Will A Dimmer Switch or Transformer Control An Induction Motor's Speed: 038

I just made a dis Center from a washing machine motor thanks to your videos it works fine and I've added a speed controller to it is this okay can I use voltage or current reduction devices to lower the AC voltage and run an AC motor at a lower speed so the speed of an induction motor is based on line frequency LAN frequency here in the US 60 Hertz many places in Europe is 50 Hertz of that in combination with the number of poles that the motor has will determine its speed and I'll put the formula on the screen but this is easy to look up basically a four pole motor at 60 Hertz will run just under 1,800 rpm I say just under because the motor has to slip a little bit if the rotor actually catches up with a spinning magnetic field then there's no more relative motion and you remember that I told you you have to have relative motion in order for there to be force acting on the shaft if it catches up and reaches 1800 rpm then it loses the relative motion there's no force on the rotor and it begins to lie behind well now that's relative motion again and it keeps pulling this is a generally called slip speed and that's the actual running speed of the motor generally it's about 1750 between 1700 and just under 1,800 rpm again for a four pole induction motor with that being said if you reduce the voltage to a motor you're not changing the LAN frequency you're only changing the voltage let me show you alright we're going to finish this segment on my phone here we've got my variable transformer set up so that I can show you what happens when you lower the voltage to a single phase induction motor and then also we're going to try this light dimmer switch right now I am measuring about 45 or so votes so let's get that up to 120 this is a basic line voltage from the wall here in the US 120 volts and I'll flip this over the Hertz it's about 60 Hertz 59.9 maybe they need to turn a generator up a little bit 60 Hertz this is basic line frequency and so my formulas correct my motor should run just under 1,800 rpm let's give it a shot as you can see the boat is dropped a little bit through this line because this is where the the motor is plugged in and if we measure the speed and there it is it's about 1785 or so this is a four pole motor and so that's correct I would expect it to be 1780 rpm or just under 1,800 so I'm going to lower this to about a hundred volts alright close enough as you can see 1788 we're at about sixty four volts from my transformer and we're still registering 1780 about 1780 rpm and my motor is actually starting to make a noise now but the point that I want to make is even at half the voltage the speed is the same so one thing I want to point out here is if I had this motor under load or something there was a belt here and I was driving some kind of machinery the motor would be going slower so I don't want to make any confusions here about what you just saw the motor would begin to slip eventually you get to a point where the voltage is so low the motor is just starving it can't produce a strong enough magnetic field to keep up with the spinning magnetic field the motor is completely saturated as far as the amount of current it can flow through the rotor and it begins to slow back down you've passed the point where the motor can keep up but this is damaging to the motor because you're drawing more amps than you should be drawing and that's not good but what about something like a light dimmer switch if you'll be using a light dimmer switch this has a triac inside now old dimmer switches used to use a rheostat or a variable resistor which would actually increase the resistance in the line and that will make the lights dim because there was more load in this case we're actually flipping the light on and off very rapidly so fast that you don't see the light flickering you just perceive it as being dimmer what happens when you do that to a motor well presumably the motor is being flipped on and off very rapidly right so it's not just that there's a lower voltage there's no voltage for brief periods and therefore the magnetic field is gone so the motor will kind of coast intermittently right well what kind of effect does that have I can show you all right slightly different set up this time this time this guy is plugged directly into the wall it's not plugged into the transformer and my light dimmer switch is now wired in the series as you can see I've got 122 volts from the wall I'm going to start by turning it all the way up [Music] and just like before 1787 and if I started to turn it down I've turned it about half way already and we got 1787 all right so the light dimmer switch is turned all the way down to just before off 1785 now I don't want to run into long like that I want to potentially damage my motor but the point that I want to make is the motorists chase in line frequency it doesn't care if you flipping the circuit on and off the motor may Coast for a moment in between when the circuit is off but as soon as it comes back on now there's a whole lot of relative motion between the spinning magnetic field and the rotor and it will very quickly catch back up notice that when you kick the motor on it goes from 0 to 1800 rpm or just under and less than a second the transition is very fast so it's not turning it off and on doesn't do the kind of job you want of course you're going to have a very similar effect to what I described earlier if this is hooked up to the load it will begin to slow down and it kind of seems like it's working but that's not the way to go one more thing I want to mention while I'm here is something like this I've got this router speed controller as you can see it says do not use with brushless type motors this is a brushless motor and by the way this works with a triac the same way this does so now you know light dimmer switches router speed controllers it even tells you on the label don't use it with brushless motors and that's because it this is not designed to work with that it turns out that the only good way to change the speed of an induction motor is by changing one of the variables in the formula I showed you earlier since we can't change the number of poles in the motor we need to change the frequency and that's where variable frequency jobs come in this is a VFD it's designed to control the speed of induction motors the only thing is you can't buy these for single phase induction motors and I have searched quite a bit and I believe it was last year I managed to find one that worked for a special type of 240 volt single-phase motor and I could not find another one and when I when I knew I was going to make this video I had a hard time finding it again and that's because there's so many complications changing the speed of a single-phase motor for example you have the starter winding that you have to deal with at low speeds the starter one will kick back on among other problems this is actually a three-phase motor and nearly every VFD that I've found what every BFD that I have found except for the one that I can't find again is for three-phase motors like this but if you change the frequency from 60 Hertz from 50 errors to something else you can use that to vary the speed of the motor and I'll show you so this is just a little potentiometer which is feedback to my VFD now this is quite a powerful motors on one turn it up to high but I just want to give you the idea this is a four host power three-phase motor so a VFD is the only proper way to vary the speed of an induction motor trying to run a single-phase motor especially a capacitor start single-phase motor with the VFD can lead to many problems you might have issues with it's a difficult which if you have one of those the start of winding could kick back on whatever mechanism starts it there are several reasons why people don't make VFDs for the single phase induction motor you got any other questions about this topic feel free to post it down in the comment I love to talk about this kind of stuff well I hope you found that helpful I'm going to put give you two platelets here's the one on this out of the about how motors function and the one on this side will be about how to wire motors and how to change the speed how to reverse their rotation if you want to subscribe and join my little community here you can hit the subscribe button that will pop up down here until next time thanks for watching

Channel: Jeremy Fielding

Views: 402,772

Keywords: Dimmer Switch, Induction Motor, Voltage control, Router Speed controller, variac for speed control

Id: tXJOtWPPRwE

Length: 9min 55sec (595 seconds)

Published: Sat Aug 05 2017