diode question

[Lee]

I could use a little help with this, if anyone has had this experience. I've had a prolonged problem with my charging system...'78 SC, 3.0, external Marchel regulator, Paris-Rhone alternator.

AT first, I thought it was the voltage regulator going out, but two replacements haven't helped. The guys at the alternator shop swear the alternator is working. They've bench tested it twice. My wiring all seems good. I've cleaned and tightened the grounds.

Here's the thing...today, it wasn't charging. I drove it to the alternator shop and had one of the alternator guys look at it. Everything seemed in order. He pulled the plug off the regulator, and checked it. The ground had good resistance, the field wire was working, and The blue wire tested okay...more volts than the battery. I plugged it back into the regulator, and it started charging! The alternator guy told me it had to be a bad connection at the regulator.

On the way home, I crossed a railroad track, and the generator light came back on. AT home, I tightened the connections, and applied some dialectric grease, but it wouldn't charge. I tested the wires again. this time the blue wire carried less voltage than the battery.


Since the alternator has been tested, it seems like it ought to be the wire. Does the blue wire run directly from the alternator to the regulator, and then on to the 11 pin connector. If so, can I just snake a wire in from the alternator to the regulator?

Could diodes quit functioning on an intermittent basis?

[Lee]

I should clarify this...when checking the blue wire, I checked it first with the ignition on, motor off. It carried the same voltage as the battery. When I checked it with the motor running, it carried less voltage.

Sorry to be unclear.

[autobonrun]

There have been three occasions where I have seen an alternator test good in the shop then be bad. The first was when a brush was sticking in the holder. A spring holds it in place against the rotor. If it sticks in its guide, you'll loose continuity and consequently the charge. Check the brushes to make sure they are not sticking. Push them back so they compress the spring then make sure they return to the initial position without sticking.

The second instance was where one of the springs that holds the brushes down was actually broken, snapped in half. It did not maintain a constant pressure so I would lose the charge intermittently. Couldn't tell by just looking but when I removed the brush, the spring fell out in two pieces.

The third instance was where the solder joint on one end of a diode was cracked from age. It looked good from visual inspection, but if you pulled on the end of the diode, the solder actually lifted up. The solution was to suck out the old solder and resolder all the diodes. The shop should be able to verify whether the diode itself is good or bad. I personally haven't seen them work intermittently. When they fail, they tend to fail for good from what I've seen.

Your comment about the alternator not charging when you crossed over a railroad track may mean something like a solder joint or brush is indeed loose and vibration causes it to show up.

http://members.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm

http://www.autoshop101.com/trainmodules/alternator/alt101.html

http://www.bcae1.com/charging.htm