Left Hand Rule Applied to a Winding

[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 ! "

----------------------------------

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.

 

[maxwells_demon]

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.

there's no such thing as a "pole attraction" operation generator, if that's what you're asking.

all generators that make use of windings that cut across magnetic flux lines to generate voltage. speaking of which, where's your stator magnets?

i don't know man, it looks awfully like a stepper motor to me.

 

[maxwells_demon]

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.

Brushless DC motor = Stepper motor = "Pole attraction" operation

basically they might act as generator by the variation of magnetic flux on each rotor pole using Faraday's Law (which is basically how a transformer works), but the voltage you get is tiny, at this scale. you might want to check out how a synchronous ac generator works, that's basically how you'd reverse this process.

I won't call it a ripoff, but I'd call it an impractical way to generate electricity at this scale.

 

[jake jot]

Brushless DC motor = Stepper motor = "Pole attraction" operation

basically they might act as generator by the variation of magnetic flux on each rotor pole using Faraday's Law (which is basically how a transformer works), but the voltage you get is tiny, at this scale. you might want to check out how a synchronous ac generator works, that's basically how you'd reverse this process.

I won't call it a ripoff, but I'd call it an impractical way to generate electricity at this scale.

Brushless DC motor is used in mini fan. But I can't find any video showing how they can become 3 phase? Why does the product say it's 3 phase brushless generator? Any article or video how the AC thing from the brushless DC work? I can't find any one.

I understand AC inductor motor but not it. Thanks.

 

[jake jot]

Brushless DC motor = Stepper motor = "Pole attraction" operation

basically they might act as generator by the variation of magnetic flux on each rotor pole using Faraday's Law (which is basically how a transformer works), but the voltage you get is tiny, at this scale. you might want to check out how a synchronous ac generator works, that's basically how you'd reverse this process.

I won't call it a ripoff, but I'd call it an impractical way to generate electricity at this scale.

This is only one video i found about it.

New Invention! Make 220V AC Generator 1 Phase from Brushless DC Motor ( BLDC 3 Phase ) - YouTube

So were you saying it is actually a Brushless DC Motor. And by removing the electronics, it becomes a 3 phase AC generator if you rotate it by hand?

But for DC brushless motors used in computer fan, etc. It doesn't have any electronics.

 

[jake jot]

This is only one video i found about it.

New Invention! Make 220V AC Generator 1 Phase from Brushless DC Motor ( BLDC 3 Phase ) - YouTube

So were you saying it is actually a Brushless DC Motor. And by removing the electronics, it becomes a 3 phase AC generator if you rotate it by hand?

But for DC brushless motors used in computer fan, etc. It doesn't have any electronics.

I can't find any north or south side of the ring. I even put a magnet and try to determine where is north and south, but seemingly undetectable.

I saw this question and answer in the product:

Question: Is there a drawing available showing the number of magnets and their configuration?

Answer: Thus is a radial flux machine. There is only one ring-shaped magnet lining the inside perimeter of the rotor (black ring). I hope this helps.

So where is north and south in the ring? Thanks man.

 

[maxwells_demon]

Brushless DC motor is used in mini fan. But I can't find any video showing how they can become 3 phase? Why does the product say it's 3 phase brushless generator?

the only type of videos I can find on youtube that explains BLDC operation is this type. note that the permanent magnets used are ring segments with a designated pole, not a full ring. so let's take this for now.

let's address first why this is considered a 3-phase motor. if you watch the video, you will come to this point, and why this sequence of energizing the coils is helpful in the smooth operation of the BLDC. despite being a dc motor, the controller circuit that supplies the BLDC feeds it 3 distinct periodic voltage waveforms. these waveforms are similar, with the same amplitude and the same period, the only difference is WHEN each is triggered. it's like the 3-phase voltage we get from the grid (i'll assume you know what a 3-phase sinusoidal waveform is), but instead of sinusoids, BLDC uses something like a two-polarity (+V and -V) square-wave (the appropriate technical term might be a pulse-width modulated signal).

now, for operating it as a generator. note that if you provide the mechanical power input by turning the shaft, what you're basically doing is passing the permanent magnets over the coils. you have 6 coils, with 2 permanent magnets situated physically 180° apart. however, those 2 magnets excite 2 oppositely situated coils (which are electrically connected, if you watch how the video wired them) at a time, generating 3 distinct voltage waveforms of the same amplitude and the same period (assuming the speed you are driving the rotor is constant), which by definition, is a 3-phase voltage waveform. i don't think you'll get the same shape of the waveform that you supplied though, not sure. will need some help on that one.

for the hard part, your BLDC employs a full ring magnet,

Question: Is there a drawing available showing the number of magnets and their configuration?

