can you power a motor with RF

Discussion in 'Wireless & RF Design' started by zemanekj, Mar 25, 2019.

  1. zemanekj

    Thread Starter Member

    Jan 31, 2019
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    I've been reading, and am seeing that the when you wirelessly transfer power using RF the current that is transferred is to small to actually run something like an electric motor but will light an LED. can somebody expand on this for me?

    I thought about trying to power a 24v electric motor I have with RF but don't want to waste my time.

    Thank you.
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Don't waste your time trying to run a motor this way. Didn't you have another thread asking the same question a month or so ago? What many that put this type of thing out there are calling "wireless transfer of power" are doing it inductively at a very, very close range it isn't using RF, but just the same principle as a transformer does. Don't believe everything they say on Youtube.
     
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  3. Yaakov

    Well-Known Member

    Jan 27, 2019
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    Calculate the number of Watts you would need (Volts *Amps) multiply it by the efficiency of the power transfer, being hypergenerous we’ll say 80% (.8).

    This is the power your transmitter would have to produce to power your load even giving the system an unrealistically high efficiency.

    What do you think?
     
    Last edited: Mar 25, 2019
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  4. zemanekj

    Thread Starter Member

    Jan 31, 2019
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    So at 24 volts times .81 amps = 4.32 watts. Thus 4.32 watts times (lets say %50) = 2.16 watts. To be honest I'm not sure if that's a lot of power or not. Is that a lot of power for RF? I'm sorry if that sounds like a really dumb question. I am always learning and have to be okay with sounds dumb sometimes haha.
     
  5. Yaakov

    Well-Known Member

    Jan 27, 2019
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    That's backwards, sorry. .5 is how much will make it through, so double the input. ~10W.

    For scale, a Wifi transmitter produces about 1/4W tops. 10W of RF would produce enormous interference with electronics around it.

    You can't use microwave without risking damage to things nearby, including people. If you use lower frequencies, the antenna gets far too big. If you move farther away you quickly have to double the power.

    So, it's just not practical.

    For a sense of this, imagine powering the motor from solar panels, using LED lights. Imagine how bright the lights would have to be. This is a visible analogy for the radio transmitter.
     
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  6. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    It's because of our present technology. If we could build gamma frequency lasers, we could transmit/transfer very large amounts of power with RF, much larger than any power grid.

    And we need new detector materials. To convert extremely high frequencies into current, or separate charge.....without heat.

    The material industry is making progress, but it is very slow.
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    What kind of motor are you talking about and what distance is involved?

    Why do you want to use RF as opposed other other frequencies?
     
  8. shortbus

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  9. zemanekj

    Thread Starter Member

    Jan 31, 2019
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    a 24V DC motor. And I am not opposed to other frequencies. Are there other more practical frequencies to use?
     
  10. zemanekj

    Thread Starter Member

    Jan 31, 2019
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  11. Yaakov

    Well-Known Member

    Jan 27, 2019
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    You need to characterize your requirements better.

    What will the distance be between the transmitter and receiver?
    Why are you avoiding a wired connection?
    What is the peak current requirement?
     
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  12. zemanekj

    Thread Starter Member

    Jan 31, 2019
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    The distance would be less than an inch. I'm avoiding a wired connection just for experimentation's sake. And I'm not sure what the current requirement is....the specifications on the motor states that the amps for the motor when it has a load is .18 amps.
     
  13. Yaakov

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    Jan 27, 2019
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    The trouble is there's no legal way for you to transmit enough power for this experiment. You'd have to contain it and not have it radiate, not a simple thing.

    There is no band where you can transmit so much power without a license.

    The closest you could get is to use a microwave oven magnetron as the radio source, but that's a scary idea. There is a reason people use tiny loads.
     
  14. zemanekj

    Thread Starter Member

    Jan 31, 2019
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    I was afraid of that. Yeah cancer isn't on my to do list so I'll put this on the self for now. Thank you for the help Yaakov!
     
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  15. ian field

    AAC Fanatic!

    Oct 27, 2012
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    There is at least one documented prosecution of people "stealing electricity" in some country or other - they were all living in the shadow of an AM broadcast transmitter and found it was possible to harvest enough energy to run at least lighting.
     
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  16. sparky 1

    New Member

    Nov 3, 2018
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    Studies done around the Tesla wireless demonstration and SV Avramenko also relates to a one wire system.
    While running a motor with RF can be done, it is weak.
    It is believed that the magnetic component is responsible for the work capacity.
    There is some disagreement on how the magnetic content is utilized in an open system.
    The experiments show improvement in near field vs the far field and one wire and better ground has improvement
    over wireless.
     
  17. Glenn Holland

    Active Member

    Dec 26, 2014
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    Sounds like you're trying to use something like a Tesla Coil to radiate power into free space.

    There is a large Tesla coil in Griffith Observatory in Los Angeles and it will light fluorescent tubes and neon signs at about 15 feet, but the power falls off rapidly as the distance increases. A Tesla coil is an AC transformer and to run a motor, there would have to be some kind of rectifier on the receiving antenna.
     
  18. shortbus

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    Lights maybe motors I'd be skeptical on.
     
  19. ian field

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    Old filament house bulbs were about 100W - and an electric toothbrush motor...…………….
     
  20. shortbus

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    But not induction motors like an appliance.
     
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