What About FLAT or Square Wire for Coils?

[Matrix1000]

I couldn't resist the Magnet auction on ebay from Forcefield...12 NdFeB Block, 2" X 1" X .5" mags for only $75!

Now what to do with only 12 of them

Dual Rotor, Overlapping Coil, 6 mags on each rotor?

I'm trying to figure out a way to get the most power in the smallest space possible to fit in my multi blade windgen design.

So just to throw in some creative content for comment, I was thinking of the following...

'If' I am correct, one of the goals in coil design is to fit the maximum amount of wire into the space available for the coil, (leaving an aircore the same size as the magnet)

So would it make sense to make the wire Flat or Square(using a sheetmetal roller). This would allow the same amount of copper for the application but eliminate the wasted air space that round wire leaves. (of course enamel coating damage would have to be addressed).





Secondly...

I believe it has been said that the Air 403 uses 3 wire sizes to achieve the best output at specific RPMs turing off sets of coils as the RPMs increase beyond the safe operational speed for that size of wire.

Would it be ok to use 2-3 wire sizes in one coil? Then create/find a centrifical switch that would turn off the smaller set of wires as the rotors RPM increase past safe operating tempurature?

Or is all this trouble more than what its worth?

Thanks for your comments

[DERFMOOSE]

  don't know about flat.  but mother earth used a mercury switchset up on one her wind mills back inthe 80s

[Flux]

Flat wire will help the space factor. If it is very wide you should make sure that the flux is passing along the thin axis to reduce eddy currents.

You will have to experiment to see if you can roll it flat without damaging the enamel, the Commercial stuff is probably coated afterwards, but I believe it has been done.

For a small machine it may be possible to switch windings, It's not very satisfactory on larger machines if there is much of a step change in speed as it gives the blades a violent shock when it slows down.

Flux

[Matrix1000]

If flat wire were used the coil could look something like a slinky with as many rows both width wise as well as height wise.

[Electric Ed]

"Or is all this trouble more than what its worth?"

Yes.

To make the best use of your magnet's flux, consider a three phase winding with lapped coils.

The sketch below is a "flattened out", "edge-on" view.

Electric Ed

[Matrix1000]

Probably right, too much trouble. Well just one more image I had. Thin Sides up like a tape.

[Opera House]

Any extra coil is space that could have been used for more turns or thicker wire.  Another approach is to go with a smart switching regulator that keeps the coil amps maxed out and allows the coil voltage to rise with speed.  The regulator then turns that into lower voltage at higher amps.  Just the same as max power point in solar panels

[Ungrounded Lightning Rod]

No, you'd want the coil wound with the flat sides lined up with the field.  That means the bends go the "easy" way.

(Which, by the way, is EXACTLY how the series field coils on a starter motor are built - out of copper strap bent into rectangular spiral coils with the corners rounded.)

You get the inner end out by making a 90-degree bend, folding it back on itself with a 45-degree crease.  This gets it running parallel to the pole piece.  Then bend it 90-degrees the "easy" way and pass it over or under the coil.  Do this in the section that's outside the magnet path and you get no eddy currents in the lead-in strip and also don't get in the way of the magnets.

I wouldn't try to flatten enameled wire.  Instead I'd start with copper strip and co-wind it with a separating layer of fiberglass cloth, then pot that puppy.

[WindyOne]

"Or is all this trouble more than what its worth?"<p>
Yes.<p>
To make the best use of your magnet's flux, consider a three phase winding with lapped coils.<p>
The sketch below is a "flattened out", "edge-on" view.<p>
Electric Ed<p>

Very interesting.

PRO's:
1) A higher density of coils allows for a smaller diameter stator. You can fit two "over-lapped" coils into the same space as 3 "side-by-side" coils.
2) A smaller diameter & lighter rotor, too - easier to start spinning?
3) The smaller diameter stator and rotor can reduce weight and cost


CON:
1) A thicker stator means a larger gap means lower magnetic field strength? - Is that BEST USE or worse use of the magnetic field?
2) The stator would be thicker which increases weight and costs.

 
Is the magnet count significantly lower?

Side-By-Side Coils:
3 Phases x 4 coils per phase = 12 Coils
Ratio = 3 Coils to 4 Magnets
Requires 16 Magnet pairs

Over-Lapped Coils:
3 Phases x  4 coils per phase = 12 Coils
Ratio = 3 Coils to 2 Magnets
Requires 8 Magnet pairs - BEST USE?

Only 1/2 the number of magnets?
Do I have that correct?


Will the proximity of the three over-lapped coils cause the magnetic forces from coils to affect the performance of the two adjacent coils?

[gww]

Or, the normal 9 coil stator with one rotor with 12 mags and the other rotor just steel to complete the flux path?
gww

[WindyOne]

Or, the normal 9 coil stator with one rotor with 12 mags and the other rotor just steel to complete the flux path?
gww

 The question is can the the stator width be as narrow for the overlapped coil design as the side by side coil design?
 And if not then does DOUBLING the gap width offset all of the benefits of overlapping?

