Electric fence with solar cells. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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More than a century ago, it was discovered that a harmless electric shock could keep pets in a pen. Farmers and pastoralists put this discovery to good use. Thanks to the high-voltage wire laid along the perimeter of the paddock, it became possible, without resorting to an expensive solid fence, to restrict the freedom of movement of animals.

Unfortunately, very often livestock farm sites do not have a centralized supply of electricity needed to power an electric fence. Recently, batteries have been used to solve this problem. But rechargeable batteries need periodic maintenance and recharging, which makes the whole device quite cumbersome.

However, don't worry. Solar energy came to the rescue. After installing a small photovoltaic array, there is no need to change or recharge batteries.

Schematic diagram of the device

An electric fence requires only a low-power power source, which makes the use of such a fence more practical. The charger functions on the basis of a car ignition coil.

The coil works basically on the same principle as in the ignition system of a car. When the contacts of the breaker (in our case, the contacts of the relay RL1) are closed, a current begins to flow through the primary winding of the ignition coil, causing an increase in the magnetic field in the core of the coil.

When the contacts open, the current stops and the magnetic field begins to decrease. A changing magnetic field causes a voltage to appear in the secondary winding of the coil. Since the ratio of the number of turns of the secondary winding to the number of turns of the primary winding is very large, the induced voltage is also very high, more precisely 25 kV. This potential is quite enough to scare away any, even aggressive animals.

The relay is turned on by transistor Q1 for a short period of time (about 15 ms). During this short interval, a current flows through the coil, creating a magnetic field in the core. The duration of the on state of the relay is set by a standby multivibrator assembled on the logic elements of the CMOS structure, the time constant of the closed state is determined by the values ​​of C2 and R3. The launch is carried out by a self-oscillating multivibrator assembled on the remaining two elements IC1A and IC1B of the CMOS structure. In fact, this generator determines the number of pulses per minute, like a car breaker. The pulse repetition period is regulated by the resistor VR1 within 80-64 imp/min.

The last multivibrator also determines the duration of the charger's duty cycle. At the highest frequency (64 imp/min), the duty cycle takes 1,6% of the entire period of operation of the device, at a low frequency (30 imp/min) - 0,75%. Due to this combination of short duty cycle and the use of CMOS elements, the electric fence device consumes very little power.

Design

The scheme of the electric fence for simplicity is made using printed wiring. Although the circuit generally does not have any particularities in wiring, some care must be taken when working with CMOS elements.

CMOS cells are very sensitive to static electricity and must be handled with care. It is best to first fix all the elements on the board, and then carefully insert the integrated circuit and solder it with a soldering iron with a grounded tip.

The microcircuit, even after being installed on the board, is very sensitive to electrical interference and interference. Thus, the ignition coil must be placed as far away from the board as possible. The high-voltage wire must never run near the board!

When choosing an ignition coil for a circuit, remember that only a regular automotive coil will do. Modern coils for electronic transistor ignition circuits under the conditions mentioned will spark strongly in our circuit. You can take any coil from an old car model, however, you need to know some differences between different types of coils.

Some coils (for example, from a Volkswagen car) when turned on, give a powerful current pulse. Such pulses reduce the life of the relay contacts. You can select the current strength through the contacts that corresponds to the passport value using resistor R4, which limits the current through the primary winding of the ignition coil.

To prolong the life of the relay, you should use the capacitor that comes with the ignition coil. If you have one, put it in the circuit instead of capacitor C3. This capacitor reduces the spark between the relay contacts at the moment of breaking the electrical circuit.

Ris.1

Suppression of the high voltage pulse generated in the primary winding prolongs the life of the contacts. In addition, the capacitor and the coil form a kind of oscillatory circuit, the damped oscillations of which cause an increase in high voltage on the secondary winding of the coil.

You can look for high-quality coils that develop a higher voltage on the secondary winding compared to a standard coil. However, experience has shown that good results can be achieved with a conventional coil.

Ris.2

Ris.3

Electricity source

Now we have come to the part of the design that concerns the solar battery. As you have seen, some efforts have been made to minimize the energy consumed by the circuit. This reduces the requirements for the required power of the solar array.

The primary power source in the wire fence powered device is a sealed lead-acid battery called a gel cell. It is identical in performance to a conventional wet lead-acid battery used in automobiles. Unlike conventional lead-acid cells, gel cells are maintenance-free and can be installed in any position.

A Powersonic PS-1260 or similar battery has small dimensions (15x6x10 cm) and fits in one case with an electronic circuit.

To recharge the batteries, a solar battery is required, which should develop a voltage of 12 V at a current of 250 mA. There are several types of batteries on the market that meet these conditions.

With self-manufacturing of a solar battery, you can use elements split into four parts with a diameter of 7,5 cm.

A solar array of this size will generate about 3,6 watts. This corresponds to an average of 22 W per day or 1,6 Ah. Under normal conditions, a 6Ah gel cell is capable of powering the circuit without recharging from the solar battery for about 10 days, depending on the frequency of high-voltage pulse generation, battery temperature, etc.

Installation of a high voltage device

The installation of a high voltage fence device is very simple. Stretch a wire around the entire perimeter of the fence, which will then be supplied with high voltage. This wire must of course be insulated from earth. Ceramic insulators, which are commercially available at most hardware stores, are suitable for this purpose. Instead, you can use the necks of glass bottles.

Ris.4

The height of the wire suspension depends on the type of animals kept in the corral. For cows and horses, experience has shown that it is necessary to install the wire at chest level. The pulse frequency is also determined by the type of animal. In many cases, animals placed in a new pen need to use a high frequency. After a period of "accustoming" of animals to captivity, the frequency can be reduced.

To protect the battery from overcharging, a charge regulator is required. Suitable for this purpose this regulator. Use the low power transistor option.

The wire is connected to the high voltage output of the ignition coil. Reliable grounding is provided by a metal pin stuck into damp soil, or water pipes laid in the ground. It is strictly forbidden to use gas pipes for this purpose.

Now connect the batteries, set the pulse frequency, point the solar array to the south - and you get an electric fence!

Author: Byers T.

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