HV current measurement

Discussion in 'The Projects Forum' started by 95se5m, Jan 26, 2007.

  1. 95se5m

    Thread Starter New Member

    Jul 24, 2006
    8
    0
    Hello all,

    I need a bit of help, first my delma.

    I have 15KV AC being rectified to about 21KV DC {Full Bridge}. I need to measure the current and voltage of the output across a load, this needs to be constant monitoring as well. Basically building an HV power supply with panel meters to optimally adjust the voltage and current into a load. {plasma}

    I can do a voltage measurement with a 1000:1 resistive probe parallel to the output and a small 0 to 50v digital meter, this works quite well. The problem arrises however when I want to read the current. In Circuitmaker 2K I simulated a circuit using a 1K resistor for resolution inline with the HV. Worked in simulation, yet made the meter in real life go boom. :eek:

    I have considered the safest would be a clamp on style current measurement prior to the rectifier bridge, but I am a little lost on how to design such a measurement device. It would need to be able to read a 0 to 200ma scale with about a 1ma resolution +/- 5% is tolerable. Any direction pointing would be greatly appreciated.

    Jim
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    1Kohm is way too much for measuring 200mA, the power dissipation on the resistor is then I*I*R=40W..

    I would suggest somethin like 1ohm, which makes then 200mV on the resistor with 40mW dissipation. Then you can use any multimeter to measure the current, which is then equal to the voltage measured.

    Also it is wise to connect the shunt resistor to the grounded part of the circuit and not the 20kV, to get rid off problems with insulation etc.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    If your load is a plasma, then putting a 1 ohm resistor in to complete the circuit to ground may be a bit difficult. You could probably wire in a milliammeter after the rectifiers. I'd suggest placing it in a NEMA box with a clear cover to make sure the voltage doesn't come crawling out. The meter (I'd also suggest a Simpson analog movement. They're available through Newark Electronics, but you won't like the prices - but they are good meters) movement will have a low enough resistance that it won't arc over inside like a voltmeter would.
     
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