Strange e motor question, need help please

[buzbybixby]

I have an unusual project I am working on.

In this instance I need to use an electric motor to GENERATE power.
I know very simply that when you spin a PM motor manually it generates power. but what motor will generate the most amperage at low RPM's (600-800 RPM's)?

1. What do you think about using an Outrunner Brushless?

2. Should I use a gearing system to up the RPM's?

We need a motor to fit into a round cavity space of up to 1/2”-3/4" in depth and up to 2.5” in diameter. (Perhaps we could make this up to 1” in depth.).

The motor will be used as a generator and needs to put out a no load voltage of 2VAC / 100 RPM or at least 1.4VDC / 100 RPM if at all possible with as much current as possible. The more current the better. In the range of 600 to 900 RPM, we would like the motor to be able to put out 100 to 400 mA’s of current if at all possible.

Thanks in advance


Buz

[ScubaSteve]

Can't do it. What you're talking about doing is building an alternator/generator type system. You can do it with an electric motor, but it will take more energy to RUN the motor than is produced BY the motor... in fact, that's pretty much an oxymoron in itself... A motor is basically a LOAD on an electrical circuit. It's purpose is to take electrical energy (in our case, provided by batteries) and convert as MUCH AS POSSIBLE of that energy into mechanical energy. There's always energy that is not converted to mechanical energy, though, and instead is converted to HEAT energy (which is wasted).

This is why you see electrical-energy-producing systems on GAS engines... it's taking one energy source (gas fuel), converting it to mechanical output, taking a little bit of that output to turn the coils in an alternator past a magnet to produce electricity that runs your A/C, headlights, etc... (you can buy these types of systems for gas R/C engines to power your Rx, servos, etc... but you'll feel a slight decrease in engine power, sorta like when you're driving and click on the A/C).

Sorry for bursting your bubble, but it's thermodynamics. :wink:

[buzbybixby]

Hey ScubaSteve,

You may be refering to using the motor to drive my generator, I am not refering to that. I am simply talking about using an outrunner motor to produce electricity.

IF I took an outrunner or any PM motor and attached it to a drill for instance it would produce power. Correct? I know it is because we do it all the time with PM slot car motors but the voltage is too low for our purposes. I am exploring the new outrunners because they are multipole and if I use a rectifier, a 3 phase will produce energy.

http://www.woodrell.com/joe/3phase.jpg

My question is under the same RPMs can an outrunner PRODUCE more energy than a slot car motor?

[swatson144]

Interesting discussion.

All I have to put forth is that it is often recommended that new builders test their motors by turning with a drill/dremel etc. and measure the voltage of each phase. I would have to assume that someone has tried this. I haven't. but I do have several motors on hand and if no one chimes in with their results I'll donate the time to see for us.

I don't have an O scope to see the wave forms etc. So the best I could do is measure one phase for voltage only. If you could approximate the resistance of the load I may be able to get close to the value from parts on hand. Surely someone better equipped than me can run this test with more accurate results, and may even be able to chime in on different windings to use. IE I am sure that fewer windings will produce >V no load but more windings will produce >I and thus >V with a load.

Having no idea what you are trying to accomplish...One could generate those voltages with a cylinder magnet following a cam inside a coil.

[buzbybixby]

Thanks Swatson I will get back to you on the specifics,

Could you tell me more about how to "generate those voltages with a cylinder magnet following a cam inside a coil" ?

Will it approximate the size restrictions we mentioned at the beginning of this post?


Buz

[hansel]

These calculations aren't perfect but are ballpark.

A motor reaches some noload speed, because the voltage that it generates starts to equal the voltage that is driving it. Therefore if you want a 'motor' to generate 1.4vdc at 800 RPM, you need a motor that would run at about 800RPM at 1.4vdc, or scaling up by x5 = 4000 RPM at7VDC.

Using nunmbers from the performance database, I'd think 45 turns around a 22.71mm stator and 5x5x1 N50 magnets would put you in the ballpark.

The current depends on a few factors: 1) How strong is the force driving the motor. (The more current you draw the harder it is to turn.). 2) The resistance of the wire in the windings. I=V/R 3) Some effecienty factor for how well the wire cuts through the magenetic field, which I don't remember how to calculate anymore.

You may run into a conflict between needing high turns and too much resistance in the wire.

Steve

[buzbybixby]

Hansel,

In your design specs are you suggesting a 22.71 stator in WIDTH or Length? Assuming it is Width what length do you suggest?

Also what thickness of wire?

Finally which way to go.

I may be bringing up a whole new subject but have been doing alot of research on the LRK kits. DOes anyone have any thoughts on this method? I am still not really sure of what the differnce is between an LRK and a (Standard) outrunner.

[hansel]

Let me review some books and see if I can get you a better answer. (Or do some experiments.)

