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|  File Name      : HVMEAS.ASC       |  Online Date     :  11/25/95          |
|  Contributed by : Jon Snell        |  Dir Category    :  ENERGY            |
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                           Measuring Kilovolts with
                             nothing but a regular
                                      VOM

                                      by

                                   Jon Snell


This file is intended for those who wish to begin their journey into the world
of High Voltage Experimentation. One of the things that bugged me was my
inability to measure voltages that exceeded 700 volts AC.

This made working with multi-kilovolt inverters kinda sticky business.  I
never knew exactly what my output levels were and I trashed many expensive
components. It now seems so basic and obvious to me now what the solution is
but it wasn't then.

I hope to save those who are as HV naive as I was from committing the same
dollar intensive mistakes.

The answer came from an old T.V. technician I know. He was from the old days
of (gasp) vacuum tube circuitry. "You need a voltage shunt!" Ok, what the hell
was this guy talking about? I honestly didn't know.


        >------------------------------------------------
                                                        |
   HV in                                                |
                                                        |
                       R1                R2             |
        >------------/\/\/\/\----------/\/\/\/\---------------->
                                  |
                                  |
                                  |                         Low Voltage
                                  |                            out
                                  |
                                  |---------------------------->


    V out = V in * ( R2/(R1 + R2))

    Just make sure you use resistors rated for at least 1 watt. Use a
    1 meg for R1 and a 10k for R2 for approximately 100:1 voltage
    reduction. Close enough to read a 50kv supply as 500 volts on the VOM.

    Make an adjustable spark gap on the HV input side in order to read
    voltage at the maximum arc length. Dead shorts into HV circuits usually
    dampen the oscillations.
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