Home made HV probe

[AndreiRS]

Hi, not sure if this is the place to post this, but the hv section only has transformer and multipliers related topics.

I found this high voltage probe on a magazine called Silicon Chip. Here is the original project.
http://archive.siliconchip.com.au/cms/A_111937/article.html

And I can say that....... it doesn't work. Well the suggested resistance is way too high, 800Mohm. Just to show an example, if I blow some air into the probe it would read almost twice the voltage it was reading before. So I just looked for some technical specifications on a commercial probe available around here, it says 100Mohm resistance. Then I bought some 2 watts resistors, 60 of them, 1Mohm each and made the probe. Of course I ended with only 60Mohm, but for my voltage levels, that is enough and gives me more precision.

By the way, these things are supposed to be used with the ground side grounded before touching the hv with the probe. Since a lot of people would measure transformers, which don't have a grounded secondary, just forget about holding that thing on your hands. It could be very dangerous. I just connect both sides to the secondary and leave it far and alone.

Sorry for all the dirty around, I was working on a unfinished workshop.

Resistors around a brown pvc pipe, goes inside the white pipe. The hv tip ia a P10 plug with a copper wire soldered inside. Some silica gel to avoid moisture inside. And the wires that go to ground and to the multimeter. Also a trimpot and other resistors to calibrate the voltage divider.



The most important thing to avoid external interference due to the high resistance. Dip all in resin. I used fiberglass resin.



Some simple voltage doubler setup to calibrate it.



Left side is voltage from doubler, right side is milivolts after the probe.



Done. "Probe 1000:1".