electromagnetic coils

Discussion in 'General Electronics Chat' started by dcd528, Jul 10, 2013.

  1. dcd528

    Thread Starter Active Member

    Jul 28, 2011
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    I am planning a project that requires an electromagnetic coil which would be powered by AC at 13 amps and 125 to maybe 600 volts. The coil needs to be switched on and off at frequencies of 20 to 2200 Hz with the possibility of taking the high end switching to 20,000 Hz.
    Is there a transistor that could handle this voltage and current? I am envisioning biasing the transistor with a signal generator and running the unit off of standard 120 or 220 volt AC initially and possibly going to higher voltage later. Any input is greatly appreciated.
    thanks
     
  2. wayneh

    Expert

    Sep 9, 2010
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    What you are describing is essentially a 8kW audio amp. :eek: I'd look to buy one rather than build it. Then you can send whatever signal through it you want.

    There are ways, and components, to do what you want but 7800 watts is a lot of juice!

    When you say AC, do you mean pulsed DC (current in one direction or off) or true AC (current in both directions)?
     
  3. JDT

    Well-Known Member

    Feb 12, 2009
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    What is this electromagnetic coil actually going to do? The numbers in your post don't make much sense.

    Why the voltage?

    How much do you know about back EMF that will be generated when you switch this coil?

    Tell us more. We might be able to come up with some helpful ideas.
     
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Can't wait to see what this is supposed to be for.
     
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  5. dcd528

    Thread Starter Active Member

    Jul 28, 2011
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    Ok, sorry I was so late getting back on this. I recently built a Doug Coil machine. The design used a frequency generator that fed an audio amp. The output of the audio amp goes through a capacitor bank, it has 15 capacitors and a bank of toggle switches so you can pick one or more caps. The designer says that when you use the correct capacitor value for the frequency you are using the power output is being pulsed at that frequency. The output is feed into a large coil of 12 gauge copper wire, the magnetic field generator. The gadget cost me about $1700 to build. It seemed to work in that when I exposed myself to the pulsing magnetic field I actually felt better. I used various frequencies, one for muscle relaxation, one for a tooth infection and one for arthritic problems. Nothing was cured but I felt much better in each of these areas. Seems you could do the switching with a transistor and just power the coil with 120 Volt 15 amp. If that isn't enough power I am guessing 220 would be. The design I worked off of has some caps rated at 600V but I believe the current is limited to 13 amps, it is just plugged into the wall.
    If you search PEMF you will find a lot of info on this. Chronic Lyme disease sufferers claim this is about the only thing that helps them. I am looking to help myself and provide the info free to anyone else who wants to try it not make money.
    thanks for looking
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Wow. Any idea how much current you're actually pushing? 12 ga wire looks like a short to most things.

    Or, any idea what the impedance of this coil is? Maybe you could post a picture.

    You must deflect compass needles for miles. ;)
     
  7. Metalmann

    Active Member

    Dec 8, 2012
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    "It seemed to work in that when I exposed myself to the pulsing magnetic field I actually felt better. I used various frequencies, one for muscle relaxation, one for a tooth infection and one for arthritic problems. Nothing was cured but I felt much better in each of these areas."





    I could use some of that!:D
     
  8. dcd528

    Thread Starter Active Member

    Jul 28, 2011
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    The coil was 2" wide, 11 layers of wire with a 6"diameter hole (air coil, no core). It measured 5.5 mHenries using an inductance meter. Don't know how many gauss it produced.
     
  9. LDC3

    Active Member

    Apr 27, 2013
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    Actually, it doesn't seem to be that much. One of the web pages has a coil that produces a region with a field strength over 100 gauss. According to Wikipedia, a small iron magnet can have 100 gauss and a NIB magnet can have 2000 gauss.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Interesting. Using a core would help a lot but I suppose that has drawbacks of its own.

    The effect you describe sounds a lot like MENS or CES, two acronyms for micro currents applied across the ear lobes. I built one of those devices for a friend and I can attest to the profound effect it has. I was highly skeptical and tried it on myself, and made the mistake of turning it up too far when I didn't perceive an immediate effect. A few minutes later I felt very strange. :cool:
     
  11. BobTPH

    Active Member

    Jun 5, 2013
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    Move to CO or WA. They have just legalized a substance that also makes you feel better. And you should be able to get quite a bit of it for $1700.

    Bob
     
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  12. wayneh

    Expert

    Sep 9, 2010
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    Haha, but the device I built was only ~$5. That won't go as far. ;)
     
  13. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Where does the power GO??

    If the driver needs 8kW to generate a frequency into a coil, where does the 8kW go? Into heating something near the coil?
     
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  14. wayneh

    Expert

    Sep 9, 2010
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    Most would have to be dissipated into the coil's windings, and that's why I doubt there is anything near that much power involved. It would glow and melt. Even if you surrounded the coil by flesh, the permeability of flesh is so low that there just couldn't be much load on the coil.
     
  15. jmoffat

    Member

    Jul 18, 2012
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    The amplifier in the web site is 1800 watts. Also there is an array of 5 resistors in parallel on each channel. I didn't see the ohms value on the resistors but still that's a lot of power in a small space. Treatment times started a 15 seconds and could last up to 1/2 hour.

    I have seen induction heating machines for heating machined steel pieces and they used 10 kw triodes in a colpits oscillator arrangement with 1/4" copper tubing as the resonant heating coil. The tubes and coil were water cooled. Water and high voltage, electro-shock therapy anyone?

    Question, why is it necessary to have the coil rsonate? The project would be so much simpler without the capacitor box.
     
  16. wayneh

    Expert

    Sep 9, 2010
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    So you can sell a device that is a little harder to DIY? That's the cynical answer.

    The folks in the field would tell you that a sort of insulation effect builds up if the field or the current flow is constant. By alternating the field, pulsing it and so on, the effect is more potent at a given field level.
     
  17. dcd528

    Thread Starter Active Member

    Jul 28, 2011
    31
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    Assume that I am powering the coil with 120v AC and I have a signal generator that will bias a transistor. Can someone provide a schematic that would switch the transistor on and off at the rate set by the frequency generator? I found a dual mosfet switch online that seems like it might work but I would appreciate some expert advise.
    thanks
     
  18. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Exactly! It's doubtful that it is an 8kW resistive element "coil" and the likely situation is that it is a normal magnetic coil (ie; it is the primary coil of an air coupled transformer).

    There is zero need to put 8kW into the coil, unless his goal is to extract 8kW in power from some secondary (and we're assuming that power transfer is actually possible).
     
  19. wayneh

    Expert

    Sep 9, 2010
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    That's equivalent to saying, "assume I'm crazy". Please don't try that.
     
  20. dcd528

    Thread Starter Active Member

    Jul 28, 2011
    31
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    can anyone suggest a way of doing this with a transistor for switching the coil on and off? Assume it is run at 120v AC 15amps.
     
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