Alternator Question -- My light glows
 

Hi,

When I turn my ignition key to "on" the red alt. light comes on. Fine.. However, when I start the car up, the light will stay on at idle. I checked the battery and it's charging at 13.67 volts. Seems normal?

I realize I should probably have the alt. tested, but I'd like to drive the car and am afraid that I might be stranded somewhere.

Thanks

13.67 sounds adequate.

Sounds about normal. If you rev the engine up enough for the light to go out does the light come back on once the engine drops back down to idle speed?

what's your idle rpm? and your v-belt isn't too loose is it?

You should have a SEV Marchel 70A alt. Given that, a glowing
light may mean:

1. You have a voltage drop from the alt. to the front & battery.

2. You have a alt. diode which is bad.

Note: The voltage being 13.7 does not necessarily indicate
that the alt. is OK. The regulator will force the alt. to charge
to the set voltage even w/o all diodes.

Good Luck
Loren
'88 3.2

See Warren's post about putting a resistor in parallel with the warning light bulb: this will put more current through the D+/61 "Blue Wire" circuit and provide you more excitation of the field at low revs.

But I agree, you could have a bad diode.

Thanks for the info--I'll check it out.

One note (and I may sound crazy saying this) but it seems like the light is _brighter_ after I tightened up the belt. (It was a bit loose when I first bought the car, and the light was dimmer)

Then again, it could be the desert peyote.

A dim Alt light at idle which goes out once the rpm's are increased has several possible causes as mentioned earlier. The Marcal alternator in my car had that problem and I troubleshot the problem down to the exciter diodes. The exciter diodes are not the main power diodes in the alternator. They are used to provide feedback voltage to the voltage regulator. In my case the exciter diodes were damaged by heat over many years of use. I replaced them with a three common all purpose 1N4000 diodes. The 1N4000 can be purchased at any electronic/radio shack store. They would have to be soldered in place with the correct polarity where the old exciter diodes are located. This was a cheap fix for my problem and the low glowing light was gone.

Pat, that's cool. Do you have any pictures of the replacement of the "trio" diodes?

Do it right. Rebuild the complete alt. and don't mickey mouse
it by soldering in diodes w/o a complete fix.

Loren
'88 3.2

How are your ground straps? Clean them up. Also have the battery bench-tested.

I agree that a complete rebuild may be in order - it really is not that expensive.

John

Thanks. Knowing me, I'd solder something wrong and blow the whole thing up.

What does a rebuilt alternator run these days? (ballpark)

A rebuild cost me about $125.00. They put in a new VR and the brushes (of course) and turned down the commutator (sp?) ring on which the brushes ride, among other things. I went ahead and bought a new battery at the same time, and cleaned every darn ground and replaced every darn fuse with new ones.

Typically that ring only has so many "turn downs" before it is useless. Anyone familiar with Hunt/Lucas magnetos can understand this process.

John

I had the same problem. I tightened the belt and now it's fine. Hope this helps.

Having similar trouble on my '82. Ordered a new regulator from Pelican on Wednesday. Took the alternator out today and did a quick check of the diodes. It appears one or more of the negative diodes is shorted. I get 0 ohms in both directions on all three. It looks like I might need to get a rebuilt alternator since you can't find just the diodes and fix it yourself anywhere. I've looked on the Pelican parts list, and although it mentions rebuilt alternators, none are listed for mine. Anyone know if this is something our host carries? (I tried calling, but it's Saturday and no one is home.) Better yet, is there a source for alternator diodes? The alternator is in good shape except for the diode problem.

Have you tried going to yor local electronics store? That's where you would find diodes. You will not find them at an auto supply store or even on Pelican Parts. Remove a diode and bring it with you. They should be able to find a match.

The diodes in question are the large, pressed in type. Not the small exciter diodes. I'm not sure that you could find those at a typical electronics store, let alone Radio Shack. I've tried calling some of the local rebuilders, but of course, no one's open today.

John_Cramer:

Sorry I don't have a picture of the exciter diodes but I believe someone posted pictures of them in a previous post some time ago.

LorenFB:

MikeyMouse around? I don't mickey mouse around when it comes to my car. I did a quality fix on my alternator over ten years ago for about a $1.50 and a few hours of my own time doing something I enjoy. Fortunately I have the knowledge and skill to perform this kind of repair.

David914:

If you look in the phone book you will find alternator rebuilders who are willing to sell the power diiodes/brushes to someone who wants to rebuild the alternator themselves. You can also purchase new berrings from a berring supply house. All you need is the number stamped on the side of the berring so they can match it up.

Targa80:

Thanks. The alternator in my car was a rebuilt purchased from Automotion about 6+ years ago and is in great shape except for the diode problem. I'm a little hesitant to spend $200+ for something that could be effectively repaired by me for a fraction of that. Especially when it took 3 tries with Automotion to get a rebuilt unit that worked! I personally don't think that doing your own repairs is "Mickey Mouse" either as long as you are thorough...

How many tries did it take to get it right? It's lots of fun to
R/R the alternator unitl it works, isn't it?

Loren
'88 3.2