OK, If I bypass the PCM's regualtor, it works for a few minutes then quits. Even if I direct connect one of the field wires to ground at that point I get no output from the alternator.
I am at my wits end on this one! (assuming I had any to begin with!)
Help!

 

Have you checked the diode trio or the rectifier bridge, for bad diodes? How are the brushes and slip rings (or do they ride on the armature)?

Never been in one of our alternators to know for sure how they are set up.

FWIW.

BTW, could you link to the original thread, so I can read it?

 

I don't know how to link it, but here is the full URL:
http://wwww.dodge-diesel.org/dev/sho...050#post690050

 

That is a link.

I posted on that thread also.

Kinda sounds like an alternator problem, or a broken/loose wire somewhere. Is there a fuse on the 1st gen trucks, for there alternator?

 

If you are leaving the wires still connected to the alternator field terminals that is the problem and you have wiped the new regulator. To test it, take the wires off the field terminals and connect one to ground, one to +12, does not matter which ones. It should jump up to too much voltage. At that point it either charges full out or it does not. If it does not look for a bad alternator or bad wiring. What I said here is fact, not something to try, do it and the results are concrete.

If it charges, then proceed to hook up the regulator as in the picture. IF that does not work you have the wiring incorrect. You cannot have bothe the external regulator and the pcm hooked up at the same time. You cannot test the alternator with anything hooked up to the field termainals. If the external regulator is hook up and you run any other wire to test it, you trash the regulator, if the pcm is still hooked up you do the same.

The alternator is just a dumb alternator just like they made in the '50s before inernal regulators come out.

 

I wish it was that simple. I haven't hooked up the external regulator wrong, I even bought a new one to make sure it was up to the task. I never left the PCM field connections connected during testing either.

Here is what happens:

I can hook one field wire to ground, the other to the battery, and it charges too much, BUT, if I turn on the lights, flashers wipers, AC, and crank the stereo up on hard rock with the sub amp, the needle moves down into a safer zone.

If I then connect either the PCM's regulator, or the external regulator up right after that, it charges, but only for a minute or so, then it quits. At this point I can unhook whateve from the field connectors and go back to the (one to ground, one to batt) setup, I get nothing!. If I switch the two field wires at this point it starts working again, so I hook one of the regulators up, it chages for a minute or so then stops.

I think it's demon posessed!

 

I'm in the process of working on a 1990 d250 cummins and basically have the same problem. When you start the truck and put a meter across the battery terminals it will start charging for about 20 seconds get up to 14vdc and then all of a sudden the voltage drops to 12vdc and the wire from the alt to the positive battery terminal starts to get real hot. Weve put on a new alt, battery and a voltage regulator and still have same problem. We did notice that the voltage reg. was missing a ground so we ran a new ground wire to the frame but still have the same problem. We are going to try another voltage reg since the first one we started the engine and was missing the ground. If this does not work we will be at a complete loss. Any help would be greatly appreciated.

 

Your slip rings are either carboned, or brush tension is low (short brushes). When hot wired you are "full fielding" the alternator and no regulation takes place. When a load is placed on the system, volts drop due to ohm's law, though current output (amps) remains maximum. This alternator has no diode trio because it has no regulator. If either the positive or negative diodes in the bridge were faulty, when full fielded with a load, the alternator would crash due to at least one phase of the alternator being inoperative due to failed diode(s). Your test results show this not to be the case. You either have a slip ring or brush problem....though resistance in the output wire could also cause an open when enough heat (amperage) is passed through it. One more note....when a diode fails, or a stator shorts or grounds, the alternator will scream very loudly, you also didn't mention that, so again....not a stator, or diode problem.

good luck

Chris

 

Not always.

 

Yes bmoeller, not always......there are exeptions to every rule, but generally true. On a high output unit though it will usually whine, if it does anything at all...agreed?

 

Other than the field wiring for the regulator there is only one wire. Hook a strong jumper to the alternator from the battery, the big wire. Then do the test. If the field is jumped to the battery and the heavy wire is connected to the battery and it does not charge right, then the alternator is bad.

All alternators have a diode bridge whick convert ac to dc. There is six diodes, back to back so a set of three.

There is no wiring mystery here, just one wire and the regulator wires (2). So there are only three wires. Jumping the large wire eliminates any problems in the system wiring. It either charges or it don't. As was said there are generally only a couple of things that can go bad, brushes or diodes.

 

A good insurance for any charging system is to hook a ground between the alternator frame and the regulator, not the frame, the alternator to the regulator, if that is the pcm than between the pcm and the alternator.

 

call it a bridge or a rectifier...same thing. I said not all alternators have diode trios.....there's a big difference between the two. Diode trios supply voltage to the regulator for sensing and/or excitiation purposes only, and they are always positive. non-IR units have no need for them therefor they are not prtesent inside the alternator. Yes all alternators have at least 6 diodes...3 positive and three negative. Some high output alternators parallel two diodes on each stator phase, 2 on each polarity for a total of 12. For each phase there must be a positive(s) and a negative(s) diode for a DC charging circuit.


not to start a conflict mind you, merely to make sure no one is mis-informed

Do make sure however, as Dixie stated that your main output wire is intact, this can be verified with his test, or by reading the voltage at both ends (alt and bat) while the alternator is "supposed" to be charging. If there is more than .5 vdc difference between the two readings, replace the output cable, or make sure the fuse inside the power distribution center is screwed down tight.

 

I noted good voltage on the heavy cable to the alt, but did not note if there were any differences between the battery voltage and the alt.

I just picked up a new alt from NAPA, so I truly hope the problem isn't that!

 

keep us posted, sometimes the easiest solution is not the cure. We'll help more if needed.

GL

Chris