Thickness of magnet rotor steel

[oregon wind]

I have noticed that the round steel plate used for the magnet rotors is different thickness for different sized alternators.  The 10' alternator uses 1/4" and the alternator on Dan's generator uses 1/2" as do some of the larger wind turbines.  Is the thickness just for strength, or is there something to do with flux densities, or something I'm not thinking of?

[vawtman]

Hi Oregon Wind

 The one measuring tool is a simple paper clip on the backside of the steel.If it sticks the plate is too thin.

[Flux]

Almost entirely a mechanical issue. Even if it will hold a paper clip on the back the loss of flux will be a secondary issue as long as you have steel 1/4" thick.

You will have serious trouble finding 1/4" plate truly flat for large rotors and if you could you would have deflection and instability with the pull of powerful magnets. If the plate is too thin it may even collapse.

Also bear in mind that most people mount the prop against the front disc so you need to support the blade gyroscopic forces without deflecting the disc and changing the air gap.

Flux

[Capt Slog]

It's difficult to imagine the amount of attraction that the two rotors have to each other, hence the arrangements people build in for 'jacking'; the safe fitting and removal of the rotors from each other.  Even with the jacking, it's a nervey proceedure the first couple of times, and I'm pretty sure that my 6mm discs show some dishing due to the magnetic pull even though the radius is only around 4 inches.

Although I have bolts that hold my rotors together, they could probably manage the job by themselves if it wasn't for the risk that they might accidentally tilt on one side and crash together.

[oregon wind]

Can you make your discs too thick.  I have 5/8" scrap I could use instead of the 1/2" I wanted to use.

[finnsawyer]

In terms of the magnetic flux, no.  Increasing the rotor thickness actually decreases the reluctance of the flux path in the rotor.  But there are other issues that are not affected by the rotor thickness.  See my other comment on rotor saturation of this day for one that is usually ignored.  A thicker rotor will also act more like a flywheel, which could affect the dynamics of the wind turbine.  One could lighten the weight by a judicious placement of holes, however.