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drowning in fromulas


By spinner, Section Homebrewed Electricity
Posted on Thu Dec 14, 2006 at 02:31:43 PM MST
some kind soul straighten me out?

i have been working on an idea about a Radial Air Core and seem to have hit a wall.
sys. voltage = 14
rpm=100
T. = 1.2 (??)
single mag face=2"  
mag is 1"x2" rectangluar, 12,500 gauss
i figured on 2, end to end for each pole
4poles & 3 coils

i come up with 50turns per coil, just does not seem right
and
i am thinking that, if it is, I'd hafta plan on some decent size wire or two in hand to get any amps for battery charging?
someone take the time to straighten me out?
thanx
spinner
drowning in fromulas | 12 comments (12 topical)

Re: drowning in fromulas (3.00 / 0) (#1)
by ghurd on Thu Dec 14, 2006 at 07:54:16 AM MST

W.A.G.?  I think T is very overstated. There is no return path for the flux, or the air gap is huge... However you care to think about it.
It has the same problem as a single rotor, and a bit more because of the flat magnets in round hole.

Guessing T is more like 0.3?
G-
Ghurd.info



Re: drowning in fromulas (3.00 / 0) (#2)
by Flux on Thu Dec 14, 2006 at 09:13:46 AM MST

Yes the 1.2T figure is for Br of neo. You can never see that value in real life, it is only possible in a closed magnetic circuit.

Magnets on open circuit as you are using don't really have a value for T. it depends on how close you are to the magnet and it falls extremely rapidly with distance.

Ghurd's value of .3T is probably a fairly good value with a thin coil close to the magnet. There is no point in using thick coils as the flux will be too low to be useful about 1/2" from the magnet face.
Flux

[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#3)
by spinner on Thu Dec 14, 2006 at 10:15:50 AM MST

thank you both for replying so promptly!

when i read your replies something jumped out at me: the mag face dimension i had in there was for a single mag and not for 4 mags (each mag consisting of 2-  1"x2" mags laid end to end)

all i can think is that i somehow got parts of two diferent formulas mixed together!
 when i refigured it using the "T " amount you suggested and  16" for the mag face (1"x2" x2 for each mag x4=16" of total mag face...
I then ended up with  49T

how bad am i screwed up now?..
thanx spinner


[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#4)
by Flux on Thu Dec 14, 2006 at 10:26:02 AM MST

I am sure that formula must mean the area of one magnet. Those number of turns seem much too low for such an inefficient set up.
Flux

[ Parent ]


Re: drowning in fromulas (3.00 / 0) (#5)
by spinner on Fri Dec 15, 2006 at 07:31:29 AM MST

good morning flux and thanks for the reply!

i thought the same thing so i checked my notes: "total area of magnet face in square inches (this will be the number of magnets times the face area in square inches" from a post by hugh p., awhile back relating to finding turns per phase and turns per coil.

what i did: 17,000 x 14(system voltage)=238000/100(rpm)=2380/.3(t)=793/4 poles=50 turns
But:
that would be turns per phase, not turns per coil, according to his formula.
if one figures it with 16" of total mag face area, the result seems even more out of whack!

the formula for turns per phase in the post i mentioned:
turns per phase=17000xsystem voltage/desired cutin speed in rpm/strength of flux in tesla/total area of magnet face in square inches=turns per phase.
then, divide that answer by the number of coils to get turns per coil

i am sure i have made some sort of stupid error (and repeated it each time, the way it looks) but i cannot seem to find it!
my hope is that somebody here can set me straight
thanx
spinner  

[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#6)
by Flux on Fri Dec 15, 2006 at 07:51:47 AM MST

I don't want to put you off but I think your speed of 100 rpm for this little and inefficient thing puts you in the realms of dreamland.

If I have this right, you have 4 poles 4" long 1" wide and 1/2" thick, with no return circuit and you want 12v at 100 rpm.

Guessing at an optimistic flux density of .3T I think you need about 500 turns per coil. The wire will need to be incredibly thin so you are only looking at watts out.