The LRK motor gets a lot of torque because each time you energize a winding , it only nudges the rotor forward just a little. This means the magnetic fields are strong and have strong force, but it runs slowly. I'm not sure if that would make a better generator or not.

[hansel]

Okay, If I were going to build something specifically to be a generator, I wouldn't make it 3 phase, unless you want to be able to rectify to DC without needing a capacitor.

I'd start with a 12 toothed 25 dia mm stator, about 5mm thick and wind it with one wire. Every other tooth is turned every other direction. Then put 12 magenets on the rotor alternating N S. (If you use the flux ring you need 5x4x1 magnets) This thing will never work as a motor, but should produce a nice AC voltage / current at low RPMs.

I'd try AWG 32 wire and about 30 turns per tooth if you can fit it. Then try it out. If the noload voltage is too low, use more turns. If it's too high, use less.

In the end you need to experiment because most of us don't have to tools to figure out exactly what the magenetic flux is.

Steve

[buzbybixby]

This is great info Steve thanks,

I am just at the point of buying the components here on GB. I am probably asking alot but is there a tutorial on winding somewhere explaining what you are suggesting?

I am not sure what determines a 3 or 2 phase motor in the winding process. Sorry to be such a newb Like I said I am just getting into motors. Just point me toward some tutorials.

[hansel]

I am just at the point of buying the components here on GB. I am probably asking alot but is there a tutorial on winding somewhere explaining what you are suggesting?


This winding would make a terrible motor so it definately won't be in the tutorial.

I'll try to change my settings so you can get my email address and talk to me directly.

Steve

[buzbybixby]

That would be great.

If I understand then, take one wire start on one stator tooth wind it 32 times move to the next tooth wrap it in the opposite direction, etc, etc. If this is done how do you get two wires for output?

Is this a two phase motor?

Ill draw a picture diagram later you can tell me if I got it.

[hansel]

If I understand then, take one wire start on one stator tooth wind it 32 times move to the next tooth wrap it in the opposite direction, etc, etc. If this is done how do you get two wires for output?

Is this a two phase motor?



Yes, that's the kind of winding I'm talking about. Leave some extra wire when you start winding, and have some extra wire when you stop winding. Those are the two ends of the wire to use for your power output.

Since this first wrap is for experimentation, there is nothing that says you can't wrap 5 turns on the first tooth, then move to the next tooth, and wrap 5 (the other way) and so on, until you have gone around the stator 6 times, or until you can't get any more wire on. You use a little more wire and it doesn't look as neat, but you can pull wraps off easily if you find you have too many turns.

If you only do a moderaly neat job, you can wrap a stator in 30 - 40 minutes.

This is not a two phase motor. It's not even a motor. If you put power on it, it might do nothing, or it might sit there and vibrate, or it might move in a random direction.

A two phase motor would have 4 wires to connect to, like a stepper motor. It is possible to make a stepper motor out of the 12 tooth stator, but you need to wind differently and put the magenets in different places.

[buzbybixby]

Great stuff Steve, I am going to order up the parts and get started. I'll post the rusults here when I am done.

So would you say we are building a mini altenator?

[hansel]

Great stuff Steve, I am going to order up the parts and get started. I'll post the rusults here when I am done.

So would you say we are building a mini altenator?

That's exactly what it is, a mini alternator.

You're going to run into a problem. You can get the stators, but none of the other parts (bearing holders, etc) are compatible. I'm currently working on some plastic parts that will adapt the 25mm stator parts to the currently availble parts to people can use them. I should have my first prototypes next week. So you might want to wait to order until then.

[buzbybixby]

OK, I will wait till I hear from you just post again when you are ready, if you have a list of things I will probably just order several sets.

Thanks again you've been a big help,

Buz

PS I came across this interesting tidbit in my research

http://www.aerodyne.com/products/miice__generator.htm

[buzbybixby]

SO now I am curious, there is seemingly such a small difference between the motor you are suggesting ( the 25mm) and the one that is in stock (the 22.71mm).

You had originally suggested this before your research. If I used the 22.71 setup using the new windings and magnetts you suggested could we expect the same results, or is it the overall lenght of the stator that is wrong?

[hansel]

SO now I am curious, there is seemingly such a small difference between the motor you are suggesting ( the 25mm) and the one that is in stock (the 22.71mm).

You had originally suggested this before your research. If I used the 22.71 setup using the new windings and magnetts you suggested could we expect the same results, or is it the overall lenght of the stator that is wrong?

The important difference is that the 25mm stator has 12 teeth, and the 22.71 mm has 9 teeth. In order to be able to wind every other tooth in a different direction, you need an even number of teeth.

It might work to wind 3 phases onto a 9 tooth stator, but at the low RPMs I think the method of winding I suggested would work better. (And I think in the end you'll get away with less turns of wire, giving you less resistance and more current.)

