Is this alternator forked?

[Jim K]

I'm learning...slowly, painfully, expensively learning.

You might remember my alternator went out right before my trip, and I was saved by a friend loaning my one. Well, I decided to at least look at the brushes on my old one to see what kind of shape they're in:


Today's lessons:
-800 hours is beyond the life limit of brushes...I'm putting it on my mx schedule to replace the brushes at 500 hours.
-My shop isn't checking the brushes at annual
-The mechanic in Georgia, when I asked to have the alternator inspected, probably just took it to Autozone who spun it up and it made power

I assume this needs a new slip ring, so I might as well do an overhaul exchange instead of taking it to a local shop or even just trying to slap new brushes into it?

 

[Dan Thomas]

I'm learning...slowly, painfully, expensively learning.

You might remember my alternator went out right before my trip, and I was saved by a friend loaning my one. Well, I decided to at least look at the brushes on my old one to see what kind of shape they're in:
View attachment 108177 View attachment 108178

Today's lessons:
-800 hours is beyond the life limit of brushes...I'm putting it on my mx schedule to replace the brushes at 500 hours.
-My shop isn't checking the brushes at annual
-The mechanic in Georgia, when I asked to have the alternator inspected, probably just took it to Autozone who spun it up and it made power

I assume this needs a new slip ring, so I might as well do an overhaul exchange instead of taking it to a local shop or even just trying to slap new brushes into it?

Exchange alternator.

800 hours is pretty bad. Is this a glass-panel airplane? They use more power and are harder on brushes. The legacy airplanes would usually get more than 1000 hours out of them. Inspection requirements are typically 500 hours.

 

[Jim K]

Exchange alternator.

800 hours is pretty bad. Is this a glass-panel airplane? They use more power and are harder on brushes. The legacy airplanes would usually get more than 1000 hours out of them. Inspection requirements are typically 500 hours.

Not a glass panel. It runs about 20A in normal operation.

I was blissfully ignorant that aircraft alternators need so much attention. Alternators in ag equipment go thousands of hours at similar rpm's and higher loads.

One of the frustrations of owning an aircraft has been not knowing what I don't know. I feel like I have a good shop helping me look after stuff, but obviously they didn't check this. I'm surprised they didn't think to check the brushes as they maintain a flight school fleet that certainly racks up enough hours to wear out brushes. I'll definitely ask him tomorrow what he sees in that group.

The learning curve is steep.

 

[Clip4]

I'm learning...slowly, painfully, expensively learning.

You might remember my alternator went out right before my trip, and I was saved by a friend loaning my one. Well, I decided to at least look at the brushes on my old one to see what kind of shape they're in:
View attachment 108177 View attachment 108178

Today's lessons:
-800 hours is beyond the life limit of brushes...I'm putting it on my mx schedule to replace the brushes at 500 hours.
-My shop isn't checking the brushes at annual
-The mechanic in Georgia, when I asked to have the alternator inspected, probably just took it to Autozone who spun it up and it made power

I assume this needs a new slip ring, so I might as well do an overhaul exchange instead of taking it to a local shop or even just trying to slap new brushes into it?

Alternator brushes are not an item on most manufacturer’s annual inspection checklist. If you want time limited items checked you need to instruct the shop to perform those additional items and be prepared to pay for them.

 

[Dan Thomas]

I was blissfully ignorant that aircraft alternators need so much attention. Alternators in ag equipment go thousands of hours at similar rpm's and higher loads.

Many alternators in larger equipment are brushless. They can last a long time. We don't have that neat stuff yet in sizes to fit our little airplanes. Someday someone will offer one. https://www.delcoremy.com/alternators/alternator-features/brushless-durability

One of the frustrations of owning an aircraft has been not knowing what I don't know. I feel like I have a good shop helping me look after stuff, but obviously they didn't check this. I'm surprised they didn't think to check the brushes as they maintain a flight school fleet that certainly racks up enough hours to wear out brushes. I'll definitely ask him tomorrow what he sees in that group.

An excerpt from the typical Cessna inspection checklist from a service manual:




It seems that the typical flight school runs this stuff to failure instead of being proactive. In the end it's more expensive as well as adding risk. Worn brushes pop out of their holders and then their springs arc on the slip rings and trash them. So instead of getting a $20 set of brushes, they're buying a new $500 or $1000+ alternator.

Same goes for vacuum pumps and magnetos. They have a habit of failing just when you need them the most, and often far from home.

