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Wind energy => Wind energy generators => Topic started by: joegatt on May 04, 2006, 05:22:15 PM

Title: Alternator using recycled hard-disk magnets
Post by: joegatt on May 04, 2006, 05:22:15 PM
Here's an alternator I rigged using recycled hard-disk magnets. 21SWG wire may be a little too thick for magnets of this size. 24SWG wire seems more appropriate.  The coil size limits the proximity of the two rotors and hence also the magnetic field strength.

The voltage pulses have a 2Volt peak and cannot be easily rectified. The output power is presently 0.25 Watts but this can be improved with a sturdier construction allowing the magnets to be nearer to the coils.

To increase the power, one can use bigger magnets. (Or use superconducting wire, yeah!, and bring the magnets closer.)
One can always add more magnets and more coils, but when adding coils in series, the coil impedance also adds up.
So there you have it ... you would need bigger magnets to get more power.  And rare earth magnets don't come cheap.
I wouldn't like to have a wind turbine that spends its working life just trying to pay for itself. But if you can get big matching magnets from scrap ... then go for it!

Regards
Joseph
Title: Re: Alternator using recycled hard-disk magnets
Post by: joegatt on May 04, 2006, 05:26:56 PM
Here's a clip showing some more detail of this setup
Title: Re: Alternator using recycled hard-disk magnets
Post by: joegatt on May 04, 2006, 05:28:18 PM
And here's a power test using a small incandescent lamp.
Title: Re: Alternator using recycled hard-disk magnets
Post by: gyulasun on May 04, 2006, 08:00:49 PM
Hi Joseph,

Nice setup, thanks for showing it. I would like to know if you placed magnets under the coils too (not only above them) ?
I cannot see clearly the bottom part of your setup, this is why I ask. (If you did place magnets under the coils, then do the upper and lower magnets facing each other and the coils are between them?)
Also would like to know the pole arrangements of your magnets, how you placed them.
Title: Re: Alternator using recycled hard-disk magnets
Post by: joegatt on May 07, 2006, 02:27:44 PM
Yes, Gyulasun.

Using two acrylic discs, I placed magnets both above and below the coils to try to maximize magnetic field strength. There should be a South pole opposite each North pole and vise-versa to hopefully link the flux into a straight line crossing the coil conductor at right angles.

The hard-disk magnets have two poles on the same face. In theory they can be laid out in a complete circle of alternating north and south poles. However, my decision to recycle also the backing steel plates, (instead of using a complete steel disc,) meant that there would be gaps in this rotor.

Morover, these magnet pairs can be left-handed or right-handed ie. approaching them from a particular angle, you meet the North first with some, and South first with the others. To cater for this, I laid the magnets out in alternating right-handed and left-handed pairs going round the rotor. Then the eight original coils, which were wound together in series, had to be laid out in an alternating clockwise and anticlockwise sequence, so that the voltage pulses would add up.(See diagram attached)

Finally, in order to try and raise the power output a bit more, I winded an extra set of eight coils and installed them in the gaps between the other coils. I connected this set of coils in series with the orignial set. It was a gamble. Only one of these two sets of coils would be truly active at an instant. And now the overall coil impedance will be double. However as the frequency of the pulses was now effectively doubled the power output showed a marked increase.

Regards
Joseph
Title: Re: Alternator using recycled hard-disk magnets
Post by: gyulasun on May 07, 2006, 05:40:49 PM
Hi Joseph,

Thanks for your answer.  This poses a couple of questions if you don't mind... :)

Why the backing steel plate is needed? I mean any one magnet is magnetized through its longest length OR through its thickness?
Because if they magnetized through their length, then the steel plates short-circuit the poles don't they?
OR there are two smaller magnets placed on the backing steel plate and they are bridged by the plate to add their strength? I think this latter is the case?   

Have you considered connecting certain coil pairs in parallel too, to reduce coil impedance?

Thanks and best regards

Gyula
Title: Re: Alternator using recycled hard-disk magnets
Post by: joegatt on May 09, 2006, 10:52:04 PM
Hi Gyula.

The magnetization orientation is such, that each behaves like two short magnets side by side. And yes, the backing steel plates short out the magnetic path on the reverse side making the forward magnetic field stronger.

The impedance of the two sets of coils is about 1.4 Ohms each. So if you put them in parallel they effectively short out each other. Just for fun, I tried it out once ... and got the strongest braking force possible with this setup.

An annoying feature is that the pulses are so narrow, if you try to rectify the output with a bridge, the intrinsic capacitance of the diodes effectively shorts them to ground. But I guess there may be other ways to use this thing.

Regards
Joseph
Title: Re: Alternator using recycled hard-disk magnets
Post by: fleebell on July 08, 2006, 09:51:38 AM
I have a question and a suggestion. Is each plastic disk between the magnets and coils or outside?  I couldn't tell from the film but it looked like you had alot of extra space between the magnets and the coils. That space has to be as small as possible.   The suggestion is learned from building the same type of alternator and plastic sheet (I used round neos though and 6" disks) .. get a bigger axle and bearings - at least 3/8". 1/2" would not be too big for the size of your alternator and it would be alot sturdier (bigger washers to hold the disks).  I have found 1/4" threaded rod just flexes too much for anything over 6" or so and you can't harden it so it won't do that.

Lee B
Title: Re: Alternator using recycled hard-disk magnets
Post by: joegatt on July 09, 2006, 09:16:12 PM
Yes Lee, you are right. The gap between coils and magnets should be as small as possible. To this end, my rotating disks are outside the magnets and coils, just as they should be. However, the thickness of the load bearing plate is unfortunately in the way. I once pondered the prospect of sinking the coils into this material but with the coils now covering the entire circumference, no support would remain. The axel would then have to be suspended from two points outside the rotating disks.

However considering the low power output of this unit, I don't think it's worth the trouble.Oh yes, and I did replace the axel with a thicker one with bigger washers, but I still regard it as nothing more than a demonstration model. If you manage to achieve a significantly higher output power from your unit, I would certainly be interested to hear about it.

Regards
Joseph.
Title: Re: Alternator using recycled hard-disk magnets
Post by: fleebell on July 17, 2006, 04:21:07 AM
Mine was built just about the same way, I never got more than a few amps at 14-18v out of it.  I'm going to try it again but this time I am going to make a small version of the wind turbine alternators that are all over the net where the coils are completely potted in resin or plastic. The magnets will also be potted into the plastic disks. This time though I intend to use four coil plates with 5 magnet disks.( 6 coils per disk--6 magnets per rotor)   Only the 2 outside disks will have any metal backing and I can get get the right size magnets I will just use a Halbrach (?sp) array on the outside disks so I won't need the backing metal.  I'm still trying to find some rule of thumb info one what the coil wire gage should be for a particular voltage/current combination....Oh well.... experimentation time again I guess......

Lee B
 
Title: Re: Alternator using recycled hard-disk magnets
Post by: Paul-R on October 26, 2006, 04:22:14 PM
Fleebell: Odd spelling: I think it is "Halbach".

Do you know the torque in the shaft driving the device?
Not easy to measure. Strain gauge. Useful to know.
Paul.
Title: Re: Alternator using recycled hard-disk magnets
Post by: fleebell on October 26, 2006, 10:05:03 PM
Not yet as I have not had a chance to finish it yet.  Too much other stuff going on around here at the moment.   I plan to use a wind turbine if possible.
Lee