HDD Magnet Generator - help needed

[claude]

Hello everybody,

I'm posting this after carefully reading for about 3 weeks the board (the old one too) in search of a complete answer. My findings ended up in only bits and pieces of information on this matter. I want to build a axial flux generator but it seems that the closest I can get to Neodynium magnets are HDD drives. So I got closer and after many trips to local computer shops I managed to get 81 magnets. The quest was long and tidious, in some places having to convince people that i'm not a freek building some illegal instalations (they get suspicious when someone needs so much high-tech garbage) but some of them were patient enough to find why I need them. Some even wished me luck.

But it seems to me I need more than that since I couldn't find any plans on this matter yet. Some people tried different setups with HDD magnets but there's only bits of info's out here. I may have to make them myself and that would be fine with me but when you deal with questions like how many magnets, what kind of placement, how many coils and how many windigs things get complicated.

After all this reading I would try to build a dual rotor axial flux generator. Here comes the questions ... How many magnets should I use? I'm thinking of 12. How many poles? Well, since I gathered them so hard and they are so many sizes/thicknesses/shapes I don't feel comfortable breaking them in half. Or maybe I should, i'm not sure yet. 24 poles with the magnets lined along the circumference sounds good to me. A dual rotor with 12 magnets, 24 poles, 3-stacked should be fine. The problem is that the magnets have different shapes & thicknesses. I could use them wisely to match the total magnets height but will the smaller ones cause any field loss?

As for coils I think I'll go with 9. Is this OK? There will be 24 poles ...

The shape of the coil would be round but I'd rather make them larger (longer legs). That's another matter I need expert advice at. As well as the number of windings. Of course I'll make a test coil first and post the results out on this board for further debates.

My aim is to charge a 12V battery to run some 12 V lights and a small inverter for a couple hours a day. It shouldn't be more than 150W load I presume. All this should be done at low wind speed. The average windspeed here is around 12 mph.

I try to keep my expectations low here.

Since I'll order my rotor/bearings/etc to be made in a factory out here, I will need exact plans on the whole thing. Plans I'll have to make by looking at the pictures posted on this board. There has to be a better source... Can anybody help?

My main concern is the low magnetic flux due to smaller magnets, coil shape and rotor/bearing/furling related mechanics. Unfortunately, Hugh Piggott's book is out of reach here in Romania. I have to say I always liked to build things but that doesn't mean I got to welding or anywhere near a lathe. On top of that, everything's metric here so wish me luck, I think I'll need it.

Thanks,

Claude

[kitno455]

1. break them in half. the neighboring N and S poles on the plate should be separated by a gap.
   
2. stack them to make same height in each pile, dont worry about slight differences in area.
   
3. dual rotor, even if there are no mags on one side, will make more power.
   
4. you have very little magnet material, you will have to make a very thin stator with fine wire to reach cutin.
   
5. single phase or jerry rig will reach cutin with less turns, but requires more coils (one per pole)
   
6. motorcycle brake rotors or sprockets (if not warped) make good magnet rotors for this size gen.
   
   

allan

[claude]

Hello Alan,

So I should break them, huh? Assuming I will, would it be possible to place - say - 3 half pieces of N pole side by side toward the disk center in order to increase the magnet size and the same with S while stacking them. up to 0.7" in height in order to boost the field and increase the coil size and thickness? That would require all my magnets for one rotor but I would then use a blank disc as a second rotor. Perhaps in time I could gather some more magnets to fill it up. Thanks for your suggestions but as I said, the rotors will be manufactured according to my specs - which unfortunately I don't have. Yet.

However I've seen great results with HD magnets used as they are, unbroken. The advantage is a greater numbers of poles, the main disadvantage would be the coil size. But smaller coils allow more of them on the disc. Or with an iron core ( in dual rotor with magnets) - a greater thickness, so... I really don't know what to say right now.

[ghurd]

"after many trips", Free magnets get expensive!

No plans are available because the magnets vary so greatly, and people using HDD magnets will often want to use other recycled parts. No one will have the same pieces.

Proportions are important. Scale the parts to match the magnets.

I believe more poles help too. 81 magnets, broken in half, is 81 magnets per disk.

With 16 stacks that is about 5 per stack. The nicer HDD magnets I have here would average about 12mm deep. Plenty of room for the stator.

With 16 stacks, it could be single phase with 8 coils, or 3 phase with 12 coils.

Computer monitors and TVs have a degausing coil around them in the back, in black tape.

It is made of magnet wire and easier to use than transformer wire. Looks like a nice size wire for a project like this.

