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DayleW wrote,...
I just read your alternator brush replacement thread. It sounds like it might be a rectifier fault. Maybe the brushes too.
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If the problem is within the rectifier, in other words within the diode bridge, then the iginition light will glow at idle but as the engine revs rise, the light will go out. You'll also see more than 12V on the battery at idle. Using an oscilloscope to view the voltage waveform will certainly provide an answer in this regard.

See how you go,
Ron.
 
Yes, the ignition light does go off when the engine revs up. I'll try and get it sorted over the weekend...
 
Hi All,

The good news is with my new electronic ignition, my car seems to be running more smoothly and feels a bit more responsive. The bad news is I've been to three different car parts places today and none of them can help me with a new rectifier. Does anyone know the part number or a reliable source? I have seen a couple on ebay but each one looks different, and I have not removed the one from my car yet so dont know what it should look like.

Thanks again eveyone for all your help and patience with me in trying to get this sorted.

Dayle
 
Hi Dayle is yours an 18acr alternator? if so it looks like this.
(image stolen of Google images as I havent a photo of one)

KGrHqNjEFek0ZdsBQYOmSI5w60_35_zpsbc0eb30b.jpg


However I would caution you about buying a new one before you have the old one out and in your hands so that you can check it for function.
Rectifier stacks are very easily checked for correct operation with a digital multimeter using the diode function check, also on these older stacks you can do a visual check as to diode colour though this is not the most accurate test. To me it seems a false economy to just replace the rectifier on spec as there are still many other worthy candidates that could be causing your problem ie brushes, regulator or shorted windings in the either field or armature.

Graeme
 
Hi. I have taken the alternator out of the car and have unsoldered the regulator. It looks very similar to the one in the picture, however it was very dirty and had rust bridging between the middle plates and one of the diodes which passes through it. Also one of the solder joints was dry. I have cleaned it all up and resoldered each of the joints. I now have the regulator and a multimeter sat next to me as i write this. If i use the diode function on the multimeter with the red lead to the back plate and the black lead to one of the semi-circle segments at the front they all read around 415 - 420. Now going from the middle plate with the black lead and each of the three semi circle pieces again each read around 405 - 430. Now going from the front plate with the black lead to each of the three semi circular sections I get similar readings. If I swap the wires over with any of these connections the multimeter remains at 1 indicating no reading.

Does this help me to determine if the regulator is now working?
 
The item with the diodes is the rectifier, not the regulator. I have a new one out in the garage, which I'll have a look at later.

Given that there was rust within the plates, it sounds as if your alternator needs a complete overhaul.

Ron.
 
Sounds good Dayle, none of of your diodes are shorted which is the normal fault condition of a diode so that's a positive outcome. Diodes read normally about 0.6V in one direction when in good order and in the other direction they should have no change to the disconnected meter reading, which is what you have found. Dont worry for the slightly lower reading as it maybe a case of diode chemical composition or the quality of your Digital Voltmeter.
It looks like your problems maybe elsewhere such as the regulator, winding's or brushes, my guess would be the brushes as they are a wearing component, google image up a picture of replacement brushes for the 18 ACR reg and see if they look the same length or are considerably shorter, if they are a lot shorter then you would automatically replace them anyway. However if the length is comparable I would suggest that a new regulator for your alternator would be the next step.

Graeme
 
ghce said:
Diodes read normally about 0.6V in one direction when in good order and in the other direction they should have no change to the disconnected meter reading, which is what you have found. Graeme
Click to expand...

.6ohms??
 
OrganDoctor said:
ghce said:
Diodes read normally about 0.6V in one direction when in good order and in the other direction they should have no change to the disconnected meter reading, which is what you have found. Graeme
Click to expand...

.6ohms??
Click to expand...

No, it is in volts; Rectifier diodes have some volt drop when they are forward biased (i.e. "switched" on). Silicon diodes have ~0.6V forward biased, the old germanium had about ~0.3V I seem to recall.
 
measurements can vary depending on diode size and chemical types, silicon, germanium or schottky types. readings may go as low 0.2 of a volt ( i have seen 0.14) so 0.4 is in the range of acceptableness. When a diode is faulty it will read dead short (0.0 Volts) in both directions though in some cases they can go "leaky" this is shown up as a partial voltage reading in the non conducting direction.

Graeme
 
That's good news then. Perhaps it was the dry joint and corrosion that were casing the problems. The brushes dont look much shorter than some shown in a picture i found through google, I'd say they are still around 1 cm in length.

I have just finished putting everything back together and things appear to be much improved. At tickover I am now getting a little over 13V accross the battery terminals. The ignition light also remained off during tickover. The gunson multimeter when set on 5 tells me that i am getting just between 'undercharging' and 'alternator ok', I will check the voltages at higher rpm when my fiancee gets home. I'm quietly optimistic that the ignition system problems are now solved :) . It was a steep learning curve but at least I now have a much better understanding of how the ignition and alternator works :D .

The next thing on the list is to fix the leaking brake master cylinder. That can wait a few days though.

Thanks for the help!
 
There was one other thing I forgot to ask. When taking out the alternator I found a wire that was not attached to anything and covered with a bit of tape near the three pin socket which plugs into the alternator. Any idea what this might be for?
 
Some alternators are battery sensed and have an extra wire, which isn't used if the alternator doesn't need it.
 
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