Mini Axial Alternator - again

[gotwind2]

As I dont have any access to lathes or milling machines e.t.c

I am attempting to build an small axial flux alternator with parts I have lying around and just an electric drill.

I am using a bike front wheel hub as the bearing and 1 or 2 large speaker backing plates for the rotors.

I think at first I will experiment with a single rotor design, provision has been made to add a second rotor later.

I can fit eight 3/4" x 1/4" (19mmx6mm) neo magnets in the space given.

I know the windings will be a little tight. Drawing below to scale.

What I would like to ask is:

Given I have 8 poles, would a 6 coil setup be best, 3 phase?

Ideally 12v cut-in at 400 rpm - its intended for a 3-4 foot bladed HAWT.

If anyone has any experience at such a low power with wire gauge and number of turns to start with, that would be very useful - I will make a test coil first.

Thanks.

Ben.

[Flux]

Doing it as a dual rotor looks reasonably possible. if you insist on it being single rotor then it will be a pretty miserable thing.

6 coils 3 phase makes sense. Probably something like 100 turns of #19 with coils about 8mm thick if you go dual rotor.

It looks as though it would suit a prop of about 1 M diameter.

Doing it single rotor you are looking at a toy and it will not remotely load a 3ft prop.

Flux

[gotwind2]

Thank you Flux.

I will make it dual rotor as suggested.

I am connecting the rotor plates on the outer edge, much like Dinges once did on his mini axial a couple of years ago.

After re-drawing to scale, It appears I have even less space to play with..

Just six magnets will fit.

What would be the best coil number/configuration with this amount of poles?

Also, you mention #19 wire, is that the American AWG gauge?

#19     0.0359"     0.912mm

I'm not after much power here, just something that anyone can build relativly easily and maybe get 20-30 watts, rather than going for the larger Hugh Piggot axial design.

Ben.

[Flux]

Six magnets doesn't lend itself to a simple 3 phase arrangement, 1.5 coils per phase is a bit tricky.

For such a tiny machine it may not matter much if you make it single phase.

Yes I did mean AWG I forgot I was dealing with someone in a part of the world where such awkward things are not common. Yes about .9mm but you may have to experiment more if you use 6 magnets.

There always seems to be a major mechanical problem with these tiny alternators if you use small diameter discs. If you didn't have to support the second disc on the outside there would be lots more room for the stator.

Can't offer much help. i couldn't survive without a lathe.

Flux

[gotwind2]

Thanks again Flux.

The physical size I have limited myself to and lack of machining tools really is a limitation, I'm now having a re-think.

If this can be resolved with the help of the clever minds here on the forum, a workable low speed alternator made from bicycle parts, and maybe stacked disguarded hard drive Neo magnets that could achieve 20-30 watts for very little money might be nice?

I don't propose to make a profit from such an idea whatsoever, but maybe very useful to the less well off countries for batery charging/ direct lighting.

Ideas welcomed

Ben.

[CmeBREW]

Hi Ben.

    Impressive work and diagrams. That is a VERY good idea about the bicycle hub for a small mill. I can't believe I never realized that! It was right under my nose.

 I have been striving for exactly what you are striving for with a small "almost undetectable" (or;decoration looking) mini-mill that might do a few amps (max) on a 8'pole and/or on the roof.  Except I think I'm going to try something like see thru (polycarbonate) round blades like a house 'box fan' moving high rpm. (probably only 2.5' diam)

The great thing is round blades shouldn't make any noise when going fast and It can be a downwind mill which looks better to me.

Those tiny low friction bearings in a bicycle wheel hub are perfect. Looks like I need to find a reasonable bicycle repair shop fast. Not many do that anymore around here though. I can't even find a simple 2" sproket anywhere!

I have regrettably screwed up and reduced the output of most of my projects with high resistance. I now view resistance like my 'Darth Vader'.

Perhaps It would be better if you could go with more magnet/poles,(7" dual steel rotors) then you could go with bigger ga. wire in the coils (less turns) and get more amps in every wind speed. The one I am making has the 7.25" diam dual steel rotors (like 1/8" thick circular saw blades at 'BIG Lots')  So I hope to put 12 mags on each rotor for a normal 12/9 (9 coils) 3-phase set-up.

Except I am going for the higher voltage 24v battery system for much less line loss since it will be 75-100 feet away.

I'm not sure I can do it yet though. I think It will. It is interesting to try.

