kiev wrote:The only way i can see for smoothing to be effective is to turn on all the balancers except for the lowest cell and try to bleed them down to the target value. This could be done at any SOC while the car is stationary and not charging.
If there were any charging currents greater than 0.1 Amps, then the cells would continue to be charged even with bleeders on.
My "guess" is that the balancers "bleeders" are locally controlled by the module BMS board based on individual cell voltage values. I've never seen a BMS system that works any other way. It's significantly more complicated to centralize it more than that. In smaller applications, I've dealt with, dissected, studied, and learned to trick BMS circuits of many stripes over the last 12 -13 years. By reducing the charging amperage we could always get the "bleeders" to run 3 to 20 times longer before a BMS initiated charger disconnect.
Newer BMS systems can also include a minimum amperage charge rate to continue charging, which complicates the process of "voltage smoothing" by this lowest possible charge rate method.
Mitsu installed a very low amperage Balancing circuit in their battery BMS. Or perhaps better stated, Yuasa did. They also did not include the ability to set the car to stop charging at less than 100%. The implication is that that frequent 100% SOC charges are best for maintaining cell balance. My own experience with the cars battery packs, supports this assumption. The older a pack is, the faster it will drift out of balance. Individual cells age differently, so cell efficiencies diverge over time resulting in greater variations over time and cycles. The least efficient cells are less efficient on both discharge and charge cycles, further exacerbating any disparity.
If there is evidence that the Yuasa BMS works differently than others, I would love to see it! A floating target, or bleeder initializing voltage would be a huge improvement. I suspect that Tesla may have this built into their BMS.