dolby wrote: ↑
Mar 10, 2018 6:08 pm
So the idea is to increase the voltage of the undercharged cell by repeatedly discharging all cells by running the bike wheel of the ground. The recharging process will hopefully bring the undercharged cell back up closer to the other cells until eventually they are all the same again. Is this correct?
No. The undercharged cell is discharged at teh same rate all the others are, so all you're doing is discharging it further.
For the process to do what you want, you'd have to do something that discharges *only* the fuller cells. to bring them down to the same SoC as the emptier ones.
To do taht, you have to open up the pack and connect a load across just the high ones, either one at a time or a series of groups, to drain them down without further draining the already-low ones.
If you're opening up the pack anyway, it's simpler to use a single-cell charger to bring up the low ones to match the high ones.
Should I run the bike with the wheel off the ground for longer than 1 minute or until the pack voltage drops to a certain level before reconnecting the battery charger?
No, because it's draining all cells equally, which doesn't help you.
To fix the problem without manually draining just high cells or charging just low cells, you would need to just leave the pack on the charger for the hours, days, or weeks it will take for the BMS to automatically drain down high cells a bit, restart charge until HVC on those cells happens again, drain them down, and continue that cycle over and over until the low cells charge up to match the high ones. Because the little bitty balancing resistors in tehre can only drain a little bit of charge very slowly, it can literally take weeks for a badly-imbalanced battery to rebalance itself.
And this only works if the charger is the type that automatically comes back on after it's shut off--some of them don't, in which case you have to unplug it and replug it (sometimes from both the battery and the wall) each time the charger shuts off (usually waiting a while afterward first).
The battery pack does have a balance lead however I don't have a meter to be able to read these voltages from this plug.
Multimeters are really cheap; even if they're not great you can get them for a few dollars at Harbor Freight and the like here in the USA, and HF even sends out coupons for free ones with any purchase, now and then.
Measuring each cell from soldered connections looks a bit tricky as they are all connected to each other so I am not sure how to read each cell individually.
You only need to measure each whole parallel group. There's a lot of threads about testing batteries and fixing them, at least some of which show how to test this. Fechter recently posted one way in such a testing/repair thread; can't remember which one though, so you'd have to look thru his posts for that.