Response of a motor rotor to just 1/60th of a second of current

[jake jot]

Where can I get actual demonstration that a 1/60 sec current can move the magnet. That is. You just apply 1/60 sec current without other power in the middle of it, will the magnet move that fast in 1/60 sec? Or does motor runs because of inertia of the previous rotation?

 

[russ_watters]

Where can I get actual demonstration that a 1/60 sec current can move the magnet. That is. You just apply 1/60 sec current without other power in the middle of it, will the magnet move that fast in 1/60 sec? Or does motor runs because of inertia of the previous rotation?

I'm not sure i understand what you are asking. If you apply electricity to a motor for 1/60th of a second, it will barely move because it doesn't have time to accelerate up to speed.

Also, what do you mean by "in the middle of it"? In the middle of what? You only mention one pulse. And "that fast"? What fast? This post reads like you only wrote half of it, maybe skipping every other sentence. A lot of your posts do.

 

[jake jot]

I'm not sure i understand what you are asking. If you apply electricity to a motor for 1/60th of a second, it will barely move because it doesn't have time to accelerate up to speed.

Also, what do you mean by "in the middle of it"? In the middle of what? You only mention one pulse. And "that fast"? What fast? This post reads like you only wrote half of it, maybe skipping every other sentence. A lot of your posts do.

Meaning without applying any current. You just apply electricity to a motor for 1/60th of a second. The rest of the time the current is close or off. So it would barely move? Hmm.. what minimum time of current application so the motor will move? Because for let's say 3600 RPM motor. I can't understand how the rotor can response to 1/60 sec current or even faster. When I put my north pole magnetic near my south pole magnetic. It doesn't immediately stick to it so fast i couldn't see the movement.

 

[russ_watters]

Meaning without applying any current. You just apply electricity to a motor for 1/60th of a second. The rest of the time the current is close or off.

1/60th of a second, every second? Or just once?

 

[jake jot]

1/60th of a second, every second? Or just once?

Just once.. in the middle of no current. If it won't move. What X/60th before the motor will move in the middle of no current or electricity (meaning it's turned off rest of time).

 

[russ_watters]

Just once.. in the middle of no current.

Again: in the middle of what? If it only pulses once and then stops, there is no middle.

What X/60th before the motor will move in the middle of no current or electricity (meaning it's turned off rest of time).

I think it will move. Just not much.

https://www.physicsforums.com/posts/6422154/react?reaction_id=1

 

[berkeman]

Meaning without applying any current. You just apply electricity to a motor for 1/60th of a second. The rest of the time the current is close or off. So it would barely move? Hmm.. what minimum time of current application so the motor will move? Because for let's say 3600 RPM motor. I can't understand how the rotor can response to 1/60 sec current or even faster.

What is your background in math and physics and engineering so far? Have you studied topics like the Moment of Inertia of objects (their "inertia" that resists changes in rotational motion)? Have you learned about bearing frictional torque and other things that resist the rotational motion of a motor rotor?

 

[jake jot]

Again: in the middle of what? If it only pulses once and then stops, there is no middle.

I think it will move. Just not much.

In the middle of nowhere, that is. I forgot to add the word "nowhere". Meaning you just apply the 1/60 sec current. Ok. So it needs inertia to move. Let's say the electric fan is already moving fast. How much does the 1/60 sec pulse contribute to the rotation (I know the left and right hand rule and how movement occurs)? if not much, and you make it 3/60 or 5/60, what speed before there is significant contribution?

 

[berkeman]

Ok. So it needs inertia to move. Let's say the electric fan is already moving fast. How much does the 1/60 sec pulse contribute to the rotation

What is your background in math and physics and engineering so far? Have you studied topics like the Moment of Inertia of objects (their "inertia" that resists changes in rotational motion)? Have you learned about bearing frictional torque and other things that resist the rotational motion of a motor rotor?

It would make it a lot easier for us to answer your question if you could let us know your technical background. Whatever your background is, that is fine. But it is a lot easier for us to precisely answer your question if we can use calculus and undergraduate physics level replies. We can also use high school level replies if needed (more qualitative, less quantitative). '

It sounds like you want a precise quantitative reply (for whatever purpose), but you may not have the background yet to understand the math?

 

[jake jot]

It would make it a lot easier for us to answer your question if you could let us know your technical background. Whatever your background is, that is fine. But it is a lot easier for us to precisely answer your question if we can use calculus and undergraduate physics level replies. We can also use high school level replies if needed (more qualitative, less quantitative). '

It sounds like you want a precise quantitative reply (for whatever purpose), but you may not have the background yet to understand the math?