Answer: Thus is a radial flux machine. There is only one ring-shaped magnet lining the inside perimeter of the rotor (black ring). I hope this helps.

searching around, this is what the magnetic field of a ring magnet would look like:

since the supplier said it was a "radial flux machine", then we'll take the right illustration. gimme some time to investigate how your machine becomes a 3-phase generator with this magnetic field (your machine being a 3-phase motor is easier to prove since the 3-phase voltage was basically supplied to your machine by a controller).

As for this statement:

But for DC brushless motors used in computer fan, etc. It doesn't have any electronics.

yes they do. try and take apart some of those inexpensive laptop cooling pads that you find on the market, and you'll see the circuitry. i did some time ago, wanting to use those motors for some diy styrofoam motorboat. supplied it direct dc, and you know how it goes, since i was ignorant of the electrical and electronic concepts at work at the time.

this is from a youtube video of a laptop cooling fan. he's actually holding the stator in his right hand, complete with the coils and the circuit board with all the electronics and ICs fitted around the edge.

hope somebody chimes in for how to get those 3-phase voltages from your BLDC, I'm almost at the limits of my practical knowledge.

 

[maxwells_demon]

So where is north and south in the ring? Thanks man.

try and see if you can get your supplier to give you exactly how that ring magnet is magnetized. turns out there are a lot of ways you can magnetize ring magnets, as per this source.

anyway, I'm really hoping your ring magnet is magnetized this way, try and see if you can confirm this experimentally, before we attempt to tackle the 3-phase voltage generation problem:

if it is, then it's the same operation as with the ring segment type in the youtube video i linked on 3-phase BLDC operation. problem half-solved.

cheers!

 

[jake jot]

try and see if you can get your supplier to give you exactly how that ring magnet is magnetized. turns out there are a lot of ways you can magnetize ring magnets, as per this source.

anyway, I'm really hoping your ring magnet is magnetized this way, try and see if you can confirm this experimentally, before we attempt to tackle the 3-phase voltage generation problem:

View attachment 273895

if it is, then it's the same operation as with the ring segment type in the youtube video i linked on 3-phase BLDC operation. problem half-solved.

cheers!

I tried it with a compass for many positions for almost 20 minutes (I don't have a tiny bar magnet I can insert inside the ring). I noticed the following positions that can deflect the north of the compass toward the bottom or up (irregardless of the rotations). Can you figure out what kind of magnetic configuration the ring uses? (note the metal housing the encloses the ring magnet inside it)

 

[maxwells_demon]

View attachment 273902

can you try and keep the rotor in this position while turning the shaft slowly and see if your compass north stays up, or does it go down at some point along rotation?

 

[jake jot]

can you try and keep the rotor in this position while turning the shaft slowly and see if your compass north stays up, or does it go down at some point along rotation?

It doesn't go down in any rotation of the shalf. I tried that many times. Isn't it the magnetic north of a magnet is really south?

 

[maxwells_demon]

yup. next, set the rotor as in the second position, but with shaft in line with the needle center. slowly turn the shaft while keeping this position. is there any kind of response from your compass?

 

[jake jot]

yup. next, set the rotor as in the second position, but with shaft in line with the needle center. slowly turn the shaft while keeping this position. is there any kind of response from your compass?

Yes, it rotates. I think the magnetic configuration is like this.

Thanks :)

 

[jake jot]

Yes, it rotates. I think the magnetic configuration is like this.

View attachment 273903

Thanks :)

So the DC brushless motor is a perfect example of motor that runs by pole attraction and absolutely not by force exerted by current carrying conductor, isn't it?

All drones are powered by DC brushless motor so pole attraction can be quite strong.

 

[maxwells_demon]

Yes, it rotates. I think the magnetic configuration is like this.

View attachment 273903

Thanks :)

ayt, nice one mate.

 

[jake jot]

hope somebody chimes in for how to get those 3-phase voltages from your BLDC, I'm almost at the limits of my practical knowledge.

Your last sentence above was puzzling. Isn't you just explained in the same message that:

let's address first why this is considered a 3-phase motor. if you watch the video, you will come to this point, and why this sequence of energizing the coils is helpful in the smooth operation of the BLDC. despite being a dc motor, the controller circuit that supplies the BLDC feeds it 3 distinct periodic voltage waveforms. these waveforms are similar, with the same amplitude and the same period, the only difference is WHEN each is triggered. it's like the 3-phase voltage we get from the grid (i'll assume you know what a 3-phase sinusoidal waveform is), but instead of sinusoids, BLDC uses something like a two-polarity (+V and -V) square-wave (the appropriate technical term might be a pulse-width modulated signal).

