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Author Topic: How can I optimise an electric generator with a shaking magnet inside a coil?  (Read 7673 times)

Offline McKay

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Greetings. I was wondering if it would be a good idea to simply loosly put a strong magnet inside a copper (or other) coil to generate electric energy from the shaking of the system (say, in smartphone in a pocket while walking), BUT with the so called "Liquid metal" material coating inside to minimize energy loss and keep the magnet bouncing for longer to extract a bit more energy.. what do you think? Or is the "Liquid Metal" magnetic and the magnet will just stick? In that case - perhaps the magnet can be fixed in position and the coil be bouncing between the very kinetic energy reflecting  material plates? ..
« Last Edit: 12/02/2015 11:02:57 by chris »


 

Offline evan_au

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Re: Electric generator from shaking a magnet in a coil
« Reply #1 on: 25/12/2014 21:03:11 »
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a strong magnet inside a copper coil to generate electric energy from the shaking ... while walking
This is theoretically possible. There are a few practical problems to overcome:
- The voltage generated will be quite low, and the common silicon electronics tends to block anything less than around 0.7V. So turning this small voltage with a low-frequency AC into 5V DC to charge your smartphone may be a challenge.
- You could use very strong magnet.
- You could use more turns in your coil, but then the series resistance starts to become a problem.

Other people trying to tackle this important problem have tried solar cells, and piezoelectric crystals in the sole of a shoe.

I am a bit puzzled about some aspects of the invention as described...
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keep the magnet bouncing for longer to extract a bit more energy
If you convert more kinetic energy into electrical energy, the magnet will stop bouncing more quickly (ready for the next step).

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"Liquid metal" material
The most common liquid metal is Mercury, which is quite volatile and toxic. You actually don't want this near you, in case some leaks out (and it is banned on aeroplanes, so your device will be confiscated).
- Other low-melting point alloys are made with metallic Cesium, Sodium and Potassium. These are very reactive, and you don't want these escaping, either.
- Alloys of Gallium appear suitable, and are fairly safe.

But I don't see how a liquid metal will help the copper coil absorb more energy - if anything, the magnet will lose kinetic energy by stirring the liquid metal with its magnetic field.
 

Offline dlorde

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Re: Electric generator from shaking a magnet in a coil
« Reply #2 on: 25/12/2014 21:52:54 »
I have a small torch that is powered by shaking a magnet up & down through a coil in the handle to charge a small battery. It is a bit of a novelty, as the amount of shaking to produce a decent light for a useful time makes it quite impractical.

I have no idea how 'liquid metal' could make it better - precisely what is the liquid metal you had in mind?
 

Offline RD

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Re: Electric generator from shaking a magnet in a coil
« Reply #3 on: 25/12/2014 22:56:03 »
... so called "Liquid metal" material coating inside to minimize energy loss ...

There would be turbulence in the "liquid metal" [ferrofluid], caused by eddy-currents, which could be even lossier than the friction on a solid-magnet moving about.
« Last Edit: 25/12/2014 23:04:59 by RD »
 

Offline CliffordK

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Re: Electric generator from shaking a magnet in a coil
« Reply #4 on: 29/12/2014 20:56:22 »
I have a small torch that is powered by shaking a magnet up & down through a coil in the handle to charge a small battery. It is a bit of a novelty, as the amount of shaking to produce a decent light for a useful time makes it quite impractical.
My shake flashlight never charged anything, so it was quite annoying to constantly shake the flashlight to get light out of it, especially when one needed two hands for a task, and wanted the light focused on a single spot rather than moving.

Likewise, I have a crank flashlight that would only light while cranking. 

Some devices do function well with "stored energy".  One can wind a watch that will last a day or so, and there are self-winding watches that do quite well if worn, but the amount of energy they use is minuscule.  Even winding record players work reasonably well if optimized for a few minutes of play time.
 

Offline McKay

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Re: Electric generator from shaking a magnet in a coil
« Reply #5 on: 30/12/2014 04:06:23 »
Thats whhy I say "So called [Liquid metal]". This kind of stuff:
Its a brand.
http://en.wikipedia.org/wiki/Liquidmetal
Anyway - just a very bouncy surface, if you like, to disipate less energy at impact and add a bit more to extract-able electric energy.
« Last Edit: 30/12/2014 04:12:39 by McKay »
 

Offline McKay

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Re: Electric generator from shaking a magnet in a coil
« Reply #6 on: 30/12/2014 04:14:50 »
So it is quite difficult because of the low voltage and conversion. But you said difficult, not impossible. How difficult? And, just for daydreaming, how much electric energy be extracted in best case scenario? :)
 

Offline evan_au

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Re: Electric generator from shaking a magnet in a coil
« Reply #7 on: 30/12/2014 09:21:03 »
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Liquid Metal
It seems that the LiquidmetalTM is not a ferrofluid, nor is it a liquid. It is a metal alloy which has trouble forming crystals, so it has an amorphous structure (like glass). It returns much of the mechanical energy to the ball bearing, which is why it bounces so long.

