Building a 6" mini daul rotor.

[nothing to lose]

My newest small genny project I'm trying to build.

24pole 18 coils, #23 wire and 1/2"x1/8" disk Neos N42.

The wire I got is used 4.7lb coils from machinery. I have about 5 coils or about 22lbs, changing wire size is not an option.

 I have no idea what it was for, but a solid 1 strand coil wrapped in cloth and resin coated. It measures 0.023 with calipers after cleaning an end. Except for the turns against the clothe with a little resin stuck to it this is like new wire right off a roll.

I have mounted the little Neo disks to the 6" steel disks, I used a bicycle axle for the hub. The plan is put the blades on one side and the rotors on the other side on the axle and mount the hub solid.

 I had extra length on one end and a bit short on the other end, so I cut more threads. I think that was a 5/16 24 die.

The first rotor I tapped the center hole, so the axle nut for the bearing is in place and I screwed on the first rotor really tight. This makes like a jam nut so they lock each other, then I put on a second nut tight against the rotor plate making another jam nut and also part of the spacer for the air gap.

I drilled and tapped 4 holes for jacking bolts in the first rotor to lower on the second rotor, backwards from the way it's normally done though. I have 4 holes in the front rotor I will tap those later also. I think my tap wore down that fast since the last hole I tapped is hard to turn the screw but the first 3 are perfect.

At this time the airgap is about .36" which is kinda wide for 1/8" thick Neos. For now the spacers are 2 nuts and a washer but once I decide the final airgap I will make a wide aluminum spacer which will support the rotors and hold them apart, the rotors are only 1/8" thick. Even with the wide airgap and thin Neos I was surpised at the pulling force. With only 1 center hole the front rotor spun around to self align with the rear plate. My front and rear holes were not lined up and I was going to put a pin though 2 holes, I could not turn the rotors by hand, the attraction of the magnets keep them where they are! Not a problem but I did not expect that much pull that far apart really.

Testing was a pain today and poorly done. I held 1 coil by hand, 40 turns 1/4" thick, between the rotors and ran them with a cordless drill, axle clamped in a vise. I checked RPMs with a laser tach.

The following open volt results for that one coil.

Rpm 140=  .1V

RPM 266=  .2v

Rpm 332=  .3V

Rpm 441=  .5V

Rpm 667= 1.0V

Rpm 762= 1.1V

All AC volts

That was  rough test just to see if I would get any volts at all. Holding the coil by hand trying not to bounce off magnets was not easy!

Here are a few options I can do. The coil can be wider yet, I could do 2 inhand, or allot more turns. The airgap is too wide at 0.36" and I can close it some.

 The coil could have more turns and also be thinner but not able to to do 2 in hand that way.

There will be 18 coils total. 3 phase there will be 6 coils in phase at a time. I am thinking 3 coils per phase and 2 phases parralel. My thought on this is that 2 phases parralel would be basically same as double the wires in hand per coil, but spread out for more pole changes. Each coil will see 24 poles per revolution. Heat will be spread out also.

Sugestions welcome. Pics to follow I hope!

This will be for a 12V system if it works. A small unit for on a friends camper.

[nothing to lose]

There's parts. The extra little magnets, and the tiny coil. Bicycle hub and rotors. I plan to mount the axle hub solid, the stator braket to the mount. If ever needed to be removed like to grease or replace bearings the blade side can be unbolted and the stator also, then slide the entire genny out the back side in one piece still on the axle. No need to remove the rotors. Also a bit of balance, blades on front (where the drill is now), rotors on rear.

Another shot of the rotors.

The lumpy black stuff you may see on the rotor fronts a bit was black electrical tape so the tach would only read the reflective spot and will be taken off of course later.

For now the magnets are only super glued on for testing, later I will cast the rotors if this works at all.

You can see why I don't post pictures, I still need a decent camera! I just buy everything else and never get around to the camera. Although these turned out far better than normal, even though still crap!

The drawing above is how the stator/coils are planed to fit the magnets. The coils marked start and end and those with lines connecting are the ones with the magnets in the center hole and in 1 phase. May not be as I will wire them though. I drew in the lines because the magnets fit the holes and cannot be seen in the drawing.

Each line from the center hole is the center of either a magnet or coil, I just did not delete them before printing as they may be handy later also. Of course the 4 small holes are jacking screw holes and the center hole is in the center, not to size on the holes though, good for marking hole centers any size with a punch.

[RP]

It looks like you might have room to use 2 magnets for each one you have now (sort of like a figure 8 shaped rectagular magnet).  If so, you could get more juice without needing thicker coils.

What is your target cut-in speed?

[richhagen]

Hi NTL, I had tried a couple of mini discs, even smaller.  It is difficult because the flux between the small thin magnets weakens significantly with the wide gap.  I think that in order to get reasonable result you will have to tighten up the gap to 1/4" or so.  As it stands now, in three phase, you could charge 4 volt batteries in star and based on the resistance, with milliamps of current.  I never made a 'good' small unit, I still plan to, but I have not to date.  I hope that you will have better results.  I will watch with anticipation.  Rich

[nothing to lose]

The coils won't be any thicker, I expect thinner unless I double up on the wire like 2 in hand. Right now they can be wider because they do not totally fill the area between magnet poles.

