Anyone repacked a Milwaukee battery pack? Need help

[nzoomed]

Ive just repacked a Milwaukee M18 battery pack for a mate of mine that had tired old cells, was still working just had very low capacity, so i swapped out the old cells for new identical spec samsung cells, welded them all back in and gave it back.
Tool worked OK but would not recharge, had a red/green light flashing on the charger.
I thought the BMS board may have been at fault, i also heard that the boards are designed to die if disconnected from the power source.
Anyway I go and order an aftermarket board off aliexpress and swap it over, charger does the exact same thing.
They sent me a smaller size board than what I asked for but I thought I may as well hook it up to test it with, was designed for the same number of cells, just was for the 18650 sized packs, not 21700. Not sure if this would be an issue or not, but the only issue i see is the amount of current it would take to charge the batteries may be less and take longer to charge?
Im still trying to sort out with the seller to send me the correct board, but I dont want to wait another month from china.
I know these batteries are good, and load tested the whole pack with a dummy load and got 8ah of capacity as expected.
Any advice from anyone who has rebuilt one of these batteries would be much appreciated.

 

[Tony Stewart]

Some BMS chips need a re-cal via SMB tool + UART to make the Coulomb counting V profile to work in MAXIM BMS types. Perhaps this a safety feature .

 

[nzoomed]

Some BMS chips need a re-cal via SMB tool + UART to make the Coulomb counting V profile to work in MAXIM BMS types. Perhaps this a safety feature .

I can't find anything that suggests this is necessary, even watching videos on YouTube where people replace the boards, the whole thing just works.
There are even kits available with a complete case and new board and you supply the batteries and weld together, essentially the same thing I've done.

 

[rjenkinsgb]

Check the voltage on each cell? if any are much higher or lower than average, that may be upsetting the battery management board & you may need to manually charge the cells to the same voltage, eg. 3.8V would be safe.

Also double check that all the cell-to-cell junctions have the monitoring / balance connections intact, no bad joints anywhere.

(And the temperature probe wiring).

 

[nzoomed]

Check the voltage on each cell? if any are much higher or lower than average, that may be upsetting the battery management board & you may need to manually charge the cells to the same voltage, eg. 3.8V would be safe.

Also double check that all the cell-to-cell junctions have the monitoring / balance connections intact, no bad joints anywhere.

(And the temperature probe wiring).

Yes I measured the voltages and they were a virtually identical, well within the tolerance of a tenth of a volt I think.
Under charging(using my regulared power supply) or load, the voltages were all good across all cells.
Temperature probe is soldered onto the board itself when I got it.
I feel it's the way the board communicates with the charger that's the issue.
I dont know what signal it actually sends to the charger.
Would be interesting to hear from others who know how these batteries communicate.
I also wonder if the newer chargers are designed to detect aftermarket boards/batteries and refuse to charge?

 

[Sjvalleydave]

Hope you got it fixed. Just wanted to let you know I've done maybe 70 packs. Mostly Milwaukee, but done Dewalt, Makita, Ryobi, Snap On, Craftsman, Black n Decker. Only had 2 PCB die on the M18. I've taken 3Ah and rebuilt to 6Ah. Taken 6Ah to 10Ah with 21700. Never tried using a PCB built for 18650 for 21700.

 

[nzoomed]

Hope you got it fixed. Just wanted to let you know I've done maybe 70 packs. Mostly Milwaukee, but done Dewalt, Makita, Ryobi, Snap On, Craftsman, Black n Decker. Only had 2 PCB die on the M18. I've taken 3Ah and rebuilt to 6Ah. Taken 6Ah to 10Ah with 21700. Never tried using a PCB built for 18650 for 21700.

Interesting, ive read mixed reports that the boards self destruct when power is removed to prevent repacking the cells.
However i repacked a second unit with the batteries removed with no issues, so perhaps it was the board that was dead on this unit? I managed to find a supplier of the correct boards off aliexpress and the battery charges up fine, also has higher capacity cells than the original factory unit did.

 

[Nigel Goodwin]

Interesting, ive read mixed reports that the boards self destruct when power is removed to prevent repacking the cells.

We replace a LOTof batteries in commercial equipment, and quite often the units don't work after replacing the batteries, and this is due to the BMS shutting off because the batteries were too low. The answer is to 'pulse' them with a 9V PP3 battery, this brings the BMS back to life

Here's our battery 'bin' with a couple of weeks worth.

 

[For The Popcorn]

You might want to be careful with that bin! It's possible batteries dumped in there could short together and..... well you know what could happen.

 

[nzoomed]

We replace a LOTof batteries in commercial equipment, and quite often the units don't work after replacing the batteries, and this is due to the BMS shutting off because the batteries were too low. The answer is to 'pulse' them with a 9V PP3 battery, this brings the BMS back to life

Here's our battery 'bin' with a couple of weeks worth.

View attachment 144227

Thanks, I will keep that in mind for next time, perhaps there was nothing even wrong with the BMS, but i was told by others you have to put back on the charge to reset it.

 

[Nigel Goodwin]

Thanks, I will keep that in mind for next time, perhaps there was nothing even wrong with the BMS, but i was told by others you have to put back on the charge to reset it.

Sometimes, if you're lucky, you can just put it back on charge, and it will reset - but mostly, the old batteries were so low that it doesn't work, and it needs the PP3 'pulse' to reset it. It's worth considering, it's unlikely the BMS will have failed.

 

[asalek]

hi, it's my first post here and i'm a newbie when it comes to electronics. my question is to pulse the bms with the 9v battery i understand you disconnect all connections from batterries to the bms and then +/- nine volt to +/-on the bms?
thank you kindly for help

 

[asalek]

to illustrate my problem better i left my 9ah m18 on a mitre saw with the laser on over a weekend after this it wont charge and the first diode continues to blink. the charger shows full charge (green) after 1-2 seconds in the charger.
i opened the battery, removed all cells and charged them in 18650 charger. each shows roughly 4.2v now. the pack put together shows about 22v but the single diode is still blinking. on a drill the light will work for a few secs and then nothing. dropped into milwaukee chaarger it shows three out of 4 and charging but i didnt keep it there as i didn't want to overloads the cells. and here i am

 

[aldewb]

Hi I was wondering if anyone could explain the process of the 9v pp3 pulse to the bms, to reset the falt on the battery. Thanks

 

[rjenkinsgb]

Some types of BMS have a "Shipping" mode for want of a better term, where the external terminals are isolated from the cells, as when the battery is over-discharged.

It avoids accidental activation of whatever they are connected to, and can reduce self-discharge, depending on the application.

If they have that, it's generally the default state when cells are first connected after power has been off.

They switch to normal operating mode as soon as external charging voltage is detected.