These pages will describe the build process.
Wow. These magnets are really strong. People aren't kidding when they say "Handle with caution. These are not toys" . I could so with some plastic tools. Mine keep jumping onto the magnet rotor, and when your hand is in between the flying tool and the rotor, it really hurts..... A lot...... You soon learn to keep spanners, knives etc... well away from the rotor discs.
Having used the jig to place the magnets equally around the disc, I needed a makeshift stator to hold a test coil, and also a former to wind the coil around. I loaded up the CAD model of the alternator and designed a part with a cut out to allow the maximum size available for a single coil. I also made a "best guess" at a reasonable sized coil former. The CNC had cut the parts out in a matter of minutes, so I could get straight on with attaching the test stator in place over the magnet rotor. You can also see the coil former in the picture. (left).
With all the parts in place and the turbine back on it's pole, it was time to take some readings from the "test coil". The coil is made from 70 turns of wire. This test is done with only one magnet rotor on the machine. I turned the rotor by hand, using one of the prop mounting studs, at a steady 100 RPM. The single test coil showed 1.05 Volts at that speed, which multiplied up for 2 mag rotors, 3 phase (star connected), and rectified to DC, should be around 14 Volts. Just above cut in voltage. I'm aiming for a cut in speed of around 150 RPM. So this test coil is reaching cut in too early. As you can see from the photo, the coil doesn't use up all the available space for one coil, so I can make the winding form a little bigger and wind with a few less turns. This should also use up the space a little better, making the coil more efficient and reduce the coils resistance. The 2 metre blades I'm planning on building will run at a tip speed ratio of 7 (I hope). Which means they should hit 150 RPM in a 5 MPH wind.
I really hope my maths is in the right ballpark, or I'm going to look pretty silly. Time will tell....... I can't wait.
I've now tested some more coils and found a size and number of turns that I'm happy with. So it'll be full steam ahead on coil winding duty. How boring. I set the CNC machine up to cut out 9 coil formers. I intend to leave these in place when I cast the stator in resin. The reason is, that they're really hard to get out from the centre of the coil. That's about the only progress I've made recently. It's been hard to get much done between work and the baby. I have found some time to make a start on the charge controller, which you can see here.
The next update here, should be of making and casting the coils into the stator. See you then.