Master Switch Alarm

[ssokol]

This past weekend I just about did in my PC680 battery by leaving the master switch on. I turned it on to pull some data from my EFIS and some how missed it when I shut things back down. Fortunately I caught it the next morning before the battery went terminally flat.

This is a bit too easy to do: with the avionics master off, the only indication that the master is on (other than switch position) is a relatively dim light on the switch. On a bright day, or in a bright hangar, it's easy overlook. So...

To avoid that in the future, I've cobbled together a 12 volt buzzer with a relay. The buzzer is powered through the relay's normally closed contact which is tied to the main bus. The relay's magnet is tied to the avionics bus. When the master goes on, the buzzer starts buzzing. When the avionics bus is energized it stops (but all sorts of other bright and/or noisy stuff goes on). Snap the avionics master off and the buzzing starts back up.



This prototype works but is a bit too big, heavy, and loud for my taste. I may try to reduce the size and find a buzzer that is audible but not quite as loud / shrill as this one. The buzzer draws only a few milliamps, so a mini relay (rather than this full-sized auto relay) should work just fine. If anyone wants the schematic, PM me.

[1001001]

Cool idea. I wonder if one could just parallel into the stall warning or other audible warning for this. Could also be used as a door/canopy alarm.

[ssokol]

Originally Posted by 1001001

Cool idea. I wonder if one could just parallel into the stall warning or other audible warning for this. Could also be used as a door/canopy alarm.

You could definitely use it as a door or canopy alarm. You would just need a normally closed micro-switch that wires to the buzzer in parallel with the relay. If either condition was true (master on w/ avionics bus off OR canopy open) the buzzer would activate. If both are false (avionics bus on AND canopy closed) both circuits would be open and the buzzer would go off.

[Taltruda]

I like to always keep the beacon on, this way if you leave the master switch on and walk away, when you look back at the plane, you'll see the beacon still flashing. .I realize RVs typically don't have a beacon, but maybe you could leave on the Nav lights for the same effect?

[flyinga]

I just leave my strobe switch on all the time.

[climberrn]

Another option is an additional oil pressure sensor on the FW manifold. When the master is on, and the oil pressure drops below 15psi the pressure sensor grounds the LED, the light/buzzer goes on. Redundant oil pressure readings, and a simple master switch warning.

[PilotjohnS]

Like in the old days, I dont plan to have an avionics master. When the master goes on, the Garmin G3x boots up. I am using the GAD 2x to stabilize the voltages during engine start, so I dont see a need for an avionics master.

[airguy]

Originally Posted by flyinga

I just leave my strobe switch on all the time.

Bingo, that's what I do. After running the battery down twice, that is!

[Foghorn]

I'm adding an anti-collision light that is wired to my ENG BUS (SDSEFI). MSTR - ON or AUX ENG BUS PWR - ON, the anti-collision is on. I have the same setup in the 195 except it's a rotating beacon. Before I walk away from the plane I look at the beacon. It's a habit I got into years ago.

https://www.aircraftspruce.com/catal...?clickkey=7048

[fl-mike]

Low volts and Low Oil Pressure annunciators are on the master bus, not avionics.
Engine off & Master on = flashing annunciators.

A low oil pressure annunciator is easy. Just use the vans pressure switch.
https://shop.vansaircraft.com/cgi-bi...ct=isspro-hour