Replacing an InterAv alternator

[Matt Ward]

I've got an InterAv 015-01237 alternator in my 1966 M20E.  It's got about 1300 hours on it and is 16 years old and is starting to wear I think.  The reason I say that is that I'm getting consistent crackling static in my 430W that is eliminated by pulling the Alt Field breaker.  My JPI shows consistent 14V and I haven't seen any anomalies in my engine monitor data.  I also haven't noticed any noticeable performance degradation in flight of my electronics.  My guess is the alternator is telling me a diode is bad and before it totally dies, I want to look at replacing it.

What are the best options for this given that InterAv is no more? 

I think QAA will overhaul them but should I look at moving to a different alternator altogether?  I've got the Plane Power voltage regulator and I think they make some sort of kit but I'm fuzzy on if that's the right option or not.

Thanks for any help!

 

[Andy95W]

The Interav alternator and PlanePower voltage regulator is a great combination and nearly bulletproof.  

Most likely you have either a diode going bad like you mentioned, or worn brushes that are starting to arc.  An alternator overhaul will fix all of that for less money than any other option.  It's a common enough alternator that multiple vendors will work on them.

Let us know how it goes!

[Matt Ward]

Thanks.  I think you're right.  QAA has an exchange for $495 which seems like the best option. I'm going to leave my Plane Power VR in place - no reason to replace it right now, I don't think.

[David Lloyd]

Remove the brush set and take to any old alternator shop.  Very common alternator, they will have the brushes for less than $15.  If asked, they would tell you to clean the slip rings a bit with a scotchbrite pad, install the brushes and run for a while at no load.  If you are energetic, take the alternator and they will check it over and repair as needed for less than $100.

[Yetti]

5 hours ago, David Lloyd said:

Remove the brush set and take to any old alternator shop.  Very common alternator, they will have the brushes for less than $15.  If asked, they would tell you to clean the slip rings a bit with a scotchbrite pad, install the brushes and run for a while at no load.  If you are energetic, take the alternator and they will check it over and repair as needed for less than $100.

for your airboat engine

[BDPetersen]

Or tractor. Alternator shops are aircraft averse.

[Yetti]

19 hours ago, BDPetersen said:

Or tractor. Alternator shops are aircraft averse.

InterAv = airboat.   Presotolite = tractor

[BDPetersen]

No wonder they knew I was lying

[jamesm]

or you could say it is from your "off road vehicle"

[Vance Harral]

Before going to the trouble of pulling the alternator, first check that all devices connected to the audio panel have secure ground connections.

I say this because we just came out the other side of a 9-month saga trying to chase down crackling/squealing noises in our airplane, with symptoms exactly like yours, right down to the problem going away when pulling the field breaker.  Our efforts included an alternator IRAN which did absolutely nothing to solve the problem.  It was a PITA to get the alternator out (requires removing the lower cowl, at least on an F model), and extremely disappointing to go to the time and expense of the work of doing an alternator R&R with no success.

In the end, the problem turned out to be a loose ground wire on our voice annunciator.  Zero dollars and 15 minutes to fix, including R&R'ing the glare shield.

Edited August 8, 2020 by Vance Harral

[carusoam]

Great details, Vance!

For an interesting conversation and pics of where ground wires can be found....

Brad posted some pics yesterday... I learned a few things to look for... 

Best regards,

-a-

 

[Matt Ward]

On 8/7/2020 at 6:44 PM, Vance Harral said:

Before going to the trouble of pulling the alternator, first check that all devices connected to the audio panel have secure ground connections.

I say this because we just came out the other side of a 9-month saga trying to chase down crackling/squealing noises in our airplane, with symptoms exactly like yours, right down to the problem going away when pulling the field breaker.  Our efforts included an alternator IRAN which did absolutely nothing to solve the problem.  It was a PITA to get the alternator out (requires removing the lower cowl, at least on an F model), and extremely disappointing to go to the time and expense of the work of doing an alternator R&R with no success.

In the end, the problem turned out to be a loose ground wire on our voice annunciator.  Zero dollars and 15 minutes to fix, including R&R'ing the glare shield.

This is really good info. I'd like to check this out regardless of what I do with the alternator.  I'm not exactly sure on how though as my time behind the panel is extremely limited.  Would asking my A&P to "check for any loose ground wires" be the appropriate way to frame this?

[philiplane]

brushes are cheap and the alternator doesn't usually have to come off to change them. These alternators are Prestolite/Leece Neville/Motorola products and parts are widely available, in the rare event they wear out. Brushes should be checked and or replaced at 1000 hours on any aircraft alternator. We do them at 500 hours on Cirrus (Hartzell alternators) that have air conditioning because the brushes wear twice as fast. Worn brushes cause radio noise because there is insufficient spring tension to keep them from bouncing on the slip ring. That causes sparking, which is what will kill your rectifier assembly.

