High/Low Volts light on - Steady

[NotarPilot]

I recently installed a new Plane Power alternator and a Zeftronics voltage regulator last week and now the HIGH/LOW VOLTS light is staying on during the entire flight.  I've done four flights since I had the work done and it stayed on during each flight during all phases with the exception of one flight.  On one flight, done on the same day the work was completed, the light turned off half way through the 50 minute flight and stayed off.  On the two flights since then it stays on the entire time.  It did flash for a short time while on the ground before going to full power and staying on.  My A&P saw this on the maintenance run up and said it's probably just a sensor failure.

 

Prior to this the light would come on intermittently during the run up but always went out on take off power.  Any ideas what might be causing this?  I've been thinking about putting the old voltage regulator back on and seeing if that fixes it.  

 

Ammeter shows the battery is charging and the voltage meter on my Insight G3 shows 13.8 volts so everything else appears normal.  Thoughts?

[N201MKTurbo]

I would need to go to the hanger and check my collection of Mooney wiring diagrams, but I would think it is wired wrong.

[OR75]

Sensor failure ? The sensor was working before right ?

13.3 to 13.8 V is whereabout you want to be so that's good. And I take it the battery is charging normally.

Maybe a loose connection to the sensor ?

[gwcolwell]

Field wire on 74 M20F is shielded for noise issues.  Shield is conductive and will breach the insulator/barrier between the shield and the field wire, shorting the field wire and making the regulator think it's pumping lots of amps to the alternator field.  Disconnect the shield at both ends or run a temporary jumper to the alternator field and do a run up. Stick a voltmeter in the cigar lighter to monitor alt output.

[danb35]

13.8 is actually a little low (you want to be ~14.1), but that shouldn't be low enough to turn on the light.

[NotarPilot]

Sensor failure ? The sensor was working before right ?

13.3 to 13.8 V is whereabout you want to be so that's good. And I take it the battery is charging normally.

Maybe a loose connection to the sensor ?

It was working before but would sometimes come on intermittently, usually on the ground and would turn off at take off power and stay off during the duration of the flight.  Basically it would sometimes come on at very low power settings.

[Marauder]

It was working before but would sometimes come on intermittently, usually on the ground and would turn off at take off power and stay off during the duration of the flight.  Basically it would sometimes come on at very low power settings.

 

 

Your J may be different. My voltage annunciator will flash on a low voltage situation and stay on if it is a high voltage situation. If yours works the same gwcolwell's suggestion makes sense for troubleshooting.

[OR75]

why you had to change the alternator AND voltage regulator at the same time ? unusual to have both fail at the same time

[John Pleisse]

Notar...in the J model, blinking is under voltage and steady is over voltage.

[jetdriven]

Not in a 12V airplane.  Both are blinking.

[NotarPilot]

Mine stays steady for over voltage and blinks for under voltage.  I've seen it do both.  

 

The reason I changed both at the same time was at the recommendation of my A&P.  He said you usually want to replace the VR when you replace the alternator.  I didn't buy the parts through him and I changed the VR myself while he changed the alternator so he wasn't making any additional money by having me replace both.  However, the bearing was going out on the alternator and had about 1,100 hours which was why I replaced it.

[OR75]

take it a step at a time: i suggest you put back the old VR since it was working and see what happens