Wireless Electricity Transfer (Witricity help)

Discussion in 'The Projects Forum' started by zero_coke, Apr 22, 2009.

  1. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
    294
    1
    Hello,

    I have some questions and if you can please answer them you will be my hero, really.

    Basically what I'm trying to do is pretty much get a lightbulb to light up using the Witricity technique that MIT came up with, but I just can't seem to get it working.

    I have 2 coils, one is directly connected to the home outlet, 110 volts, 60 hertz. The other coil is right beside it, about 1 feet away, and connected to a light bulb. The coils have the following specifications:

    -11 cm diameter
    -11 feet in length
    -10 turns
    -hollow 0.5cm diameter copper wire


    What am I missing in my primary circuit that does not light up lightbulb connected to the secondary coil? I mean, theoretically this should light up, right? I have AC power connected to a coil, which should create a magnetic flux in the air to induce a current into the second coil and hence light the lightbulb up........but all I seem to be doing is shorting out my home's circuit.

    What are the materials I need and how did they do this? They managed to light up a lightbulb 7 FEET away...this is awesome and I'd like to try this. Please help guys please. I have attached a picture to take a look at my current setup.

    Thanks very much,

    -Harun

    [​IMG]
     
    Last edited: Apr 22, 2009
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    It's not surprising you are shorting your home GPO outlet. Your primary coil is nowhere near the right configuration for what you intend to do. it is effectively a short circuit to the 60Hz 110V supply.

    What you are doing is quite dangerous and potentially lethal. It seems you have little understanding of electrical design and safety. My advice whether welcomed or not, is to look for an alternative approach using safe low voltages and stay away from mains operated experiments such as this.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The core problem is you are depending entirely on inductance to restrict current flow. This would be reasonable if you had a 1000 turns on the primary coil, but 10 turns? The house could burn down. Go to the AAC book and read up on inductors. Your primary was probably in the neighborhood of 0.01µH, with a reactance of an ohm or so. Not good, very bad.
     
  4. -SK-

    Member

    Apr 14, 2009
    25
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    Another thing you missed, in addition to what the other posters have said, is that to perform wireless power transfer efficiently you need to use a resonant circuit. I believe the MIT people did that as well. This way, a small current input to your primary will result in a very large resonant current, and power transfer between coils.
    This is a fairly complex project in terms of a) designing both primary and secondary circuits to resonate at the desired frequency, b) designing all circuits to handle the large currents that develop, and c) safely isolating all this stuff from your mains supply, so as to not burn down your house.
    I would recommend doing some serious study of circuit design (this website has some good information, for find a good circuit textbook) and of electrical safety before starting to think about this one.
     
  5. zimbarak

    Active Member

    Feb 8, 2009
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    where is the core of the coil ?? since there is no core and u are the value of the magnet flux wil be very low as well as for magnet inductance and also u have a risk of electric short circuit ! so be aware of this !
     
  6. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
    294
    1
    I don't understand...If I'm not wrong you cannot do this experiment without AC current, and you can do it with DC but you need a DC source and then use an inverter to convert it back to AC and its a lot of work, so I stuck with my home's AC outlet.

    Ok, I know its dangerous, so that's why I'm researching now and making a good design before I try it out.

    So I learned that I need a resistor in the primary coil so that it won't short my house. Also, I need to increase the frequency of the AC current to 10 Megahertz from 60 Hertz , because that is the natural frequency of the copper coils I made, I think.

    Is it all good now? Am I missing anything else? If I'm able to drive the current in the primary coil at 10 MHz this will cause the two coils to be magnetically resonant and should light up the lightbulb...
     
    Last edited: Apr 23, 2009
  7. kahafeez

    Active Member

    Dec 2, 2008
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    dude, my class fellow lit up an LED at approximately 3feet away.... the idea is that u need to match the resonant frequency of both the sender and receiver.... if i'm not wrong then

    Fr=1/2*pi*L*C


    and they used an LED not a big Bulb and they used a small AC signal of about 10Vpp as input with a frequency of about 100Hz.... hope it helps.......
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Inductors, by themselves, do not have resonant frequency. Capacitance must be part of the circuit before resonance comes into play.You can learn more about resonance by reading here: http://www.allaboutcircuits.com/vol_2/chpt_6/index.html
     
  9. -SK-

    Member

    Apr 14, 2009
    25
    0
    It's not all good now. You need to make this work in steps. You cannot plug a bunch of components together and expect it to work.
    Yes, you need AC current, but AC resonant current. A resonant circuit needs to be used. Read this:
    http://en.wikipedia.org/wiki/LC_circuit
    and if you go to Thingmaker3's link, read the parallel resonant circuit bit, which is what you need for this.
    A resonant circuit continuously pulses energy between 2 storage elements (capacitor and inductor) , with minimal input to maintain it.
    You can't make it go with just an inductor and resistor, because you have only 1 storage element.
    I would recommend the following process:
    1. Get a variac (Variable transformer) to reduce the voltage from your outlet (at least to start). This way you won't burn anything. Also get a bunch of test equipment to make sure your circuit works.
    2. Make a working resonant circuit. You should have a minimal input current and a large resonant current.
    3. Make an identical resonant circuit, and put them together to see if you can inductively couple them.
    4. Make a circuit to power your load on the secondary side. Start with a much smaller load (a simple one would be a rectifier + resistor, and an LED).
     
