Jump to content

Alternator problems

Philip

By Philip
in Vintage Mooneys (pre-J models)

 Share

Recommended Posts

Philip Contributor

Philip

Posted
Posted

Hello All,

'75 M20F

I have a PRESTOLITE ALY8420 alternator that I believe has gone bad.  I get about 13.6+- volts when at cruise setting but it can drop a little lower at idle.  Lately I have had the voltage enunciator flashing from time to time.

Today I did some test and found 10.5 volts on the field wire at the alternator, my voltage regulator has a troubleshooting light on it and it's Green (a ok).  I also tested the ohm's reading of the field on the alternator and got 9-15ohms spiking to 30+ ohms if I found the right spot while turning the pulley.  

This has led me to conclude I need a new alternator.   I have contact AirPower in Arlington, TX and they only have a reman alternator ALY8520 supplied from Cessna.  I want a new PlanePower alternator if I can get it.  Where can I get a new alternator?

 

Philip

Link to comment
Share on other sites
FloridaMan Grand Master

FloridaMan

Posted
Posted

Check the wires on the alternator. If your wires are old, I suggest replacing ALL of them, at least to the firewall, and not just repairing the connectors. They will fail again and leave you stranded somewhere when it will cost you a lot more money and be much more inconvenient. 

Link to comment
Share on other sites
N201MKTurbo Grand Master

N201MKTurbo

Posted
Posted
8 hours ago, Ragsf15e said:

Or you can get a new Planepower alt from Spruce.  I got one from them about a month ago.  Maybe $550.  Probably coulda had the brushes changed for my “airboat” but I like new vs 50ish year old and my IA won’t play that game.

My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one.

It makes me wonder what she thinks about me?

  • Like 2
  • Haha 1
Link to comment
Share on other sites
FloridaMan Grand Master

FloridaMan

Posted
Posted
29 minutes ago, N201MKTurbo said:

My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one.

It makes me wonder what she thinks about me?

Pre-EPA washing machines are best washing machines. 

Link to comment
Share on other sites
N201MKTurbo Grand Master

N201MKTurbo

Posted
Posted
5 minutes ago, Antares said:

Pre-EPA washing machines are best washing machines. 

The guy at the appliance parts store and some of the customers tell me the washer I have is the best one ever made and I should keep it going forever. That’s my plan.

My wife says she loves me because I can fix anything. She also says she hates me because she never gets new things.

  • Like 2
Link to comment
Share on other sites
Philip Contributor

Philip

Posted
  • Author
Posted
10 hours ago, Ragsf15e said:

Or you can get a new Planepower alt from Spruce.  I got one from them about a month ago.  Maybe $550.  Probably coulda had the brushes changed for my “airboat” but I like new vs 50ish year old and my IA won’t play that game.

I have been searching but can't seem to understand which PlanePower model is correct for my '75 M20F with a IO-360-A1A.  Can anyone help?

Link to comment
Share on other sites
David Lloyd Mentor

David Lloyd

Posted
Posted

Just before Interav sold out, I bought a brand new alternator from them to replace one with about 2500 hours.  About 50 hours after installation the new one quit alternating.  Problem?  The brush assembly had been installed at an angle, only 1/2 of each brush was contacting the slip rings, and the brushes were worn at about a 30 degree angle until they no longer had adequate contact on the slip ring.  So much for the new is better theory.  Got a picture somewhere, will post if I find.

Link to comment
Share on other sites
jetdriven Grand Master

jetdriven

Posted
Posted
4 hours ago, Philip said:

Ok - as long as I need an alternator, I would like to upgrade while I'm at it and believe the Plane Power AL12-P70 is the correct fit for my 75 M20F.  Can anyone confirm before I order one?

That’s the one for the M20J. It replaces the 12v prestolite. 

But seriously replace the field wire from the firewall cannon plug to the alternator. Ours was acting up but the alternator was fine. So was the VR. The center conductor was shorting to the shielding. Kills the field and stops charging.  Cost us 5$. 

Link to comment
Share on other sites
Yetti Grand Master

Yetti

Posted
Posted
6 hours ago, Philip said:

Ok - as long as I need an alternator, I would like to upgrade while I'm at it and believe the Plane Power AL12-P70 is the correct fit for my 75 M20F.  Can anyone confirm before I order one?

Call the manufacturer to confirm or use the TDS or STC

Link to comment
Share on other sites
Ragsf15e Grand Master

Ragsf15e

Posted
Posted

AL12-P70 is correct.  Ref:

https://m.aircraftspruce.com/catalog/pdf/plane-power-pma2013.pdf

Ok, generally I agree with all you guys about fixing stuff.  Brushes probably easy enough, but there’s something to be said about starting fresh too.  Maybe don’t tell your wife that-she May think you’re talking about more than the washing machine!

Link to comment
Share on other sites
Guest

Guest

Posted
Posted
35 minutes ago, Philip said:

Thanks for all your help guys!  We pulled the brushes today and they were worn down to nothing.  I have decided the easy and cheap fix is to replace the brushes.  They are ordered and should be here soon.  Thanks again.

A straight forward repair.  As others have pointed out, old field wires are a common failure item as well.

Clarence

Link to comment
Share on other sites
Guest

Guest

Posted
Posted

Commutators are in starters and generators.  Alternators have smooth copper slip rings, generally no need to turn them other than if the brush spring has made contact and scored the ring.

Clarence

Link to comment
Share on other sites
bradp Grand Master

bradp

Posted
Posted
On 12/29/2018 at 8:08 AM, N201MKTurbo said:

My wife is the same way. She says “I want a new wash machine” and I ask: “Is there something wrong with the washing machine?” And she says it works fine, but it is old and I want a new one.

It makes me wonder what she thinks about me?

Same thing today    I want a new dishwasher what’s the matter with the old one - the heater element went bad.  New heater element on the way.  The dishwasher will live to see another day.  

  • Like 2
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
 Share
Go to topic listing
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.