The above is how to get those 3-phase voltages from your BLDC, isn't it?

 

[maxwells_demon]

So the DC brushless motor is a perfect example of motor that runs by pole attraction and absolutely not by force exerted by current carrying conductor, isn't it?

All drones are powered by DC brushless motor so pole attraction can be quite strong.

indeed. all thanks to stronger permanent magnets (those neodymium magnets are fun to play with, just be careful not to hurt yourself), low reluctivity pole shoes, and precise control circuits, all of which are great for miniaturized/small-scale applications.

 

[maxwells_demon]

Your last sentence above was puzzling. Isn't you just explained in the same message that:
The above is how to get those 3-phase voltages from your BLDC, isn't it?

try and see how the solenoid is wound, and you'll notice you'll run into the exact same question that made you start this thread in the first place.

edit: albeit this time, you'll be dealing with voltage polarity instead of direction of force.

 

[jake jot]

try and see how the solenoid is wound, and you'll notice you'll run into the exact same question that made you start this thread in the first place.

edit: albeit this time, you'll be dealing with voltage polarity instead of direction of force.

What? your youtube example on top is the same as the amazon motor at bottom, the only difference is the amazon motor has 9 windings. What's wrong?

 

[maxwells_demon]

What? your youtube example on top is the same as the amazon motor at bottom, the only difference is the amazon motor has 9 windings. What's wrong?

for just a while, let's limit our analysis to one stator pole, as follows:

with a rotor rotation direction given by the yellow counter-clockwise arrow, and each single coil of your solenoid having its return path being subjected to the same direction of flux, at the same relative rotational speed and direction, how much voltage would you measure at the terminals of this solenoid?

 

[agrumpyoldphysicstec]

TBH I've no idea how to analyse this sort of rotor, with an iron cored rotor and shaped field poles. You probably need and electrical engineer for that. (I expect Jim Hardy would have known). I just knew the basic principle of the motor with wires in a uniform field, as taught in Physics textbooks. After that I just put my faith in Eric Laithwaite's principle that the more iron and copper, the more efficient the motor! It's actually always puzzled me that the wires in most motors don't seem to be in any magnetic field: nearly all the flux seems to go through the iron, bypassing the wires. The magnetic flux "links" the coils and I've seen analysis of transformers based on that idea, but not motors. It's probably my bad understanding of field and flux.

You will not be the first to notice that electrical engineers design motors so that the conductors lie in regions of little flux. Also, the force on the conductors is small. If you think that you have a bad understanding it is because the subject is so badly taught. I have school physics textbooks and university electrical engineering textbooks and they do not agree. The university textbooks agree with observation whereas the school ones do not and also disagree with the established laws of physics.

It is fairly easy to analyze motors and generators as well as transformers in terms of flux "linking". Fleming's rules of thumb deal only with flux "cutting" which is really just a special case.

Is this a motor, or a generator, or a transformer?

 

[jake jot]

for just a while, let's limit our analysis to one stator pole, as follows:
View attachment 273906

with a rotor rotation direction given by the yellow counter-clockwise arrow, and each single coil of your solenoid having its return path being subjected to the same direction of flux, at the same relative rotational speed and direction, how much voltage would you measure at the terminals of this solenoid?

I don't get what you mean. Hope others can chime in or answer.

How does it differ to the amazon motor anyway? Did you mean it can't produce AC?

Also I noticed a great symmetry, in which motors can be converted to generator and vice versa. If one can (not practically but conceptually) rotate every motor by hand, one can get induced voltage at the plug? What motors are exception to this, perhaps the AC induction motors?

I wonder if MacGyver has episodes where he was trapped in a cellar and there was an old motor and he used it to produce electricity?

 

[Averagesupernova]

I happened to have a small Coleman generator apart today. The stupid thing is made so everything is impossible to get at unless a significant part of it is disassembled. That aside, I took a few pix. Thought I'd post them here. Generator is 120 volts 1850 watts max. Probably 1200 to 1500 continuous. Notice what I assume is a pair of diodes on the rotor. Also what I believe to be MOVs. This unit also has a DC output for automotive battery charging. Good for about 15 amps I believe. Two different sized windings are visible on the stator. One being the 120 VAC and the other the battery charging winding I have to assume. I would have looked it over closer but I'm in a hurry to use it.

