The contruction of my first PMA

[JeroenH]

After taking in the flow of information from this this I've ordered some magnets today, from the German site www.supermagnete.de.

I have ordered 24 magnets of the type S-20-10-N, which have a diameter of 20mm and height of 10mm. I intend to construct an axial flux, dual rotor PMA with them.

It's going to be relatively small, but that's okay, it's my first design and I don't want to sink too much money in it (yet!).

The magnets should arrive within 3-4 days, I'll keep you posted.

[Experimental]

   Great Jeroen,

   So, now you,re "hooked", and the fun begins !!!  Won,t be long before, you start thinking about BIGGER !!!

Be sure though, when you build your tower, to allow for , the larger one ......

   Happy building, Bill H........

[JeroenH]

I was hooked already (can't stop reading fieldlines!) but now I'm going to build something myself! It's all quite exciting.

It will not be a windturbine yet, but a handcranked or maybe pedal-powered PMA. Just to get the feeling for it, experimenting with coil size/shape/location etc.

Raising a turbine will most likely never happen where I live now (centre of medium-sized city), but who knows....

I can't wait for the magnets to arrive!!!

[Experimental]

    Don,t let, living in a city stop you -- thirty years ago, I lived in the Bay area, near San Francisco -- It was actually easier than where I live now, as I just put a twenty foot tower, on top of my garage -- that put me in fairly clean air -- now I have 100 foot trees around me and clean air is much harder to reach !!

   Also, the mills we are building now, operate in air, that would not even start turning the mill I had then !!

   Have fun, Bill H.........

[JeroenH]

Yee-hah! The magnets have arrived. Judging on how my order went, I can everyone ordering from Europe recommend www.supermagnete.de. The order came in fast, prices are very reasonable and they even threw in a unexpected string of 10 free very small cube magnets (5x5x5mm I think). I will have to think of something for those, some kind of microgeneratorto charge my cell phone? We'll see.

The magnets were well packaged, too. Lots of cardboard and bubble foam, and the stack of magnets had thick plastic spacers between them.

These magnets are the first large(ish) NdFeB magnets I've touched, and I can certainly see they are not toys. Of course I had to put one on the fridge, I nearly had to damage the door to get it off again. I think I could lift the fridge with a few of those. Scarily powerful. Makes me respect the Dans for working with their monster magnets.

Now, to the construction of the alternator... I have 24 round magnets of 20mm x 10mm (about 0,8"x 0,4"). I have some sheet metal of old PC casings which I intend to use for the rotors. I have two questions:

• What diameter should I make the rotors? I would say about 20cm (about 8"). Or would it be advantageous to make it smaller or larger?
  
• Using the PC sheet metal is a bit of a compromise. I already have it (for free), and it's just about the thickest metal I can work on with my current tools and skills. I know it's somewhat thin (I think about 2mm / 0.08"), but I could of course stack multiple layers. Would that help?
  

[dinges]

Hi Jeroen,

Powerful little beasts eh? Hope you've got the box of band-aids ready. In 10 years of tinkering I didn't need to have a box at the ready, but when I started playing with those magnets (mine were 20*20*10 square), about 5 per day were needed, LOL...

Have a look at my bicycle generator (though I know you already have), it may give you some starting values. Your magnets are a little less powerful, but not much, I think.

Don't use PC case steel, it's way too thin. Simple test: if you stick a magnet on one side, and something sticks to the steel from the other side, then your steel is too thin.

And whatever you do, keep your stator as thin as possible. I had to learn the hard way (twice...). Plus that airgap...

Succes,

Peter,

The Netherlands.

[JeroenH]

Don't use PC case steel, it's way too thin. Simple test: if you stick a magnet on one side, and something sticks to the steel from the other side, then your steel is too thin.

That's a simple test, I will do that tonight. Would stacking steel disks (2 or maybe even 3) help?

[Flux]

Stacking more discs will help, but it is not as good as one thick disc. They will not lie flat and you will have little air gaps between them. All these little gaps need to be subtracted from your main gap.

Probably good enough as a starting point.

Flux

[JeroenH]

These magnets are awesome. When stacked together (with the plastics discs between them!) they can influence my compass from across the room.

I am truly fascinated by them.

I have not tried dinges' experiment yet, I will disassemble one of my old PC's tonight and see what happens.

A question: what diameter should I choose with my magnets size and number? I can make discs up to about 35cm (± 14"). Should I make them that size? Or smaller? I can't judge what happens when I would choose a smaller or a larger disc.