Alternator using recycled hard-disk magnets

[gyulasun]

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

[joegatt]

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

[fleebell]

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

[joegatt]

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.

[fleebell]

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