 

[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.

Here is the amazon generator. It's much smaller than it looks.

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

The length from front to back is about 6.5 inches. The magnetic wire diameter using the caliper is about 0.20mm (0.0078 inches).

The size of the magnet (solid red and blue either side center) is about 2 inches long, the white winding plastic is also 2 inches long, and 1.5 inches wide.

Using a multimeter, the current is 10 milliampere at the fastest i can rotate it using the hand crank. The load is one LED for either direction of the hand crank directions. I don't know how many numbers of windings in the rotor. But the resistance between terminals or the winding is 26 ohms.

Using the above data. Any idea what kind of battery (3 volts? 6 volts? ) and resistor to turn it into a motor? I'd remove the hand crank to avoid more resistance in the rotor. Thanks!

(If others know. Kindly share too as maxwell_demons logs in rarely now)

 

[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.

I got 2 amazon motors unassembled. The top is the 2nd unassembled unit. After getting it to run. I noticed it won't run if it is in the horizontal positions. This was explained in the thread.

Yes the rotor seems to have some "iron core" block at the sides. Why is it necessary? Can't you create solenoid just by winding wires? The wire size is 0.34mm (0.0139").

The reason i got 2 pcs is so I can re create the rotor to make it so slim that force on current carrying conductor is totally eliminated. I want to see for myself the idea of pole attraction and how it is enough to make the motor run. So what size of wire to wind it and how many turns? And can't it happen without the "iron core" block?

(if maxwell_demons didn't come back, hope others masters in motors can answer. Thanks).

He wrote in message #43 this:

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.

If someone understands what he means. Please reword it. What does it mean to stuck a shaft through its center in the rotor picture above? I want to see it twitch (or whatever it is that can twitch)

 

[jake jot]

Here is the amazon generator. It's much smaller than it looks.

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

View attachment 274330

Comparing the amazon motor and generator. The generator has smaller wires in the winding. I guess they don't want large current in the output to avoid shocking the kids? This is the amazon generator disassembed showing the rotor with thin wires.

Tomorrow I'll try turning the generator into motor by inputting power to the output of the above. I'll start with 1.5v, 3v, 6v. But I think the wires may burn at 6v. Smaller current and there may not be enough force and torque on the conductor carrying wires to move the rotor.

So I'll change the winding wires sizes and turns. Hence I need the cookbook how to design rotor and number of turns (should one count?) and size of winding for the given stator. I'll try up to 12v dc only and see how fast the rotor can rotate. Does this need Maxwell equations? Gimme some tips guys or sample computations. Thanks.

 

[Averagesupernova]

You need to find a way to measure the current drawn by your experimental motors. An assortment of series resistors with a good auto ranging DVM should do the trick.

 

[jake jot]

Comparing the amazon motor and generator. The generator has smaller wires in the winding. I guess they don't want large current in the output to avoid shocking the kids? This is the amazon generator disassembed showing the rotor with thin wires.

View attachment 274433

Tomorrow I'll try turning the generator into motor by inputting power to the output of the above. I'll start with 1.5v, 3v, 6v. But I think the wires may burn at 6v. Smaller current and there may not be enough force and torque on the conductor carrying wires to move the rotor.

So I'll change the winding wires sizes and turns. Hence I need the cookbook how to design rotor and number of turns (should one count?) and size of winding for the given stator. I'll try up to 12v dc only and see how fast the rotor can rotate. Does this need Maxwell equations? Gimme some tips guys or sample computations. Thanks.

I was able to get the amazon generator to run as a motor. I added 1.2v battery one by one. At about 6 volts, the LED lights burned up (do all LED uses the same voltage?). The purpose of the LED lights are just to show directions of the hand crank and current. After adding 6 batteries or 7.2 volts. It still didn't run. It was only when I turned the unit sideways that the rotor can rotate (see above video).

I removed the leads less than 3 seconds as I didn't want the winding to burn up. I want to know the following:

1. Can the winding be just a single conductor? What's the problem with single conductor?

2. What is the formula for numbers of winding and size? Is there a formula or people just do it by trial and error?

3. I'll only remove the windings (destroyed it) and replace with a single conductor if there is theoretical reason the conductor can work too.

4. This proves generator and motor has relationship.

 

[Tom.G]

An LED lights up when the applied voltage is around 2V to 2.5V, and you already measured the current those LEDs draw. So when you crank the generator to light an LED, the generator is putting out around 2.2V at the current you measured.

