EMB-120 APU electrical load

[allflight57]

On the EMB-120 we need to have the load on the APU below 150 amps to start the engines. About 85-90% of the time, the load is already below 150A without having to shut off extra equipment (gasper, recirc fans, logo light etc.) Can someone shed some light as to why on some rare occasions without load shedding, (next leg, same aircraft) the load on the APU will be above 150A. My only guess is that it may be a function of temperature. If that is the case, I am curious as to why exactly that happens.

Thanks

[Tu.114]

I do not know the EMB, but assume that the electric system is mostly DC as well and therefore somewhat comparable to that of the DH8. That said, does the high APU load occur together with unusually high battery charging currents? If so, it might be that the batteries have been drained a bit by either having run the aircraft systems on them a while (if the previous crew was too skimpy to fire up the APU after the last leg and no GPU was in use either), or a GPU with a too low voltage output that has discharged the batteries.

When the GPU is connected, we normally disconnect the batteries to avoid this scenario and we are required to reject any GPU that delivers less than 25V. For an APU-driven engine start, we are not limited by APU output, but by battery charging current (it needs to be below 40%), and this seems to keep the APU generator happy.