Author Topic: Ceramic + Neo (Read 2346 times)

jimovonz · « **on:** July 25, 2006, 04:05:07 AM »

I have indicated in the past that I intended to use round neo magnets in the centre of ‘donut’ shaped ceramic microwave magnets in order to improve output while keeping to my small budget. Although I have decided to go with large neos (no ceramics) for that particular project, I have been pondering just how effective just such a setup might be. The key issue that was raised in discussion here on the board was the potential for the neo to over power/short circuit through the ceramic magnets thereby hurting performance when compared to using just one or the other. http://www.fieldlines.com/story/2005/1/21/20579/5871 I have started making a new turbine (hopefully the 4th I will have completed) utilizing what I can from the wreckage from this one: http://www.fieldlines.com/story/2006/2/27/0479/09688 along with some other bits and pieces I had lying about. I had previously salvaged some rather rusty ¼” thick x 16” diameter steel discs that are just about right for a 16 pole/12 coil micro mag alt. The micro mags are 57mm in diameter x 12mm thick with a 22mm hole in the middle giving a surface area of approx 2170mm2 and a volume of 26040mm3. The neos are N35 20mm diam x 10mm thick giving a surface area of approx 310mm2 and a volume of 3100mm3. The ceramics are approx 7x the surface area and 8.4x the volume of the neos. I cut off the old F&P mount and welded on a trailer stub axle and added some support brackets for the stator. The primary winding from a microwave transformer (254 turns of #18 gauge) makes a fine testing coil recessed into a piece of ply and fixed between two of the three stator mounts. So I could avoid gluing the magnets, I kept the air gap rather large at 20mm. This gap allowed me to get to 200rpm without any magnets flying off (yes I did try for faster – the ceramics let go at just below 250rpm!). I tested the ceramics alone, the neos alone and both together.

The results seem to show that there is little justification for concern when combining these magnets in this fashion. The voltage obtained from the combined magnets is very close to the sum of the results from each alone. Here is a shot of one of the rotors and the test coil.

Note The test was done with two rotors. This picture was taken after the testing and I have glued a washer underneath the neo to raise it flush with the surface of the ceramic magnet. I mixed up some magnetite (nipped down to the beach!) and some epoxy and used it to fill in the centre of the washer. During the testing that yielded the results above, the neo was approx 2mm below the surface of the micro mag and directly on the steel disc. After both the magnetic assemblies were glued together and the air gap reduced to a usable minimum ~16mm the same test coil gave me 0.085v/rpm.

From these results I will wind my coils 150 turns, 2 in hand #18 and go for a 3m prop. I will keep all the ends accessible to give me the of option series/parallel configurations which will allow me plenty of flexibility to test buck/boost/mppt.

SparWeb · « **Reply #1 on:** July 24, 2006, 11:43:37 PM »

I went down this road with someone else before:

http://www.fieldlines.com/story/2006/5/2/17039/94666

Pepa's result was that the microwave magnet around the neo provided a reverse path for the flux, reducing the effectiveness of the set, as compared to the neo alone. I think others have gone on about this in the past, so I won't bother repeating them. Your results seem to contradict that, but I don't know how.

Since you've taken so many microwaves apart, have you stocked up enough identical transformer coils to make it go? Or are you making sure that winding your own allows you to reduce the gap between rotors?

hiker · « **Reply #2 on:** July 24, 2006, 11:55:41 PM »

clean up your rotor --and wash those ceramic mags off in some hot soapy water--they have some kind of black greasy b.s. on them--then your mags will stay on at least a couple of thousand rpm-...everything has to be super clean for your mags to stick....

i stick the neoes on top of the ceramics--and it does help out --tried just neoes -and then with neoes and ceramics.. and scratch the side of the neoes that will be glued down -helps them to stay on better..i mainly use super glue to hold the mags down and then some epoxy on the sides -works out great.have fun.

hiker · « **Reply #3 on:** July 24, 2006, 11:59:10 PM »

for even a stronger hold wrap some nylon strapping tape tightly around the mags--as in the pict.

electrondady1 · « **Reply #4 on:** July 25, 2006, 12:45:33 AM »

jimovonz ,

this is a very timely post, i might be a bit psychic, 'cause no guff i was thinking about this very discusion today . i'm stacking harddrive neos to use on a geni. i was wondering (since these mags are all different sizes) wether it would be an advantage to place a narrower mag on the top or the bottom of the stack.

as well, on a rotor made with ceramic mags, if placing a thin neo on top of the ceramic would weaken or strenghen the magnet beneath.

there definitly seems to be a difference in the results of your tests with the findings pepa made in his experiments.

and just to clearify the method you use to reenergise ceramic mags , you place neomags of opposing polarity on the surface of the ceramic ?

electrondady1 · « **Reply #5 on:** July 25, 2006, 12:52:33 AM »

hiker,

great you posted, it was your story about stacking the neoes on top of ceramic mags that got me thinking about this . have you noticed any deterioration in power? . as in a weakening of the ceramic mag?

jimovonz · « **Reply #6 on:** July 25, 2006, 04:02:49 AM »

SparWeb, I too followed Pepa's results and have experienced similar myself. I do not believe that my results here contradict his at all. I did some simulation in Visimag and posted some diagrams here: http://www.fieldlines.com/comments/2006/4/27/16412/4908/4 that show the positive effects of a suitable magnetic path in this setup. Pepa did his testing with the magnets in repulsion where the neos literally force each others flux to pass through the ceramics, negating their effect. This does not give the same results as magnets is attraction where the neos draw the flux across the gap and allow the ceramics to contribute. In my case the contribution of the ceramics is more than double that of the neos - obviously at the expense of size. The coils to utilize this setup will have more resistance compared to using only neos at the same flux level. As I had most all of the parts I needed and because my power requirements for this turbine are modest (average load 2A @ 12V) I decided it would be a good oportunity to test the theory.

