Intercom still hot with master switch off.

[Mike McD]

HI,
When I shutdown after a flight and turn off the master switch I notice that the intercom system is still hot...is this normal? I'm having battery charging issues and just running down every possibility.
Thanks, Mike

[Andy]

HI,
When I shutdown after a flight and turn off the master switch I notice that the intercom system is still hot...is this normal? I'm having battery charging issues and just running down every possibility.
Thanks, Mike

What intercom do you have? Is it the PM3000?

How long does the intercom stay working? There is likely a large capacitor on the alternator output that may have sufficient capacity to power the intercom for a short time.

Isn't the intercom on the avionics bus on your aircraft? Are you turning off the avionics bus before the master?

[Pete D]

Hi Mike,

Andy is correct, there is a capacitor for noise filtering in the alternator circuit that can store a little bit of energy for a short time after the master is turned off. CC11 aircraft typically have the intercom (PM1000 remote) wired to the master bus, not the avionics bus.

Try this; after the master is shut off go out to the left wing and activate the stall warning. You should hear it beep for a few seconds while it bleeds off the energy stored in the capacitor. When the horn no longer makes noise, then check the intercom. As long as the master relay is fully shutting off and everything is wired correctly, the intercom should not be on with the master switch off.