4 Pole to 12 Pole AC Motor Conversion

(Side note) - Great site for introductory AC motor (rewinding) basics: http://www.uiitraining.com/b51a/100/15104ac_motor_rewind_intro1.htm
So, if a three phase, 4 pole (1800rpm) motor has 12 pole-phase groups (PPG's), can these PPG's be reconnected for a single phase, 12 pole (600rpm) motor? (Of course it would not be able to self start, not an issue if, for instance, you are creating a low rpm generator)
Here is what I did as an expirement:
I took a 10hp, 3 phase, 200V (3 lead) Baldor motor (equivelent to current cat. # M3313T-8), found the internal star connection and broke it apart. Then connected three leads and routed these leads to the outside with the other 3 leads. The 3 original leads are the starts (S) for windings 1 through 3 and the 3 new leads are the finishes (F) for the same 3 windings. I then connected the 3 windings in series, 1F to 2S, 2F to 3S. I gave the motor a gentle spin and connected 1S and 3F to 120VAC. It runs 600 rpm.
The specs for this motor state that it should run 20A on 200VAC 3ph, no load.
Having only 240VAC 3ph, I connected it (factory configuration) and measured 33 amps per leg, no load.
Reconfigured for 12 pole, single phase, it runs 33 amps on 120VAC. (This is a 2 times the square root of 3, or 3.464, reduction in input power.)
I connected a buck transformer to reduce the input voltage to 102VAC, it runs 26A, no load.
I have not been able to evaluate torque performance (although it will shread a glove in short order if I grab the output shaft), nor have I been able to evaluate performance as a generator. I did confirmed the 600 rpm with a strobe.
Any comments or recommendations?
Motor Maniac
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Motor
I like what you have done. Thats alot of effort. I suspect you've already considered measuring the stall torque of the 600 RPM motor buy installing a long arm on the shaft and measure its stall torque.
I built a dynomometer for measuring the Torque and RPM of 3 phase motors. If you are anywhere near the Los Angeles area, I'd be interested in sharing my dyno components with you for evaluating your interesting 600 RPM motor re-connect.
Jerry

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Jerry,
Yes, the pony brake setup is the next project. Hopefully at the lower rpm and approx 1/3 of the original HP a simple friction setup will work.
Thanks for your dyno offer, but I live in Texas.
I have an old Sanborn strip chart recorder (8 channel with only 4 amps?? I can't remember) set up with 3 current transformers for measuring the phase currents out of my original rotary converter at various loads. Might be a good match for your setup. Worked last time I used it, just looking for a good home for it.
MM
On Wed, 19 May 2004 21:40:33 GMT, "Jerry Martes"

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Motor Maniac,
Assume you are talking about an old fashioned Prony Brake, not an inertial dynamometer. The article, "Horsepower and the Prony Brake Dynamometer" In Jan/Feb 2003 issue of Live Steam Magazine offers a good overview and worked out examples using a conventional Prony Brake.
Bob Swinney
wrote:

motors.
sharing
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Bob,
Thanks for the input. I do not have access to the article, but this is what I therw together over the lunch hour.
I rolled the motor on to its side at the edge of my work bench, the motor free to roll approximately 45 degrees in either direction. I screwed a piece of all-thread into the hoisting hole in the top of the motor. The all-thread now extending out horizontally and past the edge of the bench. I measured and marked the point on the all-thread 12" from the output shaft center line of the motor.
I next mounted a Hunter 0-50# spring gauge to a large plate laying on the floor and connected the gauge to the mark on the rod with a wire.
I configured a pair of 1x4's into a tweezer configuration and put the front 1/3 or so about and extending beyond the output shaft.
I started the motor and began squeezing the open end of the boards together. Here are the rather disappointing results:
102VAC input setup 26.0A no load 27.0A 5 ft-# 27.5A 6 ft-# breakdown occured at 8 ft-# stalled rotor current = 33A (zero torque @ stall, no start windings)
I did not measure the shaft speed at tthe various loads, but if we use 600 rpm then, 600rpm = 10 rps = 62.83 radians/sec At 8 ft=# thats 503 ft-#/sec or 0.91hp
Me thinks I do not have a motor but a 2.6 KVA heater, possibly a nice hand warmer in the winter.....ARRRG!
MM
On Thu, 20 May 2004 11:32:39 -0500, "Robert Swinney"

