Wiring starter solenoid I terminal to GEA 24 discrete input?

[Draker]

I'd like to have a cockpit indication that lights up when the starter is engaged. Searches on VAF show the way many builders do this is by wiring a lamp between the I terminal on the starter solenoid and ground. This works because the I terminal goes to +12V when the starter is engaged.

Instead of having a lamp on my panel, I thought I would wire the I terminal to one of my Garmin GEA 24's "discrete" inputs, and configure it as active high. Unfortunately this does not work because the I terminal floats when the starter is disengaged, and the Garmin will not recognize this as "off". My thought is to wire a basic electronics 10K resistor between the I terminal and ground, to pull-down the discrete input to GND when the starter is disengaged.

Is this a sound plan?

Will this detrimentally effect the function of the starter solenoid?

What is the failure mode for the resistor? I imagine it just burns out and I'll get an incorrect starter annunciation on my panel. I'd like to avoid the possibility of a short from I to ground which would be bad.

With such a set-up, can I still connect a "starter disengage" wire between the I terminal and the starter? I believe Vans documents this as an optional method of controlling the starter activation.

[rocketman1988]

Or you could use a small relay to invert the active high to an active low.

Use the I terminal to power the relay coil. When the I terminal is high, the relay will switch on and connect the discrete to low. When the I terminal is low, the relay will de energize and break the active low to the discrete...

[Walt]

I did this experiment on a fuel pump switch once and from recollection it will take a a lower resistor maybe like 1K to pull the floating input low enough so you may have to experiment with resistor value to make it work. Even 1K will only draw about 12ma so that's not an issue. I'd use a .5W resistor mainly due to the larger lead size. You may have to go to an even lower value to make it work. Even at 500ohms its only 24ma which is 1/4W so again a half watt resistor is fine. If a resistor burns up it always opens so if you put the resistor on the contactor there's no safety issue.

[Mich48041]

R1 limits current in case wire shorts to ground.
R2 pulls voltage low when circuit is open.
Diode shorts out induced voltage spikes if there are any.
Starter solenoid will not be affected.

[Draker]

Thanks everyone for the ideas. After experimenting a little, the 10K barely worked, and it looks like indeed I'll be better off with something in the 500-1000 ohm range. I like Mich48041's circuit, probably will concoct something similar.

[Bavafa]

I don't mean to be hijacking this thread and please feel free to delete if you feel so.

I was thinking of using small relay or other method to disable the +12 to the starter relay once the engine is running, so there isn't a possibility of engaging it if the engine is running. But I can't think of a way specially that it will not prevent engaging the starter while the engine is turning but not running, like a prop milling situation in the air.

[Carl Froehlich]

Add an old fashion oil pressure low switch. Use the switch to close the relay ground when engine is not running, open the ground when it is.

Here is one of several options: https://www.aircraftspruce.com/catal...?clickkey=3855

Carl

[lr172]

Originally Posted by Bavafa

I don't mean to be hijacking this thread and please feel free to delete if you feel so.

I was thinking of using small relay or other method to disable the +12 to the starter relay once the engine is running, so there isn't a possibility of engaging it if the engine is running. But I can't think of a way specially that it will not prevent engaging the starter while the engine is turning but not running, like a prop milling situation in the air.

A bendix drive is pretty tolerant of engagement with the engine running, at least at idle RPMs. If you seem suseptible to hitting the starter button with the engine running, maybe pilot training is a better answer. What if you find yourself on final and the engine dies (low airspeed may not provide enough windmilling speed to re-start quickly) and the starter could help. Are you going to remember how to override your defeat mechanism before landing short of the runway? Assuming you have one. An OP driven relay may still lockout your starter in this example.

I fear you are adding more problems than solving with this approach. A toggle cover may be a better answer, if you are not necessarily inclined to randomly press the Starter button with the engine running, but are concerned with turbulence induced errors.

Larry