Update

The circuit presented here works good, and I have used it successfully in my mountain trips to protect my tent and good from wild animals while on trails. I have developed a newer one, so choose whichever suits you best.
electric_fence_circuit_4 electric_fence_circuit_2

The Electric fence

Here is an electric fence perimeter protection circuit designed to run on batteries and provide configurable pulses of up to 20KV, to protect a tent perimeter against bears or other animals, out in the wild. It doesn't kill as the output current is limited, but it is definitely not for those with medical (heart) problems. So be advised to use extra care and awareness when constructing or deploying such a device.

As said, the high voltage generated is not dangerous because of the low current (and power), but it will produce intense pain. Similar circuits are being employed for pastures, and I've seen many in the mountains, in several countries I traveled to.

The circuit:

2011-09-02 21.05.14 20110825031022 20110825193033

The device uses two 555 timer circuits to generated a variable frequency, variable width pulses, that are used to drive an auto induction coil. For my design I've used a VW Bosch induction coil with excellent results. The power is provided by 8 AA 1.5V batteries, connected in series for 12V. The frequency and the pulse width can be adjusted using two potentiometers. The frequency specifies how often will the high voltage pulses be generated and so fed into the perimeter wire, while the pulse width influences the amount of energy fed into the coil, and so how much high voltage energy will be sent into the wire (more energy, more painful the discharge will be).

The circuit , the batteries and the induction coil are enclosed in a waterproof plastic recipient. The high voltage output should be connected to a loop of metallic wire placed around the protected perimeter. This high voltage line should be insulated from ground (use some plastic for that). The cold output should be connected to a good ground: insert a 50cm steel pipe or wire into the ground. Rocky soils or dry soils need a better ground (use a longer wire and bury it as deep as possible).

Circuit diagram:

fence_1
The PCB layout can be downloaded here: ElectricFenceVer1.0

Note: This will not work well with a flyback transformer used instead of the induction coil. A good quality induction coil is a must for this device to work as expected. If testing the output, make sure you set the device to minimum power, by adjusting the pulse width. The shocks at higher power are painful!

Test video:

The PCB Layout in PDF: ElectricFenceV1

Update Nov 25, 2014

Noe Lourenço Agostinho Nézocas mailed me a few pictures and even a video of his own construction of this electric fence. You can see them here.
electric_fence_pocketmagic_nezocas_3 electric_fence_pocketmagic_nezocas_2 electric_fence_pocketmagic_nezocas_1

Nice work Nezocas!

For those interested in building an Electric Fence, please note that there is an update version of this circuit, presented here.

Related Post