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how do you limit 240 or 480vac current without lowering voltage

Discussion in 'High Voltage' started by jpoopdog, Feb 27, 2015.

  1. jpoopdog

    jpoopdog Member

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    basically i have a coilgun capacitor bank charger, doubling the output from a 5w car inverter. i want to step up to a 300W one i literally found laying about in my shed, didnt even know i had. In the end, ill be using a 50w dedicated boost converter, so, for experimentations, modifying coils, trying different coils, projectiles and so fourth, calculating efficiency, i want to charge my bank up faster, but, not too fast. charging a capacitor directly off mains is a moronic idea, hence the inverter.

    Now, i can imagine that the capacitor bank, having zero resistance, will immediately trip the inverter up, and 300W potential just feels too big, this being an inverter actually capable of 300W output.

    So, in my setup, my output voltage probably shouldnt be any lower, so a resistor is out of the question, besides being dangerous due to heat, so, besides a resistor, and given that soft starting is also out of the question, how do i limit the current, but not voltage, of the 240vac, 480vac or rectified 480v without sacfrificing voltage. the lower the voltage the longer it will take to charge the capacitors in the final percentage, as well as reducing efficiency i asume.

    i thought high frequency pwm of the rectified output but that somehow seems dumb, im certain theres a proper way to control the current.


    so, how should i go about limiting the current comming out of the inverter to around 50W
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    You get inside the inverter electronics and convert it from a constant-voltage output controller to a constant-current output controller. This requires getting very intimate with it, having schematics, and a lot of knowledge and experience...
     
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Can you be more specific? What is the maximum tolerable charge time to, say, 95% of full charge?
     
  4. dave

    Dave New Member

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  5. moty22

    moty22 Member

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    If the 240VAC is 60Hz You can use a coil instead of a resistor. A coil used for 40W florescent tube could be ok.
     
  6. kubeek

    kubeek Well-Known Member

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    I don´t see the reasoning behind that, the resistor will limit peak current, but will let the caps charge to the maximum voltage.
    What capactiance is your bank?
     
  7. RODALCO

    RODALCO Well-Known Member

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    Put a lamp in series with the supply. I charge up a 130 µF Cap bank up to 14 kV with a 200 Watt bulb in series with the 240 Volts supply of my 11 kV transformer. diodes I use are 15 x 1N5408.
     

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