[buzbybixby]

I tried to get that wire today while I am waiting and was unable to find it locally. I also note that it is not available on GB store.

Hansel, are you affiliated with GB? IN other words am I going to be ordering this through GB or another source?

ALso, Just curious, what would you say is the most important factor in making the motor generate more amperage, if I should need it?

Would it be diameter, magnet strength, wire thickness/wrappings, or stator length?

[hansel]

I tried to get that wire today while I am waiting and was unable to find it locally. I also note that it is not available on GB store.

Hansel, are you affiliated with GB? IN other words am I going to be ordering this through GB or another source?

ALso, Just curious, what would you say is the most important factor in making the motor generate more amperage, if I should need it?

Would it be diameter, magnet strength, wire thickness/wrappings, or stator length?

I am not affiliated with GB. I'm just a fan of their products.

I received my plastic prototype parts, and while some of the parts seem to work well (like the plastic end bells) the part you need which adapts the 25mm stator to the 6mm bearing, doesn't seem to be stiff enough to do the job. But I only started playing with the parts today so the jury is still out.

I plan to wind a generator here just to see how it works. I'm just going to start with the finest wire that I have (the finest GB sells) and put as many turns as I can on and see what that puts out.

I'm not sure about the more current question. I'll have to experiment a little. Wire size matters, but for the little currents you are talking about, I can't see it mattering that much.

[buzbybixby]

Great Steve, I was able to find the AWG 32 on the net and ordered it.
I am looking forward to your results.

One thing, in looking at a car altenator the windings are made using a fairly thick wire. Would that translate to this type of generator we are building here as well?

Depending on your results I will continue. I have tenatively selected the following components and wanted your opinion. I am again trying to generate the most voltage at the lowest RPMs

1. 43mm 12 tooth stator x 10mm thick

2. 47.6mm rotor ID

3. 10x8x1.5 mags

4. 16 poles

Using your original specs I should have quite a bit of room for additional windings or guage thickness. DO you think this has the potential to generate more voltage?


Misc. questions:
Is using "Superglue" / "Krazy glue" the same thing as CA glue? I am thinking of using a gel for the magnets.

I have been reading about double winding here, Do 2 wires wound 6 times equal 12 winds or would they be the equivelant of 6 winds of one single thicker wire?


Thanks for all the help.

[hansel]

Great Steve, I was able to find the AWG 32 on the net and ordered it.
I am looking forward to your results.

One thing, in looking at a car altenator the windings are made using a fairly thick wire. Would that translate to this type of generator we are building here as well?

Depending on your results I will continue. I have tenatively selected the following components and wanted your opinion. I am again trying to generate the most voltage at the lowest RPMs

1. 43mm 12 tooth stator x 10mm thick

2. 47.6mm rotor ID

3. 10x8x1.5 mags

4. 16 poles

Using your original specs I should have quite a bit of room for additional windings or guage thickness. Do you think this has the potential to generate more voltage?


Misc. questions:
Is using "Superglue" / "Krazy glue" the same thing as CA glue? I am thinking of using a gel for the magnets.

I have been reading about double winding here, Do 2 wires wound 6 times equal 12 winds or would they be the equivelant of 6 winds of one single thicker wire?




Okay, first of all my progress..... I haven't found a good way to mount the stator, so I think my experiments might have to wait until GB comes out with the complete line of components for the 25 mm stator. However your parts are sooooo different, I'm not sure my experiments would be very useful anyway.

Where did you find the parts for a stator / motor of that size? I've been looking for something like that for another project .

Your parts sound pretty good. The airgap between the magenets and the stator is 0.46mm which might be a little big. Unfortunately you can't go to 2mm thick magnets because it won't quite fit.

If you wind the way I was suggesting with one long wire, then need to use 12 magnets, not 16.

Given the length of your stator, I'm pretty sure you can use less turns of thicker wire if you want. Or put more turns on for a higher voltage.

Are the magenets good and strong, like N45s?

I glued the magenets in my first motor with super glue. It seemed to work okay.

Two wires wound 6 times is the same as 6 winds of a thicker wire. However they do that because they are putting many amps through the windings to drive the motor. In your case you are talking about half an amp. I don't think you need to worry about multiple wires. Do more turns to get your voltage up at lower RPMs instead.

Given the size of your stator, you probably didn't need to use such small wire, however if you are going for max voltage, use it. But don't electricute yourself. :-)

When you get your parts in, try about 20 turns on each tooth and test before you spend a lot of time winding a bunch of turns. You may be pleasently surprised.

[TightWind]

http://www.scoraigwind.com/pmgbooklet/itpmg.pdf

That is a good link for seeing how a Permanent Magnet Generator is built.

What is learned from building one of the GBv kits translates nicely to building one of these. Now to learn to carve a prop.