I am an engineer student currently building a generator from a shaded-pole motor (Fasco model D289: 6 coils, 120v, 1050 RPM). I plan to modify the rotor with permanent magnets, so that the rotation of the rotor will induce current in the armature coil. my question is:

Will the armature be more efficient at generating electricity with or without the shading coils? In other words should I keep the shading coils around the pole peace or should I remove them?

An other question from the above question. If I am to remove the shading coils: should I remove them completely or can I just cut the ring so that it is not continuous anymore?

Thank You for your answer
Francis
franc_08 [at] hotmail.com

 

Shaded pole motor as a generator

WOw , ok this is a exciting experiment. as far as the shaded pole is concerned it is better to remove it. or as you have said cut the ring so that it is not continuous anymore.

the shaded pole is a highly inductive element , and if present in the stator will form a highly inductive load. In a generator, a inductive load tends to create a armature reaction which tries to reduce the main magnetic field, leaving the shading poles will create such a effect. thus the main magnetic field, which as you say is going to created by a permanent magnet is going to be reduced even at no load conditions.

thus it is better to remove the shading coil.

The experiment in itself is going to be a difficult task , modifying a rotor as far as i know is not a simple task. you need to get permanent magnets of sufficient strength also and then make a rotor which includes the magnets and also is in perfect space alignment with the stator coils. But what ever the outcome of the experiment please reply back with the results .

and one more thing , is this the main project or part of a project ?? i am curious to know the source of inspiration for such a project.

 

Hi

This is a part of a bigger project. The main project I am working on is to make a magnetic bearing Flywheel Energy Storage device. I went to a motor winding shop for parts, and they “gave” me the shaded-pole motor, this is why I am trying to figure the most efficient way to use the armature that was given to me; instead of getting the most efficient armature that I could have got for this type of application.

The plan is to only keep the armature of the shaded-pole motor, because of its six coils with iron core perfectly molded and spaces 60 degree apart. I decided not to modify the rotor but make a new one. I will make a 24 side polygon which 4 adjacent sides will be within 60 degree. In other words 4 magnets will be side by side with the same polarity, and the fowling 4 will be of the opposite polarity (each pair = 60 degree on the rotor circumference). Thus my rotor magnetic fields will be perfectly aligned with the 6 coils of the stator.

I just examine my armature and it will be impossible to remove the shading coil because when it was manufacture the shading pole was the first thing installed on the frame, and the coils were wrapped around it. The only thing I can do is to cut a notch on the ring to break it.

What will breaking the continuity of the shading coil do? Will it make the armature a regular squirrel cage? Will it remain a shaded-pole motor but with a less powerful shading coil? Will it be better or able to be a motor/generator? Before yesterday I didn’t know anything on shaded-coil motor, so I will appreciate any knowledge (Yes I have read everything link about the subject on Google!).

Thank you,
Francis

 

Francis, cutting the shading coil should be adequate.

Do not expect, however, the output voltage wave form to be that of the sine wave. Output current will be significantly distorted.

Reur your question about performance... NO! It will not be better as an induction-generator than a motor without the shaded-coil construction.

CAVEAT: to insure output current does not exceed the nameplate current rating, be sure to measure it with "True" RMS-reading ammeter! Also keep an eye on motor temperature!

Phil Corso

 

o Process Value... Armature-Reaction is present for any type load; resistive, inductive, or capacitive, i.e., regardless of power factor!

o Francis... The FASCO data sheet indicates the motor has 5-speeds. Such variation, is done wth what is called slip control. It is usually obtained via winding-taps, that select the amount of winding to be powered.

Minimum speed occurs when the entire winding is powered. Conversely, highest speed occurs when voltage is applied to the smallest section.

Thus, I believe you may have a complication regarding which tap to use for output.

1) How many wires are present?

2) And how much power (Watts) do you expect to produce?

For additional information, contact me off-list. (Cepsicon [at] aol [dot] com)

 

Phil , yes armature reaction is present for all types of loads , but they have different natures is it not , inductive current is in phase opposition to the main field thus reduces the main field , resistive in 90 deg with the main field thus distrots the main field and capacitive in phase with the main field thus enhancing the main field. i was trying to say that the shaded pole will act as a highly inductive load in the stator thus reduce the main field flux.

