Troubleshooting alternator?

[AlexLev]

I had to replace my alternator belt only a few months ago...today I went up to practice maneuvers and see a slight discharge and a bit of a more-than-normal whirring noise in headset.

With the landing light on, it seems like the ammeter shows a discharge, but ALT INOP doesn't light up. Bottom line, something doesn't seem to be working right. If I turn the load off, I can maybe get a positive charge in cruise, but not super consistently.

Any experience to share? I have a plane-power generator to alternator conversion.

[DXB]

Alex,

There's a trouble shooting guide from Plane Power - it is a bit complex.  My event was an alternator failure, where the alternator was fine, just a corroded contact that made me make an unplanned landing en route and Uber to the nearest train station. The Plane Power alternators themselves are pretty robust, so hopefully it's another component, like it was for me.

Dev

[AlexLev]

15 minutes ago, DXB said:

Alex,

There's a trouble shooting guide from Plane Power - it is a bit complex.  My event was an alternator failure, where the alternator was fine, just a corroded contact that made me make an unplanned landing en route and Uber to the nearest train station. The Plane Power alternators themselves are pretty robust, so hopefully it's another component, like it was for me.

Dev

Thanks, Dev. Helpful diagram. Hope you've been well!

[Ragsf15e]

Definitely use the diagram and troubleshoot it before shotgun replacing parts.  It’s more likely a cheap circuit breaker or corroded connection than an expensive regulator or alternator.  There are several threads from the last year on low voltage situations that will give you good advice.  Let me know if you need help finding them.  Definitely troubleshoot it first.  I can’t say that enough...

Theres also a troubleshooting guide on the Zeftronics website. It’s the same procedure as the one above.  Works even if you don’t have a Zeftronics VR.  The notes on the one above (left side) are important... no more than .5 V drop across any connection.  Ie, check the battery voltage (say it’s 12.6, bus might be 12.3, input to the VR maybe 12.1).  If you’re seeing bigger drops, find the point of resistance.  Also check the field voltage out of the VR and then into the alternator.  Again, should be minimal drop.

Edited October 19, 2019 by Ragsf15e

[N201MKTurbo]

Definitely do the troubleshooting guide. 

The fact that it it is making a louder whine than usual and has a low current output suggests that it lost a phase. Which usually means a bad diode or a loose connection inside the alternator.

[Ragsf15e]

21 hours ago, AlexLev said:

I had to replace my alternator belt only a few months ago...today I went up to practice maneuvers and see a slight discharge and a bit of a more-than-normal whirring noise in headset.

With the landing light on, it seems like the ammeter shows a discharge, but ALT INOP doesn't light up. Bottom line, something doesn't seem to be working right. If I turn the load off, I can maybe get a positive charge in cruise, but not super consistently.

Any experience to share? I have a plane-power generator to alternator conversion.

Is the whirring noise mechanical or  electrical noise coming through the audio?  Ie, do you hear it without the headset on?  I’m not smart enough to know how, but that probably matters.

[AlexLev]

12 hours ago, Ragsf15e said:

Is the whirring noise mechanical or  electrical noise coming through the audio?  Ie, do you hear it without the headset on?  I’m not smart enough to know how, but that probably matters.

Yup, definitely through the headset. I hear it more pronounced with the avionics switch on rather than off. and @Ragsf15e - yeah if you have the links handy to the threads from last year, that would be helpful. Thanks!

Edited October 20, 2019 by AlexLev

[Ragsf15e]

Links below.  Lots of good guidance in there but none of us had headset noise.  Do you have a JPI or other digital readout of bus voltage?  What is it in flight? If not, you can get a cheap cigarette lighter insert with digital readout as a double check. 

Based on the headset noise, You may be checking out the alternator connection or diodes like Turbo said and not necessarily the low voltage issue.

https://www.zeftronics.com/wp-content/uploads/2014/06/Z14PS.pdf

 

[Browncbr1]

I replaced the rectifier on mine, which others say produces the same symptoms..  whirring and unstable voltage.   After all the work and cost, it turned out to be a loose connection of the main alternator cable on the CB at the bus bar.   Check all power and grounds FIRST before jumping to conclusions on defective parts.  

 

[Ragsf15e]

2 hours ago, Browncbr1 said:

I replaced the rectifier on mine, which others say produces the same symptoms..  whirring and unstable voltage.   After all the work and cost, it turned out to be a loose connection of the main alternator cable on the CB at the bus bar.   Check all power and grounds FIRST before jumping to conclusions on defective parts.  

 

I have a similar story about replacing a bunch of stuff and then finding the problem was with an old circuit breaker.  Troubleshoot first.

[N201MKTurbo]

Being a CB, I always start with the cheap (free) fixes first and work towards the expensive ones.

[carusoam]

lotso alternator whining... is usually  or often, a diode in the bridge... sensitive to rpm?

The bridge that turns the AC to DC... is usually found as part of the alternator, or supporting the alternator...

When they fail, they look like they failed... visual inspection may be all that is needed...

Kind of like a summary of what is posted above... 

Best regards,

-a-

[Ragsf15e]

51 minutes ago, N201MKTurbo said:

Being a CB, I always start with the cheap (free) fixes first and work towards the expensive ones.

Next time, I’m gonna show up at your hangar and ask for help.  6 pack in hand of course.

Edited October 21, 2019 by Ragsf15e

[AlexLev]

Great news: was a just a loose alternator belt, which proves that neither me nor my CFI knows what a loose alternator belt feels like!

Edit: Mooney maintenance manual is on point as well - it calls for a retorquing of a new belt after 25 hours of flight operation. My belt was replaced exactly 25 hours ago and definitely needed to be tightened. 

Edited October 21, 2019 by AlexLev

[Ragsf15e]

3 hours ago, AlexLev said:

Great news: was a just a loose alternator belt, which proves that neither me nor my CFI knows what a loose alternator belt feels like!

Edit: Mooney maintenance manual is on point as well - it calls for a retorquing of a new belt after 25 hours of flight operation. My belt was replaced exactly 25 hours ago and definitely needed to be tightened. 

I probably would’ve had a new alternator, voltage regulator and master switch.  You got nothing new out of that whole episode!