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Mystery Motor/Generator with some clues

I just bought a fantastic motor that is designed to connect to a DC generator I got last month. The pair comprise an Electrical Engineering lab setup in which various AC and DC motors can be constructed and tested with the generator and load banks as a dynamometer. I now have the manual for the system, which shows how to connect the various stator and rotor windings of the motor for single phase, two phase, and three phase, synchronous and induction types, as well as DC machines, and even frequency and phase converters. It has four brushes for the DC commutator, and a set of eight slip rings to the wound rotor for AC.

The generator seems to be fairly simple. It is specified as a 3 kW, 110 VDC, 27 amp, shunt wound machine. There are two heavy wires which are connected to the brushes and the rotor, and they read about 2 ohms. I assume this is the output. There are two other pairs of wires, one of which reads 150 ohms, and the other is about 1.65 k. The drawings I have show only two pairs, A-AA for the armature, and X-XX for the field. I would assume the 150 ohm winding would be connected to 110 VDC through a variable

0-250 ohm resistance. The schematics generally show a separate excitation voltage, probably so the output to the load will reflect the power input for use as a dynamometer. There is also a separate tachometer attached to the generator. I think it is well worth the $20 I paid for it, if only as a learning toy.

Today I got the other half (also for $20), which is called a Universal Laboratory Machine. The schematic shows 12 pairs of connections to the stator windings, 1-1' to 12-12', and ten connections to the rotor, A, B, C (at 120 degrees), B1, B2 (at 90 degrees), and Q1-Q2 and D1-D2 (at 90 degrees, for DC use). There is also a stator search coil X1-X2, and a rotor search coil X3-X4. There appears to be a search coil for the dynamometer X5-X6, so that is probably the extra high resistance winding I found. There is also an adjustable rotor angle indicator.

The problem is that all the stator wires were cut off from the original panel that had labels for the pairs 1-1' through 12-12'. Luckily, all the start windings were grouped in one bunch of 13 wires, and the ends in another. I used an ohmmeter to find the pairs, but they are in random order, and probably one pair is the search core, which probably has a higher resistance. The rotor wires are easily traced to the slip rings, so those connections are known. My problem is: how to find the stator windings in their proper order.

What I plan to try is to feed the rotor A, B, and C windings with low voltage three phase. Then, I believe I can read the voltage of the stator search coil, using an oscilloscope, and adjust the rotor until it is exactly in phase with A-N. I can then set the rotor to 0 degrees on the position indicator. The other stator pairs (I think) should each be 360/12 = 30 degrees apart, so I can set them in order.

There may be another way to set the 0 degree alignment, by energizing the stator search coil and adjusting the rotor for maximum voltage (in phase) on the rotor search coil. I might also be able to avoid using a three phase supply by utilizing the 90 degree B1-B2 rotor coils with a capacitor phase shifter.

Any other suggestions are welcome. I have been fascinated with motors for some time and this seems to be the ultimate learning toy. I'm not really sure how much I will use it. I mostly wanted the generator to make a dynamometer to test the HP output of specially wound three phase motors at higher frequency. This looks like the perfect setup for that. The generator is even mounted on rotating gimbals and was originally fitted with a spring scale to measure torque.

If anyone is interested, the guy I bought these from has several more in his garage in New Jersey. Let me know if you are interested and I'll give you his email address. I'm sure he would be happy to find a good home for these beautifully made machines, rather than scrapping them for the copper and iron. If nothing else, the generator would be great for hydroelectric or wind power applications.

Thanks for any help you may be able to provide. I'll let you know if and when I figure out the connections and get anything working.

Paul (The "FunGi")

Reply to
Paul E. Schoen
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Do you have any way of driving this thing at its rated RPM? Make sure you know what the RPM and voltage ratings are.

Obtain a variable DC supply to feed the rotor field. The field is most likely the D1-D2 connection through the slip rings. Its possible that the Q1-Q2 is a quadrature field winding, but for now, use only one field.

Run the machine up to speed and set the field so that the 6 stator windings put out some useable voltage, up to rated. By jumpering one end of a stator winding to another (a series connection), the voltage at the open ends of the pair can be measured.

The stator is probably three phase with paired windings. Assume you have set the field to produce 50 Vac at each winding. If the voltage of a series pair measures 100 Vac, you have identified two windings of the same phase. If it measures 0, same thing, except you have one connected

180 degrees out of phase. If the voltage is 86 Vac, you have connected two windings in an open wye. If its 50 Vac, they are connected in an open delta.

By checking pairs of windings and fiddling with the vector relationships, you should be able to identify the phase relationships of most winding pairs. Finally, you can 'series' three windings at a time to verify phase relationships by creating a 'unclosed' delta.

When I was in school, our power lab had a similar setup as a test. The

12 winding terminals were brought out in a random order to a patch panel. Our job was to make wye, delta and zig-zag connections wih patch cables using only a voltmeter without killing ourselves. The M-G sets we had were rated at around 40 Hp, 3600 RPM IIRC. Extra credit was earned for not receiveing electrical burns or blowing up a drive coupling at rated speed. 
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Paul Hovnanian     mailto:Paul@Hovnanian.com
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The large print giveth and the small print taketh away.
                      -- Tom Waits
Reply to
Paul Hovnanian P.E.

I'm far from an expert in 3-phase, it's approaching three decades since I had the courses in AC circuits analysis that covered that stuff, and I never used it at work. But it sounds like you've got half a handle on it already.

How much does each weigh? I'm about 800 miles away from NJ, and I suspect shipping could be a lot more than the asking price. If I were in driving distance I'd definitely give at least one generator-motor pair a Good Home.

Reply to
Ben Bradley

These are highly valuable devices that could sell very well on ebay.

That's what I would suggest to your friend.

i
Reply to
Ignoramus2833

I estimate the weight to be about 150 lb for the generator and maybe 125 for the motor. So far I have not done any more with them. The motor is still in the back of my truck, and it is just a bit too heavy for me to lift myself. Maybe it's time for me to start my project to add a hydraulic front end loader attachment to my old lawn tractor. So many ideas, so little time and energy!

Paul

Reply to
Paul E. Schoen

[snip]

A shunt-wound generator will not self-excite unless the total field resistance is below a certain value. I did an AVR a year or so ago, for a 28V/300A DC generator. The 2-ohm field required about no more than 1-ohm in series with it to self-excite, then at 18V terminal voltage I could switch the resistor out and let the PWM'd regulator start controlling it.

I also had a diode in series with the field so that it would not self-excite with a reversed remanence. The contactor that switched the regulator in also shorted out the diode.

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Tony Williams.
Reply to
Tony Williams

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