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Discussion Starter · #1 ·
Some tests showed this would work...
The magnets are Rare earth, and the setup is pretty simple.
It all houses into the aluminum(non-ferrous) bottom bracket tucked outa sight..


So does anyone know if this has been done before?
Also, if my perpendicular magnet to coil will put out some volts?

Its contactless by the way...

Hopefully its enough to charge a small battery and power some lights...

I will post the build photos in a little bit.

Thanks!
 

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Discussion Starter · #2 ·
This wouldn't be directionally hindering (can go forward and reverse)
because simplyified from a normal dynamo, theres usally another magnet
inside the coil that is effected by the magnet in motion.

Here I combined the internal coil magnet, and the motion magnet into one.

maybe im not explaining this very clear.
Its probably my lack of gluclose in the brain...

best,
joey
 

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Well, I think you need to read up on eddy currents. I do have to give you cudos for all that work. How many turns of wire in each coil? 3 phase? How many coils?
 

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Krienert said:
Also, if my perpendicular magnet to coil will put out some volts?
The magnetic flux (Green arrow) must go through the centre of the inductor. So you need to turn the coil 90°. All the metal piping around your coil will net be helpful as it will shield your coil from the magnetic field.

In regards to the + and - signs on your coil: If you use LED lights, you will need a rectifier to get DC voltage. (You will get AC from the coil).

Depending on your pace, you will get pulsed voltage from the generator (meaning NOT a sine-wave). Say you do 120rpm. That is fast, 2 revolutions per second. You will get 2 positive/ two negative pulses of electricity per second with 4 magnets and one coil. So pulsed AC with a frequency of 4 Hz. That is not much power for all the effort you put into it. You can improve that by adding another coil. Frequency will go up by a factor of 2. Still much less than what you get from a bottle dynamo or a dyno hub.
 

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On the BB you will get varying frequency (Hz) as your pedalling cadence varies. That is why dynamos are on the wheel or hub, not the BB. As pe2erwin has pointed out, your magnets are not moving in the right direction in the coil to generate power.
 

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Its a neat idea... BUT...
People tend to coast when they need maximum light (40mph down a big hill).
Its not removable like a hub dyno wheel or a bottle dyno.
 

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Discussion Starter · #9 ·
Alright... I was sad to see all the truthful responces...

It seems this setup wonte work... But to correct some things I must have misworded...

It is completly removable.
I planned to have it charge a battery, and since most of my riding is day time, this should provide adiquite nite lite.

There is no barrier between the coil and the axle. The bB lug is aluminum as well, a non-ferrous metal outside the workings of this setup. (have you ever dropped a Rare earth
magnet down strait down a peice of vertical aluminum tube? Try it!!!!)

Ive got a feeling I could reposition two coils in series in the down tube just infront of the lug, and in the seat tube just above the lug.
That way they could be two short perpendicular coils... like this sorta
http://www.instructables.com/id/Contactless-dynamo-powering-bike-safety-lights/

The setup is initaly a charging circut for a battery, that way the lights degree wouldnt be hindered by coasting or backpedaling on hills, ect.

Does this clear anything up, and sorta point me more in the right direction?

Thanks again for all the advice thus far!
 

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Discussion Starter · #10 ·
Also,
On the note of varring voltage...

I could install a limiting diode that would respectivly not overload the batterys if my cadence rose about their capacity; yet would provide varriation for any rpm below such?

(that was supposed to be phrased as a question)

:)
 

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Thats feasible, but still limited as the magnets don't pass through the coil. Better to have a rotating coil (or coils) in a magnetic field. My electronics is a bit rusty, but to make use of the small, low frequency AC that you would generate, you'd need a diode to rectify (and lose half of the sine wave) or an FWBR and parallel capacitor to give a smoothed pulsed DC. To charge a battery would need a much smoother DC supply; much higher frequency than the 2-4Hz that you would be generating via the BB.

The alu tube/magnet thing is, I think, a paramagnetic effect. But we're getting away from bike lights...
 

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The magnet dropped through the aluminum tube is an example of eddy currents. The BB tube is conductive. The eddy currents will eat most of your energy. You need a hub genny.
 

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Discussion Starter · #14 ·
Arnt eddy currents whats at play here in the induction of current into th coil from alternating solid state magnets?
 

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No, eddy currents are the enemy. As the BB axle rotates inside of the BB tubing (bicycle frame), the magnetic field will induce current into the windings, AND the field will pass through windings and into the BB tube. The BB tube is a shorted turn.
 

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Discussion Starter · #16 ·
right you are MTBf.

I tested it and each componet detached, voltage travels through the coil, and the wiring to a small test bulb...

Yet when connected, I get no test light, or any voltage at the end.

Is their any means to alleviate this issue with the BB sucking my power?

possibly placing a perpendicular coil wrapped as an electromagnet that would send voltage to the test bulb...


~~~~~~~~ S
---------------- / \
Iron core N< bb >N ?
---------------- \_/
~~~~~~~~ S
 

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Discussion Starter · #17 ·
ok... so
I found out exactly what this would be 'technicaly' titled...

A brushless motor/generator, where the provided current would be the pedaling motion....

Heres a picture.. correct me if im wrong?

And does anyone know if this would work with one coil alone?
 

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Normally one would use 3 coils or multiples of 3. You would generally hook up the coils in a 3-phase configuration. Look up how an auto alternator works. These use an electromagnet to create the magnetic field. You are constructing a permanent magnet alternator. I give you max points for inovation. You just need to learn a bit of basic electricity. Making electricity is hard work, the efficiency is generally low. If you wanted to generate 50 watts, you would prolly have to provide over a 100 watts of input power. James
 

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In an auto alternator the brushes carry current to the rotor. The current flows through the windings in the rotor creating the magnetic field. You are using Permanent Magnets to generate the magnetic field. The auto alternator uses brushes, because that's the cheapest/easyest way to get the magnetic field necessary to make some electricity. Magnets (especially rare earth) are expensive. To generate electricity, it's necessary to move either: a conductor through a magnetic field or a magnetic field across a conductor. It's is very important to have the magnetic field contained in such a way that little is wasted (flux leakage).
 
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