First real Alternator - Pt I

[kihon]

Hi All

Im looking to build a cheap wind turbine for as close to £50 as I can get. So far, my costs have been:

£4 for two 6" mild steel plates (0.25" thick)

£25 for magnets (In bulk it would be cheaper).

£5 for JB Weld.

The rest is made from scraps of wood, and some skateboard bearings I had at home.

The Design is a 12 pole 9 coil 3 phase dial rotor axial flux alternator, the magnets are 25.4 x 9.5 x 9mm N38 neo bars.

With a test coil with 150 turns 24 swg wire, I was getting ~2v DC at ~240 rpm, and 3.7v at 540 rpm. (Tested using hand spinning for 240rpm, and a cordless drill for 540 - unfortunately no variable speed on drill, so I could only get two samples so far). Speed measured using a cycle computer.

Manufacturing using hand tools, so not perfect, but seems to work.

The Voltage was measured while using it to light an ultra bright LED. Have not measured current yet.

So far quite excited with the progress. Need to make stator next.

Will try and upload images soon.

[kihon]

Ok - here is an image of the assembled test rig, showing the two rotors, and a wooden frame. The white thing on the left is a piece of tissue where I attach the drill. central axis is a M8 threaded rod.

Sorry about the quality - using my phone camera - not very good.

[TheCasualTraveler]

     Looks nice. Is this the third world machine you mentioned in an earlier post? I like the simple construction. I've done something just like it only I used brass spacers instead of using nuts to hold the rotors apart. With a small set of blades it should be a nice, lite, fast machine, enough to charge cell phones or run a radio but I think it's going to be short of your 100 to 200 watt goal. Perhaps a good prototype. Curious to hear if your test coil # of turns is pretty close to the mark. Good Luck.

[TheCasualTraveler]

     I missed where you wrote DC,

"With a test coil with 150 turns 24 swg wire, I was getting ~2v DC at ~240 rpm,"

     If the 2 volts was already rectified not sure where you would be at cut in.

[esc]

I am by no means an expert...but does that air gap look a little large?  

[kihon]

Yes, this is the one for a third world country. The tools I have available at the moment are quite poor (dont even have a proper Drill Press), but once I have a proto type up and running, I hope to provide the plans to a friend who has better tools to try and make a more refined version.

Going to try acquire some resin and make a test stator, and then work out what kind of power I can get out of it.

I can refine it more once I know what I can get out of it as is.

[kihon]

Just to clarify, 2v at 240rpm was with a single coil. (DC rectified).

From

 http://www.reuk.co.uk/Star-Delta-Wiring-Calculator.htm

I calculate that with 2.5v per coil, I should be able to get 13v output, 15.6v from 3v.

Roughly that should map to 328 rpm for 2.5v, and 420 rpm for 3v. per coil. I guess it boils down to the size of blades I can use to get those kind of speeds, and how much power I can get out of that.

[kihon]

Unfortunately my manufacturing is not perfect, so there is some wobble in the rotors, which means I need a larger air gap than the width of the stator. I might be able to tweak it some more once I have the stator cast.

[pepa]

    hi kihon, until you close the air gap down to about half of what you have, you will not see much power out of your unit. rework the arbor to run as true as posible.

    disassemble the unit, fill the arbor holes with jbweld, let it set up to cure and redrill (start with small bit first, then larger until hole is arbor size) the arbor holes in center of disk and re assemble. you can use nuts and all thread to evenly space the disk from each other or cut some wood spacers, drill bolt hole through length of each spacer and slide over bolt between rotors and use as air gap spacers.

    your stator will have the center hole large enough to clear the spacers and the od will be large enough, are its two ears, to be supported by the 2x4s. your WABBLE may be the difference in the gap, check it out first. let us know how it comes out, pepa.

[ghurd]

I agree with what pepa said.  Get the air gap tighter, even if it fits less turns, or needs smaller wire.

If UK threaded rod is like US threaded rod, there is a lot of slop in the bearings to shaft fit.

May get a decent fit shimming it with the neck of a cartridge case.

The US .30 cal (.308Win / 7.62x51 NATO,  or .30-'06) would be a tiny bit smaller than a .303 Enfield.

Soft enough it can be carefully tapped into place?

G-

[madkane]

just a small question what will this gen be powering

as it will give clues to wire size  and a questimate on blade size

as .5mm cable wont do much over a few amps and the resistance will be very high with all volts at dc  you gave will put you at 275 rpm for a 12.5 volt cut in  and 22 rpm per volt

[TheCasualTraveler]

     Just wanted to give you a look at the rotor I'm working on, basically the same as what your doing only larger. I happened to be gluing magnets on today. For securing the rotor to the threaded rod I use a flange nut on each side of the first rotor. Then I have 4 SS bolts with brass spacers Holding the second rotor as well as a final flange nut on the threaded rod on the outside of the second rotor. My magnets are 1/4", the spacer is 1" and the second disc will have no magnets so it gives me an air gap of slightly less than 5/8" into which I will fit a (roughly) 3/8 to 1/2" stator. I think using spacers will give you a much better shot a keeping the two rotors running true, at least it works for me. Here's a shot of the spacers. Don't ask what all the other holes are for.(hope this file is 50K like properties said it was)

[electrondady1]

it's difficult to see,

 but it looks like the mags might be spread out just a little bit.

i've always liked 50/50 spacing between the mags (on the inside) .

like the others have said it's important to get the gap down

and the only way to really do it is to get the thing to run true.

i used a hockey puck and a few hard drive disks for a spacer,  had the right width.

when your fixing(glue) the spacer in place, you can rotate the rotors so the mags are on the outside.

that will let you see if your rotors are running true with out having to deal with the magnetic pull.

you need a mandrel of some kind to get one rotor at 90 degrees to the shaft

then you can use all those bolts to get the second one lined up.