Electronics > Beginners
Detect ~2kV
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metrologist:
This should not be a hazardous measurement as it is simply to detect whether my new electric fence is working. I'm not inclined to the acid test...

It would be interesting, though, if I could measure the actual voltage. Any suggestions? I thought maybe a flourescent tube close to the wire or even touching, with me holding the other end or grounded, would cause some illumination?

(p.s., I know they sell testers just for this, but they cost more than my cheap unit).

Thanks
james_s:
Capacitive or RF coupling ought to work just to detect that the output is there. A small piece of wire acting as an antenna placed within a few feet of the fence loop should pick something up. A NE-2 bulb held close to the fence wire will likely flash, or if you wanted you could connect it directly through a string of resistors.
JS:
A bunch of series resistors...

Build a divider, 2kV is not as much as you think, I don't know how much current you device puts but you can put 20 1MΩ resistors in series and measure upon the last one. If it's loading it too much twenty 10MΩ resistors could do better, or at least with both measurements you could tell the output impedance of the fence. Then read with your DMM, note than the DMM input impedance is probably about 10MΩ, so you can get a rough number with the 1M divider but for the 10M is a bit harder, the DMM could be the last resistor but you would need to measure it with a second DMM or you could try measure the current, 10µA would be your 2kV with the 20x10MΩ resistors.

The build of the probe is the more problematic matter, you could solder them in series in plain air and place them in a tube, The best choice will be to use some teflon spacers inside the tube, as using a teflon tube would be pretty expensive for your application. The tube could be PCV, or just use a PCV pipe with the end caps to hold both ends of the resistor string. In the 10MΩ version you just need access to the last one to measure current... well, this also applies to the 1M as you can do the same thing but now on 100µA for 2kV.

JS
Cliff Matthews:
10 x 2.2meg 1/2 watts in series? (space out and spray the whole lot with auto ignition spray and stuff down a 2ft. ABS pipe).
DMM across last resistor and GND. YMMzzzzzzap..  :-(   Maybe do it with Kevlar gloves.
james_s:
Electric fence chargers are very low current, they're designed afterall to shock animals without causing injury. It's similar to the output of one of those little piezo spark igniters, at least it feels about the same when you touch it. I still remember playing with the electric fence that was behind our property when I was a kid, daring my friends to touch it and whatnot.
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