Alternator, voltage regulator question

[TexAndy]

I bought a NOS voltage regulator from a guy on ebay. Regulator looks new, appears to be the correct part.

At least, it did until I got inside the alternator and saw the old voltage regulator. They look VERY similar. But the new one has 4 spade pins sticking out of the potting versus the original's 3.

Old:



New:

When I broke the seal on the alternator, I could definitely smell the magic smoke residue. And you can see it in that clear potting they used which components were fried. I'm hopeful with patience I could dig the potting out and replace the bad components if I need to someday. So it's not going in the trashcan.

It looks so similar, I'm wondering if I could just hook the new one up the same as the old one and ignore that extra spade pin.

The pins do appear to be numbered the same and in the same position. Pins 1,2, and 5 are exposed on the old one. Pins 1,2, 4? and 5 are exposed on the new one.

 

[Suprman]

There are some alternator out there that are made by Hellas in Greece the regulators are different. The Prestolite and Leece Neville ones are the same I believe. Southern Automotive makes and sells both regulators. Sometimes the bearings go in the alternators causing the whole thing to smoke up.
Will

 

[TexAndy]

Hm, that's not a great sign. When I spin it by hand, it definitely doesn't feel smooth like it probably should. Maybe I should track down replacement bearings as well?

I'll see if I can get the rest apart and get the bearings off tonight.


Only other motor type stuff I've serviced is my dillon 1200 case trimmer. But I'm guessing getting the bearings off should be much the same process on this alternator as on that trimmer motor shaft.

And you know, I tried sending a RFQ to southern automotive two weeks ago and never got a reply.

 

[Suprman]

Does it look like black oily stuff has been spraying out of it?
Will

 

[TexAndy]

Nope. I just turned it again by hand. It doesn't turn rough, really. Somewhat smooth but with a faint clickety noise.

Only black stuff I see is inside. Powder. I'm guess it's dust from the brushes. Brushes themselves look like they have alot of life left.

 

[Suprman]

They do get dusty. Who makes your alternator is it a Prestolite or Hellas?

 

[TexAndy]

Seilman SA
Hellas

 

[Suprman]

It is a different regulator than the Prestolite ones. They are like 80 bucks on the bay for the replacement.

 

[TexAndy]

Thanks for the help. I think I'm just going to turn my computer off and go read a book or something. Sick of wasting money.

 

[TexAndy]

lol, doghead.

 

[Postman515]

Do a Delco alternator conversion and you'll stop spending money with alternator issues!

 

[Tow4]

I think the new regulator will probably work. It is just designed to fit more than one application ie. the extra terminal. If the numbers on the terminals match the numbers/locations on the old regulator I would use it.

You can take it to a parts store with an alternator tester after you put it back together and let them spin it up and see if it works before you put it back on.

 

[TexAndy]

The regulator won't physically fit. The ring that fits inside the alternator body is just slightly too big.

I might could make it fit by chucking it up on the lathe and turning the ring down a hair. But I don't know if that's such a great idea.

 

[TexAndy]

Ok, just measured... the diameter of the ring on the Prestolite/Southern Automotive measures about 5.240". The Hellas about 5.210"

.015" of radius isn't so much to remove on the lathe, but before I do this I'd want a little more assurance that it would actually work.

I *think* it will. Friend of mine showed me his (what looks like) Prestolite, and it had the four spade connections and the only ones used were pins 1,2, and 5. Pin 4 was left empty.

 

[TexAndy]

Talked to keithj and he mentioned I might test the resistance between the slip rings. Seemed a little low compared to what he mentioned. 8.5 ohms.

Reading between the slip rings and the alternator body is infinite, so no short there.

What should a correct resistance reading between the two slip rings be?

 

[TexAndy]

Closest info I can find in any manual is from this

TM 9-2920-225-34

On the PRESTOLITE MODEL AMA-5102UT, even those it's the round pin version, and not Greek manufacture. It says the value should be between 8.8 and 10.2 ohms between the two sliprings.

None of the other alternators described in that manual look like mine.

 

[TexAndy]

Well it appears to be charging.

Just in case anyone was wondering, it appears that a spade type prestolite voltage regulator will work on a Hellas alternator. You just have to get someone with a lathe and an 8" chuck to machine down about .015" radius (.030 diameter) off the tongue of the hellas voltage regulator to make it fit.
Also, you have to re-use the o-ring from the hellas voltage regulator. The prestolite one is too large. It will keep you from installing the regulator.

Wound up having to take the regulator to a machinist in town who was nice enough to do it for free. I've only got a 6" chuck on my atlas lathe.

Truck is charging at 26 volts measured at the alternator right now, 25.7 measured at the batts. They were pretty badly discharged though (around 11.9 volts each). When they've charged awhile this way, I'll bump the alternator up to about 26.5 or 27

Hopefully this helps anyone with a similar issue. If I had to do it over, I'd have just gotten a new AC Delco 21Si

 

[benalco1]

Hello TexAndy,

I just purchased a M998 and the voltage regulator went out on the 60 AMP generator.... It's one of the Sielman Hellas generators and Southern Automotive Wholesalers (manufacturing source) don't offer anymore of the voltage regulators (can't find them anywhere).... I was contemplating doing the same thing you did by modifying a prestolite version - is it still holding up good?.... you mention an AC Delco 21Si.... would this be a direct replacement for one of the 60 amp generators?... does it require any modifications? - brackets, wiring, etc?

 

[74M35A2]

You guys know what I am going to say.

There are 4 very common failure modes of the stock military alternator: weak electronics (regulator/rectifier) combined with terribly poor cooling, 1920's phone cable type wire connection, pulley deformation from weak interface to rotor shaft, and rotor shaft breakage at pulley. Replacement of a different brand alleviates all of these simultaneously. Even if not a genuine unit from me, the Chinese Delco clones are light years ahead of the stock unit, because they cloned a reputable one to begin with. They can be had for $89 or so, new, with warranty.

I do have genuine Delco 24V / 100A brushless units on a tremendous sale right now with 3 year warranty. Designed to go 1 million miles in over-the-road trucks. Your choice or serpentine or double V groove pulley. PM for price. Throw the stock one away, put this on, close the hood, and never look at the volt gauge again. They just work.

 

[TexAndy]

Hello TexAndy,

I just purchased a M998 and the voltage regulator went out on the 60 AMP generator.... It's one of the Sielman Hellas generators and Southern Automotive Wholesalers (manufacturing source) don't offer anymore of the voltage regulators (can't find them anywhere).... I was contemplating doing the same thing you did by modifying a prestolite version - is it still holding up good?.... you mention an AC Delco 21Si.... would this be a direct replacement for one of the 60 amp generators?... does it require any modifications? - brackets, wiring, etc?

It's still working fine, but I only did what I did because I screwed up and ordered the wrong regulator. And I had access to a machine shop owned by a machinist nice enough to chuck it up in his big lathe chuck and turn it down for me for free.

Just go with a modern Delco 24V alternator. The military alternators really are kinda garbage and what you really want is to be DRIVING your vehicle... not working on it all the time.

The Delcos are cheap and from what I've seen, reliable. And available.