HELP! My Pint BMS is sick.
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Hey all,
It’s been a wild ride getting to this point. I bought my first Onewheel, a used Pint (800 miles, Gemini 5050) about two months ago. I love the board, but the battery was pretty cooked, so I decided to VnR it.
Things went downhill from there. I ended up removing the VnR after repeated issues and found that my cells weren’t balancing properly. After a long balancing session, the BMS overcharged several cells, and eventually I lost one completely.
Fast forward: I had the dead cell professionally replaced this week (yes, I know that's not best practice, but I’ve got a Chi battery en route and just needed this to limp me through). After the first ride, I noticed the pack was still a bit out of balance, but figured it might be the new cell settling in.
Unfortunately, after a few more rides, the issues persisted. Cell 5 is getting overcharged again, and the new cell 6 is still lagging. I left it unplugged for a few days, and when I checked today, Cell 6 had dropped 0.4V, while all the others remained stable.
It’s looking like the BMS is bleeding the wrong cell... or worse.
So, does anyone here have a spare Pint BMS they’re willing to part with? At this point, I think it’s time to cut my losses and replace it.
Appreciate any help or guidance you can offer.
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@ikaruspint Unfortunately , I have only one Pint BMS left that I use for testing, seems like Xr, Pint BMS's are getting scarcer.
If you're in N. America, try Facebook. -
@lemur thanks for coming back to me. I'm based in Australia but am trolling marketplace in the US to see what I can find.
I'm also happy to offer up my BMS if you think you could fix it?
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@ikaruspint Here are the little mosfets that affect cell balancing.
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Thanks for coming back to me @Lemur . Here are some pics of my BMS. I thought it looked pretty good, save the bit of solder on my XT60's from the VnR. I do however think I had an overheat at some point as some of the plastic coating over the xt60's show evidence of temperature. I think this was during use though and not from the soldering or charging (I was super careful when soldering onto the XT60 legs, but you never know). The component at q15 looks like it may have gotten some heat? Also d5/c37.
How do you remove the clear coating from the PCB to access the components underneath. I have never worked on such small components as this before, do you use a solder rework station?
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@ikaruspint The conformal coating is soft and is easily removed with a toothpick, not use metal tools.
The discolored coating is normal as the conformal coating goes cloudy under heat especially at the Xt60 solder points.
Use a heat station for smd component removal, the solder on most factory circuit boards is non lead and reqiues more heat than leades solder.