Now a funny thing about LEDs is that they keep about the same voltage across them. If you apply a higher voltage they will conduct ALOT more current. Eventually they get hot enough to self-destruct internally.

The first stage of destruction is they melt and become almost a short circuit. At this point they no longer produce any light.

The second stage of destruction, if there is enough current available, one of the internal connecting wires will melt, acting like a fuse. Then no current will flow thru them.

From your description, the LEDs are in the first stage of destruction, an almost short circuit.

With the LEDs shorted, little current is available to flow thru the motor. I suspect that's why the motor most doesn't turn when connected to batteries.

Try disconnecting the LEDs by cutting the wire to them then see what the motor does with voltage applied. It just may work with only 1 or 2 batteries! More batteries = higher voltage = faster motor and more current - - - until it overheats and dies.

Have Fun!
Tom

 

[jake jot]

An LED lights up when the applied voltage is around 2V to 2.5V, and you already measured the current those LEDs draw. So when you crank the generator to light an LED, the generator is putting out around 2.2V at the current you measured.

Now a funny thing about LEDs is that they keep about the same voltage across them. If you apply a higher voltage they will conduct ALOT more current. Eventually they get hot enough to self-destruct internally.

The first stage of destruction is they melt and become almost a short circuit. At this point they no longer produce any light.

The second stage of destruction, if there is enough current available, one of the internal connecting wires will melt, acting like a fuse. Then no current will flow thru them.

From your description, the LEDs are in the first stage of destruction, an almost short circuit.

With the LEDs shorted, little current is available to flow thru the motor. I suspect that's why the motor most doesn't turn when connected to batteries.

Try disconnecting the LEDs by cutting the wire to them then see what the motor does with voltage applied. It just may work with only 1 or 2 batteries! More batteries = higher voltage = faster motor and more current - - - until it overheats and dies.

Have Fun!
Tom

The purpose of the leds is to show that turning the hand crank one way or another makes different lights in the led

What do you call this circuit?

I also cut the wire and measured it with multimeter. The leds are now open (not shorted anymore)

Earlier I think your scenario happened where the leds were in short circuit, so the motor didn't run. I'm recharging the batteries to see how many it can run.

I'll keep adding batteries until the rotor spins so fast and the thin wires burn. But before I do this. I ought to know. Why is the motor rotor composed of hundreds of winds, why not just one big conductor? In a transformer, the purpose of multiple windings may be to give relations between primary and secondary. But in a motor, what is the advantage of such windings? Will using just one big wire cause the same magnetic field? Or somehow hundreds of tiny wires can create greater magnetic field than one single whole conductor with the same area? Why so? Thanks!

 

[Tom.G]

What do you call this circuit?

Two LEDs connected in antiparallel.

Why is the motor rotor composed of hundreds of winds, why not just one big conductor?

As a general approximation, the strength of the magnetic field is proportional to the product of current times turns, called Ampere-Turns. You would need big batteries and larger wire connecting them if you want few turns and many amps.

 

[jake jot]

Two LEDs connected in antiparallel.As a general approximation, the strength of the magnetic field is proportional to the product of current times turns, called Ampere-Turns. You would need big batteries and larger wire connecting them if you want few turns and many amps.

Are the formulas for transformer windings the same as the winding in motors? I'm googling about the formulas and I read about inductance. Maybe the single conductor won't work because it would just short the batteries? So all these illustrations in youtube won't work at all because they would short?

Also I tried to determine the force of the rotors using the left hand rule. I can point my right hands better. That's when I read the rule for generator is difference. I read this:

"Fleming's two rules are very similar, but they must not be confused. When a current causes motion (like in a d.c. motor), Fleming's left hand rule applies. When motion causes current (like in a generator), Fleming's right hand rule applies. Since these two phenomena are the exact opposite from each other, it makes sense that direction of current would be opposite from each other. If the rules were not opposite then we could easily make electrically-driven perpetual motion machines. "

Can you give illustration how if the rules were not opposite, we could easily make electrically-driven perpetual motion machines? Just to understand the concept of the oppositeness.

 

[jake jot]

Are the formulas for transformer windings the same as the winding in motors? I'm googling about the formulas and I read about inductance. Maybe the single conductor won't work because it would just short the batteries? So all these illustrations in youtube won't work at all because they would short?