[gww]

Windyone
Although you mention that was the question, it was rapped around the statement "I got 12 magnets for $75 bucks and couldn't resist."  I don't know the best use for those magnets but my suggestion is one,  maby with square wire even better.
Cheers
gww

[WindyOne]

Windyone
Although you mention that was the question, it was rapped around the statement "I got 12 magnets for $75 bucks and couldn't resist."  I don't know the best use for those magnets but my suggestion is one,  maby with square wire even better.
Cheers
gww

OK, so here are two "apples-to-apples" designs with the restriction of using all 12 magnets ...

Over-Lapped coils:
3 phases x 3 coils per phase = 9 coils
Ratio = 2 magnets per 3 coils
Requires 6 pairs of magnets - dual rotor design
Double-width stator
Double-width stator has decreased flux vs a single-width stator
smaller diameter

Side-By-Side coils:
3 phases x 3 coils per phase = 9 coils
Ratio = 4 magnets per 3 coils
Requires 12 magnets - single rotor design
Single-Width stator
Single rotor has decreased flux vs. a dual rotor design
larger diameter

So, are these two 12 magnet designs effectively the same in watts out ?

Questions:

Q1) When the stator width is doubled how does that affect the strength of the magnetic field?
Is strength proportional to 1 / ( d * d ) or 25% of the original strength?

Q2) Is the magnetic field strength of a Single Rotor design roughly 50% of a Dual Rotor design assuming all else is the same?
 
Q3) BEST USE of 12 magnets?

[Mary B]

This was discussed long ago and one of the problems with wide flat strips or wire is eddy currents.

[WindyOne]

This was discussed long ago and one of the problems with wide flat strips or wire is eddy currents.

There was no mention of flat wire in my response.
But instead I was comparing two different designs that BEST USED the 12 Magnets purchased ...

9 coil, 12 magnet single rotor, THINNER side-by-side coil stator, larger diameter stator & rotor.

vs.
 
9 coil, 6 pair magnet dual rotor, THICKER layered-coil stator, smaller diameter stator & rotor.


... same wire used in both designs.

The original question was which design is BETTER USE of the 12 magnets purchased on ebay ...
All 12 magnets on one rotor and a thinner stator or 6 pair magnets on dual rotors with a thicker stator ?

[Mary B]

Ungrounded mentioned flat strips.

[tecker]

You can buy flat wire but the coating wouldn't stress round to flat

[joestue]

But instead I was comparing two different designs that BEST USED the 12 Magnets purchased ...

9 coil, 12 magnet single rotor, THINNER side-by-side coil stator, larger diameter stator & rotor.

vs.
 
9 coil, 6 pair magnet dual rotor, THICKER layered-coil stator, smaller diameter stator & rotor.


... same wire used in both designs.

The original question was which design is BETTER USE of the 12 magnets purchased on ebay ...
All 12 magnets on one rotor and a thinner stator or 6 pair magnets on dual rotors with a thicker stator ?

you can't really get a straight answer on this because the larger rotor diameter of the 12 magnet single sided disk means the magnets are moving twice as fast, and you will get more than twice the power out because of that.
however the flux strength is much less and half of the flux is flowing in the wrong direction, through the air.
if you can set up a system where on the other side of the coils is flat silicon steel, you would probably get more power out of the single disk than the dual rotor design. however for standard air core coils you would likely get a lot more power out of the dual rotor because most of the flux is forced to flow through the coils in the direction it is supposed to.

[kitestrings]

Interesting discussion, and I don't know the answer.  I do recall a couple posts from folks using square enameled wire though.  Probably a google-search would recover something.  To this point:

I believe it has been said that the Air 403 uses 3 wire sizes to achieve the best output at specific RPMs

And, that's worked so well for them.  Good discussion, but unless your trying to generate noise, I'm not sure I'd copy anything from this design.

~ks

[Mary B]

Square wire advantage is tighter winding and neater. Disadvantage was the wire was like double the cost if I remember right.

[fabricator]

If you want tight neat coils with little air space, instead of multiple wires in hand us the equivalent larger wire, It's much easier to wind neat tight coils.

[joestue]

The stacking factor for flat strip can be 95% in theory, but if we consider the actual insulation thicknesses required to get that... it just won't work.

.02" thick strip requires .002" thick insulation to get 90% fill factor, and that gets you 45 turns per inch of coil thickness.
this could work if you only need 50 turns per coil, but anything more than that and you're going to have to stack coils side by side and then insulate them from each other. each coil needs about .020 inches between them, so you need copper strip a minimum of .2 inches wide to get 90% fill factor, which means you're now down to 81%, which can be had with round nested wire.

not to mention copper strip is 14$/lb, copper wire is 7-9$ including insulation

[kitestrings]

Nicely covered. That's what I recalled from the earlier discussions - the potential benefits were well outweighed by the incremental cost.

Compact, tightly wound coils are just that. They look nice, but I think Dan, and perhaps others, have pointed out that [within reason] sloppy-looking coils can perform nearly as we'll.  And, if you fuss there, but miss something more influential - like load 'matching' - it can be all for not.

~ks