saptzae:
Thank you for the picture of #158. It shows bypass connections which
could be used to divert small part of the charging current across
individual cells. Bypass can be used to fully charge all cells and also
lower voltage of individual cells. This contributes to explaining why
there is lots of stuff on the PCB's.
Assuming that they are bypass connections, not just voltage sensing. The
cable thickness is no guide. That technique is used on ups systems
and balances out the differences in individual cell residual leakage
current, which tends to float some cell voltages upwards at the expense
of the others. The question is, how much control range would be needed
under fast charge conditions, arguably the worst case ?.
In the lower right, at the bus bar, there seems to be a breaker used to
disconnect the battery from the bus. If so, I wonder whether it was
opened and remained open after the initial failure.
Well spotted. A breaker of that type would have a normally open contact,
to maximise contact pressure when closed. It may be driven via a
driver and logic level from the charger, or direct. If via a driver on
the logic board and there was an overheat condition, the driver could
fail and the battery remain connected.
Interesting forensics, but we still don't have enough data :-)...
Regards,
Chris