View attachment 274510

Also I tried to determine the force of the rotors using the left hand rule. I can point my right hands better. That's when I read the rule for generator is difference. I read this:

"Fleming's two rules are very similar, but they must not be confused. When a current causes motion (like in a d.c. motor), Fleming's left hand rule applies. When motion causes current (like in a generator), Fleming's right hand rule applies. Since these two phenomena are the exact opposite from each other, it makes sense that direction of current would be opposite from each other. If the rules were not opposite then we could easily make electrically-driven perpetual motion machines. "

Can you give illustration how if the rules were not opposite, we could easily make electrically-driven perpetual motion machines? Just to understand the concept of the oppositeness.

To add. Here is some weird results.

I tried to add all my 8 rechargeable batteries (1.2 x 8 = 9.8v) (all newly charged) waiting for the rotor winding to burn (so I can try winding new one for once in my life). But the motor kept running. I measured the amperage in series to the 8 batteries and it reads 1A average. But when I used the hand crank turning the same unit into generator (original design), the output reads only at most 10mA (with the 2 leds removed). And voltage is only 0.5v! I can't even get it above 1v. How do you explain this?

Is it not if the rotor is a certain given speed. It should output the same voltage or current as when you use the battery of same voltage and current to turn the rotor (at same speed)?The wiring diameter of the rotor is about 0.20mm (0.0078 inches). Again this is how it looks like. How do you know the maximum battery voltage it can take? I no longer have extra batteries to test winding burnout voltage.

 

[Merlin3189]

First, your LEDs are diodes. Each allows the current in one direction only. So depending on the polarity of the supply, either red or green lights
.

It was only when I turned the unit sideways that the rotor can rotate (see above video).
Maybe less friction??
I removed the leads less than 3 seconds as I didn't want the winding to burn up. I want to know the following:

1. Can the winding be just a single conductor? .
What's the problem with single conductor?

2. What is the formula for numbers of winding and size? Is there a formula or people just do it by trial and error?

3. I'll only remove the windings (destroyed it) and replace with a single conductor if there is theoretical reason the conductor can work too.

4. This proves generator and motor has relationship.

1 - Yes, maybe
- You have to put a lot of current through it. If you have 100 turns with 10 mA, that's equivalent to 1 turn with 1000 mA. If it took say 100 mA with 100 turns, then you'd need to put 10 A through a single turn.

2 - You'd need to know the strength of the magnetic field in order to calculate the torque. But the force is proportional to the length of the side parallel to the axis and to the aggregate current in the winding, assuming it's all in the same field (With a fixed size magnet, you don't get more force once your coil is as wide as the magnet.)

3 - Usually we prefer more turns of thinner wire. If you halve the CS area of the wire, have double the number of turns and halve the current, then you get the same force. Resistance is double, current is half, so voltage is the same, but power lost to resistance is less, because it's $I^2R$ or $\frac V R$

4 - Abso-blooming-lutely! The motor IS a generator, even when you are using it as a motor. That's where the "back emf" comes from. That's why the voltage determines the speed - when the generator voltage (plus resistance voltage) equals the battery voltage, the battery can't push more current through, so torque can't increase and it can't accelerate. (A bit over simple, but more or less.)Edit: changed layout as it didn't look ok when posted.

 

[jake jot]

First, your LEDs are diodes. Each allows the current in one direction only. So depending on the polarity of the supply, either red or green lights
.View attachment 274565

1 - Yes, maybe
- You have to put a lot of current through it. If you have 100 turns with 10 mA, that's equivalent to 1 turn with 1000 mA. If it took say 100 mA with 100 turns, then you'd need to put 10 A through a single turn.

2 - You'd need to know the strength of the magnetic field in order to calculate the torque. But the force is proportional to the length of the side parallel to the axis and to the aggregate current in the winding, assuming it's all in the same field (With a fixed size magnet, you don't get more force once your coil is as wide as the magnet.)

3 - Usually we prefer more turns of thinner wire. If you halve the CS area of the wire, have double the number of turns and halve the current, then you get the same force. Resistance is double, current is half, so voltage is the same, but power lost to resistance is less, because it's $I^2R$ or $\frac V R$

4 - Abso-blooming-lutely! The motor IS a generator, even when you are using it as a motor. That's where the "back emf" comes from. That's why the voltage determines the speed - when the generator voltage (plus resistance voltage) equals the battery voltage, the battery can't push more current through, so torque can't increase and it can't accelerate. (A bit over simple, but more or less.)Edit: changed layout as it didn't look ok when posted.

Thanks. I made this video and thinking whether to include it in the amazon review of the product. None mentioned it can be turned into motor.



Many customers are children. And maybe for safety. I'd not post it. So don't make the above public.