The sort of power level that thing is going to produce, you ought to be looking at speeds of 500rpm upwards.
Flux

[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#7)
by spinner on Fri Dec 15, 2006 at 11:16:17 AM MST

Flux,

again, i must agree....ie, no return path and wide air gaps normally = little output at this low speed
if i coulda figured out why the formula doesn't wanna work for me i could go on with this lil project: (try not to laff will ya?)
 my intention is to form the coils INto the tube not outside of it, thus making my airgaps closer...i have been doing some experiments on forming a coil to fit inside a tube...not perfect yet, but i can do it.
it also seemed to me when this idea came along that if i formed a metal band around the outside of the tube, wide eneough to span the width of the coils/magnets, it otta be similar to a second disk without mags in a dual rotor machine, relationship wise....
( mag- to -coil- to- tube(plastic pipe)- to- metal band distances in my theoritical machine would be similar to the aforementioned dual rotor (second rotor having no mags)
i have no way to prove or disprove that theory to myself til i try it (and i can't hope to try it til i get past this #of turns vs the formula thing

i have a need for a machine that can do something useful at low rpm, and i can't afford to build a monster dual rotor machine (also, since i run a dualhelix  i have no tip speed ratio gain to make use of.

this lil idea of mine probably is a slice of neverland but it won't be my first ever screw up either!
thanx for gettin' back to me again
spinner

[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#8)
by ghurd on Fri Dec 15, 2006 at 11:48:31 AM MST

The metal band must be VERY thing when viewed from the magnet.
Simply wrapping a metal band around the outside will have bad eddy currents, huge losses and crazy drag.
The 'band' will need to be like motor laminations.  Meaning you are basicaly back to an AC induction conversion. Or the old style brake drum (by Hugh) but inside out.

Just a thought, but you could, maybe, cut the teeth out of 6-tooth box fan motors for the outside. But I can't see it as being as good as a standard AC conversion.
G-
Ghurd.info
[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#9)
by ghurd on Fri Dec 15, 2006 at 11:57:19 AM MST

Also, look at this, the part about "high winds did not see much current about 1/2 amp".
http://www.fieldlines.com/story/2006/11/17/164931/42
I think it is a fine machine, just the design concept has some drawbacks.
G-
Ghurd.info
[ Parent ]


Re: drowning in fromulas (3.00 / 0) (#10)
by spinner on Fri Dec 15, 2006 at 05:20:08 PM MST

evenin' ghurd, thanks for your reply

i had been wondering about some of the potential effects of my proposed band aroud the tube, (just got sidetracked due to this formula problem i am having*hehe) you've given me some good food for thought on the subject.
my hope is that by making the machine a simple 3coil 4magnet unit utilizing longer magnets and coils i will end up with useable output..
it is interesting tho, to mentally try and create a Radial Air Core by turning the conventional dual rotor setup into something vertically equivalent (?)
Windstuff Ed was right when he told me that if you can imagine it and it sticks in your head ya gotta at least try and build it!
just finished going thru those # again without seeing what it is that's goofin' me up; time to put it away for the nite, I guess
thanx
spinner

[ Parent ]



Re: drowning in fromulas (3.00 / 0) (#11)
by spinner on Mon Dec 18, 2006 at 10:53:24 AM MST

well, it's gone from bad to worse, this formula thing

this morning i found this formula thru Google:
V/PxRxBxAx2)N
where N=turns of a phase
for me this is:
A=2x(1x2)x000645 (size of 1 magnet)
R=2 (120rpm)
B.3
P=4
N=.012384?
makes NO sense at all, to me ...how can ya have less than 1 turn
 either this calculator is broke or my suspicions are right and my brain is broke or
BoTh

thanx,
spinner



Re: drowning in fromulas (3.00 / 0) (#12)
by spinner on Thu Dec 21, 2006 at 08:02:25 AM MST

'spect i otta be embarassed
but, i ain't...just another step along  the way!
tis a wonder what a bad  cheap calculator can do to ya, even more when ya don't make sure you KNOW how a program works BEFORE jumping in to use it!
thanks all

spinner

[ Parent ]



drowning in fromulas | 12 comments (12 topical)
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