Left Hand Rule Applied to a Winding

[Merlin3189]

I'm not feeling confident in this, particularly since I don't understand ferromagnetism. So perhaps others might correct me.

Jake seems to be thinking there are two different ways of getting a force between magnets, depending on whether they are made of coils of wire, or are permanent magnets.

...There are two forces involved in making a rotor rotates, the Lorentz force from the current in the conductor, and the tendency of magnets to align, right?

Or is only one involved? But it appears to be two. Is it not?

I would say no - that whatever combination you have, ultimately the forces arise between charges and follow Lorenz's law.
That in permanent magnets, the permanent field comes from permanent movement of charges either within atoms, or domains (whatever they may be.) (That I think gets modeled as an equivalent surface current, much like its being surrounded by a solenoid.)

So

There is only one force - the Lorenz force.
There may be different ways of modelling and calculating the actual forces in different configurations, but they must a priori give the same result as would be given by applying the Lorenz relation, were that mathematically feasible.

 

[jake jot]

That is not a modern theory. It is just an observation. Lorenz is a theory which gives the magnitude and direction of the force due to a current and a magnetic field. If the "tendency" doesn't give a numerical answer then it is of no real use; it may be used as a rule of thumb when you first look at a motor design. But, in the case of anything but a simple motor (one with multiple coils at different angles around the axis) it tells you very little. You would need to break it down into individual planes of the winding. That can be done using the Lorenz force but how would your 'tendency' help with finding the torque due to all the windings?

Your "tendency" statement is a great simplification of what Lorenz tells you quantitatively.

Yes you hit the head on the nail.

Can you share an actual circuit where "one with multiple coils at different angles around the axis" that can't be explained by tendency to align? I just want to see the picture of what it could look like.

 

[sophiecentaur]

Can you share an actual circuit where "one with multiple coils at different angles around the axis" that can't be explained by tendency to align? I just want to see the picture of what it could look like.

I can't think of any good reason to try that and I couldn't even begin to work out how I could add up the different 'tendencies' of each of the coils to point in a direction. You can't add up 'tendencies' because you haven't quantified them (unless you have some pretty revolutionary Maths) so afaics, it's a waste of time - except for the most elementary of elementary treatments of the Motor Effect.

The point of Science is to build models that represent physical reality and which will allow you to predict and explain things interns of actual values. That always involves some Maths. The Lorenz force can be calculated in principle for any situation and it can (could) tell you the torque on any motor design that you can specify.

 

[jake jot]

I can't think of any good reason to try that and I couldn't even begin to work out how I could add up the different 'tendencies' of each of the coils to point in a direction. You can't add up 'tendencies' because you haven't quantified them (unless you have some pretty revolutionary Maths) so afaics, it's a waste of time - except for the most elementary of elementary treatments of the Motor Effect.

The point of Science is to build models that represent physical reality and which will allow you to predict and explain things interns of actual values. That always involves some Maths. The Lorenz force can be calculated in principle for any situation and it can (could) tell you the torque on any motor design that you can specify.

Yes I believed you. And I've looking for different motor designs at google images to see example of "one with multiple coils at different angles around the axis". Are you talking of DC motors or induction AC motors? An example is this:

What kind of motors should I look for that satisfy "one with multiple coils at different angles around the axis". Can someone share? Merlin3189? Thanks.

 

[sophiecentaur]

What kind of motors should I look for that satisfy "one with multiple coils at different angles around the axis".

Those images are examples. The windings are not all in one plane. Their planes are all at different angles and the axis of rotation doesn't pass through the planes. I can't imagine how that could be re-drawn with equivalent bar magnets in their place.

 

[maxwells_demon]

Basically, that motor from the amazon kit does not operate the same way as described in the youtube video above it.

The youtube video above it shows how motors operate if their operation was based on "Force Exerted on a Current-Carrying Conductor in a Magnetic Field". In this case, Fleming's Left Hand Rule applies aptly.

