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The wire arived last week and by dinner-time this evening we had the 1st phase of coils in their proper layout and connected together on what is to be the beginning of the mold for the stator. The plywood is for layout purposes and will eventually be used to cast the fiberglass epoxy around the coils. It will not be part of the machine. You can also just make out the other 6 completed coils in the shadow of the shelf.

Fig 1. The stator began by figuring the arc of travel the magnets will eventually make as part of the rotor and laying that out inside the outer diameter of the stator. This will allow me to place the center of each coil in the path of optimum magnetic flux.

Fig 1: 18" square plywood with 8", 12" and 15.5" Concentric Circles

 
Fig 2. Using a Table of Sides, Angles and Sides I was able to determine that to divide the 12″ diameter circle into 9 equal parts (3 phases w/ 3 coils each) the length of each side needed to be 4.104″ (multiply the diameter of your circle by the sine of the angle).  I set my dads old dividers for that measurement and then drew radii from the center of the circle out through each mark. This gives me a placement for each coil as well as its max allowable outside dimension.

Fig 2: Dividing the 12" diameter circle into 9 equal parts.

Fig 3. Winding the coils with the spool of wire clamped behind. Keeping tension on wire with one hand and cranking with the other… 140 times for each coil.

Fig 3: Making Like a Davis.

Fig 4. Notice how this coil just fits between the radii with its center in the magnet’s arc of travel. I have a good gauge of wire & this will work, but I will keep more tension when winding the other 8 to see if I can get them a little more compact.

Fig 4: Checking the Fit.

Fig 5.  The last thing I want is to get the stator cast in epoxy and then find that my connections are no good. Since the 200C insulation on this type of wire is nearly invisible, I heated the ends of the wire until red hot and then cleaned them with emery paper to remove any remaining insulation.

Fig 5: Removing the Insulation.

Fig 6. With the coils in their proper place in the mold, I twisted the ‘end’ (the coil’s outside wire) of one with the the ‘start’ of the next one in line. Note the heat-shrink tubing slid over the wire *before* soldering this connection.

Fig 6: Connections

Fig 7. At 120 degrees of separation, each of these coils will “see” an identical magnetic situation as the magnets rotate in-front-of and behind them. When one is at it’s maximum output from the flux field, the other two will be also. Therefore, they’ll be in phase.

Fig 7: A Phase.

 The ‘end’ wire in running out of the picture from the bottom coil will be the output lead from this phase. I’ll do the other two phases in their locations just like this one and then connect all the ‘starts’ (loose wire in center) in ‘star’ and then finish the mold to cast the whole thing in fiberglass expoxy.

Larger versions of the images in this post (and more) are viewable in The PMG Gallery. Click on each thumbnail image in that gallery for a detailed descripiton of each.

Tags: Wind Turbine

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