I always group my new cells by voltage, but in the midst of building a few different packs At once, I grabbed three out of the wrong pile.
So how I have a battery where the first three cells in a series are 3.7 V and the remainder are 3.5 V. I know this will work itself out in a charge balance cycle but should I manually discharge those three cells down to 3.5v ?
Edit - screw it wanted the pack cells to be balanced out the gate. I manually discharged those three cells to match the rest of the pack. Made me feel better
BMS shows voltages way off when I connect the charger vs not having the charger connected. The BMS has been disconnected from the battery and forgot som settings, e.g temp sensors etc. Have I forgotten some other setting? Charging has worked flawlessly beforeā¦
Battery has literally never been ridden since I built it and all I did was shorten each balance cable and solder it back together. I did 1 cable carefully at a time so I really really doubt I would have managed to fuck it up. And I would be utterly amazed if the spot welds have come loose by simply existing on my floor.
The pack has not been charged for some time, but wouldnāt the BMS see the possible voltage diff even without charging?! I have monitored the battery over bluetooth every now and then and seen it looks fine so havenāt bothered to put it on the charger.
Clueless. Hoping to avoid tearing the shrink wrap etc offā¦
Edit 3:
Board is not fully put together but putting load on the motors as much as I could on the bench the voltage sag is close to equal for all cells according to BMS appā¦ Drops from ~3.415 to ~3.377 on all cells, which looks healthyā¦
With the same charger?
Iāve seen some emit crazy amounts of electrical noise causing voltages to bounce around. Admittedly not nearly that bad though.
Yup I only own one charger, it has worked for years on my old board with LiPoās and worked perfectly fine to āmaintenance chargeā this (samsung 25-r 10s4p) battery 2-3 times over the last year while I have been building the board, until todayā¦I canāt make sense of it at all.
Hereās what it looked like when charging previously when I first built the packā¦ Suspiciously 1.8 A vs 2.2 now, but pack voltage is different.
Actual cell temp or BMS temp?
Getting toasty for cells but itās not probably spending a lot of time there. IMO not unexpected for Summer and with wrapped up, insulated packs with all the cells heating each other up.
Yeah Iām suspecting either the app being buggy or the app reading the old settings from before the BMS was reconnected/without power supply. So maybe a mismatch between app and actual config in BMS or whatever. I donāt know but I will of course keep a close eye at it as always. One of the reasons I moved over from old LiPos with dumb BMS was that I couldnāt easily monitor it when stored/charged etc.
Thanks! If well bonded (thermally) to one or more cells near the middle of the pack then youāll have a pretty accurate reading of max temp. Otherwise the temp could be a lot higher.
Butā¦reminding myself againā¦this is just short-term exposure.
Ok so when it worked earlier I left it like that. Now came back a bunch of hours later to actually charge, and once again cell 1,5,10 deviates a lotā¦ And charging shows 2.2A rather than 1.8ā¦
Whaaaaaaat is happeningā¦
Edit: ok and now it looks fine again. Narrowed it down to maybe the fuse holder on the + line being shit. But it doesnāt really make sense how or why that would give this issue. So it might be me making strange associations. Or maybe the charger is going bad but the symptoms seem strangeā¦
Yaā got meā¦no clue whatās going on without a lot of monitoring (sitting in front of it and monitoring charger voltage along with app voltages) and a bunch of testing to try to force the issue (which can identify the cause).
My best suspicion is it couldāve been resistance in the fuse holder. But my computer science brain canāt connect how that would give those cell voltages. Charger going wild and sending noise? The 2.2 Amps are suspicious as the charger delivers 1.7-1.8 when everything is fine. I have very little knowledge on how a BMS is designed electrically. Anyone reading this that thinks it could make sense?
At least now I am 99,9% confident the actual voltages in the pack are fine and not worried to let it lie on the floor.
Yeah, thatās one thing. But the most worrying thing is that it coincides with this
What in the holy f are those cell values and how do they get there. It would calm me quite a bit to have any sort of logical reason behind this. Makes no sense that a few cells drop to 2.5 while cell 1 goes up a lot and total package voltage dropsā¦
I get your point but the BMS and cable and battery is literally new. Never ridden, never shaken, never even been at risk of getting moist.
This is what puzzles me the most. And the balance cables obviously read fine 100% of the time the charger is disconnected. Above happened some of the time when I connected the chargerā¦