However, that motor from the amazon kit operates on "Force Exerted by Like or Opposing Poles of Magnets". Basically, you pass current on your rotor not for a magnetic field to exert force on it, but that you pass current on your rotor to create an electromagnet solenoid, whose poles then attract/repel with the permanent magnets. For this application, the Right Hand Rule should be more applicable.

Those windings would be wound to generate a pole opposite to the permanent magnetic pole they are facing, and commutated accordingly as they pass to the opposite pole by using inertia.

The most telling clue is that in the amazon video, the motor has to be started by turning the rotor in a certain direction (i'd assume this motor would be operable if started towards the other direction as well). Whereas the motor described on the youtube video does not need such a starting method, and would be unidirectional in operation.

Hope this clears things up for you.

 

[sophiecentaur]

For this application, the Right Hand Rule should be more applicable.

The rule your picture demonstrates is, in fact, a version of the corkscrew rule (which tells you the direction of magnetic lines of force around a conducting wire). Flemming's "Right Hand Rule" applies to the emf produced by a wire moving through a magnetic field. A good way to remember which is which is that there is the GeneRIGHTer rule and that Motors drive on the LEFT hand side of the road (in the UK, that is).

But none of those rules tell you enough about the Quantities involved and so they are actually pretty useless for actual Science or Engineering.

 

[maxwells_demon]

The rule your picture demonstrates is, in fact, a version of the corkscrew rule (which tells you the direction of magnetic lines of force around a conducting wire). Flemming's "Right Hand Rule" applies to the emf produced by a wire moving through a magnetic field. A good way to remember which is which is that there is the GeneRIGHTer rule and that Motors drive on the LEFT hand side of the road (in the UK, that is).

But none of those rules tell you enough about the Quantities involved and so they are actually pretty useless for actual Science or Engineering.

yeah. they're mostly just for visual aid. them hand rules ****ed me up in college, with all of the class doing gang signs when exams came. a hilarious sight indeed. but i think they have their value enough in the visualizations, makes us understand what they'd look like if there really were iron filings suspended in the air.

 

[jake jot]

Basically, that motor from the amazon kit does not operate the same way as described in the youtube video above it.

The youtube video above it shows how motors operate if their operation was based on "Force Exerted on a Current-Carrying Conductor in a Magnetic Field". In this case, Fleming's Left Hand Rule applies aptly.

However, that motor from the amazon kit operates on "Force Exerted by Like or Opposing Poles of Magnets". Basically, you pass current on your rotor not for a magnetic field to exert force on it, but that you pass current on your rotor to create an electromagnet solenoid, whose poles then attract/repel with the permanent magnets. For this application, the Right Hand Rule should be more applicable.

View attachment 273614

Those windings would be wound to generate a pole opposite to the permanent magnetic pole they are facing, and commutated accordingly as they pass to the opposite pole by using inertia.

The most telling clue is that in the amazon video, the motor has to be started by turning the rotor in a certain direction (i'd assume this motor would be operable if started towards the other direction as well). Whereas the motor described on the youtube video does not need such a starting method, and would be unidirectional in operation.

Hope this clears things up for you.

That's the main issue. From the start, I've been wondering which one is the case, as you described it "Basically, you pass current on your rotor not for a magnetic field to exert force on it, but that you pass current on your rotor to create an electromagnet solenoid, whose poles then attract/repel with the permanent magnets". But then look at the following illustration. The windings are large. So when it is nearing the vertical position, the current on the left hand side *can* cause magnetic field to exert force on the rotor to rotate clockwise, and same for the current on the right hand side which cause the force to be downwards. How can you say the current can't exert a force since the winding is large?

This is video of it where the user simply touch the terminal and it ran. I ordered another set of it and waiting for it since I gave the first one to a high school kid and Covid restrictions make me avoid going to his house.

https://d2y5sgsy8bbmb8.cloudfront.n...rm-Generic-480p-16-9-1409173089793-rpcbe5.mp4

 

[sophiecentaur]

"Basically, you pass current on your rotor not for a magnetic field to exert force on it, but that you pass current on your rotor to create an electromagnet solenoid, whose poles then attract/repel with the permanent magnets".

