Small update:
I came back from a ride and bizarrely, the group that was .1v higher than the rest is now .1v lower than the rest; 3.6v on 9 packs and 3.5v on the outlier. I wonder what may cause this kind of behavior…?
The only thing I can think of is that 1 of the cells in the 4p group is not connected and therefore charges faster than the rest and depletes more than the rest. However, I checked the connections on all cells in the group and it’s all reporting 3.5v.
Could be a variance in the internal resistance of the cells.
Still, I would not loose any sleep over 1/10 of a volt per cell group.
Sounds to me like your pack is discharging very evenly.
Are you discharging through the bms or bypassing?
Yea I wouldn’t either, but my pack never charges to 42v anymore. Always tops out at 40.8v which is about 94%.
I’m bypassing the bms for discharge. I think I’m just gonna chalk this up as busted BMS.
I just finished doing a full charge and now two OTHER modules are at 4.17 and the rest are 4.07-08.
Still only off by 1/10 of a volt.
I suspect this has more to do with the charger than the bms.
I think your charger is just shutting off prematurely Especially if your using one of those 2a $12 chargers
Nah I’ve tried three chargers, which are all set to 42.2v.
2 are 2A generic, and 1 is a seemingly high quality fast charger
I had 2 $12 chargers and 1 5a charger from battery supports. They all stop short. Now I 'm using my Lab power supply and I never have a problem getting a full charge. My 5a BS charger is in the closet. I keep it around in case I travel. It would be a good travel charger.
The only reason it’d stop short is if the BMS is reporting back that the voltage is matching the charger output (42.2v). I confirmed this by measuring the leads where it connects to the BMS and sure enough i got 42.2v. When I probe the side where the BMS goes to the battery I get 40.8v.
BMS’s are confusing, haha. I’m ordering some BMS’s from Bestech to replace this $15 thing.
Ok, sounds like you do have some issue with that cheap bms. I bet you’ll do better with the Bestech. Mine have been rock solid. And even though my chargers where stopping short, I was still getting 41.9 on the pack.
Finally figured out the issue. I’m so dumb, just realized the BMS doesn’t have a balance current, which means all it’s doing is detecting a module is getting overcharged and shuts off charging. Ordering a couple BMS’s from bestech with balance currents
LoL… No wonder. Well there’s another strike against those cheapo bms’s Your gonna love the Bestech with its 126ma balance current. Twice what batt sup offers. Did you order the 80a model with built in E-switch Or which model did you order?
Since I need a small one, my balance current is only 42ma, which I think I prefer since it gives the other modules time to catchup. I don’t like the idea of turning on my board to charge so I’m bypassing the BMS. It’s nearly impossible to find a high discharge BMS in a small form factor anyway. These are the two I picked up.
Nice thing about Bestech besides their quality is that they offer such a wide variety of solutions.