Francis ,

what you are going to do should work theory , but i do not have good experiences changing the machine design itself. the motor though a small one will have its own design and characteristics. Changing the rotor, you need to fabricate the exact same dimensions, take care of even rotor gap, fit new bearings because the rotor you make might be heavier, there are a lot of issues with this.

i do not know what kind of facilities you have in school, but this needs quality craftsmanship and a lot of trial and error as you do not have the initial machine design to rework.

i know that in student projects, funds are frugal and we try all types of mcgyverism to find our way through the problem. from my experience such modifications seldom are not worth the effort, they take time, take even more time to trouble shoot and in the end do not work satisfactorily. make shift and new fabrications work well on pure and simple mechanical devices, fly wheels, gears, these are some areas where you can experiment. they are rugged and you can replace them with one another. even electronics, they are modularized these days and you can substitute one element for a similar one and it will work. but it is not the case here, you are planning to rework the entire rotor on a machine which you have no idea of how it was designed. this will be time consuming and it is wasted labour.

ultimately , spending a few bucks more on a good motor/generator set (you don't need a new one , an old one or a newely wound one will do just fine) which you need for the flywheel project will help you in saving time (and money) and will give you more time to focus on the main project itself , than spending all your time to make the altered motor work satisfactorily. There are many places where you can get a custom made fractional KW motor done on your specifications. a good place to start looking is electrical consumer goods servicing stores. if they repair a mixie or a table top grinder they will surely have contacts to people who can build you a motor , or at leaset rewind one to suit your needs.

Hope this helps. best of luck with your project .

 

First thank you all fro your comments.

o Process Value... The budget comes from me so since I was given a motor I will use it.

o Phil Corso...
1) Yes you are right my motor has 5 wires for the five speed low to high.

2) I have no expectation in watts as long as I can generate electricity to show that my flywheel works.

As I said I am building a flywheel, thus I have to design the system for three state:

(1) Motor spin the flywheel to its maximum RPM.

(2) Flywheel spin on magnetic bearings to minimize the energy loss over time.

(3) Flywheel spin rotor which generate electricity.

Step (1) the motor:
I learned that maybe I should not cut the shading coil because:
"without the shading of the poles, the unit when motoring will have no preferential direction to rotate. It won't be able to "make up its mind" and will just vibrate back and forth. You will have to provide some means of spinning it up close to synchronous frequency, and then it will pull in and act as a motor."

ca[dot]answers.yahoo[dot]com/question/index;_ylt=AtAYwJftDXXPc0ybSXslYdLpFQx.;_ylv=3?qid=20110122173431AAillEx

Also you said "It will not be better as an induction-generator than a motor without the shaded-coil construction"

My motor "might" not be self starting without the shading coil (I don't understand the theory if it will or not be self starting after changing the rotor with permanent magnets?), and you said it would not be a better motor without the shading coil. Therefore I think that I should use the high speed wire of my motor for this step in order to achieve the highest RPM possible, and not cutting the shading coil?

Step (2) the flywheel:
Easy no load across my motor wires so my fly wheel and rotor will spin freely on magnetic bearings that I designed (they will be attached on the same rod).

Step (3) the generator:
A load will be put across the low speed wire of my motor and the neutral; this will generate the highest amount of electricity possible? Since you said "It will not be better as an induction-generator than a motor without the shaded-coil construction" I don’t think I need to open the shading coil for this step also?

Conclusion:
For the purpose of this project I don’t see reasons to risk cutting the shading coils anymore because my motor will spin my flywheel to similar speed in both cases and the flywheel potential energy will generate similar amount of electricity in both cases. (Please tell me I am wrong if you think so and explain why!).

The output voltage and frequency of a flywheel will never be constant, so I know I will have to rectify the current to DC and then convert it back to AC for the electricity to be useful.