That's just tautology. The same thing is happening, however you choose to describe it. The only way to obtain actual results from any analysis has to do better than talking in terms of 'magnets'. What counts is how the individual elements of the stator affect all the individual elects of the rotor. I don't know of any convenient analysis that doesn't use currents through wires and which delivers results.
If you think that one exists then you need to find it for yourself.

 

[Merlin3189]

Those windings would be wound to generate a pole opposite to the permanent magnetic pole they are facing, and commutated accordingly as they pass to the opposite pole by using inertia.

The most telling clue is that in the amazon video, the motor has to be started by turning the rotor in a certain direction (i'd assume this motor would be operable if started towards the other direction as well). Whereas the motor described on the youtube video does not need such a starting method, and would be unidirectional in operation.

That sounds implausible to me.
If commutation occurs at the vertical position, when the rotor is midway between the stator poles, it will be attracted helpfully for 1/4 cycle then hindered for 1/4 cycle until it is vertical again and can commute. No net gain.
OTOH if it commutes when horizontal facing the pole , it will be repelled 1/4 turn and attracted the next 1/4 turn until it commutes when next horizontal. Great. BUT. The poles of the rotor will then have opposite polarity at top and bottom parts of the cycle. So the bottom can only go one way and the top the opposite other. That will determine the direction of rotation.

IMO thhe reason you give it a flick, with most two pole motors, is the resting detent position where, either no current flows, or the coils are shorted by the brushes.

 

[maxwells_demon]

How can you say the current can't exert a force since the winding is large?

View attachment 273642

This is video of it where the user simply touch the terminal and it ran. I ordered another set of it and waiting for it since I gave the first one to a high school kid and Covid restrictions make me avoid going to his house.

https://d2y5sgsy8bbmb8.cloudfront.n...rm-Generic-480p-16-9-1409173089793-rpcbe5.mp4

Oh, my bad. Yep, basically the "forces on the current carrying conductor" in each side would cancel out IF we assume that the winding pattern is just a simple coil around each solenoid.

For two-pole dc motors used in practical applications, this is not the case. If we use the same rotor as that amazon motor, the winding should be as follows:

(disregard those field windings, as our little amazon motor uses permanent magnets for the stator)

Then our current should then flow like this:

The reasons I concluded this motor to be "pole attraction" operation rather than "force on a current carrying conductor" are:

1) Those rotor windings awfully look like a solenoid.
2) The "central yellow arrow" should be a conductor if it were "force on a current-carrying conductor" operation, in which case it should be at least as numerous as the number of coils on each solenoid, but they're nowhere to be found on our little amazon motor.
3) The part of the coils that "face" us if we look into the motor shaft is awfully large. This part of the coil does not meaningfully contribute to torque, and should be minimized. It's just not a practical design for a "force on a current-carrying conductor" operation.

The only way to experimentally confirm our suspicions would be to try and start the motor, first clockwise, then counterclockwise. If the motor runs based on the start direction you spin the shaft to, then it is "pole attraction" operation. If the motor runs in only one direction despite starting it clockwise or counterclockwise, it is "force on current-carrying conductor" operation.

But then again, I am confident that our little amazon motor is a "pole attraction" operation, due to the 3 reasons I enumerated above.

 

[maxwells_demon]

View attachment 273642
https://d2y5sgsy8bbmb8.cloudfront.n...rm-Generic-480p-16-9-1409173089793-rpcbe5.mp4

Sorry my bad. The forces don't cancel out, but exert torque on that solenoid, but that this torque does not contribute to the rotation of the shaft, it just stresses the solenoid core.

I'm willing to bet, if you could detach that solenoid and stuck a shaft through its center coming from the same direction as the motor shaft, that solenoid would twitch due to the torque of those magenta arrows.

