Author Topic: Question about wire gauge... (Read 2030 times)

TariffDude · « **on:** January 05, 2006, 02:32:43 AM »

I'm sorry if this is a common request, but I couldn't figure out how to do a search that would give me an answer for my particular situation. Basically, I would like some advice as to the amount/gauge of wire to use in my brake disc alternator. This is what I have so far: 12 circular Neodymium magnets, N38, 2" diameter, 1/4" thick. A brake disc that will fit these magnets (I haven't put them on yet, but I used 2" cardboard cutouts to make sure there was enough room). To be honest, I am not exactly sure what the fate of this windmill will be (it's sort of an experiment), though I realize that is an important consideration. So for the sake of building something that might be useful for producing power, I will say that I am building a 12 volt machine that should be capable of starting in low winds. (I live right about in the middle of Iowa, an area that is considered "good" for wind power capacity. There is some commercial wind power production closeby. However, I live in a suburban area so I don't know if I could take full advantage of all that wind.) Any advice about what wire gauge, wiring configuration, and prop size combination would work best for me would be much appreciated. I just need a general idea. Thanks.

willib · « **Reply #1 on:** January 04, 2006, 07:47:05 PM »

what is the dia. of your brake disk?

TariffDude · « **Reply #2 on:** January 04, 2006, 08:10:04 PM »

I measure 10 1/4".

willib · « **Reply #3 on:** January 04, 2006, 08:22:09 PM »

You do realize that a two inch dia. magnet requires a four inch dia. coil,with a two inch hole?

try laying out the four inch coils on your rotors

TariffDude · « **Reply #4 on:** January 04, 2006, 08:43:32 PM »

Sorry, I don't really understand the suggestion. The page I am looking at as a reference is this one: http://www.otherpower.com/wardalt.html . I was planning on using 12 2" wide coils. I'm no physicist, so if there's a better way to do it, or if I'm missing something, let me know.

DanB · « **Reply #5 on:** January 04, 2006, 08:49:12 PM »

In this case I think there would be benifit to having the inside of the coil more wedge shaped, taller than it is wider and a bit shorter than 2". So there should be room for the coils.

willib · « **Reply #6 on:** January 04, 2006, 08:59:00 PM »

that gen. was probably what turned Dan from using round magnets .

i'm surprized it worked at all( no offence).

they have learned a lot since then.

18 poles & 18 coils does not make sence.

have a look at their 17' machine, for the way they do it now..

for a three phase machine , using 2" dia. magnets REQUIRES a 4" dia. coil , there is no way around this fact.

And the coil to pole ratio HAS to be 3/4..

TariffDude · « **Reply #7 on:** January 04, 2006, 09:13:01 PM »

Right now I am looking at this page: http://www.otherpower.com/bdwm53.html . Would I be able to do something like this with my setup? Is 4" too big a size for a coil? I'm sorry I just don't have any experience to go off of here.

willib · « **Reply #8 on:** January 04, 2006, 09:34:07 PM »

that machine is a lot better than the last one.

three phase, 9 coils and 12 magnets, But, the magnets are too close together , and they should have used 3.6" dia round coils, because the magnets are 1.8" dia...

terry5732 · « **Reply #9 on:** January 04, 2006, 11:29:24 PM »

For a two inch magnet the coil doesn't HAVE to be four inch. But the center MUST be two inch. Four inch is about your maximum effective size. You can try to figure voltage before winding, but I would just wind the wire at hand, in the space allowed and deal with the voltage produced. Just make sure each coil is equal turns of same wire. That said, it would be good to lay out your magnet arrangement for the four inch coils.

electrondady1 · « **Reply #10 on:** January 05, 2006, 09:52:39 AM »

tariffdude, there are lots of experimenters on this forum and lots of people who started out with very little knowlege of electrical generation.(myself included)
your off to a good start by using the archives. the know how contained there will allow you to build powerfull generators. here are some things you can search, magnet spaceing coil design single rotor dualrotor air core .
as your understanding increases your searches can become more specific.

as it is, i think you have too much magnet for a 10.25 disk as the space between the mags is as important as the mags.
to build a single rotor gen. with your mags you could go as big as 17.25 " dia.
((if you got another 12 mags and two 17.25" disks you could build a dual rotor machine that would really put out)
or you could get another 10.25" brake rotor and put 6 mags on each rotor.
good luck.

willib · « **Reply #11 on:** January 05, 2006, 10:23:52 AM »

four inches IS your maximum effective size.because that leaves two inches of coil windings between coil centers (ie your magnet size), one inch per coil

of coure you could make them smaller.but that would leave wasted space between the coils .and yes you had better space your magnets "AS IF" you had four inch coils , otherwise you are wasting your time.

thats why i asked the Dia. of your rotors, because two inch magnets require a large rotor , to use 12 poles and 9 coils requires a rotor size of 13.825 " inches in dia.

while a 6 coil 8 pole machine only needs a rotor size 10.028" dia.

electrondady1 · « **Reply #12 on:** January 05, 2006, 02:14:14 PM »

12 magnets x2" dia.=24" with 100% spacing between magnets=48" divide by 3.14 =15.28
that's the dimention at the widest point of the mags. you would need an additional 2"dia. to fully support the mags so 17.28"

6 mags x2" =12" +100%spacing =24" over pi=7.64" + 2" =9.6" dia. required

10.25"-2"=8.25" x 3.14=25.9"-8x2"=9.9"over 8 spaces =1.23" between mags.
that would work for three phase.
so buy another 4 mags and another 10.25" rotor and your off to the races.