I understand the basic high school and college physics. I know about inertia or even rotational inertia. But when the electric fan is moving fast. I can't imagine how the 1/60 sec pulse can contribute to the magnetic field of the rotor. Well. I bought from amazon this a few days ago.

Amazon.com: IS Icstation 12V DC Electric Motor DIY Kit Model Simple Assemble Kit for Student Physics Science Back to School Educational Practice Learning Kit STEM Project.: Electronics

(does anyone know a better one, amazon has no other listings like it).

Do you have a java site of the contribution of pulses and rotations and inertial resistance and all that. I want to know how the magnet can response so much to 1/60 sec when they are already rotating. Btw.. the above is a dc motor. I can't get an ac project motor. It only has two commutator. In AC motor. It uses the concept of the illustration in the first message, and respond even faster than dc motor.

 

[Dale]

Meaning without applying any current. You just apply electricity to a motor for 1/60th of a second.

Hmm, what do you mean “apply electricity” “without applying current”? That sounds like a self contradiction.

 

[jake jot]

Hmm, what do you mean “apply electricity” “without applying current”? That sounds like a self contradiction.

Meaning without applying any current the rest of the time. You just apply electricity to a motor for 1/60th of a second.

Knowing the answer from others is it doesn't move.

What if the motor is already rotating. And you apply 1/100000 of a pulse. It doesn't change it, isn't it. So what is the threshold or pulse of time of electricity application before there is no more effect or insignificant effect?

The reason there *might* be no effect from 1/100000 is because magnetic field can't respond that fast in so short a time. I think it is related to inertia? How do you compute the threshold or limit when rotational resistance or inertia is no longer affected by a fast pulse (like 1/10000 sec)?

 

[jake jot]

Here it doesn't describe inertia. It's as if the rotor just responds the stator in precise coordinated fashion. There must be a threshold pulse where it can't respond anymore, is it not? like can the rotor respoind to the stator magnetic field at 1/100000 sec time?

Working principle of AC motors - YouTube

the diagram from original post came from here

 

[jrmichler]

When you apply voltage to a motor, you get a current. That current starts at zero, and increases with time until it reaches a value. The rate of increase and the peak value depend on voltage, resistance, inductance, BEMF, and time.

At any instant in time, the motor has a torque that is proportional to the current (not the voltage). The motor, along with any external load, has friction, windage, and inertia. At any instant in time, if the torque is greater than the friction plus windage, the motor accelerates. The rate of acceleration is calculated from net torque and inertia. Velocity is acceleration times time, and position is velocity times time.

I have mentioned a number of terms - motor, resistance, inductance, BEMF, windage, torque, inertia, friction, acceleration, etc. It would be necessary to write book to fully explain these terms. But fortunately, they are easily searched, and lead to good explanations. I know this because I checked.

So, yes, a voltage applied for a tiny fraction of a second make the motor turn, or at least try to turn. If or how much it turns is calculated as above. All of this is for DC motors. AC induction motors, as in your YouTube video, are more complicated. And the simplified motor shown in Post #10 is simplified so much that torque varies with both current and rotor position. It probably has at least one position where it will not self start at all.

 

[Dale]

Knowing the answer from others is it doesn't move.

I don’t think that answer is correct and I don’t think that is what others have said.

 

[hutchphd]

I think part of your difficulty in understanding is that your simple motor, when given a pulse, will equally likely spin either direction depending on its initial orientation. This is also true for a series of pulses, but once started it will most likely continue and accelerate to synchrony in the initial random direction .

 

[russ_watters]

Just once.. in the middle of no current. If it won't move. What X/60th before the motor will move in the middle of no current or electricity (meaning it's turned off rest of time).

Ok, fair enough. It will probably turn a little, but how much it will turn depends on the motor and can't easily be predicted.

What if the motor is already rotating. And you apply 1/100000 of a pulse. It doesn't change it, isn't it. So what is the threshold or pulse of time of electricity application before there is no more effect or insignificant effect?

Again, the exact result can't easily be predicted. But if a motor is already rotating, then something must be turning it (or it is in the act of slowing down). So, pulsing 1/100,000th of a second of electricity to it will have basically no impact on what is doing. Even a 1/60th second pulse will have basically no impact other than a barely perceptible bump (if anything).

I understand the basic high school and college physics. I know about inertia or even rotational inertia.
[separate post]
So it needs inertia to move.

That last sentence makes no sense. Inertia is a property of matter; it's what makes matter resist acceleration. So it doesn't "need" inertia, it just has inertia. So no, you evidently don't know what inertia means.

Also, is English your native language? We're not trying to be insulting here, but so many of your posts make so little sense that it is very difficult for us to help you. If we understood why you seem to have so much trouble expressing yourself and explaining basic physics concepts, it might help.

