what would cause a F900EX apu to gon on and offline, with APU running?


After installation of loaner batteries:

This time…. Marty departing Morristown, the apu gen came online.

After APU start, APU amps pegged on hard charge. normal.

a few seconds later, the needle came down into the green range as expected.

then the APU gen went offline, then online…..APU still running fine.

during the next few moments, the same thing happened several times.

then the APU Gen went offline and the APU shut down.

Marty attempted a #2 engine start, and the batteries were too weak to start the engine.

Next day, Batteries worked fine, Number 2 engine startfine, then:


APU started fine W/ #2 engine running.  then buss volts continued to decrease through 23 and below.


Then APU shutdown.  Then buss volts  normal.
Jody had a good idea that a very bad starter might be hitting the batteries too hard and dragging them down.

APU starter gen put in this AC for this same problem Sept. 2011, so I don’t think that is it.

October 2011, there was a APU GCU installed after “Regulating” problems.

What about the HESS. maybe a CI4


Herre is what Cats has to say: