AC Generator Via Shaking only outputs MAX 20 MilliVolts

Thread Starter

Eric So

Joined Aug 18, 2016
16
I have a paper tube and 10 rare earth magnets inside and a lot of enameled 26 Gauge Wire. I have 2 coils hooked up to each other that overlaps each other and I measured the voltage and gives 8-20 MilliVolts. It can't even light a light 1-5 Volt LED. Any ideas to boost the output or create a voltage booster of some sort and at least get it to 1V?
 

tcmtech

Joined Nov 4, 2013
2,867
I would suspect that having all 10 magnets stacked together gives it many small opposing poles that cancel each other out rather than just two widely spaced ones like you need.
 

Thread Starter

Eric So

Joined Aug 18, 2016
16
I would suspect that having all 10 magnets stacked together gives it many small opposing poles that cancel each other out rather than just two widely spaced ones like you need.
How would I go about spacing the magnets out? btw I added a bridge rectifier doesn't do much.
 

Alec_t

Joined Sep 17, 2013
12,007
Can you post a pic of how the magnet poles on one of those magnets are arranged? If the magnet is a button shape, one circular face could be N and the opposite face S. Or the N and S could be at opposite ends of a diameter. The arrangement would determine how the magnet should be oriented in the tube.
Your two coils need to be 'hooked up to each other' in a series-adding, not series-cancelling arrangement.
The bridge rectifier diodes drop about 1.2V, so you won't get significant current through the coils unless you can generate at least that voltage.
 

Thread Starter

Eric So

Joined Aug 18, 2016
16
Can you post a pic of how the magnet poles on one of those magnets are arranged? If the magnet is a button shape, one circular face could be N and the opposite face S. Or the N and S could be at opposite ends of a diameter. The arrangement would determine how the magnet should be oriented in the tube.
Your two coils need to be 'hooked up to each other' in a series-adding, not series-cancelling arrangement.
The bridge rectifier diodes drop about 1.2V, so you won't get significant current through the coils unless you can generate at least that voltage.
The shape of the 10 Magnets is a Solid Cyl inder Shape like thisimages.jpg
Right now I have the magnets stacked on to one another which brings up the point on what tcm said. I now tried this setup
[N-S],[N-S],[N-S]----[S-N],[S-N],[S-N],[S-N]----[N-S],[N-S],[N-S]
which creates space between the magnets
 

Alec_t

Joined Sep 17, 2013
12,007
Might be worth trying a short length of steel rod/tube with one magnet each end. N-rod-S.
Can you post a pic of your tube+coils, and give us some rough dimensions ?
 

Thread Starter

Eric So

Joined Aug 18, 2016
16
Might be worth trying a short length of steel rod/tube with one magnet each end. N-rod-S.
Can you post a pic of your tube+coils, and give us some rough dimensions ?
I don't have any steel tubing. Must the tube be ferrous?
 

tcmtech

Joined Nov 4, 2013
2,867
How would I go about spacing the magnets out? btw I added a bridge rectifier doesn't do much.
You don't. You just use one larger magnet that is approximately same length as the coil is.

Just look at a common speaker for guidance being you are basically building the same type of linear displacement motor as the voice coil and magnet they use is set up as only in your application is using it as a linear displacement generator.
 

Alec_t

Joined Sep 17, 2013
12,007
Must the tube be ferrous?
Yes. The idea is to create what is in effect a larger single magnet (as Tcmtech is saying), by, hopefully, 'cancelling out' the two inner poles. May not work, of course. If your coils are cylindrical and the magnet is moving to and fro inside the cylinder in the direction of the longitudinal axis, then if the magnet's field lines are mainly also parallel to that axis very little magnetic flux is cutting the coil :(. The situation is different in a speaker, because the fixed magnet's field lines are radial, i.e. at right angles to the coil movement, for maximum flux cutting.
 

Thread Starter

Eric So

Joined Aug 18, 2016
16
Yes. The idea is to create what is in effect a larger single magnet (as Tcmtech is saying), by, hopefully, 'cancelling out' the two inner poles. May not work, of course. If your coils are cylindrical and the magnet is moving to and fro inside the cylinder in the direction of the longitudinal axis, then if the magnet's field lines are mainly also parallel to that axis very little magnetic flux is cutting the coil :(. The situation is different in a speaker, because the fixed magnet's field lines are radial, i.e. at right angles to the coil movement, for maximum flux cutting.
Are there other ways to improve the output?
 

tcmtech

Joined Nov 4, 2013
2,867
Buy a 'shake it flashlight' and take it apart and see how they did it. ;)

Mostly just use a magnet that just fits inside your tube and is about the same length as your coil is.
 

Alec_t

Joined Sep 17, 2013
12,007
The voltage generated is proportional to the rate of change of the magnetic flux cutting the coil. This will be a maximum when the magnet enters or exits the coil.
 

Thread Starter

Eric So

Joined Aug 18, 2016
16
The voltage generated is proportional to the rate of change of the magnetic flux cutting the coil. This will be a maximum when the magnet enters or exits the coil.
How would I configure the coil to be in proportion to the magnets. Eg same length or thickness. Does more turns mean better output or would it take longer time to charge up the magnetic field.
 

Alec_t

Joined Sep 17, 2013
12,007
For a button magnet you will probably need a pancake-shaped coil. Experiment is called for. You could also try turning the magnet through 90° so that its faces are pointing towards the tube wall rather than along the tube axis.
Yes, the more turns the merrier for increased voltage.
 
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Thread Starter

Eric So

Joined Aug 18, 2016
16
For a button magnet you will probably need a pancake-shaped coil. Experiment is called for. You could also try turning the magnet through 90° so that its faces are pointing towards the tube wall rather than along the tube axis.
Yes, the more turns the merrier for increased voltage.
I'm not sure what you mean by a Pancake shaped coil. If I were to wrap this kind of coil around my tube, how would it go?
 

tcmtech

Joined Nov 4, 2013
2,867
How would I configure the coil to be in proportion to the magnets.
post 8, first sentence. :rolleyes:

would i need multiple coils or just one? If i were to use multiple coils how would the connections be.
Until you have it working well with one coil I wouldn't put too much effort into trying to add multiple coils to the design. :(

IFf I was you I would be spending a good deal of time reading about how magnetic fields work and how they interact with electrically conductive materials.

Magnetic flux principles and Volt Ampere turns would be things to read up on regarding how to best match your coil design to the magnet being used.
 
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