Here is the mystery. Putting a multimeter in series to the batteries, the current of the above setup is 1A. But using the hand crank, no matter what rotations, it can't output more than 10mA and 0.5volts. If you will notice in the video, the rotations are not that fast. Well. Even if it's fast when put sideways to avoid friction. The handcrank can make it as fast. Is it possible or the case that in a generator. You need more input power to make it match the voltage and current you would use when using it as motor?

 

[Merlin3189]

First - don't worry about children. Using it as a generator they can't get a significant voltage, so no danger.

Putting a multimeter in series to the batteries, the current of the above setup is 1A. But using the hand crank, no matter what rotations, it can't output more than 10mA and 0.5volts.

The generator emf should depend only on speed.
When using it as a motor, the applied voltage has to match the generator emf plus the Ohmic emf caused by the current passing through the windings (and other bits.)
Looking at the 1 A current with 9.8 V battery, the resistance (windings, connections, battery internal resistance) is less than 9.8 Ohm. How much less depends on the motor speed. Maybe your multimeter could measure the resistance at zero speed?

Looking at the open circuit voltage of 0.5 V at max cranking speed, the short circuit current is 10 mA, which implies a resistance of $\frac {0.5}{0.01) = 50 Ohm$ , which includes the winding, contacts and ammeter.
So, a big discrepancy, for which I have to guess at possible causes.
Is it rotating at the same speed when measuring voltage and when measuring current? There is no load other than friction, when measuring o/c voltage. When measuring s/c current, there will be a load torque added, so it may be going slower and the voltage is really less than the 0.5 V max. But 5 times slower ?
Hand cranking probably gives a varying reading, which will be harder to take accurately.
Is any current still going through the dead LEDs? (But I think you've taken them off.)

As far as I can see, 9.8 Ω must be greater than the winding resistance, so something must be wrong with the generator measurement.

 

[jake jot]

First - don't worry about children. Using it as a generator they can't get a significant voltage, so no danger.

The generator emf should depend only on speed.
When using it as a motor, the applied voltage has to match the generator emf plus the Ohmic emf caused by the current passing through the windings (and other bits.)
Looking at the 1 A current with 9.8 V battery, the resistance (windings, connections, battery internal resistance) is less than 9.8 Ohm. How much less depends on the motor speed. Maybe your multimeter could measure the resistance at zero speed?

Looking at the open circuit voltage of 0.5 V at max cranking speed, the short circuit current is 10 mA, which implies a resistance of $\frac {0.5}{0.01) = 50 Ohm$ , which includes the winding, contacts and ammeter.
So, a big discrepancy, for which I have to guess at possible causes.
Is it rotating at the same speed when measuring voltage and when measuring current? There is no load other than friction, when measuring o/c voltage. When measuring s/c current, there will be a load torque added, so it may be going slower and the voltage is really less than the 0.5 V max. But 5 times slower ?

What is meaning of o/c voltage? overclock? or open circuit voltage? or over charge? Also what is the s/c in "s/c current", shut current? step current?

I measured the resistance of the winding of the amazon generator by directly tapping the leads at the 2 commutators. It is exactly 24 ohms. I put the multimeter in AC instead of DC and tried hand cranking it so fast i don't mind if the rubber band would snap and highest I can get is 1.2 volts and 25mA. If it is set in DC, the voltage highest is 0.7 volts and 20mA. Why does putting multimeter in AC gives higher voltage?

Whereas the voltage (in generator mode) that can even make the rotor rotates by putting it sideways (to avoid friction) should be at least 7 volts dc and it's not rotating as fast. Why couldn't I get it to rotate at 1.2 volts? (i put it sideway to lessen friction from bottom).

What I exactly want to know is this principle. Whether if the rotor at motor mode rotates at a certain RPM at a given voltage and current. Whether if the rotor is put in generator mode. It will output the same voltage and current at the same RPM. What do you think?

Hand cranking probably gives a varying reading, which will be harder to take accurately.
Is any current still going through the dead LEDs? (But I think you've taken them off.)

As far as I can see, 9.8 Ω must be greater than the winding resistance, so something must be wrong with the generator measurement.

 

[jake jot]

What is meaning of o/c voltage? overclock? or open circuit voltage? or over charge? Also what is the s/c in "s/c current", shut current? step current?

