How induction motors work

How induction motors work


In my last video
I explained how DC motors like the one in this drill work. And in this video
I’ll cover a different kind of motor Induction motors.
Like This furnace motor or the motor in this fan. or a small shaded pull motor. This is a shaded pull motor which is the simplest form
of induction motors. And I’ve already taken
the screws out. So let’s take the rotor out. And you can see here
this is a simple thing and it’s not in any way magnetic.
It doesn’t attract the screwdriver
in any way. But it dose have these lines accross it. And these lines are essentially
a short circuit winding
on the rotor that’s been cast in place. It’s a bit like the rotor
of a DC motor but with all the windings
shorted out. The rotor’s actually
passively magnetized
by the stater. But these short-circuited coils here they actually prevent
the magnetic field from
changing too quickly because as the magnetic field changes a voltage induced
that causes the current to flow which then counteracts
the change in the
magnetic field. So we basically have a rotor that, even though it’s
very permeable
to magnetism It doesn’t like it’s field
changing very quickly. I can demonstrate the same principle
with this aluminum disc. It’s also like a short circuit winding. So if I put this disc
between these 2 magnets that induces a current in the disc
as it rotates and that counteracts it
so it slows it down. With the shaded pull motor
if I apply DC to the coils that creates a magnetic field
which also slows down the motor. With this furnace motor
I applied just a few volts DC to the stater
will also slow it right down. The breaking effect is enough
to keep this 10 pound weight
from dropping very fast. But if I cut power
it really goes. So the rotor for and induction motorreally doesn’t like to spin
in a magnetic field. But if we spin the magnetic field then the rotor will
try to follow. Coming back to this aluminum disc if I now move the magnetic field
accross the disc that actually spins it up
a little bit. So we could spin the magnetic field
by pinning the stater
around the rotor. But as a motor that would
be very useless. So in a 3-phase motor
we pin the magnetic field
electrically. So, imagine we have current
going through the blue wires so that north is here
and south is here. And next we’ll apply current
to the green wires and then to the red wires. And then we’ll apply it
in the opposite direction
throught the blue through the green
and through the red so that we have this magnetic field
that keeps spinning around. In a 3-phase motor
we actually apply these currents continuously as Sine waves
so that this transition
is very smooth. And you really do get
the spinning magnetic field. This spinning magnetic field
will magnetize the rotor but the short circuit windings
in the rotor resist changes in the magnetic field so as the magnetic field spins the rotor will follow. To get this nice spinnning
magnetic field we need
3-phase power. But the problem is
most houses aren’t wired up
for 3-phase power. With single phase power
all we can make is a magnetic field
that goes back and forth. And on this motor, I cut the
starter winding so if I
power this motor up it just sits there and hums a bit.
But if I give it a slight spin that spins it up. Now because it’s only going
back and forth, this motor
has no preference in direction.
So I can just take this motor
and spin it the other way around and its just as happy
going that way. There are many ways to give a
single-phase induction motor
it’s initial kick. The simplest of these is a
shaded pull motor. In here we have 2 copper
short-circuit windings around part of the pole
and that’s what called it shading. And as you recall, the copper winding
the short circuit winding doesn’t like the change in
magnetic field very much. So, as this goes north here the north side on here
is delayed a bit and then
as it switches to south again, this part of the pole
is delayed switching to south. So, as the magnetic field
goes back and forth this part will always be
a bit behind. And that will give the rotor
it’s initial kick
to get it going. In fact, even if I even if I
just give this motor
some DC pulses every time the shaded part
is a bit behind then the rotor tries to follow
to change a little bit. But now, if I switch the current to AC. And I get up to operating voltage. The motor runs just fine. These shaded pole windings
are actually short circuit windings and they’re very inefficient. So this sort of thing
is only used on
very small motors. Larger motors, like this
furnace motor use an auxillary winding
to start up. That winding’s also very inefficient
so its always disengaged once the motor’s up to speed. And as it slows down that click you hear is the
centrifical switch turning the auxillary winding back on. There are many different ways
that are used for
starting AC motors. And that could be a
whole video unto itself. I’ll explain more of that
at the article that I’m
linking from the description.

100 Replies to “How induction motors work”

  1. What about, how to control the speed of an AC motor single and three phase with & without loss of torque?

  2. I like your explanation of the shaded pole motor. I think it would be great if you could add another video explaining the electronics behind controlling the speed (rpm) of a shaded pole motor.

