Really Old Hand Driven Dynamo

Junkologist

Subscriber
Looking for any info on this outfit. I picked it up today at an antique shop and the shop owner said he got it from a dentist. It's in real nice shape, but the slip rings and commutator need rebuilding. It appears that it could generate AC and DC current. Any insight as to how the field coils wire up to the brushes would be appreciated. This is the first early bipolar dynamo I've ever messed with. Thanks.
 

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Thaumaturge

In Memory Of
A pic of the belt end might be useful. Looks to me like a very old (~1920s-1930s) demonstration model like would be used in a school. Two of the brushes are obvious, but that end third contact makes no sense unless it it leads to a field winding... Which suggests yet another connection on the other end.
Doc
 

Junkologist

Subscriber
The two narrow slip rings are continuous and each is connected to one end of the armature winding. There were two small brushes that matched up to those. The winding leads then continue past those two rings and were connected to a two segment commutator which has crumbled and I only have one half of it. The two large brushes rode on that commutator. How would those field windings connect to those brushes? There really isn't anything to see on the pulley end, electrically.

I never really thought of this as being an educational piece due to its size, but I suppose it's possible. The guy really thought it had something to do with dentistry and I know there were dental "drills" that worked like a tattoo needle, so who knows?

Edit: It does appear that The Alfred L. Robbins-Martin Co. did manufacture demonstration pieces. Just that little bit of insight helps tremendously!
 

Junkologist

Subscriber
Oh, then from description the solid rings would output AC while the split ring would output DC....
Doc
But what do you do with the field leads? In series with the DC brushes? Same with the AC brushes? This is where I'm a little foggy.

Found an 1892 ad for the company mentioning dynamos in Google Books.
 
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Thaumaturge

In Memory Of
But what do you do with the field leads? In series with the DC brushes? Same with the AC brushes? This is where I'm a little foggy.

Found an 1892 ad for the company mentioning dynamos in Google Books.
For demonstration purposes the field leads would be connected to a battery. Then test output of DC leads (end slit commutator) and see if it puts out enough to charge battery. It may be you could feed DC out back into field (parallel, one brush to either side of field) to power field, but you may need a temporary jump to get field going. Probably depends on residual magnetism of frame. Observe polarity connection on field so that turn direction is such brushes run on downside of rotation. That's my best guess.
Doc
 

Junkologist

Subscriber
Just a little update on this piece. I have built a new commutator and slip ring setup for it. It now runs fine as a motor and will easily generate 6 VDC all by itself and 6 VAC with a battery hooked up to the fields. I have it all cleaned up and looking nice, just waiting for a perforated Barnes style leather drive belt to be made for it. There must not be too many of these that have survived. I can't find a photo or mention of another one through tons of web searching. Photos and video to come when the belt arrives. :)
 

Junkologist

Subscriber
Fantastic pieces, Ron and Gus! Thanks for the photos!

Gus, would you be able to post some closeups of the brush and commutator area? I know some parts on mine are not original and I'd like to make it look as close to original as possible. I knew there had to be another one out there! Thanks!
 

Junkologist

Subscriber
I got the dynamo up and running with a new belt from John Knox at leatherdrivebelts.com. I highly recommend John for any of your leather belt needs. He is first class. I really enjoyed getting this thing going again. Hope you enjoy the video. :)

 
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