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| kramled |
 Posted: Tue Mar 18, 2008 7:50 am Post subject: Help do build a witricity circuit. |
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Forum Freshman
Joined: 18 Mar 2008
Posts: 2
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Hi my name is Mark,
I´m a electronic professor in Portugal and i am trying to build a witricity circuit,so i´m asking you for help.
Can you ppl give some usefull links or made circuits.
Please help me 
Thank you
MR |
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| bit4bit |
| Posted: Wed Mar 19, 2008 8:13 am Post subject: |
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Forum Ph.D.
Joined: 14 Jul 2007
Posts: 623
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| Do you have any specifications for it, or is it just as a demonstartion/experiment kind of thing? For example, if you have a DC source, you would need an oscillator, since electromagnetic induction only works with changing currents. If you need the output to be DC, you will have to have a rectifier, smoothing caps, and voltage regs. |
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| kramled |
| Posted: Wed Mar 19, 2008 9:09 am Post subject: |
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Forum Freshman
Joined: 18 Mar 2008
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No i dont have any specifications,it is just as a demonstartion/experiment.
And yes, i have a Dc source and an oscillator.
Thank you. |
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| SuperNatendo |
| Posted: Wed Mar 19, 2008 9:18 am Post subject: |
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Forum Masters Degree
Joined: 10 Dec 2007
Posts: 518
Location: Nashville, TN USA
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The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb from a power source that was 2 meters (7 ft) away at roughly 40% efficiency. They used two capacitively loaded copper coils, 60 centimeters (24 in) in diameter, oriented along the same axis, The coils were designed to resonate together at 10 MHz. One was connected inductively to a power source, the other to a bulb. The setup powered the bulb on, even when the direct line of sight was blocked using a wooden panel. Aristeidis Karalis says that "the usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system".
Thats all I know 
I got it from wikipedia 
http://en.wikipedia.org/wiki/WiTricity
I would love to build this as well. Tell me what you know about it Professor, PLEASE!
Am I right in assuming you make two similar copper coils, Kind of like what you use for electromagnets and inductors?
If they resonate at the same frequency, then the power goes to the bulb, even when something is placed between direct line of sight?
Is this right? If it is, Im gonna buy some copper wire! I'm hoping on testing this for my self! Please post if this really is how it works! I Just hope we can get them both to resonate at the same frequency
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“It’s no wonder that truth is stranger than fiction. Fiction has to make sense.” - Mark Twain |
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| bit4bit |
| Posted: Wed Mar 19, 2008 9:50 am Post subject: |
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Forum Ph.D.
Joined: 14 Jul 2007
Posts: 623
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The principle of the system is electromagnetic induction, which has been around for ages, and is used in transformers and radios, for example. The difference with this system, is that it is able to tarnsfer power over larger distances, with more efficiency, using a particular antenna design, called a magnetic loop antenna. Apparently (don't quote me on this), these antennas concentrate the majority of the magnetic field produced, over some particular direction, so that the power transfer has a fairly narrow band of view.
You would be looking to create a parallel or series resonant circuit, using a capacitance, where the antenna itself would act as an inductance. next you can calculate the resonance frequency for the circuit. (alternatively, you can know, your frequency, and inductance, and calculate the capacitance needed). Then make sure your recieving circuit, which will also be a parrallel resonant circuit, has the same resonant frequency, and it should work well. then add in a rectifying/regulating stages id you want a DC output. |
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| SuperNatendo |
| Posted: Wed Mar 19, 2008 10:07 am Post subject: |
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Forum Masters Degree
Joined: 10 Dec 2007
Posts: 518
Location: Nashville, TN USA
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A DC input into this circuit would output in AC due to the nature of the inductor-like antennae right?
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“It’s no wonder that truth is stranger than fiction. Fiction has to make sense.” - Mark Twain |
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| bit4bit |
| Posted: Wed Mar 19, 2008 10:21 am Post subject: |
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Forum Ph.D.
Joined: 14 Jul 2007
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| No, to get an osillating signal, you need a feedback system, wehre you feed an amplifier into a filter, and then feed the output of that back into the amplifier. To save yourself having to do this, if it is just for experimentation purposes, it would probably be easier to run it off the mains and use a step down transformer to give you a sinusoidal waveform of whatever voltage you need. |
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| SuperNatendo |
| Posted: Wed Mar 19, 2008 11:25 am Post subject: |
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Forum Masters Degree
Joined: 10 Dec 2007
Posts: 518
Location: Nashville, TN USA
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Baterries are dc. so then how do batteries create electromagnetic induction if you claim that requires ac power as you say above?
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| bit4bit |
| Posted: Wed Mar 19, 2008 12:19 pm Post subject: |
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Forum Ph.D.
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What induction do you refer to?
All currents have a magnetic field associated with them, including DC. However, an emf is only induced when when the magnetic flux, and hence the current, through a conductor is changing. An AC waveform is necessary, to maintian a changing current, and hence induced voltage, and hence transfer of electric power.
The main equation for an inductor/coil is V=L*dI/dt |
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| Harold14370 |
| Posted: Wed Mar 19, 2008 1:20 pm Post subject: |
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Forum Professor
Joined: 13 Apr 2007
Posts: 1622
Location: Pennsylvania
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| SuperNatendo wrote: |
| Baterries are dc. so then how do batteries create electromagnetic induction if you claim that requires ac power as you say above? |
The way to make a-c out of d-c is with an inverter. http://en.wikipedia.org/wiki/Inverter_(electrical) |
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| SuperNatendo |
| Posted: Sat Mar 22, 2008 7:33 am Post subject: |
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Forum Masters Degree
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Location: Nashville, TN USA
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I guess what I am asking then is light bulbs use AC or DC, so if they are AC and you are using DC inputs (which I would much rather use!) you need to use this inverter before or after you resonate the inductor that is connected to the lightbulb?
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| Harold14370 |
| Posted: Sat Mar 22, 2008 8:25 am Post subject: |
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Forum Professor
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| SuperNatendo wrote: |
| I guess what I am asking then is light bulbs use AC or DC, so if they are AC and you are using DC inputs (which I would much rather use!) you need to use this inverter before or after you resonate the inductor that is connected to the lightbulb? |
Your source of power probably starts out as a-c, but if 60 Hz (or 50 in Europe) is not the ideal frequency for your resonant circuit, you might have to rectify it to d-c then invert it at the transmission frequency. If that is not the right frequency for your end use, you would have to have a rectifier or rectifier/inverter at the other end. |
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| bit4bit |
| Posted: Sat Mar 22, 2008 11:33 am Post subject: |
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Forum Ph.D.
Joined: 14 Jul 2007
Posts: 623
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| I agee with Harold. It's all about using basic circuit building blocks and putting them together in whatever order to perform different 'operations' on your signal as needed. In this case those are namely rectifying/inverting circuits. |
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