Steel Rotor Thickness?

[FranklinsAce]

Hi, thanks in advance for your advice.  Lots of great information here!

I got Dan's book (1st ed) and was reading about "Complete Magnetic Circuits" (p74) and it mentions using a steel rotor rather than wood etc.

My question is, how thick of a steel plate should I get for my magnets?  My rotor is 5" diameter, magnets are 6x N52 1" x 1/2" x 1/8" - ~ pull 13lbs (BrMax: 14800 gauss).  Is there a good formula I can use?  In the book Dan notes if you can pickup a paperclip on the back of the rotor the metal isn't thick enough.  Since I'll have to pay someone for this part I'd like to get it right first time and not guess.    (side note, I also have another set of magnets N52 1" x 1/2" x 1/4" - ~ pull 21lbs (BrMax: 14800 gauss - so will be using this in my next build)

Background:  I'm currently working on a small prototype and made my rotor out of cardboard - until I read Dan's book - and I'm ready to upgrade to steel

Any advice, links to existing articles would be most appreciated!

[MagnetJuice]

Hi FranklinsAce, welcome to the Forum.

I just happen to have some of the same size magnets and did some testing using metal plates of different thickness.

For the 1" x 1/2" x 1/8”, a plate of 1/8” is adequate.

For the 1" x 1/2" x 1/4", a plate of 3/16” is adequate.

If they were weaker than N52, you could get away with a bit thinner plate.

As far as I know, there is no formula to find the thickness of the steel. That is why builders go with the paper clip guidance.

It would be possible that someone could write an equation for that purpose. However, they would have to do it after extensive testing to get the data, because there are too many variables. Magnet area, thickness, magnet grade, just to name a few.

We would love to hear what you are working on. We are all here to help each other and to learn from one another.

Ed

[FranklinsAce]

Ed, you're amazing!!!  Thank you so much

I'll let you know how it goes.  So far I've been having a blast.

[MagnetJuice]

I saw your video of the little Savonius on YouTube. Interesting, that is the best way to start learning, by doing. Once you put your magnets on a steel rotor, your voltage could double.

I plan to build a Savonius after I build my experimental Darivonius. The harder part about the Savonius is building a low RPM generator. It needs many magnet poles and many turns of wire in the coils to be able to produce about 15 volts at around 60 RPM, but it can be done.  I already have an alternator design that will work at that low speed.

Ed

[Karana]

Hi FranklinsAce,

The main goal is to seek to concentrate the magnetic flux into the coils on your stator. Plating the magnets on a thick iron back will help to do so. In my workshops, I would put a paperclip on a table and have my students see how much distance is necessary to pull the paperclip to them. Then I have then put a metal back on the magnet and try the same exercise. The metal backing multiplies the field and flux of the magnet. You can rely on formulas but since the dimensions and the conditions of your magnets will vary, experiment yourself and you will see the results. Good luck with your efforts in this area.

[FranklinsAce]

Very excited, got the rotors Ed recommended!  Took a while but my barber's husband owns a mobile welding business and did this at no cost to me (I'm not going to look the gift horse in the mouth  )

The two 1/8" rotors weigh 275.5g and 284.5g, the 1/4" rotors weigh 444.0g and 451.5g.  Over the next few weeks I'll get the magnets mounted and incorporated into my alternator.

[MagnetJuice]

Looking good.

Thank you for the update. I would love to have your barber cutting my hair. 

Ed

[SparWeb]

That's a great start.
What do you have for a hub so far?  Trailer axle?