I don't have a target speed right now, just low as I can get then mount the blades for that speed.

[nothing to lose]

Hi Rich,

Yes I plan to tighten the airgap some. Testing coils is a bear for me, the rotors are not cast yet so it's 48 hard spots trying to grab the hand held coil. Once everything is cast smooth that won't be a problem anymore. Also I will make a jig to hold the coils better for testing.

These are an N42 a bit stronger than normal also.

One of the reasons I went 24/18 is I don't think I will use normal wiring methodes like star or delta. I plan to bring all the wires to the outside of the stator so I can rewire and try different things. I am trying for fast pole changes at lower RPMs, one of the reasons I went with smaller magnets. I thought about using 3/4" or 1" wide Neos but that only gives me 15 or 12 poles, was something like that. I figured the center of the magnet for the rotor dia. X PI using disk Neos to get the count and angles to fit.

With a disk the widest part is the center.

I've done up allot of math on this, probably all wrong! I think I can get some volts, but rather I get any amps I won't know for awhile.

I am thinking 3 phase X 2, maybe less resistance in the smaller wire and less heat spread out in 2xs the coils, then parralel the phases?

[willib]

NTL , can you double up the extra mags that you have there ?

are there enough?

[nothing to lose]

I don't want to do that, and I seemed to have lost about 14 of them somehow? Should be 48 on rotors, I have 38 left, wheres the other 14? I had 100! I bet the dog snuck them outside to play with on his collar

Not worried, I'll find them, but seriously I have a handfull missing, about 14.

Actaully I have 100 1/4" thick on the way, was supposed to get them all in one box but they paid shipping for all of them and forgot to put the second set in the box! They paid to ship 3lbs and I got 14oz! They were sent today though so know problem. A place kinda near by me sort of. Should have them maybe Thursday?

The 1/8" plates had a minor flux loss on the back side untill I mounted the rotors together on the axle. I think stacking the neos or thicker ones will have a loss on the backside again.

I do have 1/4" plate rotors in 6" same as these 1/8", if needed I will test the 1/4" Neo disks on those 1/4" plates. That was kinda the plan, but since I only got 100 1/8" and not the 100 1/4" yet plans changed for a few days.

[Flux]

Those test results are useless. You are down below the useful range of the meter. The volts should increase linearly with speed. You have 2 readings with a doubling of speed giving more than a 3 times increase in volts. Things are better than you think.

I wouldn't go for silly small air gaps you waste too much in mechanical clearances. The present air gap is not too bad.

If you double the number of turns in the coils, make them oval so that the hole is about 3/8 wide x 1/2" tall and reduce the thickness so that they just fit you should do ok. Reduce the air gap to suit the new thickness and do another test, preferably at a higher speed so that you get several volts that the meter can measure reasonably.

I think you can make a 1M diameter machine that will produce about 50W.

Flux

[nothing to lose]

Thanks Flux,

I'll give that a shot, about 80 turns then. I may have room for that yet without going to 3/8" wide, any advantage to going smaller width or just to get more turns in?

[Capt Slog]

It's nice to see someone making something a little smaller than the norm. This is the sort of thing that I will be making eventually and I look forward to seeing what it will do.

And by the way.....

I never fail to be impressed by the QUALITY of the advice given when people ask for it on here. DanB, Flux and the many others who regularly write, my hat goes off to you all.

[dinges]

I've built a similar small axial flux once:

http://www.anotherpower.com/gallery/album46

http://www.fieldlines.com/story/2005/11/13/32021/791

It was a lesson learnt: airgap is very very important. Mine was too large. It works, but not great. The best thing I learned was how to handle Neo magnets and how to deal with rotorplates. It learnt me that I should be -extremely- careful when handling a full-sized rotor

It was good fun to build, but with just about the same amount of time & effort I could have built a full size generator...

[nothing to lose]

Yep, this will probably take longer for me to build than a large one would.

I already played with the larger rotors a bit with bigger Neos, but I need some small gennies and so does a friend. If this don't work out too well then back to a small motor conversion I geuss.

[gotwind2]

I wish you all the success in your 6" axial flux and bicycle wheel hub PMA.

I was hoping someone would attempt it, and successfully.

Please keep us posted of the outcome, may I suggest 1/4" thick x 1/2" Dia  Neo's - Im no expert but thicker mags might help.

Ben

[tecker]

Yes the round coils have a very short duration of flow that happens when the two opposite magnetic fields are tangent to the outside edge of the coil this is a very short time if you look at the wave form you can see the problem high peak long null cycle and some time if the mags are too far apart you'll see a null cycle at the peak which are two peaks as the center mag and the approaching mag set a chrage in motion.

[tecker]

the sphercal effect plays in this also as soon as a b field develops it shuts down any other induction .