I need your advice about generator design options

[pepa]

I have four 20" saw blades(two each welted together)for the magnet rotor disk and thirty-six microwave, and still counting, microwave magnets 21/4" donuts, with 3/4 hole. I also have twenty-four n40 3/4x3/4 round neodymiums to use in the holes of donuts. My intention was to copy Wind stuff Ed's microwave design, only bigger. I have enough 11/4x1/16 banding strap to make a 20" od laminate ring, two inches wide. i have a hub, 2" spindle and bearings from a large bushhog that should work very well. would a 12/9 duel rotor give me more power than a 24/laminate machine or would some other use of these materials be better? thanks for any help or suggestions on this project. pepa

[electrondady1]

build two genies.

[electrondady1]

 sorry i had a difficult time replying to your post. you might want to check the files of a member named jimovonz  or google search "heavy iron"  a story he posted , there was an indepth discusion on what your attempting.  

[electrondady1]

ok, sorry for the interuptions , first i'd like to know where i can get some 20"saw blades.

 the ceramic mags in your photo are too tight. the space between mags should be the same as the width of the mags .

[jimovonz]

Hi pepa, I set off down a similar route some time ago. I was looking to use microwave mags + neo infill for a largeish alt. I have dismantled close to 100 microwaves and recovered more bits than I'll ever use as well as getting seriously ofside with my wife due to the piles of carcases in the yard. I have since obtained a swag of nice large neos to do the job so have happily given up the microwaves. I will hopefully get around to using them sometime soon.

As to your question, instinctively I would say that using all of your magnets on one disc with laminates opposite will give you the most output, however my experience with neo infills in ceramic magnets leads me to offer caution. You have probably found that the neo magnets have no trouble remagnetizing the ceramic mags. One thing I found while testing the neo infills, was that unless they are in the appropriate magnetic circuit, the flux from the neo is large enough to re-magnetize the surrounding ceramic magnet. This is illistrated in this Vizimag simulation:





This is a cross section of a ceramic mag with a neo in the centre with no backing. You can see that the flux lines from the neo travel back through the ceramic mag in the reverse direction. I used a gauss meter (hall effect sensor) and determined that the ceramic was permanently effected as a result of this configuration (you can return the magnet to its original flux configuration by the appropriate application of a neo). In the proper  magnet circuit (such as in a dual rotor setup) the relatively intense flux of the neo is given an easier return path that does not fight against the ceramic:





Here you can see that both the ceramic and neos that form one pole do infact contribute all of their flux in the right direction. I think that this (dual rotor) setup would best utilise the ceramic/neo combination, however you need to consider what damage(flux reversal) is done to the ceramic magnets as they are placed into this configuration - I think that by the time the second rotor is placed opposite the first to achieve this, the flux reversal in the ceramic has already occured... Also, if you intend to place the poles as close together as they are in the picture, I think that the contribution of the ceramics will suffer even further due to leakage.

With so many factors unknown, I feel that the best way forward would be to wind a coil and test the options. You might consider using the tops (the 'I') of the microwave transformers for the laminated backing for such a test. I find the easiest way to separate them is to make a single cut along the weld approx 2-3mm deep using a 1mm cutting disc on the grinder, then give them a tap on the side with a hammer - should come right off. A couple of these should be fairly effective for testing a single coil setup.

[DanB]

"the space between mags should be the same as the width of the mags . "

I would say 'could be' but not 'should be'.  He'll get more power from this arrangement - maybe not getting the best bang for the buck from his magnets but I expect those didnt cost much.  With round magnets especially it makes sense to have them much closer.  I think it would be somewhat of a waste of space (And copper perhaps) to put have the distance between the magnets equal the diameter of the magnets with round ones.

[electrondady1]

pepa, danb is absolutly correct .i had no intention of misleading you. in my experiments (with pie shaped and rectangular type mags ) i have had good succes with 50/50 spacing. but i recall now in using round mags and coils,i have read its possible to place them closer together as there is less magnetic material at the closest point and therefore less cancellation.  

 regards and good luck,

shawn

 

[pepa]

hi. thanks for the comments. windstuff ed"s model used the magnets without spacing and used slotted laminates. this is the way i was going until my son gave me the 24 neos and i have been playing with different setups to use the total dia. of the disk as a single rotor or as a 12/9 duel rotor as seen by the plexiglass templet layout. i was hoping someone had done this and would share the results. either way, i am building this unit as a low wind machine with blades to match the low to moderite winds at my site. would moving every other magnet to the inside of the one left on the edge and make the legs of the coils long enough to cover both magnets and spacing magnets closer by pulling everything toward center? your thoughts please. i would have to buy more wire and magnets but it would put a lot of wire under a lot of magnets. just enjoying myself, thanks pepa

[Flux]

This is such a strange set up that it is virtually impossible to predict what will happen.

I am not at all convinced that the ceramic magnets are worth bothering about. The neos look to be nearly twice as long and you will have large air gaps over the ceramics. Also as others have said, the neos will reverse magnetise a lot of the ceramic and it will not contribute a lot. As it stands you will have a lot of copper and a lot of resistance.

I suspect you could make a better alternator with the neos alone on a pair of 8" discs about 5/16" thick.

If you use banding strip you will have a lot of iron loss and poor low wind results.

If you make it dual rotor with the neos alone you will have good low wind results and I think it will be powerful enough to handle about a 7 ft prop. I really have no idea what the combined thing will do with both magnets but it will be big and heavy and most likely will not take a much bigger prop.

The neos will not be used to best advantage with saw blades.

Flux

[hvirtane]

Why not making two

generators? One with

only neos and the other

with only microwave magnets?

- Hannu

[DanB]

Yes - my first worry would be that the ceramics are actually 'shorting out the neos' but the last picture doesnt show that.  The ceramics are not adding much though and I almost wonder if just building the thing smaller/using the neos - and having a lot less copper in there wouldn't yeild a more powerful machine.

[Flux]

Interesting point you made Dan.

It is correct that in the second picture the ceramics are helping, but I think you can only reach this condition if you magnetise the assembly with the 2 rotor discs in place.

If you reach the stage in the first picture and just assemble the rotors I think the ceramics will come back up on a recoil line as they have gone off the linear region in the 3rd quadrant. A fair proportion near the neo will not be effective.

Flux