I measured the resistance of the winding of the amazon generator by directly tapping the leads at the 2 commutators. It is exactly 24 ohms. I put the multimeter in AC instead of DC and tried hand cranking it so fast i don't mind if the rubber band would snap and highest I can get is 1.2 volts and 25mA. If it is set in DC, the voltage highest is 0.7 volts and 20mA. Why does putting multimeter in AC gives higher voltage?

Whereas the voltage (in generator mode) that can even make the rotor rotates by putting it sideways (to avoid friction) should be at least 7 volts dc and it's not rotating as fast. Why couldn't I get it to rotate at 1.2 volts? (i put it sideway to lessen friction from bottom).

What I exactly want to know is this principle. Whether if the rotor at motor mode rotates at a certain RPM at a given voltage and current. Whether if the rotor is put in generator mode. It will output the same voltage and current at the same RPM. What do you think?

I wonder if it has to do with the split commutator. Mine is the 2nd one.

13.7: Electric Generators and Back Emf - Physics LibreTexts

How do you turn a pulsed dc to direct dc? Maybe this was why I was only measuring 1.2 volts at most? (when in motor mode, the voltage that can get the rotate to start rotating must be at least 7 volts?)

 

[jake jot]

I wonder if it has to do with the split commutator. Mine is the 2nd one.

13.7: Electric Generators and Back Emf - Physics LibreTexts

View attachment 274632View attachment 274633

How do you turn a pulsed dc to direct dc? Maybe this was why I was only measuring 1.2 volts at most? (when in motor mode, the voltage that can get the rotate to start rotating must be at least 7 volts?)

Could the reason be the so called back emf? that is.. in motor, you need larger voltage to make it run and not proportional to the voltage in the output when it is in generator mode? I read in article above:

"
The generator output of a motor is the difference between the supply
voltage and the back emf. The back emf is zero when the motor is first turned on, meaning that the coil receives the full driving voltage and the motor draws maximum current when it is on but not turning. As the motor turns faster, the
back emf grows, always opposing the driving emf, and reduces both the
voltage across the coil and the amount of current it draws. This effect is noticeable in many common situations. When a vacuum cleaner, refrigerator
, or washing machine is first turned on, lights in the same circuit dim briefly due to the IR drop produced in feeder lines by the large current drawn by the motor. "

 

[Tom.G]

The OP repeatd this query to me in a private msg. I chose to address it here publically.

Is it not if the rotor is a certain given speed. It should output the same voltage or current as when you use the battery of same voltage and current to turn the rotor (at same speed)?

When measuring as a motor and as a generator they should be measured at the same motor current. Under that condition they should be close to the same. If measured as a generator with little or no load they will be different. The lower voltage and current as generator indicate other, unknown, problems somewhere in the test setup.

Looking at the 1 A current with 9.8 V battery, the resistance (windings, connections, battery internal resistance) is less than 9.8 Ohm. How much less depends on the motor speed. Maybe your multimeter could measure the resistance at zero speed?

As far as I can see, 9.8 Ω must be greater than the winding resistance, so something must be wrong with the generator measurement.

WIth the stated wire size of 0.0078 inches, 9.8 Ohms indicates about 50 feet of wire, the 24 Ohms measured by the OP indicates about 130 to 150 feet on the winding. Bad commutator contact?

Overall, the various measurement inconsistencies point to both an instrumentation problem, such as an average-reading (or maybe peak-reading) meter being used for a pulsed measurement, and probably poor, bouncing, contact between the commutator and the brushes.

I suggest the OP find someone locally that can work on the actual device with him and may have more appropriate equipment and more hands-on experience. Trying to debug convoluted problems remotely with limited information is not very practical.

 

[jake jot]

The OP repeatd this query to me in a private msg. I chose to address it here publically.When measuring as a motor and as a generator they should be measured at the same motor current. Under that condition they should be close to the same. If measured as a generator with little or no load they will be different. The lower voltage and current as generator indicate other, unknown, problems somewhere in the test setup.WIth the stated wire size of 0.0078 inches, 9.8 Ohms indicates about 50 feet of wire, the 24 Ohms measured by the OP indicates about 130 to 150 feet on the winding. Bad commutator contact?

Overall, the various measurement inconsistencies point to both an instrumentation problem, such as an average-reading (or maybe peak-reading) meter being used for a pulsed measurement, and probably poor, bouncing, contact between the commutator and the brushes.

I suggest the OP find someone locally that can work on the actual device with him and may have more appropriate equipment and more hands-on experience. Trying to debug convoluted problems remotely with limited information is not very practical.

Please see message #97 and #98. Is it not caused by back EMF? Meaning you need to use larger voltage when used as generator to counter any back EMF?