Current is the problem.
Exactly, but yet another to add to the list
. Looking at the figures,
a cell with greater ampere hour capacity might have been a better
choice. I wonder how many discharge / charge cycles these batteries
would experience per week and in particular, how many cycles for the
replaced batteries and those that failed ?. Fast discharge / charge
cycles do have an affect on cell aging and overall lifetime.
Designers must always interprete data sheet values. Not everything is
specified in the data sheet, but if
the cell data only graphs discharge curves up to 250 amps, then they
are implying that that rate is the maximum they have envisaged for
the component, even if the absolute limits are higher. Any half way
decent design would work well within those limits, but it seems not
in this case, or am I missing something ?.
Just to be sure that I understand your post, are you suggesting that
the inverter may have been limited to taking something like 375A max.
and was able to start the APU in 35 seconds with this limitation?
(I know nothing about APUs.)
An apu is just an engine driven generator, with starter motor. In
this case, the starter motor is dual purpose and acts as a generator
once the engine is started. Iirc, it's a 3 phase ac machine and starting
works by applying ac to the windings. In starter mode, the AC supply
comes from the battery via a dc to ac inverter, which is software
controlled to provide a current limited ramp up of power to the
motor. I dont have the figures, but the inverter dc input current will
be limited to a safe value to protect the motor, inverter and battery
from overload...