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.
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.