| T O P I C R E V I E W |
| gotwind |
Posted - 20/04/2008 : 21:59:05
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. |
| 15 L A T E S T R E P L I E S (Newest First) |
| DENNIS A |
Posted - 05/05/2008 : 19:37:53
Yes Ghurd you are right, I can not count magnets and things correctly.
This now only leave the fingers, which I consider should not be parallel sided as an approach to reducing the cogging on the SA units.
Dennis |
| ghurd |
Posted - 04/05/2008 : 03:24:14
A different number of evenly spaced magnets and fingers will not generate voltage.
Yes, they cog.
I think you counted fingers in the plastic version and magnets in the metal version.
Small version has 11 finger on top, 11 on the bottom, 22 magnets.
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| DENNIS A |
Posted - 03/05/2008 : 20:00:25
Hi Ghurd
I think we will just have to disagree on the number of magnets and fingers.
If there is the same number of both, all the magnets will try to hold all the fingers & cogging will be very high.
If however the number is different as the unit tries to start, some of the magnets will be pulling on the fingers that do not completely line up & so cogging is reduced.
On the Minigen ther is 26 magnets & 22 fingers.
Dennis |
| gholt |
Posted - 02/05/2008 : 00:34:56
The minigen was/is very impressive. Too bad Ed no longer has them available. His description of how to remove the cogging is interesting. Does anyone know if it remotely applies to the SA dynohub?
quote:
... The cure is to remove the nut and flip the entire cage over. To do this you'll need to disassemble the unit and un-solder the wires going to the coil. Split the cage halves and remove the coil. Take the bottom cage section and place it on the top cage section and drill the two wire holes using a 3/16" drill. Reassemble the cage and re-install it on the post, solder the wire leads and the cogging issue is gone. Make sure you don't center the fingers on the cage, you want to offset them when you re-assemble it.
G. |
| ghurd |
Posted - 02/05/2008 : 00:09:57
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- |
| DENNIS A |
Posted - 01/05/2008 : 22:37:40
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 |
| ghurd |
Posted - 29/04/2008 : 01:59:24
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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| gotwind |
Posted - 28/04/2008 : 22:12:12
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. |
| DENNIS A |
Posted - 28/04/2008 : 21:55:30
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 |
| fungus |
Posted - 28/04/2008 : 21:54:24
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. |
| DENNIS A |
Posted - 28/04/2008 : 21:47:43
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 |
| windymiller |
Posted - 22/04/2008 : 13:13:03
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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| gotwind |
Posted - 21/04/2008 : 21:20:27
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. |
| gholt |
Posted - 21/04/2008 : 17:41:34
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. |
| ghurd |
Posted - 21/04/2008 : 15:37:52
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- |
