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Pitot heat indicator problem

R

Ron B.

Well Known Member
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I’m installing a Dynon heated pitot in my RV-14A. I’m at the point of testing it before buttoning things back up. The probe heats up fine. I’m using an indicator light ( not LED) that uses .07 amps while lit. I’m quite sure this indicator came with a B and C alternator , for its indicator.
With ships power on and power going to the indicator light and the white wire from the pitot connected to the other side , the indicator is not lit as it’s supposed to be. Turn on power to the pitot and it heats up. Turn pitot heat off and the indicator is still not coming on. Remove the white wire from the indicator and provide ground, the indicator illuminates.
Ideas as to what I have wrong?
Thanks Ron
 

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Ron B. said:
I’m installing a Dynon heated pitot in my RV-14A. I’m at the point of testing it before buttoning things back up. The probe heats up fine. I’m using an indicator light ( not LED) that uses .07 amps while lit. I’m quite sure this indicator came with a B and C alternator , for its indicator.
With ships power on and power going to the indicator light and the white wire from the pitot connected to the other side , the indicator is not lit as it’s supposed to be. Turn on power to the pitot and it heats up. Turn pitot heat off and the indicator is still not coming on. Remove the white wire from the indicator and provide ground, the indicator illuminates.
Ideas as to what I have wrong?
Thanks Ron
Click to expand...
Could you post a diagram of the pitot wiring so we can better offer a solution?
 
My wiring diagram shows the indicator wires to “switched aircraft power”, not ground. Verify with your diagram.IMG_0893.png
 
That’s the diagram. I have switched power from a 2 amp breaker going to one side of the lamp and the white wire to the other side.
 
Raiz said:
Is the power to the light being switched off when the pitot heater is switch off?
Click to expand...
No. It’s not designed that way. The pitot provides the ground side when it’s off or not working. While producing heat the light is off. When the switch for heat is off the light is on. If the pitot isn’t heating with the power on the light comes on.
 
FAILURE WARNING
The controller for the Dynon Avionics Heated AOA/Pitot Probe is designed to meet the
indication requirements of FAR 23.1326 by providing an output that can illuminate a PITOT
HEAT STATUS warning indicator in the cockpit whenever the probe heater is turned off or is not
functioning properly. While this is not required for Experimental and LSA category aircraft, this
feature provides feedback that your Heated AOA/Pitot Probe’s heater is working as designed.

Straight out of the manual.
 
Ron B. said:
No. It’s not designed that way. The pitot provides the ground side when it’s off or not working. While producing heat the light is off. When the switch for heat is off the light is on. If the pitot isn’t heating with the power on the light comes on.
Click to expand...
I agree that’s how it’s meant to work. My point is that there must be power to the lamp even when the pitot heater is switched off for it to work as intended. If the power to the light is switched off when the pitot heat is switched off, it would behave as you described, so that is a possible cause of the problem.

When the pitot heater is switched off, the white wire should be grounded via the controller. What is the resistance between the white wire and ground with the heater off?
 
Raiz said:
I agree that’s how it’s meant to work. My point is that there must be power to the lamp even when the pitot heater is switched off for it to work as intended. If the power to the light is switched off when the pitot heat is switched off, it would behave as you described, so that is a possible cause of the problem.

When the pitot heater is switched off, the white wire should be grounded via the controller. What is the resistance between the white wire and ground with the heater off?
Click to expand...
I have the power to the indicator from a different source than the pitot heat , and yes I verified the indicator was working with this source by removing the white wire and providing ground to the indicator where the white wire was attached. It illuminated. I never thought about checking the white wire for resistance when the power for heat was applied. I will do that tomorrow.
Thanks Ron
 
The white wire from the controller is an “active ground”. That means that you should be able to check continuity to ground when the power is removed from the pitot heat.
 
RVDan said:
The white wire from the controller is an “active ground”. That means that you should be able to check continuity to ground when the power is removed from the pitot heat.
Click to expand...
Plan to check later today.
Thanks
 
Checked white wire for ground with pitot switch off using a multimeter. No ground.
Sent help request to Dynon, waiting to hear back.
Thanks
 
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