JeremyB Posted June 17, 2020 Share Posted June 17, 2020 Like the title says, I need to know what voltage my 100V Monster starts balance charging at. I built myself a 6amp charger and I'd like to set the voltage halfway between where it starts to balance charge and the max 100.8v Quote Link to comment Share on other sites More sharing options...
mrelwood Posted June 17, 2020 Share Posted June 17, 2020 (edited) While I don’t know the exact voltage, what I would consider is that: - On BMSs that the threshold has been examined on, the balancing threshold seems to be at or very close to 4.2V per cell. - The components that determine the threshold have large manufacturing tolerances. - The equipment you will use to set and measure the threshold also have large tolerances. It’s not uncommon to have a tolerance of +-0.5V or even +-1V for 100VDC measurement on a $100 multimeter. (Edit:) - So far no one has reported a wheel being rendered useless due to aged cells. But there are numerous cases of dead battery packs due to insufficient balancing of cells. Edited June 17, 2020 by mrelwood 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted June 17, 2020 Share Posted June 17, 2020 6 hours ago, JeremyB said: Like the title says, I need to know what voltage my 100V Monster starts balance charging at. There is not really such a thing as the BMS would start balancing the pack. It is just a resistor in parallel to the cells at and above 4.2V. So if all cells are balanced it starts at 25*4.2V=100.8V. The more the cells are out of balance, the earlier it starts. The current these resistors can bypass is not too much - so if the cells are too much out of balance the first cells getting the bleeding resistor activated have good chances to be slower, but still charged up to ~4.25V. At this point the cell overvoltage protection kicks in and cuts off the charge input - so no charging or balancing happens anymore. One can try in such cases to discharge the battery a bit and charge it again. With some luck after a couple of such small discharge/charge cycles the battery could get balanced again. But this balancing system is very limited and can only balance small differences each time - once cells differ too much they have to be replaced. (Or the whole pack) 6 hours ago, JeremyB said: I built myself a 6amp charger and I'd like to set the voltage halfway between where it starts to balance charge and the max 100.8v ? I could not see why one would like to do this? But maybe i'm missimg something? More details on battery packs/bms: 1 Quote Link to comment Share on other sites More sharing options...
RagingGrandpa Posted June 17, 2020 Share Posted June 17, 2020 16 hours ago, JeremyB said: I built myself a 6amp charger and I'd like to set the voltage halfway between where it starts to balance charge and the max 100.8v Far better to let it CV at 4.2V/cell and then to stop charging at a specific current value. I suggest stopping at [P-number x 50mA], to provide ample opportunity for balancing. 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted June 17, 2020 Share Posted June 17, 2020 (edited) 4 hours ago, RagingGrandpa said: Far better to let it CV at 4.2V/cell and then to stop charging at a specific current value. I suggest stopping at [P-number x 50mA], to provide ample opportunity for balancing. Batteryuniversity.com suggests 3% C - which would be 3500mAh * 3%= 105mA per paralleled cell. I'd assume that this number from batteryuniversity is just a rule of thumb and so anything in about this magnitude should be ok - according to ones personal preferences. Edit: this post is my way to agree to yours . Edited June 17, 2020 by Chriull 2 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.