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Direct Current Generator

QJC

Registered
I recently acquired this neat generator. The tag was conveniently removed at some point in its life, so I have no way of knowing the unit's specifications. There is a serial number 500795. It has three connection points. Pos, Neg, and field. I plan on making it operational again after a restoration, but I would like to know it's rated voltage to start. Other information like no load voltage, ball park field rheostat resistance range, and rpm would be great too.
 

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Vanman

Subscriber
Last Subscription Date
06/10/2020
Just as a truly WAG, based on the heft of the armature conductors, the size of the commutator, and the number of commutator bars, I'm going to GUESS that this is a 40 volt machine, ie for charging a 32 volt battery....

To get a better idea of it's rated voltage, I would drive it at a constant, reasonable speed, say 1,000 rpm, then plot a magnetization curve.

This is done by incrementally increasing excitation current and noting the resulting armature voltage. This will be a straight line, at first, but at some level of field current it will begin to flatten out, ie less increase in armature voltage for a given increase in field current. The voltage required to reach that level of field current will likely be near the designed operating voltage, give or take. It'll get you close enough to tell whether it's say 40 volt, or 115 volt, for example.

Once you know that, and while still applying that much field current, you can now change the driven speed until you get the same voltage on the armature as you've determined is correct. Now you have an approximation of the design speed. In reality it will be somewhat faster than that. And if you want to make the speed even higher, that's when you can start playing with inserting some external field resistance.

Oh, and Welcome to the 'Stak! :wave:
 

Newoldstock

Registered
If you measure the surface area of the poles or the total amount of armature surface iron and compare this with this with another known machine of about the same era you can guess at the amount of flux the machine operated at and torque and power.

This does not work well with newer machines because the insulation systems and alloys of the steel are different (makes new machines more powerful.)
 

QJC

Registered
Vanman

Thank you for your reply. I too was thinking it was a for a 32V charging system, based on the heavy gauge of all the wiring on the unit. I have read about how to determine the gens ratings by running it, but I like how you described it better. I never thought of plotting the curve. That's a great idea too. I will start at a low speed as you suggested, and go from there. I have a 2hp 240V 1800rpm motor to use for testing, but I will need some kind of VFD to vary the speed I guess? Ultimately my goal would be to run the gen with a antique engine, as slow as possible to run some loads for demonstration, but not cause damage to the gen.

I have a few more questions if anyone can help. Correct rotation would be CW if viewed from the commutator end? What effect does rotating the brush holders have on the generator? Reason I ask is there was a factory mark on brush holder and base, but the brush holder was rotated 1/8" CW from factory mark when found. Also would like to know a good brush supplier, to replace the worn down ones. Having issues finding a supplier with the correct size. 0.5"Tx0.75"Wx 1.5" to 2" long.

Thanks
 

Peter Short

Registered
Last Subscription Date
11/09/2017
CJQ,
I don't know much about generators, but it reminds me of a Canning dynamo I sold recently. The Canning was made for electroplating work and was made well into the 20th century. It was 6 volts.
 

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QJC

Registered
After restoring and testing this generator this is what I found, to help others in the future. It's a 40V DC self excited, compound wound generator, that likes to be run around 1100rpm. Rotation when standing at the commutator end is clockwise. Not sure what max output would have been, but output wire gauge was #4 awg. A few pictures of it's current state running a few light bulbs.
 

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QJC

Registered
Thanks Pete

For some reason my thank you button is missing....

It was a fun and challenging restoration. The coils needed a lot of attention. At least if the power goes out, I have something to play with. :)
 

Elevated

Registered
Looks great! The brush ring is moveable on dc generators used in elevator drive systems, in order to allow for setting the neutral plane.
 

DKamp

Registered
Excellent job, CJ!

at #4 AWG, you'd be somewhere in the CAPACITY of 80-100A. At 32v, you're in the 3.2kw range (conservatively).

It very well could've been a lineshaft-driven lighting supply for a steam or water-powered factory.

I like it. Wish I could get my paws on a 230 or 460v AC open-frame dynamo about 6ft tall, but similar style... I have a steam engine that needs a purpose! :D
 

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