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Registered Member #62109
Joined: Sun Jan 28 2018, 10:00PM
Location: Porto Alegre
Posts: 56
I found this high voltage probe on a magazine called Silicon Chip. Here is the original project.
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, I would not hold that thing on my 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 on that place, 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.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
you can make them using capacitors too if you are only measuring AC, I never really finished mine, but it's something you can research if you are interested.
Registered Member #62109
Joined: Sun Jan 28 2018, 10:00PM
Location: Porto Alegre
Posts: 56
That is a very good idea there. Nice. Yes right now I'm only measuring AC. DC only when I was calibrating it... lol
I like the way your divider looks, both sides meant to go on hv. My probe can be dangerous if someone uses the "low voltage" end on hv or connect only 1 side. Thread from 2006... I think that year I was in school and I didn't even know about AC.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Yup. Built one a while back in a used white plastic solder casing but a small child destroyed it!
How the heck? Poked a *very* expen$ive projector with it, in just the right place to cause the power supply to short out. Fortunately the insulation held. The projector didn't survive
The parent of said small child then proceeded to lecture me about leaving my junk lying around and saw fit to destroy the probe with a pair of wire cutters and send it to the Special Hell (tm)
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HV probe, don't hold it with your hands...
