External Power Connection

[Bob Skalka]

My PA24-260 has the arrangement of the circuitry for the external power connection changed from that shown in the maintenance manual. The solenoid in line with the external power plug only activates when the master switch is turned on. The output contact of that solenoid connects directly to the battery side of the master solenoid. It is necessary to turn on the master once the external DC power is applied to be able to start the aircraft.

The Piper drawings show a diode connected to the coil of the solenoid in line with the external power plug. That diode would cause those contacts to close whenever power is applied to the external power plug. (The diode is still mounted in my aircraft but its ground connection has been removed and a wire from the master switch installed instead.) Additionally, the drawings show that solenoid's output contact connecting to the bus side of the master solenoid rather than the battery side. Applying power to the external DC connector results in DC voltage being applied immediately to the aircraft voltage bus. The starter could be activated without turning on the master switch.

I am not aware of any AD or service bulletin that made a change to the circuit arrangement for the external DC power connector. Does anyone know of such a change?

[Zach Grant L1011jock]

I'm not sure I totally understand your question, but there were at least two different ways the extenal power was wired. One was with the self activating solenoid that powered the main bus with power application to the external power plug. This did not required the master switch to be turned on. The other wiring method did not have the extra solenoid and you had to turn on the battery master to use extenal power. It sounds as if your setup is a hibrid, and is not probably 100 percent kosher, but I see no reason that it is unsafe.
-Zach

[Bob Skalka]

Thanks for the feedback. Today I had a chance to look at another 260B's setup and it was slightly different from mine. The connection from the master switch was connected through the diode connected to the solenoid in line with the external power input. The advantage of that would be that the external power solenoid would not activate if the connection to the external battery was polarity reversed.

The connection from the external power solenoid was directly to the battery, the same as my aircraft.

I agree that the connection on my aircraft is not unsafe. I was just curious as to why it might be changed from the Piper drawings.

Again, thanks for the reply.