Electric Fence Checker

[bryan1]

Hiya Guy's,
Last night on the box a bloke was showing an electric fence checker that showed if the wire was live by just placing a unit close to the wire not touching it and the unit just sounded a beeper. He mentioned it picked up the static (electro magnetic interference) of the fence. Anyone got any idea's how this would work as I'd be keen to learn more about it.

Cheers Bryan

 

[ericgibbs]

Hiya Guy's,
Last night on the box a bloke was showing an electric fence checker that showed if the wire was live by just placing a unit close to the wire not touching it and the unit just sounded a beeper. He mentioned it picked up the static (electro magnetic interference) of the fence. Anyone got any idea's how this would work as I'd be keen to learn more about it.

Cheers Bryan

Bryan,
I would try a small portable radio, tuned OFF a channel, hold it close to the wire, [not too close] if its a pulsing fence you should hear a click, click.

 

[JimB]

Here is my best guess, see the attached sketch.

In the fence wire is a high voltage pulse, by holding the tester close to the wire there will be some capacitive coupling into the circuit in the box.
There will also be a resistive path the ground through our little stick man*.
At the junction of the capacitor and resistor there will be nice spiky pulses which can be used to trigger a beepy thingy.
So informing our man "dont touch this you great galah"

* a guy called LS Lowry became famous for this paintings of stick figures, which now command high prices.
How much for my magnum opus?

JimB (in frivolous mood)

 

[ericgibbs]

hi Jim,

* a guy called LS Lowry became famous for this paintings of stick figures, which now command high prices.
How much for my magnum opus?

JimB (in frivolous mood)

Don't give up your day job, just yet!

Regards

 

[ronsimpson]

I need to find electric wires under ground. (60hz 220v)
I built two different “boxes”. The first one worked much like JimB suggests where the antenna is a copper plate that capacitive couples to the power line. The second box picks up the magnetic flux lines from current in the wires. They both work.

I think detecting electricity in a fence is much easer. Higher frequency components, higher voltage, much closer to detector,……

Close to the barn there is serious current on the fence and much high frequency signals. A mile away the current is not detectable and much of the high frequency is gone.

When I was young there was a very good way to tell if the fence was hot. “Ha Bryan, come and touch the fence!”

 

[Andy1845c]

When I was young there was a very good way to tell if the fence was hot. “Ha Bryan, come and touch the fence!”

When I was a kid, I helped install an electric fence. When we were done I turned it on, and being stupid, touched it. I had rubber boots on and the ground was dry and I only felt a slight tingle. Not knowing anything about electricity, I thought it wasn't working right. Then with my other hand I touched the metal wire mesh along the bottom of the fence that was buried a few inches into the ground for several hundred feet. Pretty much knocked me over To this day I still shy away from HV projects.....

 

[Pommie]

I use to test our fence by touching it. I would have thick soled trainers (sneakers) on and the effect was just a tingle. One day I was out in the rain in bare feet, ended up in a load of mud and ended up touching the fence. Boy, did that hurt. I am now very wary of the fence when I have no shoes on. For the curious, it's quiet normal here to walk around shoeless.

FYI, here's a link to the device in question.

Mike.

 

[Sceadwian]

How about a pen style voltage detector?

**broken link removed**

That's Fluke's website they probably cost a fortune. You can find them cheaper by shoppnig around I'm sure.

 

[RODALCO]

I use one straw of green grass.
Hold it at the end and slowly slide it closer over the live fence wire.
You will feel a small tingle at some stage, depends also upon how wet the grass is.
The distance on the grass from when you feel the tingle will give you an approx idea that the wire is live.

 

[Nigel Goodwin]

Just throw a young kid on it, see how far he jumps!

What's wrong with kids today, we used to always be playing with electric fences as kids!.

 

[Marks256]

I used to test fences by just grabbing the wire as well. I never got anything more than a tingle, but then again, i was always wearing shoes.

 

[sam2]

I was feeding horses at a friends farm one day, it was raining and the ground was soaked and muddy.

I had a heavy bucket of grain in each hand and stepped right near a wooden fence that had an electric wire on it. My foot sank deep into a mud hole and I leaned against the wire, and could not get off of it.

I had touched electric fences many times, but ths was different, the pulsing shocks were much stronger than normal, my heart started skipping beats.

As I tried to get off the wire I thought about all the animals ( deer , rabbits turkey and snakes I had seen dead on and tangled in electric fence wires, and I thought, oh! thats how they all died!

After maybe 10 seconds,- I finally got off that damn wire and my heart was still skipping and I felt very weak and sick to my stomach.
I felt like crap for a couple of days after.
I was only 29 and in good health when this happend.

sam

 

[Marks256]

Well, you are still alive, so maybe you won't be joining that snake for a while more, huh?

 

[Speakerguy]

I always tested our electric fence for the dogs with the above mentioned blade of grass technique.

 

[Lesh]

The old style testers used a neon light with a current limiting resistor, and a nail you pushed into the ground

 

[Gordz]

You *can* pick up the pulses from an electric fence with a simple capacitive FET detector circuit. I designed several fence energisers with alarm and monitor circuitry for perimeter protection of small properties, with rubber soled shoes on a dry day it hurt like crazy ! I would NEVER have tried with bare feet. Testing the output without a direct connection was tricky.

 

[Hero999]

Just hold a neon lamp next to the fence and it should flash when there's a pulse.

Small fluroscent tubes will work and even an energy saving light bulb.