Author Topic: solid or laminated magnet rotor?  (Read 2416 times)

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collidog

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solid or laminated magnet rotor?
« on: November 23, 2015, 10:49:19 AM »
solid disc magnet rotor or laminated thin sheets as in transformers? I have tried building up rotor thickness gradually and measuring results. Initial results indicate  similarities with varying magnet/ coil gap, i.e. rotor speed increases to provide a fixed final power into a resistive load. Is this the expected result?

hiker

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Re: solid or laminated magnet rotor?
« Reply #1 on: November 23, 2015, 12:01:42 PM »
solid steel mag rotors....no need for laminated on rotors...laminated ...is used  for the coils..on motors..and gens that are built like motors..
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collidog

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Re: solid or laminated magnet rotor?
« Reply #2 on: November 24, 2015, 02:46:54 AM »
  Thanks for that. Let me reword the question slightly.
  Are there any DISADVANTAGES to using laminated rotors? (axial flux type, of course). I do not have the facilities to machine solid rotors, so some years ago when I began practical experiments, I used tinplate that I could cut with tinsnips then laminate the discs to required thickness, using various methods.  By gradually building up the thickness, this gave me a "real-world" awareness of how adjusting rotor thickness to magnet strength affected power output. I also wanted to minimise rotor weight and thus lower starting  inertia. If solid rotors have been proven in practice to be more efficient electrically rather than merely convenient for the car disc brake aficionados, then for my own convenience I shall have to live with it. Perhaps practical comparisons have not been made?

electrondady1

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Re: solid or laminated magnet rotor?
« Reply #3 on: November 24, 2015, 07:24:02 AM »
i found 10" table saw blades to work OK as rotors for ferrite mags.
if your using neo mags, you will need multiple layers of blades to contain the magnetic flux.
you can test with something like a paper clip on the back side to see is it wants to stick.
if it does you need more steel.


collidog

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Re: solid or laminated magnet rotor?
« Reply #4 on: November 24, 2015, 09:01:32 AM »
  Thanks for responses so far but let me rephrase the question again.
 If transformers use laminated cores to reduce eddy currents, as do electric motors, then unless there are no eddy currents in axial flux magnet rotors (expert opinion, please) surely laminated rotors would be beneficial, especially if the laminations were insulated from each other?

P.S. I do know about saw blades and paperclips. I have spent many interesting hours hunting through the forums

hiker

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Re: solid or laminated magnet rotor?
« Reply #5 on: November 24, 2015, 09:41:21 AM »
Theirs no eddy currents in the rotors...
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SparWeb

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Re: solid or laminated magnet rotor?
« Reply #6 on: November 24, 2015, 02:32:00 PM »
Eddy currents only happens if the flux through the material changes.  The flux in the STATOR changes a lot, so eddy currents would flow and generate heat if there is any thickness of metal there.  But in the ROTOR, where the magnets are attached, the flux is pretty constant, and eddy currents aren't a problem.  If it's practical to use several thicknesses of material to build your rotor, then go ahead.  There will be no benefit, but no downside either, provided you have a thick enough rotor to carry the flux from magnet to magnet.  Since you say you've been experiementing with paperclips sticking/not sticking to the back of the rotor, it sounds like you're OK.
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collidog

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Re: solid or laminated magnet rotor?
« Reply #7 on: November 25, 2015, 06:02:44 AM »
Thank you Hiker and Sparweb. Asked and answered.
Yes, I do find it convenient to make up laminated rotors. I do not have the facilities to machine sold rotors. I can build up thickness to exactly match magnets to keep rotor weight to a minimum, and use anular ring (doughnut?) configurations. I use non-metallic face plates with holes drilled to suit circular magnets which are press-fitted, and remain securely in place by magnetic attraction only. I can prise them out and refit if necessary. I was wary at first that centrifugal force might make the mags fly off, but over the years this has not happened, even when spinning up 8" rotors to 4000rpm.
Overall, I find it a versatile and convenient way to experiment with the "if in doubt, try it and see" method.