Using Computer Hard Drive Magnets

[Mick S]

I have been reading some recent threads about computer hard drive magnets with interest.

Over the past 3 years I have been experimenting with computer hard drive magnets.

I have had good sucess configuring them as shown in the following photos.

(I can figure how to post the photos I will show you how I went about it)

The above photho shows a typical magnet on its backing plate

Use 2 spanners or pliers and bend the backing plate slightly - the magnet will lift off easily

Use a non nagnetic cutoff disc in your angle grinder and cut the magnet in half.

They have a north and south pole magnetic field built into them.

By cutting them in half, then turn over 1 half you have 1 larger magnet

Several magnets cut in half

This is how to place them on the metal disc.

I cut an accurate template from plywood to accurately place the magnets

The rotor is taped up ready to pour

Resin is poured into the mould.

I put them in my wood turning lathe and used sand paper to to make the surface nice and smooth to assist with final balancing.

More photos to come if anyone is interested.

This geny uses 240mm diam rotors (20 mags pers disc)

15 coils - 1mm diam wire - 5 in series per phase - star config.

DC resistance of each phase is 0.6 ohms.

with a moderate breeze (2.4 metre diam prop)I get 10 amps into a 12 volt battery.

Editors Note:


I tried to fix your photos but it was just too much effort fixing those screwed up filenames from Windows.

We have only explained the windows and photo names problem a couple dozen times. Sorry, I don't have the energy to fix them.


Editor

[Norm]

  very nicely done....now if we could figure

how to get the pics posted....I'm not sure

your photos are on file  reread the procedure

on how to post

....click on preview and preview first

             try posting one of your pics

in your reply to me....but preview it first.

  see if that doesn't help

                 



 like I just did              Norm.

[kitno455]

the first five...

[kitno455]

the next 5

in order to do this, you have to set your posting to HTML Formatted instead of auto, cause scoop is too stupid to not apply auto formatting inside a link or tag. or at least, this version of scoop.

allan

[electrondady1]

hey norm, love your mug shots. looks like you got the same expression on . like someone is trying to sell you something you don't want . hope your shoulder is better now.
  mick s , i went into your files. the photos are there,post some more about your stator if you can . be shure to click on the hot mail format. and repost  i'm glad to see you cut yours up like i did  

this shot is a couple months old  i've got more uniform  mags now and  will spend today laying them out.

[DanB]

Very nice - thats the finest use of little hard drive magnets I've seen yet!

[FrankG]

Very Slick...

Have you tried laying a sheet of paper over a completed rotor and dusting with iron filings to see if the density across the various magnets is consistent?

I'm unsure if visually one could tell, but it may be another point of reference such as weighing each magnet.

[asheets]

Doesn't splitting these magnets just make smaller magnets with the same "face"?

Before split:

nnnnnnnnnnssssssssss

nnnnnnnnnnssssssssss

nnnnnnnnnnssssssssss

nnnnnnnnnnssssssssss

after split:

nnnnnsssss     nnnnnsssss

nnnnnsssss     nnnnnsssss

nnnnnsssss     nnnnnsssss

nnnnnsssss     nnnnnsssss

nnnnnsssss     nnnnnsssss

but if I read your design properly, you think you get:

nnnnnnnnnn     ssssssssss

nnnnnnnnnn     ssssssssss

nnnnnnnnnn     ssssssssss

nnnnnnnnnn     ssssssssss

nnnnnnnnnn     ssssssssss

or am I just reading this wrong?

[craig110]

Hi Alan,

For most magnets, you're right, splitting it would give a N/S on both pieces.  Hard drive magnets are odd magnets in that they are the equivalent of two magnets that are attached together.  Looking at them sideways, they have the following poles:

  N      S

=====

  S      N

(BTW - Does anyone know why HD magnets need this pattern??)

So splitting them in half results in two traditional magnets with a single N and S pole on the opposing big faces.

Incidentaly, I recently took an old HD apart to play with the magnets and instead of each magnet being in the pattern drawn (horribly ;-) above, the two magnet covers each held two smaller traditional magnets inside them.  In a sense, they saved me the hassle of splitting the doubley-poled magnets in half.

Craig

[craig110]

Oops, my drawing was partially eaten when it was submitted.  The line of equal signs representing the body of the magnet was supposed to continue to the right beyond the second set of N/S letters.

[kitno455]

craig- bet it was a 100-200 meg maxtor? if you look at the original poster's rotor, he has a couple red mags in there. i have some too, and a plated set. already split. thin though...

allan

[Norm]

   Thanks Allan ...never had that trouble with

pics, myself, but nice to know about....

