Left Hand Rule Applied to a Winding

[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 a lot 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 a lot 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.