I have more than enough matched primaries for an alt like this. Unfortunately because they are not tapered they do not fit. Ideally the coils for this alt would be shorter and have slightly wider legs. No big deal to wind more optimal coils. I intend to salvage the wire from these primaries.

Flux · « **Reply #7 on:** July 25, 2006, 04:07:20 AM »

If you want to mix ceramics and neos then it is probably better to stick one on top of the other as Hiker has done. You will not get the best of both world however you do this.

With magnets in series (one on top the other) there is no demagnetising but the ceramic looks like an air gap to the neo.

With magnets in parallel there is likely to be some reversal of the ceramics. It may be temporary or permanent depending how far you run back along the demagnetising quadrant.

It would be interesting to know whether jimovonz tried the run with ceramics again after adding the neos.

The fact is that neos are so much better than ceramic that even if you loose flux from the ceramics you will almost certainly end up better off.

Not the ideal thing to do, but like most things, if it makes something better than it otherwise would have been then go for it. Not an idea to start out with, but using something that is around is sometimes necessary.

My suspicion is that it will be a bit better than the ceramics would have been if they didn't have holes. You are probably using half the ceramic material to advantage but gaining more from the neo to make up for the bit of creramic that is working badly.

As always the trial gave more useful data than speculation and messing with FEMM or anything else.

Flux

jimovonz · « **Reply #8 on:** July 25, 2006, 04:16:08 AM »

Without too much thought into it, I would say there is not much difference between narrow on top/bottom - the total air gap in the circuit is the same either way. I think placing a thin neo on top of a larger ceramic would be a similar setup to my test here. I don't think that there is any issue if the two are similar in size (as in the area that makes contact). To 're-energise' my ceramic mags I simply place a neo either side - in attraction not repulsion. It should work either way as the neos I use are capable of reversing the polarity without any apparent loss - though some materials magnetise better in specific orientations. Before I got neos large enough to totally cover the microwave mags I simply applied the smaller mags and rotated the ceramic between them slowly. Worked just as well

jimovonz · « **Reply #9 on:** July 25, 2006, 04:20:36 AM »

Thanks hiker, I have already stuck down the magnets using polyurethane glue (as seen in the pic). I haven't had any trouble in the past. I only had magnets come off in the test as I didn't glue them at all - so I could swap them around. I used CRC Brakeclean on the magnets and rotors before gluing.

jimovonz · « **Reply #10 on:** July 25, 2006, 04:34:29 AM »

"It should work either way..." By this I mean that the polarity of the neos shouldn't matter but they should both be in attraction (to each other - it probably doesn't matter about the ceramic but to be sure of optimal improvement keep them all in attraction)

Flux · « **Reply #11 on:** July 25, 2006, 04:56:55 AM »

electrondady

if you wish to stack magnets of different area then I suspect you will get a slightly better result with the largest area nearest your coils. From the magnetic circuit point of view it shouldn't matter, but leakage flux will be less important with the big magnet next to the coil.

Again it may depend on the size of coils and spacing you use. If your coils are sized better for the small magnets it may work better the other way up, but if coils are wound to suit the biggest magnet then I would go with the magnet next to the coil.

Flux

hiker · « **Reply #12 on:** July 25, 2006, 06:02:56 PM »

no loss in power as of yet-i only use it once in a while -for charging batts on the motorhome--i did let it run all night -on its first try out-still puts out the same amount of power...i just finished a little 7.5 alt dual rotor-sawblades-6 and 8 combo. ceramic and neo mix.found a local harware store that sells small round neoes-1 buck apiece--

made it from scraped old alt parts-coils from big black-tail and mount from another..

kind of a high cut in speed-so i chopped down my double blade prop to fit on it[made from a 2by6]--what a bunch of racket that damm thing made --with a pipe in pipe mount it dosent take much vibration to make a lot of noise--any way kept it on long enough to make some tests--it puts out about 3/4s of what my 9and 12 alt does--prop was really screaming no furl- winds about 30mph+..my furling alt does a lot better at a lower speed--and with four blades it dosent vibrate like the double blade prop..

it would be a good wind gen with a three or four blader on it---time to make some chips fly.......later

willib · « **Reply #13 on:** July 25, 2006, 10:16:14 PM »

Hi jim ,

i get ~ .45" between mags

looks like it'l work

your coils can be 3.59" dia and 12 will fit nicely.

if you feel like trying something a bit different

maybe you could wind a test coil with a small hole and compare it to one with a standard hole.

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