 

[sophiecentaur]

I'm willing to bet, if you could detach that solenoid and stuck a shaft through its center coming from the same direction as the motor shaft, that solenoid would twitch due to the torque of those magenta arrows.

I think the problem here is the jump between description of a motor with no iron in the rotor (and with a simple flat coi)l and a practical motor that uses an iron core in the rotor and where the system behaves more like two 'magnets' (rotor and stator) at different angles to each other.

On the subject of where the commutator action is required, the switch over has to be at the angle where the armature would be attracted and find itself with no net torque. It's an Energy Minimum and there is stable equilibrium. When the commutator switches, there is still equilibrium but it is unstable equilibrium (and Energy Maximum) and a small amount of angular momentum will carry the armature past the equilibrium position towards a Maximum Torque condition and then to the other side, where the switch reverses again.

A multipole motor uses a number of windings and a number of pairs of commutator segments but the same thing applies.

 

[Merlin3189]

First your "pole attraction" motor is still unidirectional.

As Sophie says, you need to commute at the equilibrium point, where the rotor would want to stop, if it were not commuted. Here the horizontal rotor position. Then the torque is always clockwise for this one.

If you tried to do a vertical commute, you'd get a quarter turn of CW torque and a quarter turn of ACW torque and go nowhere. It would actually just sit in its equilibrium position. If you gave it a "flick" it might complete a turn, or even a few, but would slow down due to friction, then oscillate about the equilibrium position until it settled.

Your points 1 & 3 are reasonable. If a motor is designed with a core, it's hardly surprising if the optimum layout is different from that without a core.
I can't see any reason for 2. Both designs need one wire crossing the axis.

The only way to experimentally confirm our suspicions would be to try and start the motor, first clockwise, then counterclockwise. If the motor runs based on the start direction you spin the shaft to, then it is "pole attraction" operation. If the motor runs in only one direction despite starting it clockwise or counterclockwise, it is "force on current-carrying conductor" operation.

Great. I love experiments. But whether you consider it as wires in a magnetic field, or two magnets, or a magnet in a magnetic field, IF commutation is locked to the rotation of the rotor, its direction of rotation is determined by the polarity of the supply.

I believe you may be thinking of either an AC motor or brushless DC motor, where the polarity of one of the fields or magnets changes independently of the rotor position.

I don't know whether a "pole attraction" motor is really a different sort of thing from a wire in magnetic field motor. My feeling is, they are different ways of modelling and analysing these things. Sometimes one model may be easier to handle than the other, or simply easier to understand.

If you left out the rotor core and constructed the motor with either a short fat coil, or a long thin one (solenoid style), would one be a magnet and one a wire? Then make ones intermediate between the two. Make them rectangular in cross-section instead of circular.
And maybe take a simple rectangular coil, like the diagram in post #1 . Put in a core. Start with a simple thin sheet in the plane of the coil. Gradually extend it perpendicular to the coil. Does it stop being a wire as soon as you put the tiniest bit of iron in. When does it become a fully licenced electromagnet?

 

[jake jot]

First your "pole attraction" motor is still unidirectional.
View attachment 273714
As Sophie says, you need to commute at the equilibrium point, where the rotor would want to stop, if it were not commuted. Here the horizontal rotor position. Then the torque is always clockwise for this one.

If you tried to do a vertical commute, you'd get a quarter turn of CW torque and a quarter turn of ACW torque and go nowhere. It would actually just sit in its equilibrium position. If you gave it a "flick" it might complete a turn, or even a few, but would slow down due to friction, then oscillate about the equilibrium position until it settled.

Your points 1 & 3 are reasonable. If a motor is designed with a core, it's hardly surprising if the optimum layout is different from that without a core.
I can't see any reason for 2. Both designs need one wire crossing the axis.Great. I love experiments. But whether you consider it as wires in a magnetic field, or two magnets, or a magnet in a magnetic field, IF commutation is locked to the rotation of the rotor, its direction of rotation is determined by the polarity of the supply.

