HV Transformer

Discussion in 'General Electronics Chat' started by Doros, Dec 18, 2013.

  1. Doros

    Thread Starter New Member

    Dec 17, 2013
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    Dear all hello,

    this is my first appearance and question since I am a new in the electronics, and I need some help which I believe I can find here. I have a HV ignition transformer at 6kV, which I want to limit the current from 25mA which is now at 5mA. The reason is I want to have no arcs, just corona discharge. Any idea how to do it? By a resistor maybe?

    Many thanks for your help
     
  2. #12

    Expert

    Nov 30, 2010
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    6,833
    1.2 million ohms will limit the current to .005 amps. The difficulty is that the power could be as high as 30 watts on the resistor. It is difficult to find 1.2 million ohms in a 30 watt size, and the usual safety rule is to use a 60 watt resistor.

    In addition, a single resistor will be so small that 6,000 volts will arc right across the outside of it. This calls for several resistors in series.

    More likely to limit the current on the input side, but you're still looking at 30 watts of heat to get rid of.
     
  3. eeabe

    Member

    Nov 30, 2013
    59
    9
    If you have the option to change your circuit, a voltage multiplier is a good way to get a steady DC current at a high voltage, i.e., for a slow discharge to get a corona.
     
    inwo likes this.
  4. Doros

    Thread Starter New Member

    Dec 17, 2013
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    Many thanks, I know there are HV transformers that give 5mA max. I was wondering how they are doing that. Can a transformer be manufactured that is having a limitation in current?
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
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    Yes...............................................
    Another way to simulate the magnetic shut is series resistance or reactance in the primary. (if memory serves)
     
  6. #12

    Expert

    Nov 30, 2010
    16,346
    6,833
    Yes.
    Some are built with very tiny wires so the resistance and wasted heat is distributed throughout the windings. This is what is meant by, "impedance protected" which you often see on small motors.
     
  7. Brownout

    Well-Known Member

    Jan 10, 2012
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    HV transformers use magnetic shunts to limit primary magnetic flux that couples the secondary, which in turn limits output current. These shunts cannot typically be changed.
     
  8. Doros

    Thread Starter New Member

    Dec 17, 2013
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    So the only way for my project is to find a special HV transformer which limits by construction the currnet at the secondary. Trying to modfiy one, by adding resistances or capacitors at the primary or secondary is waste of time?
     
  9. eeabe

    Member

    Nov 30, 2013
    59
    9
    I wouldn't say that. I think like #12 mentioned, you could use some number of series resistors so you don't over power or over voltage them. A typical prototyping resistor is probably rated for 100V or 200V, so you would need quite a few in series.
     
  10. Doros

    Thread Starter New Member

    Dec 17, 2013
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    Any idea where I can find such a transformer?
    many thanks
     
  11. davebee

    Well-Known Member

    Oct 22, 2008
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    Corona discharge comes from high voltage, so why do you want any current flow at all? Why not run the transformer with the secondary open?
     
  12. Doros

    Thread Starter New Member

    Dec 17, 2013
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    just in case someone or something touches it to limit the current could flow
     
  13. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Find an old electrostatic plain-paper copier [ mita - savin - kyocera ] as salvage at an office store, a dedicated repair facility, or wherever you can locate one... There are a ton of other nice "toys" in the machines...

    The copier, to place the image on paper for the toner to be attracted to, uses a specifically designed corona transformer, that puts up very near the voltage you need, some give you a choice of AC or DC with very small amps --
    listed on the units anywhere from .01 mA to .08 mA .

    I was going to say I have a couple available, until I noted you are in Greece... :D Shipping would be horrendous, as these units are around 5 -15 pounds Avior depending on source...

    Good hunting... picture pending
     
    Last edited: Dec 19, 2013
  14. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    Not at all difficult.:confused:

    Here is some information.
    Tesla builders do it all the time.

    Search.........transformer current limit for tesla

    http://www.richieburnett.co.uk/ballast.html
     
  15. Doros

    Thread Starter New Member

    Dec 17, 2013
    20
    0
    Many thanks to all of you. I have plenty of info to dig in, and start and hopefully complete my project. I will inform you at the end. it will take a couple of months I believe. great help, excellent forum.
    Many thanks again
     
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