karrak wrote: »
I can sort of see the logic in this, I would be interested in your results
dak664 wrote: »
My take is not to balance, but take corrective action only when a cell drops below some low voltage alarm level.
But when one cell hits the low voltage alarm its time to bring it up again, preferably with a single cell charger, next best by shunting all the other cells during the entire charge cycle, next best by reducing charge current and shunting high cells when they reach 100%, and absolute worst by cycling a high current charger on and off, momentarily overwhelming the shunts then allowing them to bleed off excess voltage. Unfortunately most BMSs use the last method. A compromise might be to shunt at 90%, but only when the longer life is more important to the end user than a reduced capacity. And of course shunting reduces the overall coulombic efficiency.
So oversizing a lithium ion battery is an advantage, for fixed storage anyway. Used 30kWh automotive batteries would be a good match for a nominal 10kWh storage cycle, with excess PV not being wasted on balancing.
karrak wrote: »
This implies to me that for Electric Vehicle use you want to know as accurately as possible how far you can travel until your battery is flat, while for off-grid use you are more interested in maximising the energy you can store for that rainy day or more correctly that cloudy week while also maximising the life of the battery. To me this implies bottom balancing of the battery for EV use and top balancing for off-grid use.
In principle, I think that you could get a situation in which the CC is sending current full blast into a pack with all of it going through the bypasses and heating things up.