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gotwind
Forum Admin
United Kingdom
762 Posts |
 Posted - 20/04/2008 : 21:59:05
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Today,
I have been thinking and attempting making a sturmey Archer dynoub modification.
I intend to replace the steel cored single phase stator - 20 pole teeth and a poor ceramic ring magnet to a non iron (air core) with zero cogging.
Below, the original - with some tiny Neo mags added - it still cogs badly, as expected.
Below, My new idea, a non magnetic stator. the chrome bit is actually brass, with a bit of pvc pipe and a cut down CD at the base.
I intend winding as many turns as possible of 26 gauge wire (0.45mm)to the new stator, and get the single phase winding as close to the magnets as possible.
Question:
Does the number of rotor magnetic poles matter with this single phase setup?
The actual magnets are 6mm Dia x 6mm cylinders, with some 6mm Dia x 1mm magnets added to close the air gap if needed.
All experimental - might come to nothing...
Ben.
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windymiller
New Member
United Kingdom
57 Posts |
Posted - 21/04/2008 : 10:09:37
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Hi ben....im really interested in what your doing as i have something similar "on the go" at the moment.
Ive read your post carefully and im not sure what your plan of construction entails.
Did you want to remove the original steel pole fingers with your design.....if you did then im fairly sure it wont work.
You need the steel fingers to act like switches for the change of the magnetic field direction around the coiled wire.....without them ,you will not be able to create an ac current.
Id be able to comment further once you give more details of your project.
Ive got the same hub with rectangular magnets in place of the weak ring magnet and its very hard to turn due to cogging issues(as expected)
My line of attack to try and cure the problem ,is to totally replace the original pole fingers with ones similar shape to the car alternator electo magnet rotor.
If you think about it the sturmey archer hub was a brilliant design.....the way i understand it is on one revolution of the bike wheel(hub)you will get 20 pulses of ac current due to the number of pole fingers
If you reduce the number of pole fingers then you reduce the number of pulses of ac current per rev of the hub.......which in turn may reduce the hub performance in relation to rpm.
Theres alot to think about....Hope ive helped in someway
Cheers WM. |
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gotwind
Forum Admin
United Kingdom
762 Posts |
Posted - 21/04/2008 : 10:32:40
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Hi Windymiller.
I may well be barking up the wrong tree here.
I am doing away with all the iron in the stator including the stator fingers, to remove any cogging.
There will certainly be a drop in performance, maybe a couple of watts
It is a recognised approach, known as an air core design - I'm not sure if I will be cutting the flux properly however.
Some interesting similar designs here - 3 phase though.
http://www.windstuffnow.com/main/radial_air_core_alternator.htm
Ben. |
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windymiller
New Member
United Kingdom
57 Posts |
Posted - 21/04/2008 : 13:28:47
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Hi ben......thanks for the link.
Ive had a look at his project and i can see how he created an ac current with his design.
Im still not sure how your going to manage a field direction change obove the copper winding without help from pole fingers an the sturmey archer hub though?..
As i understand it ,you need to change the magnetic field above a coil(north/south/north/south) to create ac current.
The steel pole fingers are designed to carry the flux,back and forth around the copper coil,
Im still interested in what your initial concept you had in mind....im all for lateral thinking and new designs.
Cheers WM |
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gotwind
Forum Admin
United Kingdom
762 Posts |
Posted - 21/04/2008 : 13:41:05
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I think your right windymiller.
I will need some form of steel pole fingers, skewed to reduce the additional cogging from the neo magnets.
Ben. |
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ghurd
Junior Member
USA
274 Posts |
Posted - 21/04/2008 : 15:37:52
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I'm with Windymiller about needing the teeth.
'Sloppy' magnet placement can greatly reduce the cogging.
Maybe a different twist? Virtual poles?
The first photo has a magnets on every other tooth, meaning the teeth under the magnets are connected at the top? (or bottom)
If the magnets are N-S-N-S, then the output is 0V. The flux path is completed with the disk the teeth are on, and no flux change happens in the coils.
What about if the same number and placement of magnets, but N-N-N-N?
If the "N flux" is going in, it must come out somewhere, leaving the other teeth as an exit.
I have a feeling it would reduce the cogging.
I have a feeling the factory unit would work better with a stainless or brass axle too.
G- |
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gholt
Starting Member
USA
47 Posts |
Posted - 21/04/2008 : 17:41:34
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For those of us who do not have access to a S.A. Dynohub, it would be nice to see all of the parts (in some sort of logical array).
