Voltage from rotation

[wdariusw]

Yeah, i saw Halbach array, but i have only cylindrical magnets now, so there are only two positions for the magnets. What is stronger than N52 ? Maybe bigger N52. There are another device with battery and i want to comunicate with him (thats why i need wireless). Perfect would be 8 pulses in one rotation from RF, 4 pulses are satisfactory, but i will happy if i make at least 1 pulse per rotation. Faster rotation would help, but the average cyclist pedals at about 60 rpm, and advanced cyclists pedal at much higher cadences, from at least 80 rpm to more than 100 rpm. So i can't make experiments with 200rpm for example...Can one coil cover 2 magnets, one of P and other of N ? Will paint few variants of magnets and coils with solidworks for forum members opinions. I have another ring (waiting for bigger magnets for testing).

Need to find correct coils positions, and correct coil sizes. There is AC, circuit requires DC. Another problem how to rectify such low voltages. With shottkey there are about 0.6V voltage drop. Found this http://digitaldiy.io/general-electronics/552-a-no-voltage-drop-bridge-rectifier.html , but I have doubts about that "perfect" bridge.

 

[wdariusw]

Merlin3189, will see tomorrow in electronics shop what they have of cores. I had thoughts about oscillator , but it is unreliable. What if two systems near each other? Fault... MCU is needed anyway, for transmitting proper pulse, maybe one bit for identification. I have also 0.15mm cooper wire, will try ti make exact size coil for comparison.

 

[Gryd3]

A good key to your puzzle mentioned by merlin is how you space the magnets and coils.
If you use more than one coil, make sure that they are all positioned so that they pass the a magnet at the same time (Same polarity magnet if coils are in parallel). You don't want one magnet passing a coil as a gap is passing by another.. they could potentially cancel each other out.

 

[wdariusw]

I think the sine on oscilloscope was not perfect because of not ideal positioning of coils. And it is bad, that coils are differents ? Because when i winding it, there are a lot of turns, and i do not count it.

 

[Merlin3189]

If you look at the instructables video posted by Grydd, notice the two small pulses and a double height one in between. That's because the computer magnets are a N and a S pole side by side.
The key is flux CHANGE. You get a small pulse as the N pole comes in (0 to +1) and a small pulse as the S pole leaves (-1 to 0), but a big pulse as it moves from N to S (+1 to -1). So if you put two of your small round magnets immediately next to each other you can get this double flux change as they pass.

But I still think the key is always improving the magnetic circuit. Flux likes going through iron and ferrite much more than going through air. So for any given magnet you get much more flux in your coil if the flux can go from one pole to the other via the coil through the least amount of air.

Fair comment on the radio interference. That was always an issue with simple radio devices.
But, does it matter? An odd pulse now and again isn't going to be detected as someone pedalling at 4 pulses a second (and you could up that to 6 or 8 say, using more magnets on the disc.)
The only time you're likely to get a stream of pulses at the right speed is with two such bikes travelling along together. In that case they're probably both pedalling at the same rate. If you're only interested in them pedalling above a threshold, doubling the pulse rate when it's already above, won't matter.
It might be worth setting the sensitivity of the receiver so that it detects local radio pulses reliably, but not a lot more sensitive than needed. The spacing between transmitter and receiver is always the same, so the strength of the proper signal should be reliable.

I know the answer to everything these days is to use microprocessors and spread spectrum radio links and these are now so small and cheap that maybe people are right to do that. I just grew up in an era when scientists used Occam's razor andengineers believed good enough was good enough.
I looked at your system and thought, that's a great idea (been done before of course, but then, hasn't everything!) and then I saw the price! You're in an upmarket sector and no doubt your marketing guy says you have to charge a lot or people won't buy it! But for me it would remain a 'wow, what a great device' but not get on my bike unless the price dropped a lot. Perhaps you could find one of those old engineers? You know, they guys who can do for 5 bob what any fool can do for a pound.

 

[Arouse1973]

Have you thought about turning the coils side on to the magnets?
Adam

 

[wdariusw]

Have you thought about turning the coils side on to the magnets?
Adam

Do you say that this arrangement:

would work better than this one ?
[img=http://s11.postimg.org/vdb4dq5lr/image.jpg]

 

[Arouse1973]

Yes there is no harm in trying. If this doesn't improve then turn the magnet side on also.
Thanks
Adam

 

[wdariusw]

It is very difficult to wind coils...And what about the coil inductance ? It is important or not ?

