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Alternator repair question

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70herald

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I think I have a weak or failing alternator and I know that there are a few of you who repair these things.

Twice, returning from a drive at night, the car has refused to start afterwards, in the day I haven't had any problems.

At night, I noticed that the ignition indicator light was on but VERY dim. Racing the engine made no difference.

There are no obvious problems (broken wires/ shorts / etc)

I took the alternator apart, and tested the diodes, and diode are ~570 ohms and shut off in the opposite direction. One of the brushes appear to be a bit worn but still nearly 1/2" long.

Is there any way to test the regulator? Unfortunately I need to order parts so it will take a while and I would like to make sure I get the correct stuff.

The started and battery worked just fine the last 20+ times. The only difference is that I took a night time drive with the headlights on.

Any other ideas? Thanks

BTW, the alternator is a Lucas ACR17
 
Mornin' Y.

You did clean the commutator while it was apart, right?

'bout the only thing left to blame is the regulator, IMO.
 
I cleaned the commutator. The copper has a nice little dimple in the center but looks like it has good contact with the carbon. I going to order a regulator hope it does the job.
 
70herald said:
I think I have a weak or failing alternator and I know that there are a few of you who repair these things.
Click to expand...

Could be the brushes on the alternator. They are easy to replace and should be able to be sourced locally. I also had an issue years ago where my alternator refused to charge and no one would believe me when I said it was due to dust and dirt. I took it apart, cleaned it, and voila. After it was clean, still, no one believed me.
 
The alternator failed on the wifes 72 and I took it to a starter and generator repair shop with hopes he could fix it. He did! It was the regulator that went bad. I was surprised that they were still available for the Lucas alternator. Had him put in new bearings and anything else it needed. $60.00 well spent. Been working fine now for 6 years. PJ
 
Using a digital ohm meter to test alternator diodes can sometimes be misleading. Analog meters work fine for this if you set them at the 10k range, as then you are testing with 12V instead of the 1/2-2V that the typical digital meter uses. Also, for digital meters, it's better to use voltage drop (seen as the diode check), which most digital meters have. It's better then using ohms, but still not as good as an analog meter. Having said that, diodes can still break down when higher currents are supplied.

Your symptoms indicate one or more of the following...
1. Slipping fan belt
2. Bad diode
3. Bad stator
4. Bad (intermittent) brush contact, but it sounds like you have enough brush material, so that might leave weak springs or dirty and/or grooved slip ring.
5. Bad regulator... Least likely, as you are getting some charge and <span style="font-weight: bold">usually</span> regulators either work or they don't, so you would get nothing.
 
I had a problem with my 5-wire MGB alternator not long ago.

It ended up as the ~Frankenstein alternator~ .
Still working.
grin.gif
 
Improvise...

Adapt...

Overcome!

:laugh:
 
DrEntropy said:
Improvise...

Adapt...

Overcome!

:laugh:
Click to expand...

One of my favorite quotes!! :laugh:
 
My new regulator came in the mail, and I put it in after quite a lot of head scratching and searching around on the internet. The new version has changed the wiring around from the case being ground to the case being the output, and a ground wire.

I got it all back together again and it seems to be charging up again. The battery was almost totally discharged (~10v) but after a few minutes was back to over 12 volts. Turning the headlights on didn't drop the voltage so hopefully it is working properly. Also, the indicator light is off at least as far as I could see in the bright sunlight.
 
martx-5 said:
Using a digital ohm meter to test alternator diodes can sometimes be misleading. Analog meters work fine for this if you set them at the 10k range, as then you are testing with 12V instead of the 1/2-2V that the typical digital meter uses. Also, for digital meters, it's better to use voltage drop (seen as the diode check), which most digital meters have. It's better then using ohms, but still not as good as an analog meter. Having said that, diodes can still break down when higher currents are supplied.
Click to expand...

I prefer the old analog instruments and test equipment over the digital. Could be just me, but I seem to get a better reading. I don't use the digital to much. I like Sun Machines and model Ts too! :laugh: PJ
 
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