Odd generator charging problem question...

[Marshall V. Daut]

I know, I know...You're shaking your heads at yet ANOTHER generator charging problem, right? Well, this one is a little different and I've yet to read about similar circumstance in other threads. Here goes...
Working on electrical components has never been my strong suit, nor of an interest to me. But in the last two years I have had good success rebuilding Model A generators for my cars and for friends. The usual learning curve problems were encountered along the way, of course, but the generators always charged well afterwards. I have rebuilt about a half dozen generators now that are all still working fine. 'Feeling pretty cocky about rebuilding these things now.
But...I have encountered a new problem recently with a friend's generator rebuild that has me puzzled and I don't think it actually relates to my rebuilding skills (or lack thereof). I tested this freshly rebuilt generator with a battery and it motored the way it's supposed to. Another successful rebuild, I thought to myself. Installing the generator on the engine, I used an original points style cutout to check the charging rate. It was necessary to polarize the generator, but then it began charging properly. I then switched to a new Nu-Rex electronic cutout that my friend wants to use on this generator. No charge! Thinking the cutout was defective right out of the box, I put on a different Nu-Rex cutout that had been functioning well on a different rebuilt generator I have stored away. Same result: no charge! Two defective Nu-Rex cutouts??? And one is known to be good? Scratching my head at this new problem, I put the original points cutout back on the generator. Instant charge. What is going on here?
Before you all tell me to contact Nu-Rex, I sent them a detailed description of the problem on Monday via their email "Contact Us" on-line service. Today is Thursday and still no reply. That should be more than sufficient time to send a reply or at least acknowledge that they are mulling over the problem. So that is why I am turning to the "Fordbarn" electrical gurus for their opinions why this generator with all new parts will charge merrily away with an old, crusty original points cutout, but balks when two expensive Nu-Rex cutouts are installed. I am stumped and frustrated. This experience reminds me of why I had studiously avoided working on starters and generators for the past 60 years. .
Marshall

[Marshall V. Daut]

I should emphasize that I did NOT polarize the generator with the Nu-Rex electronic cutout in place. That would have fried it. I jumpered the original points cutout and that started the generator charging.
M.

[jrelliott]

Is there a good ground path for the Nu-Rex cutout? If you repainted the generator case, it may not get a good ground. Put some star washers between the Nu-Rex cutout and generator case and see if that works. You could wave the proverbial rubber chicken across the generator.

[Marshall V. Daut]

Yes, thank you, the ground is good. The case is down to bare metal all over. Until generators I rebuild test o.k. in all areas, I don't paint the outsides like I used to do. That was one of the hard lessons I learned along the way. If something was wrong inside after testing, the nice black paint job invariably got scratched or smudged upon disassembly and re-assembly to find and repair the problem. A sanding and repaint was then necessary. So, this generator will not be painted until the present problem has been resolved. 'Can't get a better ground than bare metal!
Marshall

[rotorwrench]

I don't know what type of diode is utilized by Nu-Rex. It should be capable of passing up to at least 20-amps. It can be tested with a battery, but whatever load is applied should be less than the max rating of the diode. A simple flow direction test can be performed with a multi meter. It should flow in only one direction.

[ndnchf]

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New isn't always better. Original Ford cutouts are very high quality. They can often be serviced and put back in service. They can provide many years of trouble free service. I made a youtube video explaining how it is done.

[Herb Concord Ca]

Marshall, X2 on what Rotowrench said about checking the diode in the Nu-Rex cutout.
With the Nu-Rex cutout off the generator, using the ohm scale of a multimeter, you should have continuity in one direction only, should be near zero one way and infinite the other way. Check both you Nu-Rex cutouts, the readings had better be the same, if reversed, one may be for a Negative ground car, need to check with Nu-Rex on that.
Good Luck

[Herb Concord Ca]

Marshall, in my last post, when measuring with ohmmeter, measurements are across the two terminals. Not to the case.
I have not seen a Nu-Rex cutout, (use alternators on both my Model A's). Both terminals need to be isolated from the case.

[bobbader]

Hi Marshall. This is not a direct answer to the problem, but, if all else fails and you assume at least one of the nu-rex units works on another generator you have .............. how about putting that cutout back on the other generator and test both again. If successful, you can then try the second nu-rex unit to see if it works on the other generator. It's a bit of extra effort to do all this, but it would at least tell you if these cutouts work.

Sorry I can't offer anything more substantial. Good luck.

[1939mars]

By chance is this generator on a car that has been switched to negative ground? The points won't care, but the diode will.

[nkaminar]

X 2 on post #10

[Badpuppy]

X 3

[Marshall V. Daut]

No, the battery in the car is still positive ground.

Not a lot of fun in the heat, but I'll switch generators and cutouts around to see whether both Nu-Rex cutouts I have tried on my friend's rebuilt generator are at fault.

My multimeter died a couple weeks ago, so I can't use that to check the cutouts. 'Guess I'll have to break down and buy a new one. But I just can't believe that both Nu-Rex cutouts I tried are bad, especially since one has already proven itself good on a different generator and the other is brand-new from a sealed box.

M.

[Badpuppy]

Originally Posted by Marshall V. Daut

No, the battery in the car is still positive ground.

Not a lot of fun in the heat, but I'll switch generators and cutouts around to see whether both Nu-Rex cutouts I have tried on my friend's rebuilt generator are at fault.

My multimeter died a couple weeks ago, so I can't use that to check the cutouts. 'Guess I'll have to break down and buy a new one. But I just can't believe that both Nu-Rex cutouts I tried are bad, especially since one has already proven itself good on a different generator and the other is brand-new from a sealed box.

M.

You can check a diode cutout for polarity by spinning it around and connecting it backwards. You can't mount it that way but it doesn't need ground.

[jrelliott]

Marshall when you get the problem solved, please post to let us know the answer.

[Marshall V. Daut]

I haven't had a chance to do testing and swapping parts around. But I'll get to it later this week and report back.
Marshall

[Tom Endy]

A lot of mysterious electrical problems in a Model A can be solved by removing the battery ground strap where it is attached to the frame and cleaning the boss where it attaches to bright shiny metal. Wire wheel both ends of the cable. Ninety years of crud and paint on the frame at the connection makes for a poor ground.

Tom Endy