I believe you may be thinking of either an AC motor or brushless DC motor, where the polarity of one of the fields or magnets changes independently of the rotor position.

I don't know whether a "pole attraction" motor is really a different sort of thing from a wire in magnetic field motor. My feeling is, they are different ways of modelling and analysing these things. Sometimes one model may be easier to handle than the other, or simply easier to understand.

If you left out the rotor core and constructed the motor with either a short fat coil, or a long thin one (solenoid style), would one be a magnet and one a wire? Then make ones intermediate between the two. Make them rectangular in cross-section instead of circular.
And maybe take a simple rectangular coil, like the diagram in post #1 . Put in a core. Start with a simple thin sheet in the plane of the coil. Gradually extend it perpendicular to the coil. Does it stop being a wire as soon as you put the tiniest bit of iron in. When does it become a fully licenced electromagnet?

I ordered 2 pcs of the amazon motor coming early next week. One will be used as control. The second one i'll modify the rotor to make the solenoid so thin there is no more contribution of the force in the windings and it becomes a N-S magnet just like what maxwell_demons was describing. It's possible, right? In the following, the top copper of the rotor is the commutator, the bottom two the windings.

Second. I'll change the rotor into one like this still making use of the commutator in the kit.

What puzzles me was this is simpler to construct, why didn't the amazon motor just use this conductor rotor instead of wiring the solenoid? any got a clue? Perhaps the above needs higher current to run?

Eventually i will learn to compute the the magnetic forces and strength of the amazon rotor. I have a dc gaussmeter.

 

[maxwells_demon]

What puzzles me was this is simpler to construct, why didn't the amazon motor just use this conductor rotor instead of wiring the solenoid? any got a clue? Perhaps the above needs higher current to run?

I guess it's for economical reasons. They didn't want to waste some wire on the diagonal traversal (that same center yellow arrow) to the other side, because of that rotor design.

Also solenoids are very simple to wind, you literally can't go wrong.

 

[maxwells_demon]

First your "pole attraction" motor is still unidirectional.
View attachment 273714

Yeah, my bad. Sophie and Merlin are right on this one. That little amazon motor is still unidirectional, contrary to what I said earlier.

You might want to chech the rotor. I think I see something like a metal strip on its end, this might be the outer end of our "iron core" block.

Such a metal block would be unnecessary for a "force on a current carrying conductor" motor. I should know. I built a simple two-pole dc motor for a friend's child's high school project using permanent magnets for the stator, with the rotor frame of just barbecue sticks. And some magnetic wire with those thin insulation varnish as the winding. Worked just fine.

Nothing beats building from scratch to see for yourself, or taking things apart. Lol.

 

[jake jot]

Yeah, my bad. Sophie and Merlin are right on this one. That little amazon motor is still unidirectional, contrary to what I said earlier.

You might want to chech the rotor. I think I see something like a metal strip on its end, this might be the outer end of our "iron core" block.

Such a metal block would be unnecessary for a "force on a current carrying conductor" motor. I should know. I built a simple two-pole dc motor for a friend's child's high school project using permanent magnets for the stator, with the rotor frame of just barbecue sticks. And some magnetic wire with those thin insulation varnish as the winding. Worked just fine.

Nothing beats building from scratch to see for yourself, or taking things apart. Lol.

Look at this video. It's much like the amazon rotor with large square winding. But why does it still analyze it with right hand rule like force on a conductor?

Working of a 2 pole DC Motor - YouTube

 

[jake jot]

Look at this video. It's much like the amazon rotor with large square winding. But why does it still analyze it with right hand rule like force on a conductor?

View attachment 273741

Working of a 2 pole DC Motor - YouTube

maxwell_demons, if you were right in message #43 that "The forces don't cancel out, but exert torque on that solenoid, but that this torque does not contribute to the rotation of the shaft, it just stresses the solenoid core.", then the youtube video above is wrong.

