Author Topic: polarity directions? (Read 6706 times)

jkrienert · « **on:** August 09, 2010, 09:49:14 PM »

Hello,
love the knowledge here.

Will this setup work (pictured).

  It is on a bicycle wheel, and the stator is just a control arm of the axle of the hub.
  The coil would ideally have a fixed magnet to pull the flux through the coil.
   I wondered if the rotor had all 4 magnets facing north into the coil, that the pull magnet should match?

   Will i be generating pulsed dc?

Should I scrap this idea path for another trail (ideas welcome!)

Thanks!!!

wooferhound · « **Reply #1 on:** August 09, 2010, 11:02:19 PM »

Power is generated in the coil when the magnetic field changes in intensity. Since the magnet that is attached to the coil never moves in relation to the coil, it will not have any affect. Plus since that magnet will be attracted to the magnets on the spinning rotor it will be hard to start and the spinning rotor will have a bumpy ride as it tries to spin.

It will generate AC and will work much better without the magnet attached to the coil.

I'm not exactly sure what you want to do with the power, but if it was me I would use 3 more magnets and coils for a total of 8 magnets and 4 coils, Then make a dual rotor single phase machine

jkrienert · « **Reply #2 on:** August 09, 2010, 11:07:30 PM »

Should I ditch the outside pull magnet... put some kind of core in the coil... and alternate the 4 on the rotor to 'N-S-N-S' ?

wooferhound · « **Reply #3 on:** August 09, 2010, 11:15:18 PM »

Absolutely alternate the magnets NSNS, that will double the voltage. adding a core to the coil still presents the sticking and bumpy ride problem that the 5th magnet would cause.

jkrienert · « **Reply #4 on:** August 09, 2010, 11:21:06 PM »

im stuck, mostly because what I have read from the axial designs, there has to be a force 'director' behind the coils/stator right?

wothout the ability to have a rotating disc behind this one armed stator.. I'm at a loss how to solve....

this?

jkrienert · « **Reply #5 on:** August 09, 2010, 11:21:53 PM »

is there any preventative of cogging while switching to N-S-N-S ?

the plan is 4 1" x 1/4" neo discs.

for a coil, would 18g. be good? # of turns?

wooferhound · « **Reply #6 on:** August 09, 2010, 11:48:35 PM »

Without a second spinning rotor you greatly reduce the machines ability to make high voltages at reasonable RPM speeds, but it has been done. You can have 4 magnets on one rotor, then the stator, then a second spinning metal rotor without magnets and get better results. this will help the return path for the magnetic field.

The magnets are a bit thin at 1/4 inch. Your coils would need to be 1/4 or 3/8 inch thick to be very effective. As for the number of turns in the coils, you would need to build the magnet rotors and spin them up to your target RPM, then make test coils and test them until you get the voltage you are looking for.

What voltage are you looking for and how do you plan to use the power ?

Check out this PDF, Loads of good information in there on wind turbine construction . . .
http://www.sparweb.ca/Forum/AXIAL_FLUX_HowItWorks.pdf

jkrienert · « **Reply #7 on:** August 10, 2010, 12:01:58 AM »

thanks for your hand to hand combat on this question sir!

I plan to ignite as many LEDs/CREEs as posssible for nightime travel (this is on rear bicycle hub)

The stator can be very close to the rotor, yet is seperated by framing at the common axis. this prevents having a rotating return path.

is there any means to providing a return path otherwise? or maybe....
...to compensate for the slight loss... have two coils?

Im looking for simplicity... while still able to generate a decent flow... roughly something like 3-4 volts at 700-1000mA?

jkrienert · « **Reply #8 on:** August 10, 2010, 12:16:55 AM »

got to pondering...

sorta like a tumbling generator... (-tumbling + axis)

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would this solve the cogging, flux return, and lacking effcency [with a N-S-N-S setup] ?

wooferhound · « **Reply #9 on:** August 10, 2010, 12:24:19 AM »

Keep the NSNS setup, that is fundamental as it will double the voltage output and is most efficient.
I now understand why you want to use a single magnet rotor. just a couple of thoughts . . .

When a generator is making power it creates drag on the magnet rotors
When the magnets spin close to the bike frame it will try to generate power in the structure and create more drag
you will need a bridge rectifier, a large capacitor and a regulator to make acceptable DC to power your LEDs
You will need as many coils as possible to get enough voltage to make everything work without a second rotor

You may be doing OK because you only need 4 volts, of course everything will turn off when you are going very slow and stopped

You might be able to scale this generator up and make it work for you . . .
http://www.otherpower.com/hamster.html

jkrienert · « **Reply #10 on:** August 10, 2010, 12:33:51 AM »

cool link! reading now...

any thoughts on that internal pancake magnet flipping in sync with the main rotor?

wooferhound · « **Reply #11 on:** August 10, 2010, 12:35:05 AM »

I have tried the Tumbling magnet setup you drew but I did not have much luck with it.

I'm going night-night so I hope some others will jump in here and help you some more . . .

jkrienert · « **Reply #12 on:** August 10, 2010, 12:40:47 AM »

rest well man. Im sure to join in the land of nod shortly....

...soakin up some dream ideas before i hit the hay...

jkrienert · « **Reply #13 on:** August 10, 2010, 10:38:35 AM »

dang. I hate nightmares....

anyway, back from nod, and here is my best compiling for this simple light gen. for my bicycle...

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any advice from somebody to simplify, rearrange, or scrap and start from scratch?

