I realize I have not updated this site with any new information or video of MOSFETs blowing up lately. Despite the lack of posts, we are still working on this project. In November we were experimenting with another battery balancing scheme that involves using inductors to transfer charge between adjacent cells. I got the idea from a TI application note. While I was able to make it work on a small scale, it was very inefficient and was going to prove to be a lot of trouble to get working in a useful way. Sorry I don't have any circuits or scope photos to show you for this.
We didn't work on it a lot after Thanksgiving and during the holidays. But since the new year we have been working on the motor controller design. Progress has been made on a mechanical design and we are working on the schematic. Hopefully I will have some drawing and specs to post before too much longer.
For battery balancing I have decided to start with a shunting-only scheme. That is, when charging, cells with the highest voltage will have shunts switched on during the late stages of charging in order to let the lower cells "catch up". I have decided on this scheme in the interest in keeping things simple and achievable. Yes I realize this is somewhat inefficient since it wastes energy during charging. However I am hoping that after a few charges/balancing cycles that the pack will become balanced and not require too much shunting to keep balanced. If that does not prove to be the case then I will revisit the battery balancing problem.
I'll post more about the battery balancing circuit in the future, but I would like to get the controller design finished first.