Formulas and calculators > Coil winding

Oscilloscope videos?

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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.

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