Question:
(see message "Posted by Francis on 22 January, 2011 - 7:42 pm")
Am I right with my magnets configurations? I am starting to think that in the 60 degree occupy by one coil there is about 1/4 occupied by the shading coil, but there flux sometimes oppose each other. So I was wandering if polarity of the rotor’s magnets should be arranged differently?

Francis

 

Francis... feel free to post my off-forum comments to you!

Phil Corso

 

>Francis... feel free to post my
>off-forum comments to you!
>
>Phil Corso

Magnetic bearing and flywheel project

from you post i gather that you need to do that following things

(1) Motor spin the flywheel to its maximum RPM.

(2) Flywheel spin on magnetic bearings to minimize the energy loss over time.

(3) Flywheel spin rotor which generate electricity.

so first things first

1. DO NOT cut the shading coils of the motor , the shading coil is responsible for the generation of the rotating magnetic field in the motor , if there is no rotating magnetic field the motor will not be self starting.

2. There is no need to modify the rotor , why would you want to do that ?? you can run the machine as a induction generator all you need is a external field

creating device , which is nothing more than a capacitor bank connected parallel to the induction motor. an induction machine will run as a generator when it is run at super-synchronous speed. if you are connected to the electricity mains , let us say that the machine is a 6 pole 50hz one and you drive the induction machine at speed more than 1000 rpm it will supply active power to the mains rather than taking power from it. during this time the reactive power required by the induction machine , to create the field is taken from the mains. thus a super-synchronous induction machine draws reactive power from the grid while supplying active power to the grid. hope you understand this theory part.

now what you need to do.

1. in the test setup connect three things parallel to the main utility supply , a resistor bank ( a light bulb will do) , a capacitor bank (its design is important i will come to it later) and your shaded pole motor with the magnetic bearing and the flywheel

2. when connected to the mains the induction machine will run as a induction motor , the light will glow in the bulb , the capacitor bank will be charged and the flywheel will store the rotational energy.

3. now cut off the mains supply , either with a static switch or a ordinary one. now the mains supply is 0 hz while the induction machine is running at 950 rpm which is a supersynchronous speed. the load here is the resistor bank or the bulb and the capacitor will supply the required reactive power to maintain the magnetic field in the induction machine. now the flywheel will cause the induction machine to maintain the speed but eventually it will dissipate the energy. you will see that the light bulb will become dimmer and dimmer as the machine speed reduces. thus the energy stored in the flywheel is transferred to the resistor bank or the bulb.

design of the capacitor bank

the capacitor bank should be designed so that it should be able to supply a stable reactive power , ie a stable magnetising current for a time greater than the stable operating time of the fly wheel. this is to endure that the generator has sufficient magnetising current the whole time the flywheel supplies the active power.

why a shaded pole motor is a "bad" choice for the above application

in a fly wheel system the energy of the flywheel is determined by the moment of inertia I and the speed w. it is given by the formula
energy = 0.5 * i * w2

thus to store more energy you should have a high speed machine with high inertia , as you will have a restriction with the radius of the flywheel you will need to have a heavier flywheel to store more energy.

shaded pole motor has a very low starting torque , it is used predominantly for fans and blower applications. attaching a heavier flywheel to a shaded pole motor is not a good idea. it will not start as the starting torque needed will be beyond the motor capability. you should check with the starting capacity of the motor before designing the flywheel.

this is what i would do , this is my opinion alone , there is always other ways and better ways to do the same. if you want to go ahead and modify the rotor, my experience tells me that it would not be a good idea. once again good luck with your project and yes please post your results for us all.

 

Thank you for your answer for now I don’t have to debate what to do with the shaded coil.

"There is no need to modify the rotor , why would you want to do that ??"

Well because shaded-pole motor don't generate electricity when spin in the opposite direction, and I was focusing on designing a rotor that will have no contact to anything. I did not know that a stator could generate electricity from a nonmagnetic rotor; and at the same time the stator to receive electricity from a capacitor bank so that it can produce a magnetic field to the rotor.

Yes I know for shaded-pole motor being of la very low starting torque, but the motor was free. I will start it on low, and then I will switch to medium-low, medium, medium-high, and then high until it reach its maximum RPM.

I will post the result when finished; the due date is in 4-5 weeks.