It also might help if you asked your real question. The question you are asking is very specific, so it is almost certainly part of a larger thought process. Something you are trying to do, perhaps? Ask us that question, and maybe we can give you an answer that skips this vague yet at the same time overly specific scenario. .

 

[jake jot]

Ok, fair enough. It will probably turn a little, but how much it will turn depends on the motor and can't easily be predicted.

Again, the exact result can't easily be predicted. But if a motor is already rotating, then something must be turning it (or it is in the act of slowing down). So, pulsing 1/100,000th of a second of electricity to it will have basically no impact on what is doing. Even a 1/60th second pulse will have basically no impact other than a barely perceptible bump (if anything).

1/60th second pulse has no impact, so a 1/30th or 30 hz AC will make the electric fan turns as fast?

The LHC is more intuitive because you use magnets to manuever the particles, and it is kilometers wide magnets. Electric fan is harder to understand because magnets you play south and north are weak, yet the electric fan moves so fast. So momentum and acceleration is the key besides magnetic field. Ok.

Look. A few days ago. I was deciding whether to buy this thing at amazon.

Amazon.com: IS Icstation 12V DC Electric Motor DIY Kit Model Simple Assemble Kit for Student Physics Science Back to School Educational Practice Learning Kit STEM Project.: Electronics

After I got it and tried assembling and running it, I became curious about motors it and it piqued my interests.

I will absorb the concepts in this thread, watch Youtube videos about them, and try to get java website with motors where you can vary the resistance, inductance, BEMF, windage, torque, inertia, friction, acceleration, etc. and see how it rotates. If you know some link, please share them.

Thanks a lot guys!

That last sentence makes no sense. Inertia is a property of matter; it's what makes matter resist acceleration. So it doesn't "need" inertia, it just has inertia. So no, you evidently don't know what inertia means.

Also, is English your native language? We're not trying to be insulting here, but so many of your posts make so little sense that it is very difficult for us to help you. If we understood why you seem to have so much trouble expressing yourself and explaining basic physics concepts, it might help.

It also might help if you asked your real question. The question you are asking is very specific, so it is almost certainly part of a larger thought process. Something you are trying to do, perhaps? Ask us that question, and maybe we can give you an answer that skips this vague yet at the same time overly specific scenario. .

 

[Dale]

1/60th second pulse has no impact,

Why do you think that? I do not believe that is correct.

 

[jake jot]

Why do you think that? I do not believe that is correct.

quoting russ_walters : " Even a 1/60th second pulse will have basically no impact other than a barely perceptible bump (if anything). "

 

[Dale]

quoting russ_walters : " Even a 1/60th second pulse will have basically no impact other than a barely perceptible bump (if anything). "

I think that you are distorting his intended point.

He also said:

I think it will move. Just not much.

Which you seem to have chosen to ignore. His position is not that it has “no impact”

 

[jake jot]

I do not think that is correct, and I think that you are distorting his intended point.

I'm not distorting. This is his exact sentence:

"Again, the exact result can't easily be predicted. But if a motor is already rotating, then something must be turning it (or it is in the act of slowing down). So, pulsing 1/100,000th of a second of electricity to it will have basically no impact on what is doing. Even a 1/60th second pulse will have basically no impact other than a barely perceptible bump (if anything). "

I wonder if there is a minimum pulse where the motor has significant rotation where additional pulses would be in the 5th percentile.

But in the case of dc motor, there is no pulse. It is one continuous dc. I'll ponder on them as i watch more youtube videos.

 

[Dale]

It is absolutely a distortion to read that and then claim it says:

1/60th second pulse has no impact,

It also ignores other clarifying statements he made like

I think it will move. Just not much.

 

[jake jot]

It is absolutely a distortion to read that and then claim it says:It also ignores other statements he made like

Sorry. So I think it says the 1/60 second impulse has barely perceptible bump (if anything). Whatever, the 1/60 second impulse can keep pushing the rotor to keep turning, isn't it.

 

[jake jot]

In the following motor. The rotor has north and south

While in other examples in youtube. It has this setup.

What is this setup called and the one with north and south rotor? So I can maybe return it to amazon and look for one with the above format.

 

[jbriggs444]

I can't imagine how the 1/60 sec pulse can contribute to the magnetic field of the rotor.

If you cannot imagine how the 1/60 sec pulse can contribute to the magnetic field then it follows that you cannot imagine how a 1/30 second pulse could contribute.

If you cannot imagine how a 1/30 second pulse could contribute it follows that you cannot imagine how a 1/15 second pulse could contribute.

If you cannot imagine how a 1/15 second pulse could contribute it follows that you cannot imagine how a 1/8 second pulse could contribute.

[...]

