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Re: [Electronics_101] Re: HV measurement?

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  • Jan Kok
    Dave, Why do you want to measure the transformer output voltage? Is the lamp not turning on, and you re wondering if the transformer is OK? If you are in the
    Message 1 of 18 , Mar 2, 2013
      Dave,

      Why do you want to measure the transformer output voltage? Is the lamp not
      turning on, and you're wondering if the transformer
      is OK?

      If you are in the US, you have ready access to 120VAC. You could put 120VAC
      into the primary and expect 675VAC out. Maybe a bit more if the output is
      unloaded. Some meters will measure 750VAC directly without needing a high
      voltage probe.

      If you want to measure the floating transformer output under normal
      operating conditions, you could use TWO high voltage probes, or the
      equivalent homemade voltage dividers. Make sure to GROUND the bottom ends
      of the voltage dividers, connect the inputs of the voltage dividers one to
      each output of the HV transformer, and measure the voltage between the
      outputs of the two voltage dividers.

      Note that you don't need super high megohm resistors for the voltage
      dividers, because the current you will draw is insignificant compared to
      the currents normally flowing in the circuit. For example, you could use a
      10 Meg 1% 1W resistor and a 10K 1% resistor to get a 1000:1 2% divider.
      Just check the maximum working voltage spec for the input resistor is
      substantially greater than the voltages you expect to see -- and stand back
      when taking measurements anyway!

      If the lamp is not working properly, describe the symptoms and we'll try to
      diagnose it.


      On Fri, Mar 1, 2013 at 8:36 AM, Larry Beaty <lbeaty@...> wrote:

      > Excellent idea. However, expect 12AC in to give 270 Vac out.
      >

      Really? I would expect about 67.5VAC out. (Remember, normal input is
      480VAC.)


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