Pitot Heat Issue

[Rotorhead]

Flying a 81 M20J around and encountered visible moisture below 10C. Put pitot heat on and received an instantaneous low volts warning, volts dropped on all eye-brow lights and the pitot-heat switch went to the 'off' position at the same time. Switched the 'Pitot Heat' and 'Strobe' Klixon switches since they are the same amps and same issue. Possibly a bad ground? Anyone experience this in flight? Any ideas? 

Currently at Spokane far away from home station.

[GeeBee]

Sounds like a dead short.

[carusoam]

Welcome aboard, rotorhead...
 

Sounds like you are attacking things randomly...

If your Pitot Heat is using a lot of available power...  it won’t be related to normal grounds or circuit breakers... these things have no resistance on a good day...

When their resistance increases, the flow through the circuit decreases...

 

It does sound like electrons are shorting to a ground without tripping a CB or fuse...
 

You can start at the heater wires at the pitot tube and chase wires back to the panel...  and start at the other end... where the CB is and chase wires from there...

If you are handy with a volt meter, you can probably find where something isn’t working correctly...

 

Good time to consult with a mechanic... loose electrons can be hazardous.

If the pitot heater is failing, it may be over heating as well...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[N201MKTurbo]

It is shorted somewhere. 
 

If the lights are dimming when you turn it on, it isn’t the breaker. 
 

Did it work OK when you preflighted the plane?

[RobertGary1]

8 hours ago, carusoam said:

Welcome aboard, rotorhead...
 

Sounds like you are attacking things randomly...

If your Pitot Heat is using a lot of available power...  it won’t be related to normal grounds or circuit breakers... these things have no resistance on a good day...

 

Not sure about that. The pitot heat normally draws a lot of power. In fact looking for the drop in amperage is generally the acceptable way to test them. The OP's may be excessive but no resistance isn't a likely goal.

 

-Robert

[carusoam]

2 hours ago, RobertGary1 said:

Not sure about that. The pitot heat normally draws a lot of power. In fact looking for the drop in amperage is generally the acceptable way to test them. The OP's may be excessive but no resistance isn't a likely goal.

 

-Robert

Good catch... so busy with the spelling issues... I missed a word... or two...

 

’A lot more power than usual....’  would have been more descriptive.

 

Thanks for the help... 

Best regards,

-a-

[Rotorhead]

Back at home and found these issues. Hoping this is the only culprit and nothing else in the wing. 

[carusoam]

Great find RH!

Thanks for the follow-up...

1) Looks like the results of heating the wires really hot... melting the insulation... could be caused by the pitot heater itself..?

2) Looks really unusual as if the insulation failed on a twisted pair of wires.... possibly by rubbing over something...?

What  are these connected to?

 

Seeing if orienting the pic changes anything...

Best regards,

-a-

[Rotorhead]

That is also connected to the pitot probe. Anyone know where to find these types of leads on the interwebs??

[N201MKTurbo]

1 hour ago, Rotorhead said:

That is also connected to the pitot probe. Anyone know where to find these types of leads on the interwebs??

If you are talking about the wire, it looks like 16 or 18 gauge tefzel twisted pair. You should verify the gauge.

 

I would just splice the wire where it is chafed and heat shrink the repair. The problem appears to be caused by the wire rubbing on something. that wire should be secured so it doesn't rub on stuff. Mooney uses little clips that clip on to the skin stiffeners. get a couple of those and secure the wire properly.