Brief Description: Plane Power Alternator INOP Light
My Plane Power alternator has overvoltage protection circuitry internal to the unit. There is an optional warning light that you can add that will illuminate if it goes offline. Plane Power will sell you their light at just over $60 to mount in your panel to let you know the alternator went offline. That seemed to be WAY too much for a light, so I did a bit of research. LED lights won’t work per Plane Power and the incandescent bulb has to be a 100MA light to function properly. I bought a simple PTT light on ebay and set off on a quest for a 100MA incandescent bulb to put in it. I saw on several EAB sites that this bulb was made of “unobtanium”, very difficult to find, so don’t even try. Challenge accespted. It took about 10 minutes of an internet search and found them. Not only are they available, but they are plentiful and cheap. So for just less than $10 I bought a more than lifetime supply of 0.1A (100MA) bulbs. Here's the info on the bulbs and where I bought them: https://www.memotronics.com/box-of-10-8918-auto-bulbs-14v-1-4w-0-1a-sx6s-midget-flange-base-new/ It’s interesting on how the light works. It is wired in series downstream of a 1A circuit breaker, through the light then to the alternator, leaving an open ground internal to the alternator. When the alternator fails, the protection circuit grounds out the bulb and the light comes on. This was important in the wiring of the PTT bulb holder. The third PTT tab is wired to a ground, not a power source. So, when you test the light it just grounds out the circuit and the bulb lights.
