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I need some help with dynamo generator..

After stumbling upon the project at https://www.instructables.com/id/Contactless-dynamo-powering-bike-safety-lights/ i decided to try it out first small-scale using just one magnet and coil in my hand connected to a multimeter.  Hoewever, i had no success.  I was only getting .01 (a hundredth of a volt) and I tried all kinds of ways swiping the magnet past the coil and just couldn't figure it out.  I still don't know what I'm doing wrong.  Im using the same hard drive magnet and a 5 volt relay coil.  If you have any suggestions, thanks in advance/


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kelseymh6 years ago
The generated current is proportional to how fast the magnetic field changes (technically, I = dB/dt), and the voltage is, of course, proportional to the current (V = IR). 

I don't think you can "swipe" with your bare hand fast enough, or for long enough, to get any decent reading off a multimeter. 

That's why, for example, the hand-crank radios have a crank and gearing, and bicycle dynamos are hooked up to bicycles.
jules15 (author)  kelseymh6 years ago
Yeah, I thought about that, so I actually hooked the coil on my swingarm on my bike and the magnet to the wheel to a little light bulb to the wires and i pedalled as fast as I could on my bike and still nothing. I placed the coil to the center of the wheel too, so I could get more speed instead of placing it towards the outside.
The outside is what gets you more speed. The angular velocity (RPMs) of a solid wheel is independent of radius, of course, but the linear velocity of a given point is proportional to radius: a tooth of one gear, for example, might be moving at 1.5 m/s (for a 20 km/h bike speed), while a point on the tire itself is going about 7 m/s. See Jack's comment below for why your multimeter may not be responding.
jules15 (author)  kelseymh6 years ago
Ohh, ok. I guess i was confused. I'll move it towards the outer part.
kelseymh6 years ago
A couple of suggestions to help people answering you narrow things down. You should probably add to the text above the information about how you hooked your build up to your bike to improve the induction. It would also be quite useful to add some pictures of your setup: it may be that you've got something connected wrong.
Re-design6 years ago
First I've never seen that inst. until now. IT's nice. Second, a relay coil usually has MANY turns of very thing wire so any magnetic flux it crosses causes more voltage than a smaller coil. Third, a magnet hooked to a bike wheel spinning past the coil is going to cause more voltage in the coil than using your hand to swing it back and forth. Forth, the closer you can get the magnet to the coil the stronger will be the effect. Fifth, keep at it and fix your deficiencies and you'll get better results.
jules15 (author)  Re-design6 years ago
Update: I forget to mention that Im only using one magnet and one coil. I imagine I could produce more energy with more.
As per Jack and Kelsey as to the physics, but the key reason you ain't seeing anything is that your meter can't respond anything LIKE fast enough to register the pulse. Try an oscilloscope, if you can get the use of one. Steve
The number of turns in the coil is a factor also. More turns will give you proportionally more voltage induced in the coil for the same dΦ/dt.  So a large number of turns might help, if you cannot get the magnet to move very fast. 



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