Repairing alternators?

[cbvet]

I've got 2 dead alternators, which I'd like to repair for spares. One is a Leece-Neville, the other a Prestolite. There is a shop nearby that will rebuild them for $150, but that's more than I want to spend. Has anybody ever worked on these?
What usually goes bad in them?
Where can you get parts?
Thanks,
Eric
CBVET

 

[ken]

I've never had good luck with alternators. They usally only last me about 18months. I had rebuilt here at a leece neville shop. It cost me about $150 also. I'm thinking of tring a 100amp and see if i get better service.

 

[bottleworks]

I had the internal regulator on my Prestolite model fail. I know another person on here also had his Prestolite regulator fail. Get out the DVOM and find out what failed in your units. Link below...

http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=8035&highlight=regulator

 

[therbert]

The first important thing to know about high power alternators is they get hot. External regulators should be used and mounted inside the cab. In a cooler enviroment. I would say they fail the most of any part.

The second item that gets killed is the rectifier assebbly. If you know anything about electronics. Look at digikey.com and find a 100 Amp diode. You will notice it is huge compared the one installed internally. Usually with a 1/4 20 thread or bigger. The internal ones are under rated assuming you wont use them at full load for more than the duty cycle. Each internal rectifier has 6 diodes. My suggestion is to do this external as well. They can be mounted outside or inside. Try not to mount in the engine comp.

Bad regulators usually fail in two ways no power or shorted at maximum power. When it is outputting maximum power. You may not know. But your rotor winding will. It will usually breakdown after a few hours over over voltage. Especially when you are using a boost regulator that sends more than 13.8 volts.

Staters don;t usually fail unless you have a bad load or lots of inrush on a larger power item. Bad Batteries can cause a stater to fail.

You can test for theese problems very easily.

You can test the regulator with a simple volt meter. Make sure the output is at or around 13.8 volts. If that is what you get, it is most likely good.

Most Prestolite and Leece-Neville alts have 3 phase conections on the back where the regulator would connect. Using the AC setting on the volt meter test for voltage between all three connections. You should see about 14 volts more or less. If you see that it is most likely OK. ( May have a break down under load, not easy to test without a load)


Rectifiers can be tested by using the diode setting on the meter and checking for .540 one direction and the other should be 1 or a dead short. If yoy get nothing both ways you have a open rectifier. If you get a 1 or short both ways you have a shorted rectifier.


Hope this helps.. I have years of experience with them from the mobile power market. I have built truck with more power than you could ever use..

15 Leece-Neville alternators with staged and boosted regulators is the largest I have ever worked on.

 

[OPCOM]

15 Leece-Neville alternators with staged and boosted regulators is the largest I have ever worked on.

The only thing I have ever seen more than two of those alternators on was a suburban with a 5000 watt bootleg CB radio setup. He had to give it some gas when he keyed up..

 

[readyman]

cbvet,
I started working on mine. It's a Prestolite AMA 5104 with an internal regulator. One thing leads to another. First the obvious, the brush wires were frayed and disconnected, connected them up and it still didn't work. Checked all the diodes with seemed ok, infinite resistance one way 1.3megs the other way(seems high tho), still didn't work. Noticed that the pulley bearing was worn and gettin' real sloppy, which probably means the roller bearing at the other end needs replacement(ugh). After all that, still get almost a dead short (4 ohms) across the main connections so I can't even power it up to the test batteries, to test the regulator(which is probably fried). I'm nowhere after 3 days, but I'm sure getting real acquainted with it.
$150 to rebuild is sounding pretty good to me right now.

 

[cbvet]

I "hear" you readyman.
My problem is I always figure I can do as good a job as another guy, so why not save some money?
I still have one spare working alternator, so I'm not worried yet.
Thanks guys,
Eric
CBVET

 

[OPCOM]

Does anyone have a spare pulley for the 60-amp alternator of the M35? Do I need a key on the shaft? I should really think about replacing the one ADR and I 'fixed' over a year ago and repairing it. Can anyone suggest a shop in Dallas that could handle the 60-amp alternator's repairs?

 

[bottleworks]

You can test the regulator with a simple volt meter. Make sure the output is at or around 13.8 volts. If that is what you get, it is most likely good.

You do know that these trucks have a 24 volt electrical system NOT a 12 volt system, right?

 

[maddawg308]

I am ready to send my alternator off to be rebuilt. With the power off, and the accessory switch in the off position, it slowly drains the batteries down to nothing. I put new batteries in it (the old ones were garbage anyways, only 200 amp output, they were toast), but it still does it. I think the diode in the alternator is busted, slowly allowing the batteries to drain.

 

[readyman]

maddawg,
Got any estimates for that rebuild? I'm just starting to call around now.

 

[maddawg308]

CME Armature does it for $220 shipped back to you, like brand new. However, my buddy's brother-in-law will do it for cost. I think that's a "family" discount, he wouldn't extend the offer to others.

However, it might pay to find out how much he would charge others for the rebuild process. Will get back to everyone on that.

 

[therbert]

Sorry about the 13.8 typo above. My mind is still in the 12v world.

HA

 

[halftrack]

$150 seems like a really good deal to me.