Wrong in the sense the torque doesn't contribute to the rotation of the rotor. What creates and determines the rotation of the rotor whether clockwise or counterclockwise is the positions of the magnets in the stator and polarity of current in the solenoid rotor.

Or the best way is to compute. Based on estimate of the dimensions. How do you compute whether force of the conductor carrying current can contribute to the rotation or not?

 

[maxwells_demon]

maxwell_demons, if you were right in message #43 that "The forces don't cancel out, but exert torque on that solenoid, but that this torque does not contribute to the rotation of the shaft, it just stresses the solenoid core.", then the youtube video above is wrong.

Wrong in the sense the torque doesn't contribute to the rotation of the rotor. What creates and determines the rotation of the rotor whether clockwise or counterclockwise is the positions of the magnets in the stator and polarity of current in the solenoid rotor.

Or the best way is to compute. Based on estimate of the dimensions. How do you compute whether force of the conductor carrying current can contribute to the rotation or not?

The youtube video explaining the single conductor motor motion is correct. It just doesn't apply to our amazon motor, as I described when I first posted here.

You can go with calculations, but look at the path of the current. And the path of the current for that solenoid exerts torque on the solenoid, whose moment arm is at the center of the solenoid, and not the motor shaft.

Forgive me for my laziness, but just looking at the current path, you'll see. The arrows you drew were correct, and should suffice.

 

[maxwells_demon]

maxwell_demons, if you were right in message #43 that "The forces don't cancel out, but exert torque on that solenoid, but that this torque does not contribute to the rotation of the shaft, it just stresses the solenoid core.", then the youtube video above is wrong.

Wrong in the sense the torque doesn't contribute to the rotation of the rotor. What creates and determines the rotation of the rotor whether clockwise or counterclockwise is the positions of the magnets in the stator and polarity of current in the solenoid rotor.

Or the best way is to compute. Based on estimate of the dimensions. How do you compute whether force of the conductor carrying current can contribute to the rotation or not?

Srry wasn't looking at the attachment. I'm on mobile rn. Yup, that motor in your attachment is still a "pole attraction" motor, based on the wiring in that picture.

I don't know if it's meant as a simplification, but you are correct. That's not how a motor operated by "force on a current-carrying conductor" principle should be wired/wound. Don't take those youtube illustrations too seriously, especially if they're not practicing in the field. You'll be better off watching how motor manufacturers approach explanations.

 

[jake jot]

The youtube video explaining the single conductor motor motion is correct. It just doesn't apply to our amazon motor, as I described when I first posted here.

You can go with calculations, but look at the path of the current. And the path of the current for that solenoid exerts torque on the solenoid, whose moment arm is at the center of the solenoid, and not the motor shaft.

Forgive me for my laziness, but just looking at the current path, you'll see. The arrows you drew were correct, and should suffice.

Ok. I'll communicate with you again after I received the amazon motors and create my own rotor with very thin solenoid or single conductors and all sorts of combinations that works with 3 to 6v DC. And when I encounter problems like the single conductor not rotating, etc.

The reason I'm very interested in all this is because of the fact you have only magnets. And when you rotate them, it becomes motor. What if there is something like it too in new forces or fields of nature. Something that is simple like magnets but when you rotate it, it has emergent properties, etc.

 

[agrumpyoldphysicstec]

“The Jabberwock was a monster with many heads. As such it resembles, in some way, the manner in which we divide our science into Physics, Chemistry, Biology, etc., and then Physics into Heat, Light, Sound, Magnetism and Electricity. Often one can spot the various heads as being Laws of Physics, and some of them look into mirrors, see their reflections and think that the total number of their kind is bigger than it really is. Thus they attempt to co-exist with their own shadows and reflections. One of the best examples I can give you is the collection of Laws of Electromagnetic Induction.
When I was at school*, I was taught Fleming’s left- and right-hand rules, and taught to remember what the fingers and thumbs represented by emphasising the initial letters of the electrical quantities thus:
thuMb – Motion
Fore-finger – Field
seCond finger – Current
Then we had to remember which hand to use for motor and which for generator. After that we were taught Lenz’s law, the Gripping rule, Corkscrew rule and Ampère’s swimming rule. What a business! They were all, apparently, separate, independent heads. But those were the bad old days – I hope. Electromagnetism is a good deal easier than that.”