 

[Arouse1973]

Keep the same coils you have. Just stick them side on to see if it helps. Then turn the magnets. Use sticky tape for now just to see if it improves. Yes inductance is important as this is linked to number of turns. You get a greater output with more turns for a given magnetic flux.
Adam

 

[wdariusw]

Today have bought 7x7x7mm N42 neodynium cube magnets. Will try to arrange magnets into Halbach array, hope to to that next week (need to buy new ring with holes for squared magnets). And if i use small coils with every magnet, than every second coil should be winded into different direction? Or same dirrection, buy should be wired different ?

 

[Arouse1973]

No all coils to be side on was what I meant. Then turn the magnets side on.
Adam

 

[Gryd3]

Do you say that this arrangement:

would work better than this one ?
[img=http://s11.postimg.org/vdb4dq5lr/image.jpg]

Take a look at the top arrangement. There is a huge improvement that can be made.
Look at the axis of rotation, and the path the magnets will take when they pass each coil.
If the magnets spin clockwise, they will travel 'across' the first coil, and 'along' the second coil, then 'across' the third at a different angle.
You want each and every coil to have the same orientation in relation to the path of the magnet.

 

[wdariusw]

Gryd3, great advice ! Maybe then the signal would be with less noise and more magnitude ! It is very expensive to do differents magnets holders from PVC for every idea. I think will do PVC holder for coils, then i will achieve perfect orientation and minimal airgap between magnets, no matter how it costs... Naybe someone have advices for coils winding ? How to wind all coils identically ?

 

[Gryd3]

. Naybe someone have advices for coils winding ? How to wind all coils identically ?

Only suggestion I have for winding the coils the same, is to count the number of rotations...
There are a number of examples for people winding their own guitar pickups...
Simplest/cheapest method seems to be using a momentary button and an old calculator to track the turns, and anything to spin it.. (Ie, drill, sewing machine etc.)

Additionally. To save some money during the experimental phase, I would suggest playing with different mounting ideas. I know milling a holder can be pricey, but if you can get away with using some strong doublesided tape to temporarily mount the magnets to a blank disk, you should be able to re-arrange them numerous times.
Playing with the coil orientation could be as simple as using only 1 coil and holding it as you move it closer/further or rotating it to see which orientation works best for the current magnet arrangement. Once you find an orientation you like, mount a second coil the same way. (Note that each coil should be rotated along the axis of rotation.. so the magnet passes by each coil in the exact same direction)

 

[wdariusw]

I saw that technique. I can do it stepper, can rotate stepper lets say 1000 turn, but it requires to spend some time and money for coil form and mechanical fixing to stepper axis..Maybe this is logic idea with stepper..

 

[wdariusw]

Take a look at the top arrangement. There is a huge improvement that can be made.
Look at the axis of rotation, and the path the magnets will take when they pass each coil.
If the magnets spin clockwise, they will travel 'across' the first coil, and 'along' the second coil, then 'across' the third at a different angle.
You want each and every coil to have the same orientation in relation to the path of the magnet.

One thought about that orientation. Lets say i positioned coils that the magnets will pass it with same angle. But...I think the coil area is smaller than post #27 second picture. This will affect output. Or i'm wrong here ?

 

[Gryd3]

One thought about that orientation. Lets say i positioned coils that the magnets will pass it with same angle. But...I think the coil area is smaller than post #27 second picture. This will affect output. Or i'm wrong here ?

I don't know quite enough details to determine if and how the cross section area of the coil will affect the output...
Of course, you could try making a couple of sample coils to find out:
Take the plastic casing from a Pen and wrap the wire around that as an example, then try the same thing with the casing from a marker or highlighter.
Cheap components. Will cost you wire, and maybe a few cents for the pen/marker.
Here's where it gets tricky though... the same number of turns in a smaller coil will have a different inductance and length of wire than the larger diameter... again, I'm not quite familiar enough to determine exactly how this will affect performance. I know about enough to know that more turns will provide a higher voltage output, and that the coils should be wired in parallel if you were to use the arrangement in the second image on post #27.

Perhaps someone has a formula or some example math to help determine the characteristics of the coils and how they will generate electricity.

 

[wdariusw]

Parallel ? I got 560mV when coils was in series...And another thing - rectangular coils would have bigger cross section..hm..will think about that tomorrow ! !

 

[Arouse1973]

At the risk of my idea being diluted by other great ideas.More voltage will be induced in the coil when the magnetic flux changes in strength over a period of time. The magnetic flux should pass through the coil which is why I said about turning the coils and magnets.
Adam