My mags are 1" diam (N42) 1/4" thick. I'm going for a 1/4" thick stator (3/8" mag to mag air gap)   with 20 awg wire/ 80 turns per coil.  

Hopefully, 24v cut-in around 400-500rpm??

You are doing a very interesting project there. I hope it goes well and look forward to what you make. You do good work.   Thanks for sharing the idea about the bike hub. It helps my project a lot.

[ghurd]

Be advised.  

US bike bearings and axles are not a standard thread.

And the cheapest Chinese bike bearings are a bit tougher than standard duty US made taps.

The 5/16" parts are 26 TPI.

Re-tapping the 5/16 28 to 5/16 26 was a flop.

Ruined all the parts.  

Found a mail order place with decent, low cost 5/16 26 taps (Akron?).  I will look for the catalog if anyone is interested.

Any high end bike dealer can get the parts.  Cannondale, LeMond, Felt, Velo... even Trek.

G-

[Bobbyb]

Hi,

Well your idea looks surprisingly like the one that I've tried.





This is it. It's also based on a bicycle bearing.

As u can see it is a dual rotor and was designed for 12 12x6mm neo's 6 per disc.

The original idea was the plex stator but that did not work at all.

As mention before resistance is the problem. I tried sum other coils and differed wire size.

The best result I got with a 60 turn coil of .8mm wire(on the left). I thou away the test result's but as I remember I got 2V at 2A at 1000rpm(one coil), I had to push my drill in to hi rpm's to get anything.

After these result's I did a motor conversion witch gave me much much more result for the same magnet's.

From my experience I think it's a waste of time if your looking for 5W+. If your looking for a good lesson on axial flux generator's, coil and wire resistance, this is a project for u.

As for small an easy windmill (for developing country's) just go with the car alternator, easy to get easy to replace.

[electrondady1]

i think you almost have it .

a hole saw would allow you to open up the center of the second disk,

 and slide it over the hub.

i doubt the millions in refugee camps will  complain about single phase.

 

[gotwind2]

Thanks guys.

I have opened up the back rotor plate and assembled.

Space is very tight, as thought.

I can now fit six 1/2" square by 1/4" thick neos magnets on each rotor.

I think single phase as Flux suggested - is that all the coils connected together in series?

I'm expecting even less power from it now, and did indeed give up, for an hour and decided to carry on.

Learning if nothing else..

Ben.

[CmeBREW]

Thats a good idea-- never thought of that. But the magnets look awefully close to those rotor cross bolts which very well might cause cogging esp with single phase. (not to mention flux loss)

Since it is only a 3 foot diameter mill , that cogging could make it have difficult starts.  Can you weld mounting 'ears' on the rotors to take the bolts further away from the magnets?  

Since you are going with single phase , cant you fit 8 magnets on instead of only 6?

I'm just afraid only 6 (per rotor) would cost you a lot of power in coil resistance.

I made a small dual rotor axial single phase alternator with even less magnet material than your 6 mags (3/4"diam) per rotor, and it was getting over 30 watts at around 1000rpm with drill test. Never flew though. I am putting bigger mags on it now.

So keep going -- I like the idea.  

-Be careful of hooking up single phase, you can hook it up TWO different ways.

Easiest is to just flip ever other coil over.

[CmeBREW]

Daaah... Or just use stainless steel bolts. I am always a 'cheap skate' is why that didn't occur to me sooner.

[electrondady1]

sweet little machine !

if stainless rod is tough to locate just use bronze.

let us know what sort of juice you get out of it. and at what rpm.  

[Flux]

You have really limited your chances by having those bolts at the outside holding the discs together. The spacing would easily justify 8 poles but the holding bolts restrict the stator to a ridiculously small winding area.

I don't see much of a solution unless you go for larger discs. There is another option and that is to mount the discs on the flanges and fix the axle and let the hub spin. That gives far more room but I don't believe the thing will survive for long with just one end of the spindle supported on a thin bracket. If you tap a 1" or more deep hole in a piece of 1" bar and support that then it may be strong enough. Yes the old British stuff is 26tpi ( cycle thread) don't know about the imports and I question their material technology as well.

Flux

[gotwind2]

As ever Flux.

I think you are right, I limited myself too much with what I had to hand.

The same basic principle should work however using larger steel discs, maybe 6 or 7" diameter.