Eric Laithwaite: Engineer through the looking glass (1980) – a revised and expanded version of his Royal Institution of Great Britain Christmas lectures, 1974/75.

* ‘When I was at school’ would have been shortly before WWII – nothing much has changed!

The problem according to Eric Laithwaite is that too much reliance is placed on 'rules'. These rules have been built up over centuries, starting with lodestones.

Flemming's LHR is one such. It applies to the special case of a conductor in a magnetic field - often described as a conductor 'cutting' field lines. It is inapplicable to a real commercial motor where the conductors are wound in slots in the armature where there is little magnetic flux. This case is often described as the field lines 'linking' the winding.

The 'rules' do not help in reconciling these two viewpoints. If we attempt a mathematical analysis, we find that the only electromagnetic base unit is the ampere; there is no mention of field 'lines' or of magnetic 'poles' - they are just not needed.

If we add that the example motor is not well defined and indeed does not even work very well (is inefficient and does not turn smoothly) a mathematical analysis is impracticable.

The best approach is to throw away all those 'rules' and work things out from first principles - this reply is not the place to do it. Start with a voltage source connected to a simple loop of wire with no thickness and no resistance (the flux through the loop is given by voltage times time and the units are volt.seconds or webers). From there you can add a core (assume a perfect, lossless magnetic material but do leave a gap in it). You can go on to create a (perfect) motor, generator, or even transformer. Finally, if you are inclined, you can introduce losses in your machines.

The great irony is that you can do all this with a couple of physical laws (conservation of energy and Faraday's law of induction) and the four rules of arithmetic.

 

[jake jot]

Amazon.com: EUDAX School DIY Dynamo Lantern Educational STEM Building ,Labs Demonstration Motor Activity Teaching Model Hand Cranked Power Electricity DC Electric Generator Physical Science Experiment Education: Toys & Games

I tried to get another goody at amazon, a generator kit. If you will look at delivery date, it is after Christmas. I tried ordering it along with the amazon motor. But since "shipping when items were both ready" option was chosen, Amazon couldn't ship the motor without this generator. This is the reason I'm not receiving the motor yet. But I chose separately ship at added cost so I'll get the amazon motor this weekend. Morale: don't choose "shipping together'.

I want to ask something about this amazon generator, since the item may arrive late, and before either this thread is locked or I'm booted out here. So let me ask this now.

For this video about the difference between motor and generator.

Magnetism: Motors and Generators - YouTube

The reason I tried to order the amazon generator is to test the above. That is. By connecting a battery to the output terminal and removing the hand crank, it should turn the kit into a motor, right? It's nowhere mentioned in the product. What do you think will happen? I can find out in 2 weeks if it got that delayed, and I need to know now what you think. Thanks.

 

[Averagesupernova]

The field looks like it is wrapped in plastic. So it's really hard to know anything except 'there is a magnet involved'. But, it is likely it will function as a motor if there is an actual commutator instead of slip rings. Looks like it does have a commutator.

 

[maxwells_demon]

The reason I tried to order the amazon generator is to test the above. That is. By connecting a battery to the output terminal and removing the hand crank, it should turn the kit into a motor, right? It's nowhere mentioned in the product. What do you think will happen? I can find out in 2 weeks if it got that delayed, and I need to know now what you think. Thanks.

It will. but do not connect the battery directly to the generator terminals. You might burn those windings. At least put a resistor in the circuit. Start with large value resistance and wattage, then try next lower resistance values if the setup doesn't start.

If you could determine the size of the magnetic wire they used for winding that generator and find out its ampacity, it would help lots with determining the resistance to put in place, given standard battery voltages.

