blueflyer

blueflyer

Well Known Member
I have a Mitchell float type resistive fuel sender (0-180 ohms) that I plan on wiring into my Dynon D120. Here is a picture of it.
mitchellfloattyperesistivesender.jpg


But, I also want a separate "low fuel" dummy light to be run by the fuel sender itself. My question is, how do I do that?

Thinking outloud here, I know the resistance gets lower as the fuel gets lower, so would I want the dummy light to come on at some specified resistance?? How would I make a light come on at some specified resistance? Am I making this too difficult?
 
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I'm not sure I would do what you are trying to do, but each to his own. Here is what you would need to do if you decide indeed you really do want to build this function.

You are correct that the resistance varies, but in reality the measured voltage varies as a result of the resistance change. It is the voltage that you would need to look at. There are electronic components called comparitors that compare voltages on their input and switch their output accordingly. You would need to setup a reference level for comparison against. Then when the fuel level went lower than this reference level the output would switch and intern turn on your indicator.

You can do a search for comparitor and see tons of circuits. Its just a matter of if you really want to do something like this. I would think that the Dynon status may be sufficient.
 
I have found some old posts discussing this issue and it seems you are correct. I do not want my Dynon and dummy light working off the same power source.
 
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blueflyer said:
ok, so this may not be the best idea. How have others wired up their low fuel dummy light?
Click to expand...

My fuel flow / fuel totalizator can have an alarm set that goes off when only a preselected amount of fuel is remaining. With this function, I see no need to add a 3rd redundant indicator that will add weight, cost more money, and increase the build time of the aircraft.

IF you must have a indicator light, it would be simple to buy a system that bolts in instead of designing an electronic system that will use one probe to drive both the gauge and an indicator light. Yes it could be done but more work and time that I would be willing to put into my airplane.
 
Since the fuel dummy light seems to be a little more involved than a "plug and play" application, I may not install one. I could use the "AE Fuel Gaurdian", but it would mean another hole (a place to leak) in the fuel tank and more importantly, it wouldn't fit aesthetically. I may give AE a call to see if I can cut off their yellow indicator lights and use my own LEDs.

I think between the Dynon fuel gauge and my watch, I should be able to fly without running out of gas.
 
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That does look like the most simple solution. I was just trying to think of a way to have a dummy light, but I didnt want to cut a second hole in my tank to get it.
 
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