                (  :>) Norm

[electrondady1]

kitno455, those maxtor hd  have nice mags.    frankg here's a cool test, pace paper on both your mag rotors. on the bottom one put a few table spoons of iron fileings. spread it around to show the flux lines. now slide the top rotor into place. if your mag placement is correct the fileings that ran side ways from one mag to another now bridge the gap verticaly between top and bottom rotors . any thing still going side ways is going to miss the coils . a waste of flux .



i used a special primer on these brake rotors. it turns iron oxide into iron sulfide. smell just like dog poo !

[nothing to lose]

That one picture there had me a bit confused.

Are you trying to say you have a magnetic atraction to snakes, or snakes are attracted to magnets??  

That is a great looking job there. You did very well with the drive magnets. Have you got this together and tested it yet. What kind of power should it be making, and what size is it.

Very nice job, I hope it works as good as it looks.

[nothing to lose]

Ooops, geuss I missed it,

"with a moderate breeze (2.4 metre diam prop)I get 10 amps into a 12 volt battery."

120watts in a breeze is nice.

[craig110]

Hi Allan,

Yes, it was a Maxtor in the 100-200meg range.  Gee, I didn't realize I had such a special drive!  The magnets are thin, but I pulled them just for fun as I was tossing that old disk.  Once my test generator design(s) settle down, I'll be most likely ordering 3 or 4 dozen 2x2s instead of using HD magnets for anything real.  Life is a balance and to me, HD mags require too much disassembly time for too little surface area.

Craig

 

[zap]

(BTW - Does anyone know why HD magnets need this pattern??)

Craig, the pattern makes for a simple motor or voice coil. Early drives sometimes used stepper motors with a linear throw(rack and pinion) and before the dual pole face came along they just used two magnets side by side. http://yuan.ecom.cmu.edu/rotaryvoicecoil/

For some massive magnets keep your eyes peeled for old 5.25" Micropolis drives.

[asheets]

I actually know why this is the pattern -- the HD heads are mounted to a lever make with a small coil, in between the sets of mags.  It makes a really sensitive voice coil -- a small known voltage across the coil moves the heads very accurately and to a known position.

Before the advent of cheap(er) neos, stepper motors had to be used, and bit density on a platter was very limited.

[gonedrovin]

Hi..It was good to see your photos. I have been collecting old hard drives for a year or so..very hard to get as people are paranoid about data and privacy. However, I have about 50 or 60 intact magnets (as well as the 10 or 15 that got broke..no matter whose advice I followed). I also just picked up another dozen 20 to 80 Gb Fujitsu drives from a mate, so I'll be extracting the magnets from them tomorrow.

Its so bloody hard to get sets of matching magnets. Does anyone know how many I should have to start a reasonable project. If I am using my mill to..say, charge my mower battery and a few NiMH batteries, do the magnets all have to match?

The voice coils from the hard drives have me thinking as well..the great thing is that they are already very neatly, tightly wound, exactly to match the magnets. I ran the trusty old Fluke over a couple and got resistances of 30 or so Ohms. Is that too much? Can the fineness of the wire be overcome by using a lot of them in parallel?

Their perfect shape means that the airgap can be absolutely minimal. The hard drives also have great sets of bearings for small projects. I can imagine the bearing the arm carrying the heads pivots on being the basis of my tail pivot. Actually, it wouldn't be hard to use the whole arm.

The bearings in the actual disc drive mechanism must be awesome...if a bloke could  only separate them from the drive motor. I have dissected and experimented with a few of those motors and they are a total mystery. Seems like a radial flux, permanent magnet motor with laminated cores in the coils, (like the "Smart Drive"..but tiny)...but there must be some tricky circuitry in there.

In the process of dissecting the hard drives, I also now have enough highly reflective discs to make a great heliostat. Heh, heh, if 120 or so suns focussed on a 95 millimeter diameter target won't run my still, there's something wrong!!! I have an old door that I figure I can hotmelt glue one edge of each disc to, and put a couple of screws through at 60 degrees round the diameter to focus each disc on the same spot..

I've also been scavenging microwaves ever since I discovered this forum...I now have 22 of those ferrite ring magnets..but only about 14 matching. There's a shirtload of copper wire in each one...fine stuff in the cooling fans, then a couple of heavier grades in the big transformers, and occasionally intermediate sizes in other transformers. I have had virtually no problem unwinding the transformers..even tho the wire has been sort of glued together, the windings seem to come apart ok without losing insulation. Just have to get onto the laminations with an angle grinder to separate them.