 

[jake jot]

It will. but do not connect the battery directly to the generator terminals. You might burn those windings. At least put a resistor in the circuit. Start with large value resistance and wattage, then try next lower resistance values if the setup doesn't start.

If you could determine the size of the magnetic wire they used for winding that generator and find out its ampacity, it would help lots with determining the resistance to put in place, given standard battery voltages.

What if I turn the hand crank so fast and measure the amperage in the light bulb or any load with a multimeter. Can you determine the amperage capacity of the windings that way? And use this to determine the battery and resistor requirement? But then with a battery, the rotor can move much faster than when I hand crank it so it may not be related?

 

[maxwells_demon]

What if I turn the hand crank so fast and measure the amperage in the light bulb or any load with a multimeter. Can you determine the amperage capacity of the windings that way? And use this to determine the battery and resistor requirement? But then with a battery, the rotor can move much faster than when I hand crank it so it may not be related?

that would work. you can then calculate a suitable resistor's ohm value and wattage that way. though i wouldn't get my hopes up too high if i were you. in theory, that setup should turn into a motor. in reality, observe how the windings are not within the flux field lines all the time, because the stator top view does not cover the entire rotor. better hope the rotor inertia is enough to carry the commutator to the next cycle.

Good luck.

 

[jake jot]

that would work. you can then calculate a suitable resistor's ohm value and wattage that way. though i wouldn't get my hopes up too high if i were you. in theory, that setup should turn into a motor. in reality, observe how the windings are not within the flux field lines all the time, because the stator top view does not cover the entire rotor. better hope the rotor inertia is enough to carry the commutator to the next cycle.

Good luck.

Ok. Thanks. The kit will arrive next week, but I already have the following now with me so may as well scrutinize this. I want to know what kind of 3 phase AC generator this is so I know what kind of youtube animation to look for.

Amazon.com: CrocSee Micro 3 Phase AC Mini Hand Brushless Motor Generator Model Experiment Teaching Aid: Toys & Games

more clear pic in the amazon page

Here is the specs:

• This is a Micro 3 phase Brushless AC Generator Model
• This is a great way to teach or learn about generating electricity or as an experiment starting place for larger projects.
• Output voltage : 3V-24V; Output current : 0.1A-1A;
• Rated speed : 300-6000 rev/min; Rated power : 0.5-12W;

One reviewer successfully turned it into a motor. Here is his description:

"This thing is smaller than I expected, but if you look at the Amazon page carefully and compare with the LED, you can estimate its size. Or, look at the photo here. I tested it this evening with another product bought on Amazon (a 3-phase motor controller from Sydien), and was able to get the CrocSee Micro 3 spinning nicely. But only after feeding the controller with 12 to 15VDC. Lower than that and I could not get it to spin up and sync with the Sydien controller pictured.

Used as a generator, it also works, of course. Comes with an LED plugged into two of the three pins on the connector. If you spin the shaft quickly with your fingers, it nicely lights up the LED in a pulsed fashion. Not terribly bright, but it seems to have a lens to focus and is fine for indoor observation. Unloaded, I measured about 2V AC (peak) with a quick finger-spin. With my DMM, I seem to read around 2K Ohms per winding - but that varies (maybe due to AC noise picked up by the coils from the room lights?).

So don't expect much current from the thing used in generator mode. 2V and 2K is 1mA at this speed. 10 times faster and I would expect maybe 10 mA - which seems consistent with the kind of numbers I got when monitoring the full current when operated as a motor (about 30 mA at 50 RPM).

Of course Safety should always be considered. You don't want a big high-powered, high voltage, high current device for teaching and experiments. (All my motor experiments on the CrocSee Micro 3 used a low-voltage (< 15V), wupply with current limit)

Your mileage may vary of course - but for a nice little motor/generator intended for experiments and as a teaching age, it satisfied my needs - especially at the price ! "

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With the above clue, what kind of 3 phase ac generator is it? Are there many kinds? Because most videos in youtubes are large scale, so i don't know which of them matches this kit.