One of the nice features about the Emco-based high pot tester I built is it
requires only a simple fixed 12 VDC input. The variable voltage for the
output is controlled internally in the "cube" with an outboard 10 turn pot.
This avoids the potential instability (dropout) problems associated with
varying the supply voltage to what I presume is a bi-stable internal
oscillator in the average DC - HV DC converter. The device is current
limited internally as well. Although maybe not essential, it is nice to
know exactly what the voltage is to the DUT. One feature of this is when
you approach the breakdown voltage where current starts to flow through the
DUT, you can see the voltage sag a bit as the uA start to flow. I have had
many a dirty ceramic insulator on vac caps or amplifier tubes where there
may be 12 or 15 uA of current flow with no flash-over effect observed. If I
clean the ceramic with a degreaser like Formula 409, the cap will then have
NO or way under 2 uA of current flow at the same, well known, supply high
voltage. It is amazing what finger prints or other contaminants can do to a
DUT!
Whether testing with HV AC or DC, what matters is what the manufacturer
establishes as their product's testing voltage criteria. Disregard a
manufacturer's voltage testing parameters at your own risk!
73
Paul WN7T
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