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Motor Maniac, You won't be able to construct a prony brake around torque readings only. You also have to take into account RPM and the length of a torque arm. An inertial dyno may be easier. Check with Jerry re.doing the inertial dyno thing. I think he researched inertial dynos pretty well and may be able to help you.
Bob Swinney
wrote:

inertial
In
worked
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Bob
Not inertia dinos. But I do have a considerable amount of time involved with building a regular dyno where I measure the Torque and RPM while adjusting the load on the motor. I get the best resulkts with the aluminum disc thats attached to the motor shaft, and load it by applying DC thru it. Excel does all the hard work and produces nice graphs of either Torque or HP as a function of RPM for the motor under test. This system sure makes it easy to evaluate the effects of adding idlers and tuning.
Jerry
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wrote:

Pay attention to Jerry..he has devoted a hell of a lot of time and energy developing his data. And the gent is smart as hell too.
Gunner
"A vote for Kerry is a de facto vote for bin Laden." Strider
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involved
aluminum
it.
HP
Guner
Jerry is not so smart, but he does know Don Foreman.
Jerry

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Motor
I might be able to save you some time when you do get around to making a dyno. I made about 20 different dynos in my attempt to 'get things right'. Depending on how much you want, you can build a dyno from an automobile disc brake for 10 HP and less. The way you build and instrument your dyno is dependent on how much accuracy you want to get. But, you can get some pretty good information about the 12 pole motor's HP by mounting a car disc brake on the motor. The best dyno I've been able to make uses an aluminum disc and some electromagnets to "load the rotating disc".
You are welcome to contact me 'off line'.
Jerry
wrote:

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Jerry,
I think we were both posting at the same time. I think the disk brake rotor is a great idea, especially if this motor has anywhere near the factory torque of 30 ft-#. Read my post above, the motor puts out only 8 ft-# which I easily soaked up in a couple of 1x4's. A hoaky setup indeed, but I got the info we needed for this expirement.
MM
On Thu, 20 May 2004 17:46:14 GMT, "Jerry Martes"

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Jerry,
Can you elaborate on these statements?
1) ....aluminum disc and some electromagnets to "load the rotating disc".
2) ....aluminum disc thats attached to the motor shaft, and load it by applying DC thru it.
#1 I understand that you are inducing eddy currents into the disk, the higher the magnetic field, the higher the currents and resulting torque.
#2 Sounds a bit like a homopolar rotor where, if I remember correctly, current is applied through brushes, one set on the outer diameter, the other set on a smaller diameter or on the shaft.
Thanks,
MM
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MM
I made a 14 inch diameter disc from a plate of 1/4 inch aluminum and bolted it to the pulley. I mounted a strong electromagnet, thats free to rotate, out near the disc outer radius. The electromagnet puts its field thru the aluminum. As the current in the electromagnet is increased, the spinning motor is loaded more heavily. I have a load cell on the "free to rotate" electromagnet so the force can be measured with a simple voltmeter and fed directly to Excel, where it the computer does all the 'hard work'.
This 'spinning disc' and 'electromagnet' is dirt simple. No brushes, no super science, all I needed was alot of scrap parts and One Don Foreman.
Jerry
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Jerry,
Thanks, sounds like a great setup. I will continue to dig for rewind info to make a 12 pole motor. It can be done, just gotta keep digging. When I get a motor an old shoe can't stop I'll be diggin through my scrap parts (damn, I just love shopping at the dump!!)
Until net time.
MM
On Fri, 21 May 2004 15:43:46 GMT, "Jerry Martes"

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On Fri, 21 May 2004 17:34:15 GMT, snipped-for-privacy@MM.com (Motor Maniac) wrote:

The basic problem is that your reconnections have produced a field with a 12 pole component but the winding configuration does not distribute the field efficiently.
For simplicity consider a 2 pole 3 phase machine. When any one phase is energised it produces a roughly uniform diametric N-S magnetisation polarisation of the entire rotor. This is because each bunch of phase windings spans as nearly as possible 180 deg - a rotor diameter.
In a 4 pole machine each bunch of phase windings will span 90 deg producing a 4 pole N-S polarisation of the rotor iron i.e 2 N poles and 2 S poles spaced alternately
The same stator wound as a 12 pole 1 phase machine would need 12 sets of windings each spanning 30 deg. Because of the limited number of stator slots a "set" of windings may be no more than a single coil spanning 1 or 2 teeth. The rotor magnetic pattern is then 6 N poles and 6 S poles spaced alternately.
The problem with your 3 phase reconnection is that it is producing 6 overlapping 4 pole fields each spanning 90 deg of the rotor instead the correct 30 deg.
This means that a rewind is needed. With a 12 pole 1 phase machine it is worth remembering that only the wire passing through the stator slot produces useful torque. The wire outside the slots simply connects the ends of the torque producing wires.
The magnetic polarity of the adjacent teeth is determined by the axial direction of the current in the torque producing wires. If the go and return currents on either side of a single tooth produces a N pole the route taken by the external connecting conductors can be routed as convenient.
As an example, a 12 pole winding on a 12 tooth stator could be individual coils on each tooth series connected. A much easier arrangement for experimental purposes is a single prewound large diameter coil which is zigzaged thru alternate stator slots. This produces the same field pattern in the rotor but may be easier for you to manufacture.
For a 24 tooth stator, zigzag thru alternate slots. A second coil zigzagged thru the remaining slots would behave as the second winding of a 2 phase machine. Zigzag winding is rarely used commercially because it's only efficient on multipole machine with small numbers of slots per pole. On most other machines the conventional configuration is more efficient.
You will need to use thinner wire for the rewind because the lower rotor speed means, for a 4 pole to 12 pole conversion, you need 3 times as many turns to generate the same back EMF.
Jim
P.s. Don't forget your rewound 12 pole machine will operate at roughly the same flux density as the parent 4 pole machine. This means that the maximum torque will be about the same and the horse power will be reduced by a factor of 3.
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Jim,
Thank You Very Much!!
Your post is very informative, I believe I am beginning to understand.
I will continue to search da net and continue to piece things together.
Again thanks goes to you and to Jerry and the others for the dyno discussion, all useful information.
MM
On Sat, 22 May 2004 13:40:14 +0000 (UTC), snipped-for-privacy@yahoo.com wrote:

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MM
If you want to convert old 3 phase motors, maybe you would like to disconnect one of the three windings and make the motor into a sngle phase motor. That takes a little time to dig into the windings and reconnect. But you sure can get alot of HP from old 3 phase motors and get pretty good start up torque too. Or -- You can go buy the right sibgle phase motor and not bother with reconnect and digging inside the old 3 phase motor motor.
Jerry
<Motor Maniac> wrote in message (Motor Maniac) wrote:

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Jerry,
I don't learn as much for just taking money out of pocket to buy a new single phase motor. (Don't get me wrong, I seems most of life's learning expirences have taken money out of pocket)
It would be great to study the windings and see if reconnecting the PPG's would have the desired final result, but I have not stumbled onto enough info on exactly how the thing is wound. I may need to get my hands on a burnout and unwind and learn that way. I have disected an alternator stator, took good enough notes to be able to rewind it. It is not much, but it is a start.
MM
On Mon, 24 May 2004 23:44:25 GMT, "Jerry Martes"

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Jerry,
How about this connection:
For a six lead motor: A phase, start/finish = 1S and 1F B phase, start/finish = 2S and 2F C phase, start/finish = 3S and 3F
Three phase "Y" connection: Connect 1F to 2F to 3F Connect L1 to 1S, L2 to 2S, L3 to 3S
Three phase "Delta" connection L1 to 1F to 2S L2 to 2F to 3S L3 to 3F to 1S
"Single phase Delta connection" Connect 1F to 2F Connect 2S to 3S Give it a spin and then Connect L1 to 1S Connect L2 to 3F
(essentially, take the 3phase delta connection, swap 1 winding end-for-end, open the delta and apply single phase power)
This will run the same RPM as the original 3 phase motor, at reduced horsepower.
MM
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On Fri, 21 May 2004 15:43:46 GMT, "Jerry Martes"

Greetings Jerry, It seems that, from your description, the torque measured is equal to the radius of the location of the magnet. So, if a disc of, say, 5 inch diameter with an electromagnet mounted such that the field passes through the 1' radius would give me inch pounds if a pound scale was used. And using the laser tach I just got through Spehro the HP could be figured out by multiplying the rpm by the torque. This sounds like a project that I could do. I could use the digital scale that's used in my kitchen right now. Thanks for posting. ERS
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