over the reset pin on the board. i also found a manual about it

https://www.renesas.com/us/en/docum...igration-guide-r8c-rl78-reset-function-rev100

i tried to deliver the low voltage with my multimeter, using diode-test-modi from reset pin to gnd, afterward bringing 5v to it via vcc +5v pin. sadly nothing happened...

its really suspencefull and complicated. Guess i just go on with reading and trying.

Or does someone have some ideas to try?

Thanks!
 

bassbindevil

Joined Jan 23, 2014
824
I'd suspect the cells before the BMS. If some cells have failed, there will be others that are weak. Most likely in the middle of the pack where they get the hottest during charging and/or discharging. New(ish) cells in a healthy pack can have capacities that are matched within a couple of percent, so failing cells suggest a pack that is on its last legs or was built with bad cells to begin with.

It would help to do a load test on each bank and see how much the voltage drops instantaneously under load. That's an indication of internal resistance. And to also do a capacity test on each bank. Some hobby chargers can do that, or there are inexpensive tester modules on Aliexpress etc. The one I got came with resistors for a 1 amp load, which is light for a 2P tool battery, but it would give you some measure of how healthy the battery is. It should be feasible to use higher power/lower resistance load resistors, though maybe you'd need an external relay or power MOSFET to handle the higher current.
 
Top