It follows that you do not understand how an electromagnet can ever work when you connect it to a DC power source.

 

[jake jot]

If you cannot imagine how the 1/60 sec pulse can contribute to the magnetic field then it follows that you cannot imagine how a 1/30 second pulse could contribute.

If you cannot imagine how a 1/30 second pulse could contribute it follows that you cannot imagine how a 1/15 second pulse could contribute.

If you cannot imagine how a 1/15 second pulse could contribute it follows that you cannot imagine how a 1/8 second pulse could contribute.

[...]

It follows that you do not understand how an electromagnet can ever work when you connect it to a DC power source.

For 1 second pulse or longer, I understand. I have studied this in detail.

Torque on a Current Loop: Motors and Meters | Physics (lumenlearning.com)

When it turns slowly. It is intuitive. But when it turns at 3500 RPM. I am still imagining how Lorentz force can act or catch it so fast (perhaps just boosting it?). I'm looking for something like this I can buy and test. If the Lorentz force is so strong. It is understandable. If the current is increase so much in the following, could you stand on the bar?

If the current is so strong, perhaps one can even make some sort of Lorentz projectile? I can't find one like in in amazon. Searched for "Lorentz force" or "Lorentz bar". Any tips guys?

 

[Dale]

For 1 second pulse or longer, I understand. I have studied this in detail.

Regarding what you studied, which detail do you think changes from a 1 s pulse to a 0.999 s pulse such that the former is understandable but the latter is not?

 

[jake jot]

Regarding what you studied, which detail do you think changes from a 1 s pulse to a 0.999 s pulse such that the former is understandable but the latter is not?

Because most people are only familiar with a bar magnet, north and south pole. When you put 2 pcs on the table. You can make them move slowly. We don't have a lorentz force demonstration material in everyday life, so many not familiar with it.

The induction motor is very profound., Imagine the magnetic field in the fixed stator rotates and the rotor gets synchronized with it creating 3500 RPM. Even Maxwell hadn't figured this out. It took Tesla to discover it.

What I learned in this thread was 1/60 sec pulse and lorentz force was not enough to make the rotor moves. It needs rotational momentum. And it's still profound how the rotation momentum can synchronize with the rotating magnetic field (almost except for slip).

I bought the motor kit in amazon to give to some high school student. And ended up using it.

By the way. How come many people kept saying Tesla discovered other things too? It's all false? He is really a genius, that not even Maxwell had figured out.

 

[Dale]

Please directly answer my question of post 28.

 

[jake jot]

Regarding what you studied, which detail do you think changes from a 1 s pulse to a 0.999 s pulse such that the former is understandable but the latter is not?

It's more like 1 s pulse vs 0.0167 sec pulse.

If the lorentz force were a thousand times stronger, then no problem believing a 1/60 sec pulse can move the rotor (without other current or the motor off except that pulse). But thanks to rotational momentum. I think the stator magnetic field and rotor got kinda synchronize because of resonance akin to tuning folks so no need for the lorentz force to be a thousand times stronger.

 

[russ_watters]

...so a 1/30th or 30 hz AC will make the electric fan turns as fast?

Turn as fast as what? As a normally powered fan? No, obviously not.

 

[Dale]

It's more like 1 s pulse vs 0.0167 sec pulse.

Ok, so do you still understand a 0.999 s pulse? Do you still not understand a 0.017 s pulse? Where is the exact cutoff and what changes at that cutoff that makes it understandable above the cutoff and not understandable below?

If you cannot identify a sharp cutoff and you cannot identify something specific that physically changes at that cutoff then maybe your assertion of understanding or not understanding is flawed.

 

[A.T.]

If the lorentz force were a thousand times stronger, then no problem believing ...

Because "thousand times" sounds big?

 

[Vanadium 50]

There is a lot of brush in this thread. @jake jot , you will get more out of this forum if you put more into it. Thus far, you have not really explained your question well enough, and dragging Tesla into it sure won't help.

(1) In the US, AC power is at 60 Hz, so you have one cycle after 1/60 of a second. If after the first cycle the motor does not move, it is in the same state at the end as the beginning of this cycle. Agree? Then it starts the second cycle in the same condition as the first cycle, and is exposed to the same current and current profile, so of course has the same outcome. Agree? That means it doesn't move after the second cycle either. The same argument can be made for all cycles - thus forcing us to conclude that motors don't ever turn.

But they do turn. So our premise - that they don't move in 1/60 of a second must be wrong.

(2) If I turn a motor by hand (i.e. without electricity) for 1/60 of a second (providing the same force - or if you prefer, torque - as the magnetic fields do when the motor is operating normally) , will it turn? If not, how does the motor know that the force is being provided by my fingers and not the fields?