Detect ~2kV - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: September 07, 2018, 06:14:52 pm
content: 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

author: james_s
author_rank: Super Contributor
timestamp: September 07, 2018, 06:40:50 pm
content: 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.

author: JS
author_rank: Frequent Contributor
timestamp: September 07, 2018, 06:44:15 pm
content: 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

author: Cliff Matthews
author_rank: Unknown
timestamp: September 07, 2018, 06:55:23 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: September 07, 2018, 07:24:53 pm
content: 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.

author: MarkF
author_rank: Super Contributor
timestamp: September 07, 2018, 07:34:17 pm
content: Sorry. I couldn't resist.

author: floobydust
author_rank: Super Contributor
timestamp: September 07, 2018, 07:45:12 pm
content: Fencers are usually capacitive discharge into a flyback transformer. So voltage is higher at no load.Seen an NE-2 and 500pF 20kV cap and 100k resistor for the indicator.High efficiency LED's are better than a neon lamp. Brighter and less current needed, try white/greens back-to-back and "something" to drop the voltage down.An old CCFL tube works too, with a ballast resistor.

author: SeanB
author_rank: Super Contributor
timestamp: September 07, 2018, 08:27:36 pm
content: Just grab an old CFL lamp and remove the base and electronics. clean the glass and then touch the wires to the fence wiring, while holding the bulb glass far away from the wires. it will flash with each pulse. if you do not have a old CFL use a PL lamp, any type, 7W, 9W, 11W, 13W, 18W and do the same, not touching the end with the wires, and they will do the same.

author: Gyro
author_rank: Super Contributor
timestamp: September 07, 2018, 08:42:56 pm
content: The traditional farmers' method is to touch it with a long blade of grass.

author: floobydust
author_rank: Super Contributor
timestamp: September 08, 2018, 04:41:35 am
content: Quote from: Gyro on September 07, 2018, 08:42:56 pmthen what happens? muh shoes are rated to 5kV

author: SeanB
author_rank: Super Contributor
timestamp: September 08, 2018, 10:15:20 am
content: Don't worry, you will feel it.......

author: metrologist
author_rank: Super Contributor
timestamp: September 08, 2018, 02:07:20 pm
content: I remember peeing on electric fence when I was a kid - no drama. I opened this unit and saw a simple transformer and a small HV ceramic cap. I made a small arc gap between the terminals and plugged it in, and got a good burst of sparks. I wonder how long this can take a short circuit?

author: Zero999
author_rank: Super Contributor
timestamp: September 08, 2018, 05:07:34 pm
content: My four year old nephew got a horrible burn on his chest from an electric fence.An ordinary multimeter can measure up to 1000V, just add a 1kV rated 10M in series with it or perhaps 10 × 1M resistors if you can't get one rated to 1kV. The trouble is it's pulsed, so that might not work, as the meter might not respond fast enough. Perhaps a 2kV bridge rectifier and 100nF capacitor before the 10M resistor could be used to get a smooth DC voltage.

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2018, 05:12:39 pm
content: Quote from: metrologist on September 08, 2018, 02:07:20 pm

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2018, 05:34:59 pm
content: Quote from: Hero999 on September 08, 2018, 05:07:34 pmI think you'd want a bit more protection for your multimeter than that - I'd go for a high voltage x10 divide (90M).

author: Zero999
author_rank: Super Contributor
timestamp: September 08, 2018, 08:37:40 pm
content: Quote from: Gyro on September 08, 2018, 05:34:59 pmI agree. There's no point in pushing the DVM to its limit and you'll get the same level of precision, i.e. decimal places, on the 0 to 200V range, as the 1kV range.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 08, 2018, 08:46:10 pm
content: Quote from: MarkF on September 07, 2018, 07:34:17 pmYou must be cold then.

author: rstofer
author_rank: Super Contributor
timestamp: September 09, 2018, 04:01:31 pm
content: I wouldn't use it to actually touch the fence but it should be able to detect the voltage from a small distance:https://www.fluke.com/en-us/product/electrical-testing/basic-testers/fluke-1ac-ii

author: ahbushnell
author_rank: Frequent Contributor
timestamp: September 09, 2018, 04:13:41 pm
content: Quote from: JS on September 07, 2018, 06:44:15 pmI think fences put out pulses.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 09, 2018, 04:35:08 pm
content: this should warn you from some safe distance... no spark zap, no chest burn no pain whatsoever, the only sensation is the ears and the eyes. not cost more than your cheap unit..