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How to build a 3amp-min Circuit.

  1. Aug 5, 2006 #1

    I am trying to build a 3 amp-min circuit and measure the magnetic field generated along the wire, but having problems figuring out how to build a stable circuit.

    I have a:

    DC power supply (150V 3amp),
    insulated copper wire
    rehostat (Which I think I have a wrong one as it glows red hot when placed in the circuit, and was beginning to smell).

    Any links and tips on what I could do to generate a magnetic field around 50V/3amp would be great. The above is just the setup I am imagining which may be far off. (It's maybe the most inexpensive or maybe there is a better option).

    Help is most appreciated.


  2. jcsd
  3. Aug 5, 2006 #2


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    Staff Emeritus
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    Gold Member

    To get 3A from a 150V source, you must 50 Ohms resistance in the circuit. You did not say what gauge of wire, or how long your wire is.

    for a 50 Ohms resistance you need about 50,000ft of 10ga copper (this is according to my CRC handbook of Chem & Physics)

    If you are using 20ga wire it is down to 5000ft.

    So how much wire do you have and what gauge is it?
  4. Aug 7, 2006 #3


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    Staff: Mentor

    And that 50 Ohm power resistor will dissipate 450 watts. This experiment sounds a bit ill-conceived, xszaui. Can you please post more details about exactly what you are trying to do, so that we can help you design the experiment to be safe and acheive your goals?
  5. Aug 13, 2006 #4
    More details


    I am trying to build an exploded version of a quartz oscillator.

    Pictures of something similar can be found at:

    However, commercial versions are always magnetically shielded or coated with metal which distorts the field making it near impossible to measure the magnetic field.

    The voltage I would like to apply is 50V and 3 amp-min of DC current. The resonant output of the quartz oscillator should produce a magnetic field ('if I understand the articles correctly').

    I dont know if I need to have a very thin sheet of quartz or there is a way to make a whole uncut crystal resonate. This is my first time working with piezo electrics and I'm pretty new to building circuits in general.

    Help would be most appreciated.


  6. Aug 14, 2006 #5


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    Staff: Mentor

    No. They are hermetically sealed for a different reason -- long-term stability of the oscillation frequency.

    No. There is no significant magnetic field involved in quartz crystal oscillators.

    And you sure as heck don't need 50V and 3A to run a crystal oscillator. Crystal oscillators are low-power, low-voltage circuits that are used to provide a stable timebase. If you want high power oscillations, you start with a low-power crystal oscillator circuit, and then amplify the voltage waveform output from the oscillator. You don't try to build a 150W crystal oscillator.
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