Ready made 1/8" thick round steel plates are difficult to find off the shelf, does anyone know of such things used in different applications that I could use?

Unfortunatly I don't have a laser cutter in my shed, just an electric drill and vice

Ben.

[hasse]

maybe a stupid question from a newbie, how do you get the leads out from the stator as i see it it is surrounded by rotating parts.

christmas greetings from denmark

Hasse

[gotwind2]

Good question.

The rear plate needs a larger clearance hole to allow the power leads to exit.

Ben.

[gotwind2]

A Youtube video of how freely the bike bearing spins, I think this design could have some mileage in it for those not wanting to go the whole hog with the larger machines.

http://uk.youtube.com/watch?v=NCexKBh4EIg

I guess the bearings are not designed for thrust forces, but I would imagine they would last a good while with props less than maybe 4Ft diameter.

The bearing could be mounted verticaly within a steel scaffold pipe for a VAWT or clamped horizontally on a length of angle iron as a HAWT.

Ben.

[electrondady1]

for disks,

  use table or skill-saw blades.

old ones cost nothing and there are millions.

[Simen]

I think those bearings in a bikehub will keep up; i'd be more worried about the axle itself.

My little bikehub-dynamo windmill held up all last winter until the whole ting came down in a storm, and the bearings are still tight and smooth. The rotorblades are another story... I also used a front-hub as yaw bearing, and that axle was bent after the fall...

http://www.mwlmf.net/gallery/BikeDynamo

[wdyasq]

My KBC tools catalog lists 5/16 X 20; 27; 28 and 30 tpi taps.

Curious,

Ron

[scoraigwind]

Arriving late as usual.  If the bolts connecting the disks are a problem then you might consider using square rotors cut out with a guillotine and put the four bolts in the corners.  

If you only have room for 6 magnets why not use 5 coils in 5-phase star, and put the rectifier up there.

[ghurd]

Must have gone to recycling.

I will follow up when they send the next one, if I am still on the list.

G-

[gotwind2]

Thanks Hugh for the comment.

I am getting some larger 6" diameter rotors turned now, 4" is just to small (now where have I heard that before..

I should be able to use an 8 magnet, 6 coil setup then.

If anyone has tried this setup could they please point me towards a posting or diary entry - most setups here seem to be 12 magnets and 9 coils.

Thanks.

Ben.

[ghurd]

Thanks to my friend who never deletes an email,

Turns out I was using the larger 3/8" axles.

Threaded 3/8-26TPI.

JTS Machinery, Mentor OH.

Die 1-368-13-26

Tap 1-372-164

http://www.jtsmach.com/jtswebshop/asp/home.asp

Prices went up considerably since Feb '07, or I didn't dig deep enough on their website.

G-

[Junkie]

Here's a suggestion: Instead of using the hub part, use the free hub instead. You can then adjust the spacing using standard cassette spacers, pvc blades bolted on, job done.

This is what I mean : http://mos.bikeradar.com/images/news/2007/10/03/shimano%20dura-ace%20hub%20with%20titanium%20freehub
-480-70.jpg

Bolt your steel disc to this using the standard lock ring and spacers for a single speed bike. The bearing part will be bolted to your windmill frame with 3 bolts coming out to hold the stator. I think this is a much simpler solution. I have used these  before for similar things, you will need a shimano lockring tool and chain whip. This will be a nice windmill with PVC Blades.

Hope this helps.

[gotwind2]

Thanks Junkie.

A good idea.

I think the more readily available 'old fashioned' front wheel hubs may be more accesible to people, and readily available for free (hopefully) particularly here in the U.K.

Always good to hear new ideas.

Ben.

[Junkie]

Well you's be suprised, nearly all new bikes are manufactured with those hubs, they are really easy to find, even here in the UK, and best of all the government hasn't found a way to tax the scrap supply yet  ;-)

[kihon]

Hi Ben,

Any update on this? Im in the process of building a 6" alternator using 24 (12x2) bar magnets, and Im interested in how much power you are getting out of yours.

At the moment, Im using 6mm thick 6" diameter mild steel discs from FH Brundel in uk. (~£2 each). They are not as precise as laser cut, but a lot cheaper Im using the 25.4x9.5x9mm bar magnets from cermag and 24 swg copper for the coil. Spinning by hand the best Im getting is about 2v per coil - will need to work out the RPM when I get a chance.

Anyway good luck, and let us know how it goes.

Kihon.