magnet backplate

[artv]

Hi all,.. I've been working on my magnet rotor and it just dawned on me ....if you don't put a steel disk behind the magnets, will the magnets loose their strength??....because it acts as a keeper. Also does putting two magnets together act as their own keepers??..........might have to change my design.........thanks for any replies.....artv

[DanG]

Neo and Samarium-Cobalt magnets are especially good at NOT becoming demagnetized - no keeper required.

[Flux]

DanG is right in that neo doesn't need a keeper to avoid self demagnetising. I am not sure they you realise the basics of magnetic circuits and the need to complete the circuit except in the air gap to get full advantage of the magnet.

By not using iron backing you won't demagnetise your magnets but you won't get anything like the full advantage of them either so in a way it comes to the same thing in that the final output of the machine is disappointing.

Stacking magnets in series does to some extent act as a self keeper but that is not the reason for doing it, it is to make the working air gap short in relation to the working length of the magnet, again you need to complete the circuit as far as possible to get most benefit.

Flux

[GoVertical]

I had all the parts for a simple experiment. Metal back rotor verses No Metal rotor. Yes there is a monster air gap. The RPMs where the same in both cases, same coil, same air gap. The open circuit output was the same in both cases. The one thing I did find is that the metal backed rotor does contain the magnet field so there is no reduction of RPMs that could be caused from the magnet field pulling on metal parts near the rotor. 

[Flux]

With the monster air gap you won't see any benefit from the steel backing. There is effectively no magnetic circuit with the crazy gap so the little bit you shorten it won't have much effect. Virtually none of your flux is linking the coil anyway.

Just as a matter of interest try the set up again, with or without the backing but move the coil over so that it is virtually touching one coil and compare the voltage.

Flux

[GoVertical]

I  decreased the air gap as much as possible. I repeated the same test again several times with and without metal back on the rotors. Volt meter readout was not sable with a deviation of + - .005. The open coil voltage increased as a result from decreased air gap to 0.90 AC.  I used the same coil, same air gap, same RPM each time I ran the test with and without the metal backing.  I was only able to detect a slight increase in voltage of approximately a few thousandths of a volt when using the metal backed rotors.

[Flux]

That's a big improvement, 3 times the volts means 3 times the flux linking the coil. That's giving the potential for 9 times the power on load.

You look to have very thick magnets so the backing may not contribute as much as it normally does. I am a bit surprised that it makes so little difference with the new gap.

With the steel backing I suspect you would get the same flux in that gap with magnets 1/3 of the thickness. You can always get more by throwing excessive magnet at things with neo, something you couldn't have done with the older magnet materials.

It is still true that to get the maximum flux for minimum cost you still need steel backing and sensible magnetic circuits. If you do your tests with geometrics far removed from the normal you will probably come to conclusions that don't apply to normal use.

Flux

[artv]

Hi Govertical,..My setup is quite similar to what you are doing. I'm using single rotor but with a coil on both sides, and laminated core behind the coils. Could you give what rpm you were at and coil size (turns, guage)?  I did test with and without the laminated core on my first attempt and did find that the laminations behind the coil, almost doubled the output. I just wish I had a way to get a steady rpm  as I don't have a lathe..........keep up the good work , am following your diary.........Also DanG and Flux thanks for the replies...........artv

[GoVertical]

I have been working with a multiple stator and rotor configuration. By stacking the rotors and stators the configuration allows for more coils to added requiring less magnets.  So far I have found that for the best results the coils from each stator have to be aligned vertically and can be wired as a 3 phase or in series. I do use metal backed rotors for the top and bottom rotors mainly for away to attach the magnets to the rotors and the metal backing does contain the magnetic field preventing any decrease to the RPMs that could be caused from  magnetic attraction to any stationary mounting hardware above or below the rotors.      

artv, I hope to see some photos of your design. Enjoy the day.

[GoVertical]

Hi Govertical,..My setup is quite similar to what you are doing. I'm using single rotor but with a coil on both sides, and laminated core behind the coils. Could you give what rpm you were at and coil size (turns, guage)? 

Hi, the coil is 100 turns, 18 AWG. The magnet size is 3/4 diameter by 1 inch tall cylinders. The test RPM was 200. I use a router speed controller to set the RPMs of the lathe. It tends to become very hot and becomes unstable. It works but I am searching for a better method. It was very difficult to establish a constant RPM and very difficult to detect any increase from the output voltage. Is the laminated core behind the coils on your project stationary?

[jaysicle]

Hi Govertical,..My setup is quite similar to what you are doing. I'm using single rotor but with a coil on both sides, and laminated core behind the coils. Could you give what rpm you were at and coil size (turns, guage)?  I did test with and without the laminated core on my first attempt and did find that the laminations behind the coil, almost doubled the output. I just wish I had a way to get a steady rpm  as I don't have a lathe..........keep up the good work , am following your diary.........Also DanG and Flux thanks for the replies...........artv

I used a drill press to get numbers at the beginning. Not precise, but apples to apples vs. various arrangements. If you don't have a drill press, a cordless fully charged, or corded hand drill should get you constant rpm. I like cordless since you can usually switch lo/hi RPM.

For $15 you can buy a laser RPM meter (ebay) has reflective tape in kit - that is what I am using now. I have mounted it to a mic stand and aimed at the shaft end / bearing. Good / repeatable numbers that way.

[GoVertical]

Greetings, thanks for the info. The unstable volt meter reading is from very small discrepancies of the magnet position when attached to the rotors, they were the best as I could fabricate at the time. That plus the coil  when wound is not perfect fully square. The two combinations resulted with a very small changing air gap when the rotors were spinning. The minuet change caused the meter reading to constantly change its measured values; oscillating between a max and min valve; making the collection of data very difficult.  All that plus the changing rpm caused from the controller heating up also made the collection of data very difficult. I was not able to produce any real significance increase by adding metal to the back of the rotor. The real gain was from reducing the air gap. I have seen other posts verifying these results.  I tried to keep the test parameters as consistent as possible. The affect may be greater if using larger magnets.  Enjoy the day.   


RPM meter and motor controller I used for testing.

   

[GoVertical]

Just as a matter of interest try the set up again, with or without the backing but move the coil over so that it is virtually touching one coil and compare the voltage.

Flux

Hi Flux, I moved the coil next to the rotor when configured with the large air gap. I was not able to detect any increase in output. It was tried with and without metal backing. I was surprised not to see any change.

[artv]

Hi all,...This is a little old ,been busy with my solar hot water,
I was running a test coil today ,..I put my back plate in the center of my magnet stacks (to complete the magnetic circut) between opposite poles....then I tried the same coil with various backing , air (poor) ,thin steel (good), thick steel (same), laminated backing (same)
The thing that I noticed was that the thin steel piece created the least amount of drag(cogging)?
Does this sound right?? or maybe just my bad attempt at doing some testing.....
note:I used a piece of E-Core out of a transformer for the thin steel, the others were regualar steel............artv















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[JW]

 


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[JW]

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