[Matt Ward]

Just now, philiplane said:

brushes are cheap and the alternator doesn't usually have to come off to change them. These alternators are Prestolite/Leece Neville/Motorola products and parts are widely available, in the rare event they wear out. Brushes should be checked and or replaced at 1000 hours on any aircraft alternator. We do them at 500 hours on Cirrus (Hartzell alternators) that have air conditioning because the brushes wear twice as fast. Worn brushes cause radio noise because there is insufficient spring tension to keep them from bouncing on the slip ring. That causes sparking, which is what will kill your rectifier assembly.

Thanks for that.  Would you say radio noise is predictive of a pending (short time frame) alternator failure?

 

[Vance Harral]

5 hours ago, Matt Ward said:

Would asking my A&P to "check for any loose ground wires" be the appropriate way to frame this?

"Check for loose ground wires" is far too generic of an instruction.

If you want a quality job, explain that you want to pay the mechanic for several hours of labor to remove access panels and glare shields, identify the ground leads from every electrical device in the airplane (again, the ones that output audio to the audio panel are of particular interest), carefully trace them to their terminating connectors, inspect the wiring along the way, and gently finger-twist the terminating screws to ensure tightness.  Not all mechanics will agree to do this.  Some simply don't want the job because it's tedious.  Others are too afraid of breaking something new that used to work during the inspection process.

If you just ask an A&P to "check for loose ground wires", I expect in most cases they will remove and touch nothing.  Rather, they will likely just peer under the panel from the foot wells with a flashlight for a few minutes, and then say something along the lines of "Well, I didn't see anything, but you never know".    Usually this service is thrown in for free while working on something else.  It's worth what you pay for it.

[Raptor05121]

On 8/7/2020 at 7:44 PM, Vance Harral said:

Before going to the trouble of pulling the alternator, first check that all devices connected to the audio panel have secure ground connections.

I say this because we just came out the other side of a 9-month saga trying to chase down crackling/squealing noises in our airplane, with symptoms exactly like yours, right down to the problem going away when pulling the field breaker.  Our efforts included an alternator IRAN which did absolutely nothing to solve the problem.  It was a PITA to get the alternator out (requires removing the lower cowl, at least on an F model), and extremely disappointing to go to the time and expense of the work of doing an alternator R&R with no success.

In the end, the problem turned out to be a loose ground wire on our voice annunciator.  Zero dollars and 15 minutes to fix, including R&R'ing the glare shield.

I just had this issue. Cracking on the radio that goes away when the alternator is disconnected. Pulled the unit and sent it out for service. Brushes were at 80% length and diodes were good. In reinstallation, we cleaned all the terminals and degreased all the wires and made sure everything was hunky-dory. After reinstallation, we fired up the plane and the problem disappeared.

[carusoam]

Brushes sliding on the rotating shaft can have some sparking when it is less than perfect... those sparks will become audible as crackles...

When diodes go bad you get a completely different sound...

Interesting fingerprinting of alternator issues...

Pp thoughts only, not a mechanic...

Best regards,

-a-

[cliffy]

With brush wear and arcing comes slip ring wear and truing on a lathe is the only way to really smooth out the slip rings. Just replacing the brushes is a temporary fix. Been there, done that several times. 

You can try just the brushes but don't expect a final solution until you overhaul the unit. Think about it, it has 1300 hrs and 16 years. Its given itself up by now. Its had a good life. Another thought. how old is your battery? Have you ever had it capacity checked? Has it ever been run flat so the engine won't turn over? Now you "fix" the alternator quick and dirty and what if it gives up mid flight again? What if its IFR? How much REAL capacity does your battery have in it? 

I have one also. Its a good alternator. Did the brushes and 2 years later did the swap out to a  much better outcome. You'll get 1,000 hrs on the swap out. You won't get that on just brushes. Think about it if you fly any IFR. 

[FloridaMan]

Also verify it isn’t any of the wires on the back of the alternator/regulator. Those tend to break at the connector when they get old. 

[Matt Ward]

It was definitely the alternator.  Replaced it and the crackling is all gone!  And that alternator was *done*!  As in, broken blades done.  I'm really surprised I got my core charge back but I did.

[cliffy]

If no one has ever noticed you might look at the way the front fan "pulls" the air from inside the cowl out to the inlet of the cowl for cooling. Motorola makes a fan for the other direction but I talked with an Interav engineer many years ago and he confirmed that that was the way they wanted it work. 

[carusoam]

Great follow-up Matt!

Thanks for sharing the details...

Best regards,

-a-