  10. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
    294
    1
    Thanks guys, you guys are awesome :) Thanks I really appreciate it. I'm going to do some reading on resonant circuits and get some basic knowledge of these concepts and then I'll try the experiment again.
     
  11. b.shahvir

    Active Member

    Jan 6, 2009
    444
    0
    Do try the Tesla coil homepage. it provides lot of info on wireless electricity. Gud luck ;)
     
  12. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Not to be picky here but that's not quite true. There is no such animal as a purely capacitive capacitor. There's no such thing as a purely inductive inductor, and there's no such thing as a purely resistive resistor. Hang a sweep generator (that can sweep from 0 to 1GHz) on a small value cap or inductor and you will inevitably see resonance somewhere over that spectrum. Even a low value resistor will find a point of resonance. RF Engineers know this and compensate for it in there equations when designing. Capacitors have series inductance in there leads. Inductors have capacitance between their windings, between the windings the ground plane, and to other components in close proximity. In fact, large value caps can exhibit quite a bit of inductance. Surface mount components have gone a long way in significantly reducing these effects.


    DISCLAIMER!! The information below is intended to be a demonstration of what NOT to do... EVER!!!!! It can only be by the grace of God that I'm still here to tell this INSANE story!!!!


    As far as the OP's dangerous testing method is concerned, I think I've known worse.
    In 1968 I was building a hi power transmitter. I managed to find a military surplus power transformer that gave me the required 1KV but I needed to test it under load because my project required 1KV@1A as a plate supply. I searched through all my parts goodies but couldn't find a 1K@1KW resistor for a load. What to do??? I pondered the problem to no avail but knew there had to be a field expedient solution.
    While tossing and turning through a sleepless night, I had an epiphany! Hell... I thought it was absolute genius!! At about 0230hrs I went down to my basement and filled a bucket with water. We didn't have many plastic buckets back then, so this one was galvanized steel. Using alligator clips I connected one secondary lead to the bucket rim. The other lead was secured between two bricks in the bottom of the bucket. I anxiously plugged the transformer into the outlet (Mains on the other side of the pond) and observed my Ammeter. Darn, the resistance was not low enough to draw an amp, not even close in fact. So I unplugged it and tried fiddling with the distance between the bucket walls and the lead between the bricks. It was past 0300hrs when I had another brilliant stroke of genius. By 0310 I was standing there in my pajamas pouring salt into a bucket of water with 1000 Volts of potential death at my slipper clad feet! Long before the Ammeter reached 1A the water started to boil!

    When looking back over my life and evaluating the dumb things I did, this ranks numero uno! :eek:
     
    Last edited: Apr 26, 2009
  13. boba052

    New Member

    Apr 22, 2009
    1
    0
    Zero I just signed up tonight so no one knows me . However those guys are giving you great advice. I'd suggest maybe you go read Horowitz & Hill's book the art of electronics and there's some old stuff by Rufas Turner that Sam's pub put out years ago, get through that stuff and at least you will still have your house.
     
  14. electronictech

    Active Member

    Apr 1, 2009
    35
    0
    The wireless transmission of electrical energy is a technique developed by Nikola Tesla over a hundred years ago and it is possible............. but 'witricity' that the MIT kids did only works at a few feet of distance.

    I built a pair of matched Tesla coils and performed the 'wireless'. I was able to light an LED at a distance of 65' using a spark gap driven transmitter. The key is to prevent any type of breakout (or discharge) from the transmitting coil and to have both coils in mutual tune. You have to measure the resonant frequency of the transmitter and then match that frequency with the receiving coil. Tesla Coils (or Helical Resonators) are unique in many ways. Tuning is typically done by either increasing or decreasing the amount of isotropic capacity that is atop of the coils....you'll need a signal generator and an oscilloscope to properly match the two....but once they are matched you will be able transmit power. (you'll also need a very elaborate grounding system for both coils, I used multiple ground rods and soaked the ground area with salt water)

    I'll admit upfront that the amount of power transmitted will be small and the efficiency will be very poor(if using low power amateur setups) .......but if you study the system, you will learn that at low frequencies and power levels above 75kW, you can transmit power to any point on the globe.

    The hidden key, is that you will learn about 'longitudinal EM waves'.....something that conventional electronic theory does not cover....and may never cover. One thing that always interested me about the system, was that the propagation velocity of the system was capable of superluminal velocities.....another thing that conventional electronic theory doesn't seem to touch.

