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APU DC generator power bug


Strekaya

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There seems to be a situation regarding the APU failing which seems to be tied to whether it is being used as a standby DC power generator.

 

In 1.2.11 and prior when running the APU, power could be seen on the voltmeter when the DC selector knob was set to the standby DC generator section, even before flipping the standby DC gen switch.

 

In the most recent 1.2.12.34848 beta, there is a different behavior where sometimes flipping the standby gen switch once the APU is on causes the voltimeter to come up and show power, and likewise on the accessory (AKK) bus if the equipment test switch is on. Also, the battery voltage sometimes doesn't drop after turning on the APU (it stays at 24 VDC instead of dropping to 20-21 in prior versions).

 

What seems to happen for reasons I can't figure out is that at some point, the APU DC generator suddenly 'gives out'. The newly functional AI-9U ammeter will drop to zero, along with the DC generator voltage. If it happens during engine startup, the APU still functions to crank the engines. (Of course, I do disengage the DC generator before cranking the engines, but this has happened with using only the APU DC generator by itself, no attempt to start engines.)

 

However, after this event happens where the power drops out, the APU can't be restarted once stopped. The APU EGT never seems to completely zero out. In prior versions, I can start and stop the APU on the ground or in the air, as needed, certainly useful maintaining system power in engine out scenarios.

 

It is nice to see the AI-9V ammeter working; the only thing I noticed regarding that was that engaging the minimal circuit breakers to get the APU running and switching the DC generator, it was showing a roughly 50 amp pull, but once I turned on the minimum CBs to get the engines started, it was close to 100 amps. After a certain amount of time at that level, the power just cuts out. When I get a chance, I'll try other things like turning on spotlights and see if it cuts out quicker.

 

There was a reply in the main forum regarding this being fixed soon, but thought I'd mention it.


Edited by Strekaya
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