G. |
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gotwind
Forum Admin
United Kingdom
762 Posts |
Posted - 21/04/2008 : 21:20:27
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Here you go gholt, it's a PDF file.
http://www.gotwind.org/images/Dynohub_assembly.pdf
It's a 20 pole alternator reaching 6 volts open circuit at a mere 60 rpm - it cogs a lot, but unoticeable for it's designed purpose 50 years ago, i.e the central dynamo hub within a 26" bicycle wheel
Ghurd.
I tried your N-N-N-N magnet pole idea, no joy, it still cogged badly. Nothing ventured, nothing gained, 'it was worth the 15 minutes of playing'
However the 'Sloppy' magnet placement' reduced cogging a lot, but output was poor as there was only 10 magnets.
I think the dynohub could be improved with more modern technology - i.e Neodymium magnets and clever pole teeth skewing.
It may appear as pointless task for just 5 or so watts of power, but the actual bicycle hub construction lends itself very well for a very robust mounting for a turbine with a great bearing.
It may however take a more clever man than me to achieve this 
Ben. |
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windymiller
New Member
United Kingdom
57 Posts |
Posted - 22/04/2008 : 13:13:03
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Hi ben...
Came across a previous project by windstuffnow which in many ways is identical construction to the sturmey archer Dyno.
His project is called the minigen and gives good tips on how to modify it to give less cogging and better power output
Maticulous presentation (as is all his projects)made it easy to understand and learn (thanks )
Well worth a look .
Cheers WM.
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DENNIS A
Starting Member
United Kingdom
13 Posts |
Posted - 28/04/2008 : 21:47:43
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Hi Ben
If you get this right, you will has a good generator as the Windstuffnow Minigen is a high voltage unit that charges 12 V batteries.
My problem is that I can not see how the flux path flow so please could someone help.
I have had a unit running for 2 years, but still can not work out how the current is generated.
Dennis |
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fungus
Junior Member
249 Posts |
Posted - 28/04/2008 : 21:54:24
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| Dennis: basically how they work is that there is 'fingers' of iron going across the coil, each adjacent one is attached to the opposite side of the coil, when the magnets pass these teeth the magnetic flux is conducted around to the top of the coil, producing an alternating magnetic field in the right plane for you to get an electric current. |
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DENNIS A
Starting Member
United Kingdom
13 Posts |
Posted - 28/04/2008 : 21:55:30
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Hi Ben
If you get this project right, you should have a good generator as the Windstuffnow Minigen is simmilar but generates high voltage and can charge a 12v battery.
My problem is allthough I have had a SA Unit working for 2 years, I can not understand the flux flow pattern and see how the current is generated, can someone help.
Dennis |
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gotwind
Forum Admin
United Kingdom
762 Posts |
Posted - 28/04/2008 : 22:12:12
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Hi Dennis.
I will admit.
This project has gone a bit wrong - I can't make the dynohub coggless
I'm happy to report failures as well as successes
As is previously pointed out the steel 'fingers' on the stator are critical to generate the AC output - I was a little nieve to think otherwise..
I tried skewing the 6 mm dia Neo magnets with the original steel core stator which resulted in either more cogging produced, or less power output - tricky.
I would love someone to prove me wrong - and produce a zero cog dynohub??
Fungus?
Ben. |
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ghurd
Junior Member
USA
274 Posts |
Posted - 29/04/2008 : 01:59:24
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Dennis,
Pretty simple actually,
This will be what I assume an SA is, and the same as Ed's mini-gen, and a few others.
Voltage is induced when the flux changes, like changes direction.
The top disk has teeth bent down.
Then the copper coils.
The bottom disk has teeth bent up.
There are the same number of teeth as magnets. Placed N-S-N-S-... toward the teeth.
When the top disk's teeth are lined up with north magnets, the entire top disk acts like a north magnet.
At that time, the bottom disks teeth are lined up with south magnets, and the entire bottom disk acts like a south magnet.
The flux between north and south disks, which are acting like magnets, goes through the copper coil.
A slight turn of the magnets or teeth, and the disk polarity changes. South on the top disk, and north on the bottom disk. The direction of flux through the coil is changed.
Changing flux makes voltage.
Some photos that may match closer to that explaination...
http://www.windstuffnow.com/main/minigen.htm
G-
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DENNIS A
Starting Member
United Kingdom
13 Posts |
Posted - 01/05/2008 : 22:37:40
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Thanks Guys
I can now understand the flux path flow. Additionally I can see why the SA unit cogs so badly, as it has parallel sided fingers and the number of fingers matches the number of magnet poles.
Dennis |
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ghurd
Junior Member
USA
274 Posts |
Posted - 02/05/2008 : 00:09:57
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If the number of fingers and magnets were different, then it wouldn't work.
That's why brushless 3 phase is better. Things don't line up so much with 3 phase.
Less cogging and less vibration.
G- |
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Topic |
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Dynohub air core alt