   All magnets will be (including pancake one) [1" dia. x 1/4" thick]. The coils.. to be determined...

   striving for an output of roughly 4(+) volts at 700-100mA.

jkrienert · « **Reply #14 on:** August 10, 2010, 10:42:40 AM »

the stator above would have a constant 45 degree axis, and the rotating (pancake) magnet would have an identical axis. It might be less of a tumbling style... and more of a imaginary geared flux return

(this does have some inspiration from the (relights, free-lights) tumbling magnet idea... yet i am trying to boost the efficiency a smidgen for this application)

The best part is I really don't have and fabricating. The rotor 'disc' came with the bike, and is one of those pie protectors pans you see sandwiched inside the cassettes on the rear hub.

ghurd · « **Reply #15 on:** August 10, 2010, 10:47:02 AM »

RPM will determine the open voltage.
The more magnets (more change of flux), the less RPM is needed.

The voltage and current will come in brief spikes when the magnet passes the coil.

I doubt you will get 4VDC rectified and 1000ma average with that design.
If you do, you will be going pretty darn fast.
G-

jkrienert · « **Reply #16 on:** August 10, 2010, 11:11:08 AM »

well... My gear ratio will generally provide for good rpm.

I have a 52t in the front, and a 17t in the rear so... with a low end(slow) cadence of 60 rpm on the 52t, the rear wheel will rotate at about 120-200rpm.

each subsequent rotation will provide 4 alternations in flux... (because of the 4 pairs right?)

so were talking something like 400-800 flux changes per minuit when going slow.

- - THIS IS A CONSTANT FIXED GEARED BICYCLE: meaning there is no coasting. Therefore the generator will always be active aside from stopping. Cool with me.
-what would happen to power-output if the rotor reversed direction??? (as on a fixed gear bicycle, your rear brake is your ability to backpedal)

this doesn't seem like a pathetically inefficient plan.... of course I am comparing to the wind designs on here... so the application is different. still... $:-\$

would this be a better magnet geometry for flux return?

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jkrienert · « **Reply #17 on:** August 10, 2010, 11:33:45 AM »

maybe I should even consider uping the anty...

instead of only 8 rotor magnets, 16 slightly smaller ones?

ghurd · « **Reply #18 on:** August 10, 2010, 11:39:09 AM »

4 or 8 poles at 120RPM is almost stopped by most peoples idea of speed.

The last sketch would be better if the coil was square, so the coil is closer to the magnet.
Then it would pretty much be like one of Ed's,
http://www.windstuffnow.com/main/radial_air_core_alternator.htm

If you have space for something like that, maybe try a small motor conversion.
Pretty easy to get 4V at low RPM. That 1000ma may still be a problem.

Pretty sure you would be better off going with higher voltage and lower amps, with the LEDs in series.
And 1000ma of LED is a lot. Realistically, do not need that much.
G-

jkrienert · « **Reply #19 on:** August 10, 2010, 11:47:01 AM »

word.. I was looking at a 'Buck' voltage regulator for 350-100mA thats all. And 1 or two Luxenon K2 LEDs.

realistically, 500mA would deffiantly be sufficant at about 120-140 lumens... but im not going to get to much on the light end of things...

jkrienert · « **Reply #20 on:** August 10, 2010, 12:22:04 PM »

alright... more like this then?

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jkrienert · « **Reply #21 on:** August 10, 2010, 12:23:48 PM »

comming back to my last post...

the poor artwork kinda resembles an old stone grain mill.
(and also, my fault if my terminology is 'off'. I am not to technical)

heh. Thanks for all the help so far!

ghurd · « **Reply #22 on:** August 10, 2010, 12:47:03 PM »

I don't think that flipping magnet in the center will do much good.

If there is room, use more than 1 coil. The more the better.

jkrienert · « **Reply #23 on:** August 10, 2010, 02:52:21 PM »

if that magnet is useless, why would having a double rotor axial be advantageous?

does it not funnel the flux into, and through the coil?

a better way to put what I am saying....

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Would these not both generate the same (roughly, if the tube magnet is the same power as a single bar)

?

I must be stupid...

ghurd · « **Reply #24 on:** August 10, 2010, 05:16:28 PM »

The 2nd rotor provides a means for the flux path to be completed with as little air gap as possible while being easy to construct, efficient, and have no (nearly) BH curve/ hysteresis losses.

The second rotating magnet is like an island in the ocean.
While swimming from California to Japan, it is nice to find Hawaii, but my butt would not make it out of sight from CA.
I am sure it is better than nothing, but I have a hard time believing it is better than more coils.

Ed made something similar a long while back. Might find something about it looking for "Popcorn Alternator"?
It had some issues.

artv · « **Reply #25 on:** August 15, 2010, 10:49:41 AM »

Ghurd......wouldn't the flux path be more concentrated with the mag centered inside the coil as opposed to a dual rotor setup.........that is use a rotating mag in the center of every coil...........I searched ,but had no luck with popcorn generator,but spent three hours reading Eds' postes........or maybe use dual rotor and still put rotating mag inside coils .........wouldn't that create stronger flux linkage.........sorry for the interruption but just had to ask..........artv

electrondady1 · « **Reply #26 on:** August 15, 2010, 11:27:43 AM »

having built and bench tested a version of this all i can add is the synchronization between the driving mag rotor and the single driven magnet is tenuous at best.
changes in speed and load will cause the connection to fail and a complete stop is required to re sync the two parts.

wooferhound · « **Reply #27 on:** August 15, 2010, 12:23:37 PM »

I would think that the magnetic flux would connect between the rotor-magnets and the magnet inside the coil. But to make voltage flow you need the flux to connect through the coil and not between the magnets.

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Author Topic: polarity directions? (Read 6706 times)