G-

[electrondady1]

"after many trips", Free magnets get expensive!

thats for shure gurd .

and after the first hundred harddrives the store owner expects you buy stuff!!

layng out the mags and trying to get some kind of uniformity is  very tedious

the one i'm doing now is a dual rotor.

 16poles on 10" disks.

 i'm using 3 magnet halves to get longer legs.

no test coil yet. i think i will over drive it with a belt or bike chain.

[claude]

ghurd, yes, they really get expensive. One of the vendors even took out the controller plates off them before giving them to me. Perhaps they figured I could use parts form all the disks to make some good ones... Anyway, some of them asked money for them. I wouldn't mind paying the man a pizza but they went up to 60% of the brand new disk value! How's that? No comments.

I ageee, with the variations. I identified 19 kinds of magnet among my 81's.

So you suggest 16 stacks per disk, 5 per stack and 8 or 12 coils... Hmm...you do realize that's 16 poles instead of 24 with the magnets unbroken... but still that's 5 per stack.... I'm thinking out loud here, don't mind me.

But hey, that half magnet-sized pole would need minute coils! Where's the advantage here?

As for the magnet wire, I intend to buy it new. I can't afford limited supply with so many variables hanging around. The magnets are limited enough. Thanks for the tip though..

Claude

[claude]

electrondady1, that's my idea too!

I wrote it up here, 3 magnet halves to get bigger coils. So it is possible.. How many will you stack? Could you post some photos of your work in progress? I ask that because I imagine you have the plans in your mind... Why overdrive? Do you expect low readings otherwise?

As for the magnets I found one small company (maybe the only one here) that can import them but the prices...

Here for instance : N35A502505 ( L=50; l=25; H=5 mm ) -price 12,49 EUR/piece. (about 15 bucks) + VAT (14%) + shipping from England (unknown value so far)+ delivery in 1 month. Is this a ripoff or what?

With 15 bucks i'll visit every computer shop in the two neighbouring counties and maybe fill my trunk with HDD's... The magnets are small, true, but what a puzzle I could make... :-) Tedious work is my middle name, I graduated fine arts... :-)

[ghurd]

With the magnets unbroken, the N and S will be too close together.  The flux will be shorted, so not be as good.

I pulled a degaussing coil from a 32" TV, it is 0.813mm wire, 4.5M circumference, estimate it at ~400M!

G-

[claude]

Right now, three scenarios cross my mind. I'll post the pictures here, it's worth a thousand words. Especially since my english gets rusty...














Will someone please tell me which way to go... I can't be sure of anything at this point.

[electrondady1]

calude,
build your geni like danb builds his.
 gurd and kitno laid it out for you.
your first diagram is the route i'm taking but you need to tighten up your mags
the space between mags should be the same as the width of you mag
some thing like this.







once the mags rotors are laid out. do a test coil.

[ghurd]

I like Willib's diagram of a layout.  2 coils are High, meaning a N and S magnet is over each leg, while one coil is low.

The magnets in this one are square, the coils are round.

http://www.otherpower.com/images/scimages/2965/g_alt_6C_8M.JPG

It is a better spacing of the magnets, like electrondady means.

The measurements do not matter so much, as long as the proportions are good.

G-

[claude]

Yes ghurd, I like it too but imagine small arched pieces of half HDD magnet trying to look like a big square one... And if I want some usable power i'd had to stack so many of them that I'm afraid I won't have any magnets left for the second rotor.

Danb's layout looks more promising to me. With three halves in line and stacked it should work, I guess. I'll try to find some more magnets, seems to me that the "Search of the magnets" is far from being over... despite my folks opinion that I started to have an obsession.. :-)

Anyway, I'll refer to the mechanics now since I'll obviously need more magnets. Here's a plan I made from my readings on this board. Can anyone see something I forgot? Faults... possible improvements...

[MickS]

Claude,

Here is how I do it.

I usually use anything up to 300 hard drives per genny.

I am lucky I have a good source.

You must cut them in half to get any decent results.

You must make your coils hole the same size as the mags and the width of the coil legs the same as the width of the mags to get optimal results

Mick S

<BR<BR>

[MickS]

Here is one of them up on its tower with 3 metre diameter blades.

Mick S

[claude]

Wow MickS, that's impressive!

Thank you for posting your pics. You used car brake discs I see... Hmm. Perhaps I should use them after all. Can you tell me the rotor diameter? And some output of that impressive 3m windmill? Also important would be what's the total height of your stacked magnets/pole. That way I could figure out how many years of searching hard disks I have ahead. :-)

Thanks a lot,

Claude