TariffDude · « **Reply #13 on:** January 05, 2006, 02:19:20 PM »

Actually, because I don't really have the funds to get more magnets, I was thinking of just using 8 magnets and 6 coils. I could put the 8 magnets in the 24" circumference of my current brake disc and that would leave 24" for 6 4" coils. Perfect match. Still, it would be nice to have some idea of the wire gauge to buy, (I haven't bought the wire yet) in that setup.

willib · « **Reply #14 on:** January 05, 2006, 03:26:49 PM »

yes it is almost a perfect match, with the six coils..

below is your coil you coil layout .

your magnets will be centered on an 8.043" dia. circle, with the outside dia. = 10.043" and your stator will have to be 12.043 " at the narrowest part not including the stator mounting tabs ..

You would probably want to shoot for around 100 turns per coil..

13 gage wire will give you a little more than 96 turns , and will give you .145 ohms per coil, ballpark..

this site may help

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html

coil layout

http://www.otherpower.com/images/scimages/2965/2in.dia_mag._6_coils_8_pole.GIF

have fun..

craig110 · « **Reply #15 on:** January 05, 2006, 03:27:55 PM »

My question might be more appropriate to a discussion about square magnets, but the issue of how many angels can dance on the head of a pin, er, ah, how many magnets can fit on a rotor has puzzled me and this seems like a good discussion in which to pose the question. (Warning -- I'm a newbie to the generator world.) Why are the magnets normally placed flat? It seems to me that since the alternating N / S flux density drives the electrons, the "middle" section of an end-poled magnet represents an area that is a much less productive use of the rotor's surface area than are the ends of the magnet. Presuming end-poled square magnets, wouldn't it be more efficient to put them edge down - picturing the rotor flat on the workbench - with each magnet aimed at the center of the rotor as in a starburst pattern? The poles could be aligned (alternating, of course) with one pole on the inside of the circle and the other on the outside of the circle which would allow coils on both the inside and outside. Not only does this increase the number of poles that can fit on a given rotor, but the comparatively small distances between the ends of the magnets should greatly reduce the amount of magnet wire that is used to make sure that the power producing edges of the coils are 4 inches apart.

And yes, I realize that putting powerful magnets this close together would require some strong spacers to hold them in place while the resin goop sets up. That's "just" an implementation detail while I'm still trying to understand the theory behind the common designs. ;-)

Craig

willib · « **Reply #16 on:** January 05, 2006, 03:30:22 PM »

oh , the coil thickness i chose was 1/2 inch..

willib · « **Reply #17 on:** January 05, 2006, 03:34:59 PM »

you are forgetting that most of the magnets flux is located on the flat side, standing them up will produce very little power.

electrondady1 · « **Reply #18 on:** January 05, 2006, 04:51:01 PM »

craig110, what your describing is known as a radial flux alt.

tariffdude ,yes, the mags are expensive.you still need a way to draw the flux through your copper. consider placeing a second steel rotor(with out mags) on the back side of your stator. it should rotate in sync with your mag rotor. later on as funds permit low cost ceramic mags or neos could be added.

craig110 · « **Reply #19 on:** January 05, 2006, 08:22:29 PM »

>you are forgetting that most of the magnets flux is located on the flat side

Oh. Like I said, I'm a newbie.

I see where my thinking went wrong. All those wiring diagrams showing the edges of the coils over the edges (poles) of the end-poled flat magnets led me to think that that location was where the maximum instantaneous power was developed. I see now that this is just a convenient diagram style for showing the proper coil spacing.

Since I had my "pole thinking" backwards, please pretend that I had asked about magnets that are polarized on their flat side. That should give the most flux along the edge, right? I'll go do some research into the radial flux alternators.

Craig

theTinker · « **Reply #20 on:** January 06, 2006, 05:04:08 PM »

im a beginner still too, im close to getting my windmill building

im just curious about ur post there willib. with a 2" hole, why do u suggest that the legs are only 1"? when the magnet is over the center of the leg, wouldnt this waste 1/2" of magnet on each side of the leg? would it not be perfect to use a 2" leg so the whole magnet is been used ?

im a big fan of ur photo section great diagrams.

willib · « **Reply #21 on:** January 06, 2006, 07:41:35 PM »

thanks

as to your question , that is true for single phase , the optimum size coil for a given magnet is three times the width of the magnet , the hole being the width of the magnet of course,for a two inch dia. magnet that is six inches in dia. ,so that a whole magnet fits over exactly each leg of the coil, a lot of resistance , which is another reason three phase is better. smaller coils = less resistance.

Three phase is totally different though , in the pic below , notice the magnet between coils B and C , it spans across two legs of two different coils at the same time , so the coil width is twice the magnet width , while the hole is the same size as the magnet width ,

That is the reason i said the optimum size coil for a two inch dia. magnet is four inches(twice the magnet width or dia. ) .

http://www.otherpower.com/images/scimages/2965/1a.GIF

hope this makes sense..

theTinker · « **Reply #22 on:** January 07, 2006, 03:43:44 PM »

that makes perfect sense

thank you.

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Author Topic: Question about wire gauge... (Read 2030 times)