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Bi-Polar Motor/ Dynamo Identity?

Tommy Stojanov

Subscriber
Last Subscription Date
05/31/2020
Hello All,
I recently acquired a bipolar motor/ dynamo of unknown manufacture and was hoping those on this board could help identify it. It sports a ~5/8in shaft, is roughly 13in tall, has a coil height of 6 1/2in and weighs approximately 100lbs. There are brass oil cups along with brass outboard brush holders/ bearing supports. Based on the rotor diameter I suspect this is a fractional hp motor/ sub 1000W dynamo. The construction of this unit leads me to believe it is of late 1880s to 1890s vintage. The slate panel with brass terminals appears to be original as well. I see no identifying markings or location where a tag would have been riveted. Please see the attached photos. Thanks in advance.
 

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Last edited:

roscoepug

Registered
this is loosely based on the design of the Scientific American "Eight Light Dynamo" from 1887. This was as far as I know a machine that was offered in various kit forms, and there are a lot of nuances in examples found based on the kit mater and the assembler/builder. Here is a pic of the cover attached, sorry for the poor resolution, all I could find.

I am sure Ron McClellan can chime in with more info in this, its a machine he knows white a bit about.
 

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Tommy Stojanov

Subscriber
Last Subscription Date
05/31/2020
Hi roscoepug,
Thank you for posting these details and the periodical cover page. Assuming a 50W load per light and an "8 light dynamo" my estimate of below 1kw wasn't horribly off (well, less than half). I wonder if a series or parallel combination of bulbs was common at the time. It would be interesting to know the recommended shaft speed and output voltage of the dynamo. I'm sure I could scrub the the web for a copy of this article and glean what I need.

Hi Ron,
Thank you for posting pictures of your dynamo. It appears to be very nicely restored. Yours certainly adheres most closely to design shown by the Scientific American article, more so than mine.
Have you ever attempted to spin your dynamo at an appreciable speed while mesuring the output voltage?

Last, I have very recently decided to pair my dynamo with a 2hp tank cooled gas engine of slightly later vintage. I will either source or turn my own pulley.

Thank you again for the feedback.
 

Tommy Stojanov

Subscriber
Last Subscription Date
05/31/2020
A bit of Google research shows that the April 23rd, 1887 edition of Scientific American can be purchased as a .pdf or as a newly printed copy. I may have to obtain a copy myself. Also, some more digging yielded a Connecticut- based establishment offering this unit commercially. If their ad's illustration is accurate the expected lighting loads are in parallel. Thanks.
 

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Vanman

Subscriber
Last Subscription Date
06/10/2020
You can at least approximately determine the rated voltage and speed by first driving the machine at some reasonable speed, say 1000 or 1500 rpm, doesn’t really matter, then applying exciting current externally.

Plot the armature voltage vs field current and look for the knee in the curve. Note the required field voltage at that point. This will be the machine’s approximate rated voltage.

Then adjust the speed until the armature voltage is the same, and this will be the machine’s approximate rated speed.

Reconnect in shunt configuration and it should make that voltage at that speed. Probably round the voltage up to a nearby “normal” voltage for the period.

Of course it could then be run at a higher speed if desired by the addition of an external field resistor.

Keith
 

Ronald E. McClellan

Subscriber
Last Subscription Date
01/05/2020
Tommy I've been taking my dynamos to Coolspring for several years and running them with my 1 3/4 HP Nelson engine. The engine runs about 450 RPM. I needed 1800 to 2000 RPM so I built a speed increaser. I am lighting 4 light bulbs , 150 to 200 watts. When I took my 4KW C&C , I was told that I needed a 6 HP engine , yes but not if I am only using 200 W. for a demo not the whole 4 KW. If I did try to pull 4 KW out of it , it would just drain the power from my engine until it would slow down and the dynamo will stop generating. NOTE that you still need the RPM to make the generator to work. Your dynamo has the brass yokes as shown in the Sci mag , where mine has posts to hold the shaft and brushes. Your picture is not clear enough to tell for sure what they are offering. I have never tried to run mine. Here is a picture of a smaller dynamo built just like the Sci Mag , I have no info on it. Ron
 

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Ronald E. McClellan

Subscriber
Last Subscription Date
01/05/2020
The Scientific American gives this data , a dynamo electric machine capable of supplying a current for eight sixteen candle power incandescent 50 volt lamps of suitable resistance , or an arc lamp of ordinary power. The armature speed is 2200 RPM and the machine running normally requires one horse power to drive it. The machine weighs 130 pounds , and occupies a floor space of 8 X 18 inches. Ron
 
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