Quote
"Liquid metal" material coating inside to minimize energy loss and keep the magnet bouncing for longer
As you suggest, the LiquidmetalTM could bounce the magnet back again, but they don't take too kindly to being banged repeatedly - they tend to lose their magnetism.
You could achieve a similar effect by attaching the magnet to a spring, which would keep the magnet bouncing, without the sudden impacts.
The magnet does not need to bounce very long, because the coil will quickly turn any mechanical motion into electrical energy. So a cheap spring will be much more economical than an exotic amorphous metal.

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how much electric energy be extracted in best case scenario?
A human being dissipates about 70-100W as heat, just to stay alive.
During exercise, a human being could deliver another 100W as mechanical power, for an extended time.

If you clip the tube generator on your belt while walking, I am guessing that you would deliver much less than 10mW to the magnet (if you were cycling, an ankle strap would generate far more power than a waist clip!).

Since the voltage is proportional to the velocity (and power proportional to the square of the velocity), a much more efficient way to generate electricity would be with a hand-crank, where a rotary motion is geared up to provide high speed rotary motion to the magnet, and more efficient delivery of power from your hand to the electronic circuitry.

We have a small LED torch like this at home. Unfortunately, I can't find the torch at the moment to test it. [I have a vague recollection that 10 seconds of vigorous cranking could light 3 LEDs, which fade out after 30 seconds. If it takes about 10mA into 3.3V to light one white LED, for an average of 10 seconds, that is about 1 Joule of energy captured. The efficiency does not sound very high!]

GravityLight works in a similar way - a few seconds of lifting a weight is turns a pulley, which is geared up to generate electricity, lighting a small LED (50mW) for up to 30 minutes. This project is intended to displace polluting kerosene lanterns in developing countries.
 

Offline CliffordK

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Re: Electric generator from shaking a magnet in a coil
« Reply #8 on: 30/12/2014 17:08:54 »
From the Wikipedia Article:
Quote
One of the first commercial uses of Liquidmetal was in golf clubs made by the company, where the highly elastic metal was used in portions of the club face.  These were highly rated by users, but the product was later dropped, in part because the prototypes shattered after fewer than 40 hits.

Impact elasticity can be achieved in a number of ways.  As Evan suggested, perhaps a spring.  Super Balls have excellent impact elasticity. 

The "shake" may be effective in certain activities, such as a pedometer.  Perhaps adding to shock absorbers in a car.  However, just shaking a flashlight may be inefficient as it requires a lot of movement of the arm for relatively few polarity transitions.  Rotary generators are able to maximize the polarity transitions to maximize power generation.

There are, of course, benefits of storing energy in springs or with some kind of weight and gravity.
 

Offline McKay

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Re: Electric generator from shaking a magnet in a coil
« Reply #9 on: 30/12/2014 22:02:09 »
I feel dumb after reading responses to my questions in this forum
 

Offline CliffordK

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Re: Electric generator from shaking a magnet in a coil
« Reply #10 on: 30/12/2014 23:24:26 »
What I will say is that many of us have been at least intrigued enough by technology similar to what you've described to have invested in things like shake flashlights, but unfortunately have been disappointed by either the technology or the implementation, or both. 

And, most of us weren't aware of the "liquid metal" trademark materials, so it is good to see something new.

For a little bit of energy recovery, there are some well designed systems.  For example, I have been very impressed with the ReeLight bicycle lights using induction power off of a magnet attached to a bicycle wheel which is hardly noticeable. 

Evan's Gravity Light now has me thinking one might be able to attach the ReeLight to a Grandfather Clock   
« Last Edit: 30/12/2014 23:26:37 by CliffordK »
 

Offline syhprum

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Re: Electric generator from shaking a magnet in a coil
« Reply #11 on: 31/12/2014 07:02:01 »
Although silicon semiconductors require 0.7v to get going Germanium devices are available but less common that only require 0.2v   
 

Offline syhprum

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Re: Electric generator from shaking a magnet in a coil
« Reply #12 on: 31/12/2014 09:20:06 »
Around the turn of the century large windup electric generators similar to a grandfather clock were installed in some country houses
« Last Edit: 01/01/2015 00:38:25 by syhprum »
 

Offline wolfekeeper

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Re: Electric generator from shaking a magnet in a coil
« Reply #13 on: 06/02/2015 01:57:28 »
You could step up the voltage perhaps with a small transformer to help with the rectifier issue.

Another way I've seen to improve the energy efficiency is to use magnets as springs at either end.
 

Offline matthew austin

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Re: Electric generator from shaking a magnet in a coil
« Reply #14 on: 10/02/2015 14:46:19 »
I believe i have come up with a similar concept that turns sound waves into a viable a static electric source. i have roughly designed the installation and wish to pursue the invention into the prototype development stage. Only thing is i don't know who to contact to safely sell this invention to.. Can anybody help me?
 

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Re: Electric generator from shaking a magnet in a coil
« Reply #14 on: 10/02/2015 14:46:19 »

 

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