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Dual rotor is indeed the way!!!
By ejl7007, Section Newbies Posted on Sat Apr 18, 2009 at 05:08:36 PM MST
oztules and flux are my new heroes!

I would like to thank all you of you who have helped me with your insightful comments. I am a newbie to this site, and many of the questions that I have posted
on this site have been viewed and answered by the lot of you. Especially Oztules and Flux, among others have been extremely helpful. I was having an issue with my perfectly wound coils, that tended to drag wehenever I Placed them near my makeshift rotor. Mind you, I have made a few mistakes that cost me dearly, So I am very careful. I wound 12 coils, each with 14 awg, 200 degree using three strands in hand at 45 turns per coil. On a single rotor arrangement, Whenever I placed the coils, by hand, near my spining rotor I would get an initial reading of about 6 - 6.5 VAC per coil while a noticable drag, would slow down the rotor. Now oztules suggested ( and flux agreed) that a dual rotor would perhaps minimize that effect or dissipate it all together. So I used another steel rotor as a plain flux return disc. The gap between the discs was 1 1/4" and when I slipped in my test coil which is 3/4" thick in between them, I indeed felt the drag almost subside, while the voltage reading jumped from 6-6.5 vac to 8-8.5 vac. the rpm was the same at 180. So Simple. Mind you I thought my coils were defective and was about to scream at my supplier. I only wish I had more money, to purchase more magnets so that I would truly take advantage of the dual rotor setup. None of this would be made possible without your help.
Forever grateful
EJL

Dual rotor is indeed the way!!! | 6 comments (6 topical)

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#1)
by oztules on Sat Apr 18, 2009 at 03:47:05 PM MST

Thanks for checking the theory for us.

Your coil volts will go up even further if you can get hold of more magnets for the second plate, and I would explore the possibility of getting that 1/4" gap each side down to something closer to 1/8 inch per side.

More mags and closer gap will translate to thinner coils or thicker wire... to lower resistance for the same emf... which is the thing to aim for in a alternator driving battery loads.

It all depends on how much you are after and what you drive it with. Main thing is to get some enjoyment out of all the trial and tribulations.... and some wide smiles when it all works out the way you had hoped.

Glad we could help.

.......oztules

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#2)
by ejl7007 on Sat Apr 18, 2009 at 04:03:13 PM MST

Thank you, Oztules for your reply. Ultimately I will close the gap to an even 1". If I decide to get more magnets (another 16, Grade N42, 1" wide x 1" thick x 4" Long) from http://www.magnet4less.com I will maintain that gap. I can't wait to get it going....

Cheers

EJL

[ Parent ]

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#3)
by GWatPE on Sat Apr 18, 2009 at 09:01:45 PM MST

Hi EJL,

the inch thick magnets sound good. I would think that unless the magnets are at a couple of feet radius, that better use of wire and magnet would be with round, or square magnets. The widely varying flux rate between the inner part of the coil and the outer will compromise the developed emf. The largest dia that the magnets are placed is the optimum. There would have to be significant segmentation gaps at the outside of the rotor, betweeen the magnets. Without resorting to segmented magnets. My 2bobs worth anyway.

Gordon.
be more energy aware
[ Parent ]

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#4)
by Flux on Sun Apr 19, 2009 at 01:43:22 AM MST

We are still learning with these air gap alternators. Many lessons were learned in the early years before 1900 but after that all effort was directed to slotted core machines.

With slotted cores, parallel coils are not a problem except in very large machines, the flux snaps from slot to slot and links the turns equally so as long as the numbers of turns are correct there is no real issue with circulating currents.

Without slots the flux linkage changes progressively, it was discovered early on that for larger machines that heavy section copper suffered from induced eddy currents and the conductors had to be built up of smaller sections and transposed in such a way that each conductor had the same voltage induced in it. This was for larger machines but the issues seem to be present even in smaller ones and I wouldn't risk wire over 2.5mm thick in a dual rotor.

The flux is uniform enough in a dual rotor to get away with wires wound in hand with no attempt at transposing or otherwise equalising the induced volts. It seems as though that is not true for a single rotor where the flux is very far from uniform.

It is tempting to use copper foil or tape for a dual rotor and with a perfectly uniform field it should be fine, but Dan built a machine with rectangular strip that ought to have been fine but it wasn't so this issue is never far away and we are gradually learning where the limits are.

I agree with Oztules, reduce the distance between your magnet rotor and the spinning disc, 1/8" mechanical clearance should be plenty. If you can get the second magnets so much the better but it is going to be a powerful alternator and you will have to choose a suitable prop to match it properly. In the end you have to match the system and if you change magnets you may have to change turns and prop size or add line resistance or you will end up crawling in stall with very poor performance.

Flux

[ Parent ]

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#6)
by snake on Sun Apr 19, 2009 at 10:40:00 AM MST

hi friends,i want to asked something.instead of dual rotor,why dont you put dual stator in both side of the rotor thus connecting the wired in a way to give output as the dual rotor.someone can clarify me about that idea?thanks

Re: Dual rotor is indeed the way!!! (3.00 / 0) (#7)
by Flux on Sun Apr 19, 2009 at 12:55:15 PM MST

If you put a stator on either side of a magnet rotor it will need to be two single rotors facing outwards. The magnetic circuits are stupidly inefficient and you have twice the resistance of a single stator. The concept is about as wasteful of material as you could possibly devise but yes it would still be an improvement on gearing and high speed dc motors.
It's cost per watt out would be very high but at least the overall efficiency could still be reasonable. You could add a pair of rotating flux concentrating discs to make it more practical but there is no point in more than one stator unless you reach a size where one can't handle the power.

Flux

[ Parent ]

Dual rotor is indeed the way!!! | 6 comments (6 topical)

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