I am fairly new to the electronics scene, and have committed myself to several projects for the pupose of learning. I am attempting to build a tester for my electric fence around our farm, but I'm just not sure how to drop/control the voltage from the controller. I have been told that it is a DC voltage, and I know it's rated at 5kV. If I can get this voltage down into what I would consider a managable range (say, 25v) I could take it from there...

Any guidance would be appreciated.

 

Electric fences generally output a short high voltage pulse, it's probably not something that's easily measured?.

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hi,
I have made a number of electric fences for our farm [animals] in
South Africa.
If you ever require to make your own fence, goto a local car breakers
and get a 12volt car ignition coil, the series ballast resistor and the 2mFd
capacitor from the distributor.

Using a simple circuit to switch a relay on and off, say once a second you
can generate a high voltage pulse. The circuit is designed so that you can vary the 'dwell' time of the relay [ how long its closed for, which gives some control over the energy/voltage of the high voltage pulse] and the time interval between pulses. Power it from a 12v car battery.

As a test 'dummy' load I use an old spark plug. A rule of thumb is that a
1kVolt spark will jump across 1mm gap, so if you create a gap of 5mm and the
spark jumps it, you have at least 5kV. Keep opening up the spark gap until
spark fails. This will give you a rough guide.

As the impedance of the ignition coil spark generator is high, it will deliver
very little current and it is not lethal, but uncomfortable. Anyone who
has had a shock from their car ignition will tell you.

Regards
EricG

 

I always thought they were more along the line of 10kV. I know they make testers for fences that measure the voltage. Some are digital and some are neon like this one:
http://www.electricfence-online.co.u...hopscr180.html

I neon tester might be easier to make.

Just my advice as a fellow novice, but high voltage dosn't seem like a good starting point. Sure the fence won't kill you, but projects that run off a 9v battery will be easier and less painful.

 

a TV flyback xfrmr will also do the job.

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Try to measure with a string of 10 x 10 Mhm: resistors in series,
and have 1 x 1 Mhm: in series too.

So all up you have 11 resistors in series.

At 10 kV you get nearly 1000 volts across each 10 Mhm: resistor.
Across the 1Mhm: resistor you should get about 100 Volts which should be ample to lit a neon indicator ( which usually strikes at about 70 Volts)

Of course have the R's well spaced out on your tester and the 1Mhm: Res. will be at the end of the string with one leg to the ground.

It's not super accurate but it will give you an indication of the voltage level.
Also a neon imposes a negligible burden on the tester. provided it doesn't get too much overvoltage.
The neon striking voltage can be determined with a variable dc supply or mains variac driving a bridge rectifier.
Be cautious with mains wiring during testing of course.

If nothing lights up, reduce the 10Mhm: Res. string to 8 or 6 or less just to get the neon to pulse.
Than work out backwards how to get the fence voltage.
say 70 volts across 1M. and 10 x 10 M Res. about 7000 Volts makes 7700 Volts.

All Resistors rated at 1 Watts

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Electricity, Electric clocks, Meters and Trains are great.