Mastiff generator

[Dewey]

During the teardown of the Fulton engine I found the generator armature to be completely toasted. Broken wires at the commutator, everything pretty well fried. I sent the armature out for rewinding and it came back looking nicely done. Cleaned everything up and reassembled it. I noticed right in the beginning that the magnets seemed quite weak. I also noticed that the actual poles are the same on all the ends and the centers are the same. Most of the magnets I've ever seen had the pole differences on the extreme ends rather than one pole in the center and the other on the ends. But, as this uses a 4 shoe system, I guess it could work. Anyway, I put it all together and used a reversable drill to spin it @ 600 RPM and all I could get was 1.8 volts with no load. So it does want to work, just not very well. I don't think it's the armature but instead feel the magnets are quite weak. If you put the opposite poles together, they aren't strong enough to hold together if you pick them up. The one not in your hand will fall off. Does anyone know if they are normally that weak?

Dewey 

[Doug]

Dewey,

Have you reviewed this post?

https://www.douglasmotorcycles.net/index.php?topic=2461.msg8898;topicseen#msg8898

If you have the two crescent shaped magnets instead of the ring magnet (Form C, Model PA rather than Form A or B), they should have north magnetic poles at each end, and a south magnetic pole midway. Otherwise you may have cracked magnets. With the ring magnets type, there should be four poles. For the entire unit, either way, you should have four poles disposed at 90 degrees.

Output even under the best circumstances, is best described as dismal.

-Doug


[fix typo. 04Dec11, Doug]
[edit first sentence. 14Dec11, Doug]

[Dewey]

Doug - I do have 2 separate magnets. I wouldn't call them crescent shaped tho. They are the same thickness throughout until they come to the very end at which point they are ground away to allow for the mounting bolts. Could it be a ring magnet that has been cut in half? I'm going to look around for a compass to prove the orientation of the poles. Having 1 pole in the center and an opposite pole at either end seems unusual to say the least. If they were conventional as you said, that would make it a 2 pole system, yes?. 2 norths on one end and 2 souths on the other. 90deg. from the ends should be neutral.

Dewey

[eddie]

Dewey,
            Think back to your schoolboy days - there's another way you can check the magnet. Lay a sheet of paper on top of it and sprinkle some iron filings on it - the alignment of the filings will accurately conform to the magnetic field and show the position of any cracks!
          Regards,
                       Eddie.

[Dewey]

I'd totally forgotten that. It's been a loooong time since I was in school although I do still learn something new every day. One of the reasons I'm right here at this moment. I found out something interesting and relevant while searching magnetism. There was an early electric clock called the Bulle. It used a magnet with the same properties I've detected in this generators magnets. The center is North with the ends being South. It was charged using a center tapped winding. Obviously the coils were reversed from one another to achieve this. The point is - this style magnet does exist and I'm inclined to think that it was intentionally used on the Douglas BT&H generator/dynamo to utilize a 4 pole system. One of the pages also indicated that by its own design, these magnets weakened easily.

Dewey

[Dewey]

Doug - My apologies! I tend to skim very quickly over text and extract only what I need. (The faster I go the behinder I get). Your linked post showed the unit I'm working with, which you already knew. Great pics & info - thanks.

Eddie - I took your suggestion and did the iron filings trick. Interesting results. The filings showed the poles to be just as I described, North in the center and South on each end. Thanks

Doug - now that what I have for magnets has been established, the illustrations in your post have clearer "N" markings on your magnets than I have on mine. This indicates to me that my magnets are somehow screwed up from what they should be - North on one end and South on the other, as you also said they should be. I never doubted you, I just knew I had something different.

Dewey

[Dewey]

Update - I found my compass and it showed each end of the magnet as having a North pole and South located in the center. I motorized the generator with (+) to the armature and (-) to the frame. The armature rotated in the reverse direction of normal rotation. Not sure if that's right, but at least it did rotate. This all brings me back to my first suspicion - weak magnets.

Dewey