Interesting thread. Thanks to everyone for their contributions.
How about we intervene before the pack hits that point by regularly balancing out the charge on the individual cells manually BEFORE the pack is declared dead by the BMS?
I may be wrong, but prevention may be the only route here.
Hello Craftsman,
I have locked the original V6 BMS by mistake, while trying to measure capacity directly on cells. I was running a couple of charge discharge cycles directly on the cells. Big mistake, charge/discharge must run thru the BMS. Edit: if the BMS is awake and not in deep sleep mode.
I was lucky to find at Home Depot in the recycling box another V6 battery, just last Friday. I open-it and the first thing I checked, it was already charged, at around 4.0V each cell . Checked all the cells, a bit unbalanced. Run a discharge cycle until the BMS cuts the power off. The lowest battery was at 3.3V. ( EDIT: it stops at 3.1V and in my case it slowly recovers to 3.3V) I connected a cell balancing device, used for LI-PO's, and discharged all cells to the same 3.3v.
Then charge with the charger and run a measured discharge cycle (in the picture it shows a V7 battery while testing the capacity, this V7 battery I found-it some time ago. I used-it to experiment how to re-balance and measure capacity after I locked the V6 BMS).
The V6 battery I found last week now shows a decent 1650mAh, after balancing.
I understood that the battery managing chip should be able to do balancing, maybe Dyson did not implemented the algorithm in the PIC that controls it...
So as a prevention, I believe a 6S balancing header ( i only had a 3S header to solder on the cells) that can be pulled out of the case and connect every now and then to a balancing device.
Also never try to balance by charging the weak cells, that's what kills the BMS, detecting battery voltage increase without charging. ( EDIT: I assume if the BMS is in deep sleep mode, it can be charged/balanced )
I believe it's safe to discharge to 3.4V (EDIT: 3.2V or higher.)
Never discharge lower than EDIT: 3.1V, I believe that is the threshold BMS stops the discharge by itself. Lower than that may trigger the BMS to lock.
Now that I have ordered a 6S balance header I will find a way to pass the wires safely thru a hole in the battery case.
I now have the locked BMS from the original battery to experiment on it. I also ordered the Ali BMS but I would prefer to re-program the PIC if possible to revive-it, similar with user tinfever was trying to do.
Best,