Tutorial on protected Li-ion cells...

[Externet]

Found this, worth sharing :

----> http://www.lygte-info.dk/info/battery%2 ... %20UK.html

Now a question...

What additional circuit implemented inside a cell would allow to charge these Li-ion cells in series, from a single current/voltage supply ?

[dyarker]

A bypass. So when fully charged the transistor that connects end to inside turns off, and an additional transistor that connects end to that wire that goes to other end turns on. All current "goes around" instead of through the cell between the ends. May need a second wire on the side for bias for the circuitry in the end.

A problem would be the voltage of the cell in bypass would be applied to the other cells (in addition to their share of the charge voltage they already have). Maybe a zener in bypass that drops the same voltage as the cell being bypassed would drop it.

[Joseph]

I got a bunch of zener diodes, hoping to shunt voltage over the cell target level I wanted. Unfortunately, zeners, especially at low voltages don't turn on very sharply. The knee voltage graph curve (current vs voltage) is too far from a straight line. I think that is how to explain it.

[haklesup]

the link describes several protection technologies which presumably help prevent thermal runaway (fire) in multi cell battery packs. I don't see where this puts any limitations on series or parallel battery configurations. Presuming any of the protection devices has not activated, the cell will operate like a normal unmodified cell and should be able to be charged in series with other cells.

In fact the protection circuit provides a path around a defective cell (presumably one that has shorted) so that it is effectively disabled while not opening the series continuity of the battery pack. This is similar to Christmas lights that do not go off when one bulb burns out.

I don't think one could put any circuits INSIDE a cell but as part of a battery, this circuit does not monitor voltage apparently, only current flow so additional circuits to manage cell voltage could be used especially to manage lifetime issues. (most LiIon batteries last longest if they are maintained between 80% and 20% of capacity at all times).

Still waiting on the Note7 post mortem, was it the battery or the battery management software and hardware. I wonder if they will ever tell us.