    It isn't that wireless energy transmission is possible or not....it is what it will do to the existing economy that is founded upon the wired system. In America, we are a capitalist bunch, and wireless would threaten our ability to capitalize.
     
  15. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
    294
    1
    I know that Tesla came up with this wireless transmission over a 100 years ago, but if I'm not wrong it was the capitalist utility companies that were against this "wireless" power because you can't charge someone for something in the air...sort of like charging someone for listening to their radio...it's not possible (atleast I think).

    Anyhow, so I read the past few posts, and ElectronicTech I don't know if you're referring to the same topic as me because I'm not trying to use electromagnetic radiation to transmit power but rather electromagnetic induction with tuned resonance between the transmitter and receiver. I think this is a very practical means of getting rid of those wires we have in our houses because you can install these in the wall and it would be able to cover any area inside the house.

    Anyhow, I want to ask, how do you "match" the frequency of the first coil to the second? I don't understand what you mean by that...so to make this witricity a reality, I have to make a LC Tuned Circuit, right? And after that I'll need to connect it to a signal generator to alter the frequency or what?


    Someone guide me please in detail what to do. Thanks so much!
     
  16. electronictech

    Active Member

    Apr 1, 2009
    35
    0
    This is where confusion is generated, the Tesla system DOES NOT rely on electromagnetic radiation, it is actually a form of conduction through the earth itself (but there are losses associated with the system in the form of electromagnetic radiation).

    You are correct that 'witricity' is electromagnetic induction, but it is a form of evanescent coupling.....the efficiency is very poor (unless the range is very short).

    As a simple project:
    Start with a scale model like a doll house, then wind a few(10-15)turns of wire around the outside perimeter of it, this will be your primary coil. Next place a capacitor in series with the primary coil. Now measure the L of the primary coil and the C of the capacitor and calculate the series resonant frequency of your series LC circuit. Next place a limiting resistor in series with the LC circuit that will let you drive a signal generator at the LC resonant frequency while it is on its maximum amplitude setting without damaging it.

    Now for the internal circuit or secondary circuit (which will be placed in one of the rooms of the doll house). Wind a small coil with many turns say
    40-50 turns, this will be your secondary circuit. Measure the L of this coil and calculate the necessary capacitance to create a series resonant circuit whose frequency is the same as the primary circuit(transmitting circuit). Now place that calculated capacitance in parallel with the secondary coil, and now also place an LED in parallel with the secondary coil and capacitor.

    When the signal generator that is driving the primary circuit is set to the resonant frequency, the secondary circuit which is inside of this primary coil will respond and the LED should illuminate.

    Tesla made a circuit similar to this in his Lab in New York on Houston street before it burned down....his was on a much larger scale and he was able to walk around in the lab with a exhausted bulb and have light where he needed it.

    May I suggest you either buy or borrow an oscilloscope and a signal generator, then build a lot of coils in pairs (cylinders, conical or cones, pancakes, and toroidal or toroids). Experiment with these coils in as many configurations as you can think of, and you will begin to see what works and what doesn't. After that you will be able to build any wireless system of your dreams.

    Anyways, have fun and good luck!
     
  17. zero_coke

    Thread Starter Active Member

    Apr 22, 2009
    294
    1
    Hehe, thanks man, I appreciate that guide :) If only signal generators weren't so expensive :(
     
  18. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Yeah, it was eating the conductors but this dopey test was relatively brief. Generation of Hydrogen is number two on my list of asinine things I did when I was young and stupid. That story is for another day though...:)
     
  19. -SK-

    Member

    Apr 14, 2009
    25
    0
    zero coke,

    To make a matching pair of tuned LC circuits, you need to figure the frequency (fr) you want the circuit to resonate at. From that fr you can determine capacitor and inductor values. One of the elements should be variable, in order to easily 'tune' the circuit. Then build both circuits and then them up!

    I would recommend getting some kind of simulation software (pspice) and simulating your design first. That way, you can play with the values easily double-check your math, and (most importantly :)) not waste any money on wrong parts.

    How you actually measure stuff depends on what kind of test equipment you have. If you have a good oscilloscope, and a function generator, you can look at the input and output signals of the circuit. Remember a resonant circuit also behaves as a filter, passing your desired frequency and rejecting others. So if you can supply various input frequencies and observe the output, and if your circuit is correct, you will see that the magnitude of the output is much smaller than the input, except when near the resonant frequency.
     
  20. -SK-

    Member

    Apr 14, 2009
    25
    0
    I also hope you are going to start 'small', and get the principles down before trying to connect to your wall socket and light your lightbulb.
    If your circuit functions correctly, you will have large resonant currents. If you use small low-power components to make the circuit, they will turn into smoke. Another advantage of running a SPICE simulation is that you will be able to see the magnitude of this current, and spec your parts appropriately.
     
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