Oscilloscope videos?

[FranklinsAce]

I'm searching for some videos that show a user analyzing the performance of their hand wound coils but have come up dry.

Having wound my own (50 winds/24 AWG/6 coils), I've hooked it up to my inherited Tektronix old school scope and get somewhat of a sine wave on the display.  I'm wondering about tips and what type of information I should look to gather from the instrument.  The coils themselves are working well from my novice point of view.



I'd appreciate any links (videos or articles) that might show some pointers of what to watch for when using the oscilloscope.

[SparWeb]

Hi FranklinsAce,
I have a Tektronix 422 and did poke it into certain points in my WT AC output.  I saw things like what you show there.

I have photos and maybe some video if you can wait a little for me to get it uploaded.  I build from motor conversions so some of my reasons to see non-sine output are different, but only in little details.

It is never going to be a perfect sine unless you design  the Alt like a grid power station.  In the Alts we make, the flux oscillates but the pattern of flux change is not sinusoidal, so it does not make a sine wave output.
You may be using rectangular magnets, which cause even less sinusoidal shape.

[OperaHouse]

What is the AC source of power used for that transformer?

[FranklinsAce]

SparWeb - you are correct, I am using rectangular magnets.  Would love to see your photos and video when you have time to upload them.  From my picture of the scope, I imagine I can see 6 traces per cycle and I guess each one of those is a coil.  I'll have to try and annotate the photo.  I'm considering winding some coils just to see the different types of signals they generate, maybe gain some unexpected learnings.

OperaHouse - Here is a picture of my home wound stator and rotor.  I've made some minor upgrades since I took the picture but the design is basically the same.

[SparWeb]

That picture explains a lot.  I think I can describe a few things that will help understand what you see on the scope.

First, there's the physics of the thing.  The voltage you measure is produced by "electromotive force" or EMF, and that is generated by a change in flux that passes through a closed loop of wire.  There's a lot going on in that statement alone, and I could go into the math of it but for now the verbal description may be enough.  I want to emphasize the word "change" in that definition.  What that means is that flux can pass through the coil, but if it doesn't change, then you get no voltage.  No voltage, no current, and so on.  The change in flux is for all of those field lines to move toward and away from the coil.  In the case of your alternator, they pass by as the disk rotates, and the next magnet that passes by has the field lines pointed in the opposite direction.  Reversal of the flux gives you a reversal of the voltage.

Next, there's the more detailed look at the changes as the magnets pass.  At a moment that a magnet is aligned between two coils, then there's a bit of overlap of its face over the coil, but on the other side is the opposite side of the coil is the other magnet, pointed the other way, so the total flux through any coil cancels out.  Zero flux.

Next, move the magnet rotor a millimeter clockwise.  Let's say it's the N magnet that moves a little further over the coil.  And so then the S magnet face moves a little farther away (actually it is moving over the next coil).  More N pole on that coil give more + flux.  That's a change in the flux passing through the coil and you get a EMF from that, which you can measure as voltage. 

Next, move the N magnet a few millimeters farther again.  A bit more N flux on this coil, and the S flux is mostly over the adjacent coil too.  Still adding + flux to the coil we're looking at, so the change is + and there's still an EMF.

Next, move the N magnet farther, and now its face is entirely superimposed over the coil.  That S face has moved entirely over the other coil at the same time.  We have the most + flux now, but that last bit of movement didn't actually add much, it just made the corners of the rectangle cover the coil better.  It wasn't actually as big a change in + flux as it was before, so there's actually a bit less EMF.  It's still increasing, so still + stroke on the voltage, just not as much as before.

Next, move the N magnet farther.  Well it's still all superimposed on the coil, which is bigger than the magnet.  The same amount of flux is passing through the coil as it was a moment ago.  The flux didn't change.  The EMF is zero.  The voltage has dropped to zero for a moment.

I think you get the picture by now.  There are spots where the EMF goes to zero for a period of time, there are spots where the EMF is changing but at a fairly constant rate.  These cause the voltage on the waveform to go through zero, and to flatten out at various times in the cycle.

[SparWeb]

Here's a photo.

You should also look at my process of converting motors.  www.sparweb.ca 
The machine is different from an axial-flux alternator so I see things you won't see, and vice-versa.
I hope you can learn from that, but it's not exactly the same.

[FranklinsAce]

Thanks for the detailed explanation and picture.  Super helpful!  I took a look at your website, well done!   The size of those magnets are huge - I'd break my finger just looking at them LOL.

My current stator has all 6 coils wired in series.  For my next version I'm considering going three phase and wind 9 or 12 coils (rather than 6).

Using the current setup, do you think it would help or hinder overall output if the coils had a bit more (or less) space between them based on the magnet size?

