Wireless Power Transfer - TV

Discussion in 'The Projects Forum' started by maccwa_75, Aug 16, 2010.

  1. maccwa_75

    Thread Starter New Member

    Aug 16, 2010
    Hey everyone

    New here so please take pity. I am currently working on a 3rd year project to design a wirelessly powered television. Basically to confirm the premise that power can be transferred wirelessly. I have tested the theory before using a 1 Mhz signal generator inducing onto a secondary coil with an led in the field. That was successful. Im looking to enhance the demonstration.

    The design process is outlined below(This is the abstract i have used already) :

    o Convert AC signal to DC signal
    Using standard mains supply in Australia (240 Volt, 10 amps, 50Hz) and converting to DC will provide an easily manipulated and powerful supply.

    o Convert DC signal to high frequency AC signal(1 – 10 MHz)
    Using an oscillator circuit a high frequency (1 – 10 MHz) signal will be outputted to an amplifier circuit using high voltage DC source.

    o Amplify AC signal
    Designing a circuit to amplify the AC signal using rectified mains supply. The circuit will provide approximately 50 – 100 Watts across it. The circuit will incorporate the primary coil.

    o Receive AC signal through secondary coil
    The secondary coil resonating at a defined frequency will intercept the magnetic flux lines thus inducing a voltage.

    o Convert to DC
    The induced voltage will resonate at the frequency from the primary coil. Therefore it is converted to DC for use.

    that is the design process. Im sure of the fundamentals but im having great difficulty implementing. I need experienced brains to tell me the areas i need to look at. the osciallator circuit works perfect. I get a perfect 10 Mhz wave. I plan on putting it through an A.C coupled amplifier. Very simple and basic transistor circuit using a high bandwidth and high power transistor 2n3055. Im having considerable difficulty with the amplifier. Does the idea sound feasible? Any other methods of coupling high frequency with high power? Im currently doing a small scale demonstration of the project using approx 30 watts output. Can you guys think of problems with it? regardless of power efficiency etc?

    Also a fundamental question that im curious about. From the information i have read i have understood that higher frequencies or frequencies in the MHz range are ideal for this kind of transmission. Can someone describe why? I know it does but im unsure. Many thanks

    thanks in advance to any feedback.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    While hard to kill and able to output many amps, 2N3055's will not produce a usable output at 10 MHz.

    I have put in a link to STMicro's line of RF power transistors - http://www.st.com/stonline/stappl/st/com/selector/index.html#querycriteria=RNP139=1256.0 At a guess, they may be available down under. At any rate, you want to look for RF power, not AF power transistors.

    You can do a search on the site for the topic "witricity" to find a few threads that deal with it.
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
    Higher frequencies don't need as much inductance (or turns of wire) to form the resonant circuit.

    Before you get too involved in this you best check with your equivalent of the FCC as to how much power you can transmit in this frequency band, that limitation alone may stop your project dead in its tracks.
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    You will likely need a bunch of 2n3055's .

    10mhz is no joke when it comes to high power. As beenthere said, you wont get much usable power out of them at 10mhz.

    If no one here has a better option, I would contact some of the sales and tech guys at a few of the semiconductor manufacturers.

    An email stating what you want to do, a link to this thread, and a request for part numbers and/or samples for parts that may do the job better.

    They likely have put their parts through their paces, and know the higher power, higher speed devices in there repertoire.

    Analog Devices
    Linear Tech

    Hit them up and see what shakes loose.

    By the way, I would start gathering heat sinks and fans. ;)
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
    Kind of reminds me of the guy that ran a fence charger off his actual fence. It was (obviously) already insulated, and decent length of it ran under a HV overhead power line. Contrary to what you'd believe phase cancellation would contradict he was somehow able to "tune" the fence to 60 Hz and garner enough power off of it to rectify and keep a small battery charged. From this he powered a small photoflash type inverter from his junk box and fed that back into the fence. A lot of tinkering I'm sure, but the fence was in a remote area where no other power was available and doing things like this during the slow winter days gave him something to do.

    Now situations like this are handled with solar power but a few decades ago the cells weren't to be found at any sort of affordale price.
  6. Skeebopstop

    Active Member

    Jan 9, 2009
    Well mate interesting project.

    1. 10MHz, without a more sophisticated power stage, is going to probably end up requiring a linear amp. Your efficiency will be nerfed.

    2. You'd really probably want to be modulating the power through a very high frequency MosFET. Rule of thumb for MosFETs, the lower the voltage the fast they switch and the more current they can carry. To get efficient and up to 10MHz you're not going to need the higher voltages, keep it around 24VDC. Then you just modulate your sinusoid on a 100MHz PWM signal and LC filter it @ 20MHz to regain your 10 MHz signal. LC filters are nice for high current aka power. The LC filter on this output stage may create some serious havoc, so perhaps you can use the oscillation coil itself as long as you chop a square wave out fast enough!

    3. What will be the coupled inductance from the theory at the amplifier side? If it's too large 24VDC mightn't indeed be enough to get the power you are after. At 40% efficiency (only achieved by MIT), you'll be looking at having to generate 220W of output power to couple 100W < 2 meters. This means if you use a linear amplifier you'll be needing in the order of kilowatts of input power to get that kind of output.

    4. Reduce the distance and keep the coupling efficiency higher so you can use lower voltage. Run the calcs, what kind of power do you need to amplify? Having not seen one of the coils before, what does the circuit look like? Will they all be reactive components and where will the heat be generated?

    I fear my thread is running hopelessly long so I'll call a break here to ensure I don't overload your eyes.
  7. Skeebopstop

    Active Member

    Jan 9, 2009
    I wonder if a powerful enough square wave would hit a harmonic and resonate....?
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
    Harmonics will abound and most will not be welcome among the neighborhood. If the transmitting and receiving coils aren't totally shielded to prevent any RF leakage it's going to mess up a lot of things in the neighborhood and surrounding, won't be long until the authorities track it down either. Even if you can get it into a perfect sine wave it's going to need some fancy filtering.