But..with my wife complaining about an ever-increasing collection of stuff in the garage, I need to start a project soon...any suggestions?

If anyone can tell me when I should stop collecting and start building, both my wife and I would be very happy.

[ghurd]

Strange magnet / coil ratio in some of those HD motors. I only checked one, but it has 8 poles and 8 magnet disk, 3 phase (I thought).

I bend back the magnet mounting plate, then the neo pops off with a little help from a screwdriver. I score them all the way around, and snap them with 2 pairs of pliars.

I think the voice coils resistance is way too high, even for AA charging. But there are better coils in some VCR motors, just a tad larger.  I called it the 'Bad' motor in my VCR post.

My HD magnets sure are not going to match, but they will be stacked several thick.

Start building now.

Some of it is a lot easier than it sounds. Some of it is not. Won't know until you start.  Then you can tell what junk not to bring more of home!

G-

[gonedrovin]

Thanks Ghurd, good advice..start now..yeah!!

I agree the resistance is too high...but..my question is..can I reduce that resistance by using a few in parallel?..I have a shedload of them, and they are far more compact than anything I could wind.

I'll have another go at posting pictures tomorrow.

[ghurd]

Sounds like you are thinking small.

Well, in the last dozen or 2 disassembled here, only 2 coils are the same. Those came from same brand, different model. Most of the same model had different coils. There was even one aluminimum coil. Go figure.

Parallel coils should be exactally the same number of turns.  Maybe, with such high resistance and so many turns it would work out OK when the RPM got a little higher.

The resistance is still going to be a major problem for 12V. Even 4 in parallel will be 7.5 ohms. I won't bother even trying anymore if the resistance per phase is over 5 ohms for my tiny stuff.  Yea, I said 5 ohms! (LOL. A lot of people just choked, then spilled coffee in their keyboards)

The resistance per coil in the 'bad' VCR motor is under 2 ohms, that would work MUCH better.

Never checked them, but... Some floppy drive motors have 6 coils, heavier than the voice coils, lighter than the VCR coils. A little smaller ID, so the HD magnets may need snapped again.

Two identicle floppy motors give 12 coils, for use with 16 magnets per disk.

Then, each phase could be wired series and/or parallel to get the voltage or amps.

Or with enough magnets deep (to get strength across the airgap), it could be 2 coils thick in parallel, and built like a standard 6/8.

I have a feeling it would be easier to find some 24ga wire and wind your own coils, stack the magnets deeper, track the results, hope for the best. Then, from what you learned, stack the magnets deeper and make another stator with a lot more turns.

G-

[gonedrovin]

I just typed this reply, but somehow lost it, somehow.

Thanks for your advice,Ghurd,I hear what you say about the voice coils..but I guess laziness was overtaking my judgement.

I happened to open up an old floppy drive today and was intrigued to see the shape of the coils (triangular) but roughly the right dimensions to suit the HD magnets. I will check their resistance tomorrow. So you reckon 5 Ohms to be the upper limit??

Where are the coils in a VCR? Not that I am keen to go looking for more gear.

"Thinking small"....yes..well I guess I am. I'd like to charge a battery to power my horseyard electric fence energiser. It's remote from the home power supply. I guess I realy want to show my kids that a bit of innovation can be an alternative to this polluting consumer society we live in.

Is there any rule of thumb regarding the optimum number of turns in a coil relating to the strength of a magnet?

I was thinking of using a couple of old 6 1/2" diamond saw blades for my rotors (on a dual rotor machine)..they should give me the precision to minimize the air gap.

I'd be grateful for any comments/advice.

[ghurd]

The lower the better for resistance. 5 ohms is too high I think, but it takes a lot of turns in this small stuff, so high resistance is almost a necessary evil.

My idea of small seems smaller than yours.

The formula for turns figures in many things. It around the board, somewhere.

The VCR coils.  Its in this post, labeled as a "Bad" style motor.  The coils can be carefully removed, lifted off with a razor blade is how I did it.  Still small, the OD of the coils all the way accross the motor is only 2.3". They seem good for about 0.5x0.625" magnets, although I plan to use them with 1/2" disk neos.

[ghurd]

You had me thinking about the voice coils too.

Wish more of these HD magnets were closer in size.

Forgot the photo of the VCR coils.  The 'bad' motor coils.

I was going with 8/6, now I'm not sure there are enough turns in these coils.

Hunting for another VCR, then 16/12.  

If I don't get frustrated and just go 8/6, but I expect cut in about 9 MPH, and we don't get that often where it is going.