Electric fence energiser

[Chris Bacon]

I've done this with your 12V battery, ignition coil, flasher unit, and a capacitor.

[Chris Bacon]

The flasher unit off a car, obviously. ISTR the capacitor came out of a fluorescent tube fitting, dunno whether a car one would be OK, you could try it.

[Andrew Mawson]

I made one to keep foxes at bay using a Maplins 'ignition amplier' kit and a normal ignition coil. The 'ignition amplifier' was driven by another Maplin kit indended for delayed wipers. Works very well though I had to change the capacitor values to get short pulses at about half second repetitions

AWEM

[The3rd Earl Of Derby]

My effort, modifications can be implemented, any comments?

little rabbits pass by the PIR it triggers the energiser.

-- Sir Benjamin Middlethwaite

[The3rd Earl Of Derby]

oops! no negative connected to coil negative from coil should link to trigger side of relay

-- Sir Benjamin Middlethwaite

[MikeW]

That's the type of thing I was considering Retail energisers seem to run at about 500ma but a cars HT coil seem to take >2amp (input) So I was wondering what was inside the black box to conserve power.

[Dave Plowman (News)]

Car ignition systems have short HT leads usually made of a resistive material to cut down RFI. And the whole lot (usually) shielded by grounded metalwork. Think the average fence might just act like an aerial...

[Grunff]

They don't use car ignition coils, they use much smaller custom transformers.

You can wind your own using a TV flyback secondary, but flybacks are quite hard to get hold of these days.

[MikeW]

But with an elec fence there is no spark and hence no current flowing so no RFI Until something completes the circuit and gets Zapped.

I think :)

[robert]

I've always used old car batteries (one duff cell) for electric fences

- they last weeks between charges.

Without looking up the details they usually give about 5kV pulses of

0.1 - 1 Joules at abou 0.5 Hz.

There is a BS standard !

You can get some low electric netting to use against rabbits or use 2 or 3 strands of wire close together.

Robert

[Rob Morley]

That's not such a silly idea - if the impulse was triggered when something nudged the wire you wouldn't have to run it continuously.

[John]

You should be able to produce something with a UJT circuit but personally I wouldnt bother. Go around the car boot sales and see whats on offer. Over the last few years I have bought two for a fiver (uses four D cells) and eight quid (uses an external car battery) respectively. Both worked fine although the on/off switch on one had lost its rubber "boot" which cost about 50 pence to replace

John

[John]

Yes at silly money. One has just gone for £62. plus carriage

[Tim S]

The fence will exhibit capacitance to earth and there will be a pulse of current flowing in on the rising pulse, then discharging back through the coil.

A small capacitance admittedly, but combined with a fast rising high voltage pulse. It's bound to generate some RF, but how much I have no idea.

But it's unlikely to be any worse that any other electric fence gear based on the same tesla coil principle.

The OP could test it crudely with an AM radio at various distances from the fence - asking the question - "would I be pissed off by this if I were a neighbour?".

Hardly a scientific method I know, but if he's managed a peculiarly efficient interference generator by some freak of physics, it should be obvious :)

Cheers

Tim

[usenet]

We have a moderately high powered electric fence energiser for our fields - it's rated to energise 50km of fence if I remember right, I expect I could look up the actual energy in Joules if anyone is really interested. It does produce audible clicks on Radio 4 on long wave on a radio which is actually within part of the fenced area. We are in South Suffolk so the Radio 4 signal is adequate but not very strong.