Hi.
I’m looking for a clear explanation of what every button of a Cessna 172 switch panel does.
In particular I don’t:
- what DIMMING knobs does ?
- what is it for STBY BATT ?
May you help me?
Thanks in advacne.
The dimming switches control the lights to the various sections of the aircraft.
The green SW/CB switch controls lighting to the switches and circuit breaker area. The Orange controls lighting to the standby instruments. The red controls the pedestal light in the area of the fuel selector valve. The other rotary dial controls to a limited degree, the lighting of the MFD/PFDs.
The battery switch controls a standby battery in case you lose battery or alternator/generator function with the normal primary battery. If you’ve lost the alternator or generator, you’ll only have limited time that the standby battery will support the applicable functions. The engine will continue to work even without a battery thanks to the magneto’s.
Regards
2 Likes
Dimming is to brighten or dim the lights behind the switch/circuit breaker panels, the standby instrument cluster, the center pedestal (flaps, fuel selector, and trim wheel area), and avionics (all the backlit buttons, pushbutton LEDs, and the G1000s themselves). Try it at night to see the effect!
The standby battery is used to power the essential bus if the main battery fails. This includes the PFD of the G1000 (which will operate in a reversionary mode), AHRS and ADC 1 (the system that tells the airplane its orientation), NAV 1 and COM 1, plus the standby instrument lights.
Before you turn on the main battery in the preflight, put the standby in test mode for 20 seconds to make sure the green light stays lit, then switch it to ARM. This will power up the PFD in that reversionary mode I mentioned above, which will give you engine gauges for engine start. In this configuration, the G1000 is isolated from the battery/alternator and the electrical transients that can be encountered during startup. After the engine start sequence, turn the avionics switches on and the MFD will now come on (and the engine gauges will move over to that). Leave the STBY BATT in ARM for the whole flight to charge it and in case the main battery fails.
2 Likes
Here is a very nice “INTERACTIVE” c172 Cockpit electrical circuit Simulator, that will answer most of your questions about what the switches do, and give you a good understanding of what they do electrically, when they are operated.
A really cool web app.
http://avitmedia.aero.und.edu/c172sElectrical/index.html
Click on the switches (in the above Linked web app) , to see what they do !!
Shows exactly what the Standby Battery is all about, and its associated switches.
(Does not detail operated devices, like the actual lights, or their dimming circuitry)
Thank you “University of North Dakota”
2 Likes
See also Interactive Trainers | Department of Aviation | University of North Dakota for more interactive training tools 
1 Like
I’ll try it.
Thanks