  3. I took apart a coffee grinder and it has I believe a universal motor, how would I slow down the spin of the rotor? I tried cutting the wires to reduce the electric flow but I'm not sure that's safe.

  4. These motor videos go beautifully with what I'm learning in my E&M class. Thanks so much for the great content.

  5. For years my AC cement mixer´s needed a good heave to set it in motion. Now I understand why…I suspect the fat capacitor I´ve always vaguely wondered about needs replacement : )

  6. These videos are fantastic. You are a wonderful educator. Any videos on using different motor types for actuation – details on sizing, torque, speed selection, compatibility for programming via LabView, Java, Arduino – perhaps applying encoders and building digital control systems (PID feedback)?

  7. hello sir, been watching many of your very imformative videos and it came to me wondering if you could make a video on how to rewind ac motor? mostly used on our circular saw.. by the way here in the philippines we mostly use single phase 220v motors.. thanks and more videos from you sir..

  8. Why am I not taught things like this? Society nowadays degrades the importance of mechanics. They blow it off for poor uneducated "hill billys". Yet, we use these everyday! Instead of learning/teaching our children plate tectonics and water cycle from kindergarten to high school, teach this. Take things apart! I'm 15 and I learned more from Matthias in 1 hour than a school year.

  9. Matthias Wandel, tell me please the authors of books on which you are trained in universities. On the discipline of electromechanics. I want to compare how they explain in different universities.

  10. i was searching months upon months to learn the diffrence between AC and DC motors but someome finally explained it so i can understand. im dutch and i love your projects

  11. Thanks for this video, I've been through HVAC school but never really fully understood induction motors until now. 👍🏼👍🏼

  12. this was a good explanation
    too bad school are killing student interest with theory, theory, theory
    especialy the one including math stuff
    theory are born from curiosity and experiment
    you replace the curiosity and experiment, it just a boring bullshit

    i want to know how it work and why it work
    or even made one myself
    not just solving some math problem that i dont even know what for
    in my country nobody want to be an inventor, because they only taught about theory
    so no one can built a real stuff

    i think people on the past not all ace on math
    they do the math because they frustated and need some calculation
    so they can make a thing perfectly

  13. Thank you for the video. I really enjoy seeing how this stuff works. I hope to develop my understanding of motor types to the point that I am able to distinguish the types of motors I encounter, and anticipate their properties based on that knowledge.

  14. When I stick a magnet to my aluminum bike frame and it does not stick. How come the aluminum disk is affected by the field?

  15. hi matthias! , can you please make a video showing the difference between the wiring and operation of a psc (permanently split capacitor) motor and another induction motor with 2 caps (start and run caps) on it? thanks.

  16. Hi,

    Brilliant presentation.

    I made a couple of tests of those shaded pole motors on my channel using my Custom Home Made Variac device.

    But also a couple of Dishwasher/Washing Machine induction motors as well.

  17. Good explanation. Do you know if there is an induction table saw you would recommend. Not too big and heavy. I am a DIY without much space and neighbors quite close. As I understand it, they don’t make much noise running

  18. Hi Matthias, why do you faver AC induction Motors over lets say a DC tread mill motor for you home made machines. Is it just simplicity a lack of complicated electronics

  19. Your way of explaining electric motors are the explanations I needed to understand how they work. Thank you!

  20. Thanks for the informative video!

    I salvaged a washing machine motor with only 3 wires, red, yellow and blue. Couldnt figure out the wires as the motor is completely sealed.

    As red and yellow was connected to a capacitor so I figured that one of it should be neutral.

    Connected red and yellow to live and neutral (vice versa). Motor started humming then started to spin at low after I rotate the rotator.

    The motor works without the blue wire connected. Now I am curious whats the blue wire for? Are you able to enlighten me?

    If there is no more updates from me, I am probably electrocuted

  21. I'm brazilian, and i speak and understand english, but not very well. You explain and talk so well, confident and with a amazing didatics and home made equipments that everbody can understand and lear the principles envolved. Well done! I agree with Tony Watson below, would be nice and useful we learn at school, but not just teory, but the pratice, with a teacher who can explain with the same mastery as you taught.

  22. I hope you start doing more videos like this again. The current LEGO thing is interesting but these are really helpful.

  23. I had question my ac blower motor not working its humming… and i dont know what is the problem . It is 208-230 v single phase , 3/4 horse power with capacitor. how can i check the problem.

  24. You are really awesome teacher, thanks so much for such a wonderfull explanation and video on this! god bless !

  25. Thank You for sharing what You have learned and the wisdom how to bring it to us in a very understandable way

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