Source
r/18650masterrace•
bathrobehero

Update: Stanley Fatmax battery pack rebuild: still not charging

Hey, so it's an update on this post. Now I replaced all the cells and the pack does power tools but the charger still throws an error (red blink). I can't tell any difference between measuring the 4 leads between this and a working pack.

I also couldn't find any results for buying a controller/BMS/board for this pack (FMC688L). Can I reset the controller/BMS by applying voltage manually like it is the case for some BMS when they trip? Or some kind of fuse tripped permanently and I'm SOL?

What can I do here?

Posted Jul 25, 2022, 6:10 PM UTC

74
Maleficent-Ask-8437•

Did you try measuring resistance between the pins? Usually the two outer pins are + and - while the inner ones are temperature and communications. Maybe use resistance mode on your meter and go between one of the outer pins and try both the middle pins, then go to the other outer pin and both the middle pins. Compare to good pack.

Maybe clean the contacts a bit? Possibly corroded connections not connecting well enough.

Good luck!

1
bathrobeheroOP•

Thanks! Now after playing with it more after cleaning, pin 1 and 3 measured ~1600 ohms vs ~2 (good vs. bad pack), all the other combinations are very similar. Not sure what to do with that, I'll try some more tomorrow.

2
Maleficent-Ask-8437•

Easy way to get around that is put a 1600 ohm resistor across pin 1 and 3 on the bad pack. Likely the corrosion on the cells also spread to the board and possibly corroded a resistor off the board or messed up a trace somewhere. See if you can figure out where the 1600 ohms is coming from on the good pack, ie is it a temperature sensor or just a resistor? Then just simulate the 1600 ohms with your own resistor across the pins.

1
bathrobeheroOP•

Chucking on a resistor was my first thought as well, but I don't want to do anything like that until I fully understand what I'm doing. This pack is often lended to others and I can't risk the pack to cause any danger at all.

Unfortunately I'm basically at my limit at measuring stuff with a multimeter and I can't decipher what the board does and what are its components. What I also might try is to look inside a 2Ah pack to see if I can sacrifice that for this 4Ah pack (unlikely).

My hope is to find schematics and figure stuff out or try to get a 3rd party controller/BMS that would work. Either way, short of an easy answer I'll have to spend quite some time with it.

2
Drccapri•

Any luck

1
bathrobeheroOP•

Nope.

I couldn't find anything different compared to a working pack measuring random stuff with a multimeter but I'm also a noob when it comes to components so no wonder there. And I couldn't find a source for replacement so it's on hold now.

1
joulukettu•

Hi,

I've bought a bunch of broken Stanley Fatmax batteries, 1.3Ah / 2Ah, and almost all of them have the problem where they won't get accepted by the charger, but they still do work (at least when plugged into a SF worklight)

​

On a working battery, the resistance between ground and the pin next to ground should be about 10.5kohm (this is the NTC temperature sensor value), and the resistance between ground and pin 3 (the pin next to positive terminal) should be 3.9kohm (I believe this is for the device or charge to identify what battery is connected to it - how much current it's allowed to pull or receive)

​

For a quick and crude botch job, just cut the traces on the PCB for these two center pins, and solder in a 3.9k resistor for the ID pin and an 11k NTC temperature sensor for the temperature pin. At least that's my plan on fixing these 6 batteries which I have laying around.

1
bathrobeheroOP•

Hey, thanks, I saved your comment and I'll try once I get the time though I don't have resistors lying around.

What I have ran into in the past with different battery management circuits is that once the batteries were replaced they would not work (no charge) and they'd only reset and work once I applied charging voltage directy so that's also something I'm planning to try. I just don't have the time for it now.

1