[SparWeb]

If your goal is a more sinusoidal shape, then the way to do that is to make the coils smaller - closer to the size of the magnets, IMO.
I haven't done the math, but it stands to reason that if there's a moment where the magnet passes the coil and nothing changes, then there's no change in flux, and the voltage will start to fall to zero.  This would happen as the magnet passes a large coil.  That seems unproductive, here.  You could make the diameter of the disks smaller, fit smaller coils.  Or do the opposite; get more magnets.  There's plenty of room for extra magnets on the disk you have.

[MagnetJuice]

Frank, can you verify how your setup is wired?

I assume that it is like B on this image with every other coil reversed.



Is that correct?

Ed

[FranklinsAce]

Hi Ed,

Yes, image B is how things are wired up, every other coil reversed.  Each magnet is alternated N/S as shown.  If you look closely at the picture of my stator, you can see that every other coil (A, C & E) is marked from when I tested for N/S direction in each coil.  My goal with this is to produce a maximum positive and negative voltages.  When I get home I'll post my handwritten notes where I documented my intended design.

[FranklinsAce]

Ed, here is the page out of my notes.  Probably self explanatory but in the left case the magnet and coil poles are all in alignment.  In the case on the right, coils and magnets are all in opposition.



Sparweb, I like the idea of adding more magnets to the rotor.  I have another 6 so I could easily double to 12.

My concern in increasing the magnet density is that two magnets will be passing over the different sides of the same coil, one inducing positive, the other negative and canceling each other out in the process.  I know you all have way more experience in this arena so I'm guessing my thinking must be shortsighted and  I'm not understanding all the variables involved.

[MagnetJuice]

Your best configuration would be to have 8 magnets and 6 coils.

That way you can have 3 phases like all professional alternators.

Here is a diagram, I will not give you a lot of details so you can figure it out for yourself and learn.



Ed

[SparWeb]

MJ, you beat me to it!

This might help, too:  http://www.sparweb.ca/Forum/AXIAL_FLUX_HowItWorks.pdf

[GreenTeam]

umm what do you mean coils reveresed? The only time I see that is with radials, and even thats not a fire sire thing either.
I learned that all coils wind the same way regardless of the phase or the magnet polarity!
What is this reversal of coils? And explain how it changes something with an AC machine?

[MagnetJuice]

Reversing some coils works in the case of an alternator similar to the one below.



That type of configuration is not very efficient, but it can work by reversing some coils.

For this alternator to work, coils 2, 4 and 6 OR 1, 3 and 5 must be reversed. Which ones to reverse depends on what you want to do with the alternator.

Take a look at coils 1 and 4 and you will see that the magnets passing over those two coils have opposite polarity. If those two coils are wired in series, one of them must be reversed. If not, the voltage produced in one coil will be of opposite polarity and they will cancel each other out. No voltage produced.

As I said, that alternator is not very practical. That is why I recommended the one below.



By adding 2 extra magnets you can have an efficient 3-phase alternator. Note that for example, coils 1 and 4 have magnets of the same polarity passing over the coils. No need to reverse coils.

In that case, both coils are producing the same polarity voltage and they reinforce one another.

Ed

[GreenTeam]

Reversing some coils works in the case of an alternator similar to the one below.

(Attachment Link)

That type of configuration is not very efficient, but it can work by reversing some coils.

For this alternator to work, coils 2, 4 and 6 OR 1, 3 and 5 must be reversed. Which ones to reverse depends on what you want to do with the alternator.

Take a look at coils 1 and 4 and you will see that the magnets passing over those two coils have opposite polarity. If those two coils are wired in series, one of them must be reversed. If not, the voltage produced in one coil will be of opposite polarity and they will cancel each other out. No voltage produced.

As I said, that alternator is not very practical. That is why I recommended the one below.

(Attachment Link)

By adding 2 extra magnets you can have an efficient 3-phase alternator. Note that for example, coils 1 and 4 have magnets of the same polarity passing over the coils. No need to reverse coils.

In that case, both coils are producing the same polarity voltage and they reinforce one another.

Ed

Allrighty than! So, now, I did build a 6 coil 8 magnet machine. I used 0.5mm wire. And if I remember correctly, I used something like around 65 turns per coil.
Each coil, I was very carefull that they are all laid the same way. The in wire was always on the left ( looking down at it ) ANd the out wire was on the right.
No coil was reversed. At least I dont think any where!. I put my ancient power drill on it, to a rectifier circuit and that went directly to my multimeter.
And when I hit the trigger, It took a while for it to top out in RPM. But, I noticed after 10volts, no matter if the drill spun it faster, It only made 10 volts.
Could it have gone higher if I reversed the coils?