@saptzae (#369)
Thanks for commenting on my post (#364) about charging arrangements and balancing. The TI seminar talk on this was most interesting:
I was struck by how much remains unknown about how much and when to apply the balancing, with the resulting mention that balancing can do more harm than no balancing if done incorrectly.
Obviously, in those parts of the charging cycle where the correct action is unknown, there is the possibility of unsuspected harm from the balancing. Altho presumably small each time, it could accumulate. There is also mention that balancing of charge is more effective and more needed approaching fully charged; but that this part of the cycle is short, which limits the effectiveness. And similarly, balancing of discharge is recommended; but set up to drive a starter motor, this is not possible in the 787.
This 8-page talk has nine figures (9th didn't download for me), and is well worth reading. It is general to several battery types, but follows with some detail specific to lithium batteries. It is undated (unless I missed it). The examples seem to be small batteries (300-500mAh) in my impression, but some of the data can be extrapolated I think, altho not the experience.
One thing that concerned me was the MOSFET regulator chip idea-- if that is general and widely used, the concept would appear to vary the effective bypass by intermittently applying a fixed bybass. (Obviously a 787 battery regulator could not fit on a single chip.) During the no-bypass intervals, the effects to be avoided (e.g. lithium plating out at over-voltage on one cell) would still occur even if for reduced time. Another problem is that this circuit cannot be applied in discharge without consuming a portion of the charge capacity, if it were somehow applied except when cranking the APU.
Therefore, @USMCProbe (#460);
i agree that no charging should be done in the air, let the tow vehicles power the movement lights; and add that sufficient time and sensors should be provided to assure that the battery is cooling down after being charged.
Beyond all that, I wonder if these DC chargers are putting out currents with too much AC ripple on it (the smoothest filtering requiring heavy choke coils inconvenient to carry aloft)?
Again, I'm inclined to more effective system of very pure DC being supplied from the ground for balancing both up or down on charging, supplied as a regulated current output (not primarily voltage regulated) for each cell, based on a digital demand generated by voltage testing by the aircraft CBs. More elaborate and expensive (surely $16k would cover), but eliminates a couple more uncertainties. Of course, that may not do it, and this is not the time to be running tests (ie, in revenue service) as has been noted.