 

[Gary Ward]

Aerotech of Louisville Ky overhauled a alternator for me on a Monday morning after I called them on Saturday morning. They had one in stock to overhaul. My wife took our old one in as a core and picked it up at 11 am.
They provided great fast friendly service, highly recommend.

It was May of 21 and I now have almost 300 hours on it. I plan to do another exchange next year when I get to 500 hours.
Cost was 400 bucks for a ford style 28 volt 60 amp alternator.
I’d get yours and your buddy’s overhauled before you give back to him.

I have no idea how many hours were on mine when it quit working. My mechanic predicted that it would need to be serviced before it quit. He was right.

 

[Jim K]

So @NealRomeoGolf has a freshly overhauled one left over from his alternator failure saga about ~9 months ago. I'll put that one on and hope Falcon rebuilt it correctly this time. The only question now is whether I should get my bad one rebuilt now and have a good spare on the shelf or just keep it as a core. I hate to spend the money on an OH that will be out of warranty by the time one of us needs it.

My mechanic told me they replace brushes on the flight school planes every 500 hours when they do the magnetos, and send them for OH when they replace an engine. He didn't think to check mine as it wasn't at an even 500 hour interval, which I guess I can't really blame him for. The PA32 service manual lists "check condition of alternator and starter" as 500 & 1000hr inspection items.

Interestingly, he mentioned that "in the old days" when the brushes chewed on the slip rings, they would chuck the rotor up in the lathe and turn them back flat. Nowadays the time to disassemble, turn, measure, and reassemble would exceed the cost just to send it out. I have a lathe and am sorely tempted to try it, but legality aside, I can't find any specs on what's allowable, so my better judgment says "no".

 

[PaulMillner]

a flight school fleet that certainly racks up enough hours to wear out brushes.

Keep in mind that brush wear is greater where the air is thinner, at altitude. Flight schools don't average much altitude.

habe you read Mike Busch's books as a start? After those, read the Kas Thomas series!

Paul

 

[PaulMillner]

I assume this needs a new slip ring

I wouldn't assume so. You can probably hand sand it smooth, if the springs aren't rubbing on it... or it can be turned down.

IRAN is an important tool in your cost saving repertoire!

Paul

 

[Dan Thomas]

I wouldn't assume so. You can probably hand sand it smooth, if the springs aren't rubbing on it... or it can be turned down.

IRAN is an important tool in your cost saving repertoire!

Paul

The slip rings have to be concentric with rhe shaft so the brushes aren't bouncing at those high RPMs. Dressing them by hand will create small eccentricities that will cause charging issues, and arcing that makes radio noise.

I have machined them, but the rings are thin and there us little margin for cleanup. You also need a special tailstock chuck. It looks like a large drill chuck but has bronze grips in it that the alternator's shaft spins in, with a bit of lube. The chuck is stationary.

 

[baboss]

So @NealRomeoGolf has a freshly overhauled one left over from his alternator failure saga about ~9 months ago. I'll put that one on and hope Falcon rebuilt it correctly this time. The only question now is whether I should get my bad one rebuilt now and have a good spare on the shelf or just keep it as a core. I hate to spend the money on an OH that will be out of warranty by the time one of us needs it.

My mechanic told me they replace brushes on the flight school planes every 500 hours when they do the magnetos, and send them for OH when they replace an engine. He didn't think to check mine as it wasn't at an even 500 hour interval, which I guess I can't really blame him for. The PA32 service manual lists "check condition of alternator and starter" as 500 & 1000hr inspection items.

Interestingly, he mentioned that "in the old days" when the brushes chewed on the slip rings, they would chuck the rotor up in the lathe and turn them back flat. Nowadays the time to disassemble, turn, measure, and reassemble would exceed the cost just to send it out. I have a lathe and am sorely tempted to try it, but legality aside, I can't find any specs on what's allowable, so my better judgment says "no".

I'm in a similar situation @Jim K. I've got 640ish hours on my alternator and am probably going to grab an overhauled one from Spruce via Aerotech of LOU, install it, and then send my current alternator out for overhaul after the bank account recovers to have on the shelf. I've started doing this with certain components as time/$$ allows. Currently have a spare starter and mag on hand.

 

[Ted]

One of the things to keep in mind is airplanes use automotive alternators from the era they were designed. Which is to say, old. Alternators have gotten a lot better.

I put PlanePower alternators on the 310:

https://planepower.aero/

I was really happy with the results and never touched the alternators again, plus there was power right from idle. Smaller, lighter, done.

 

[Walboy]

I'm going to look into what I have as a result of this thread.