The electric fence charger circuit presented here is basically a high voltage pulse generator. The super high voltage is derived from a commonly used automobile ignition coil.
An astable multivibrator is used to generate the required frequency to drive the ignition coil. Another astable is used to control the pulses supplied to the fence.
Protecting Crops with Fence Charger
If you have large agricultural fields and desperately need to protect the crops from uninvited guests like animals and possibly humans, then this electric fence charger device is just what you are looking for. Build and install it yourself.
An electric fence is an electrified high voltage barrier which produces painful shocks if physically touched or manipulated. Thus such fencing basically function as deterrents for animals as well as human intruders and stop them from crossing the restricted boundary.
The present circuit of an electric fence charger is designed and tested by me and has proved sufficiently powerful for the application.
20kV from the Sparks
The fence charger circuit is able to produce voltage pulses up to 20,000 volts, needless to say about the fatality rate involved with it. However the pulses being intermittent, provides the subject with enough time to realize, recover and eject.
The generated pulse is so powerful that it can easily arc and fly-off between short distances of around a cm. so the fencing conductor needs to be separated adequately to avoid leakages through arcing and sparking. If not tackled, may drastically reduce the effectiveness of the unit.
Here the generation of high voltage is primarily carried out by an automobile ignition coil.
The winding ratios of an ignition coil are specifically designed and intended for creating high voltage arc between a two closely spaced conductors inside the ignition chamber to initiate the ignition process in vehicles.
Basically it’s just a step-up transformer, which is able to step-up an input applied voltage at its primary winding to monstrous levels at its output or the secondary winding.
SOME POINTS OF THE CIRCUIT AND THE IGNITION COIL IS VERY DANGEROUS TO TOUCH WHEN POWERED. ESPECIALLY THE IGNITION COIL OUTPUT IS TOO LETHAL AND MAY EVEN CAUSE PARALYSIS.
Let’s diagnose the proposed electric fence charger circuit more deeply.
Simulation and Working
In the CIRCUIT DIAGRAM we see that the entire circuit is basically comprised of four stages.
A DC oscillator stage,
An intermediate 12 to 230 volts step-up stage,
The voltage collector and firing stage and the super high voltage-booster stage.
TR1 and TR2 are two normal step-down transformers whose secondary windings are connected through SCR2. TR1 input primary winding may be selected as per the country specification.
However, TR2 primary should be rated at 230 volts.
IC 555 along with the associated components forms a normal astable multivibrator stage. The supply voltage to the circuit is derived from the secondary of TR1 itself.
The output from the astable is used to trigger the triac BT136 and the whole system, at a particular fixed intermittent rate as per the settings of P1.
During the ON periods, the triac connects the 12 volt AC from TR1 to the secondary of TR2 so that a 230 volt potential instantly becomes available at the other end of TR2.
This voltage is fed to the voltage-firing stage consisting of the SCR1 as the main active component along with a few diodes, resistor and the capacitor C4.
The fired voltage from SCR1 is dumped into the primary winding of the ignition coil, where it is instantly pulled to a massive 20,000 volts at its secondary winding. This voltage may be suitably terminated into the fencing.
The high voltage generated by this electric fence charger will need to be carefully applied across the whole length of the fence.
The two poles from the ignition coil connected to the fence wiring should be kept at least 2 inches apart.
The pillars of the fence should be ideally made of plastic or similar non conducting material, never use metal and not even wood (wood tend to absorb moisture and may give path to leakages).
Parts List for the explained electric fence charger circuit using SCR
R4 = 1K, 1WATT,
R5 = 100 OHMS, 1WATT,
P1 = 27K PRESET
C4 = 105/400V PPC,
ALL DIODES ARE 1N4007,
IC = 555
TR1 = 0-12V/3Amp (120 or 230V)
TR2 = 0-12V/1Amp (120 or 230V)
THE SCR IS BT151,
THE TRIAC COULD BE ANY 1AMP/400V SUCH AS BT136
TWO WHEELER IGNITION COIL IS SHOWN IN FLUORESCENT BLUE COLOR
The above concept can be also implemented using a BJT for the generating the triggering pulses for the transformer, as shown below
Please increase the TIP122 base resistor value to 10K for reducing increased dissipation from the transistor.
Adjust the 1M pot such the ON time of the IC 555 is much shorter than the OFF time, for reducing current consumption.
Video showing the 20kv generation from a basic fence charger circuit set up on work bench.
Mini Fence Charger Circuit
The discussed fence charge above is relatively lager and stronger with its specifications, if you need something smaller, then the following mini fence charger circuit can be quite handy, an may be used for driving away pests like cockroaches, slugs, worms, snails from any desired small premise such a terrace garden, balcony pot plants or simply for guarding food stuffs etc.
Simulation and Working
The referred circuit for the mini fence charger is shown below, it may be understood with the help of the following points:
The top part of the transformer winding basically delivers a reinforcement to the base of the transistor by means of C2 the T1 keeps being confined on to the conduction status until C2 charges completely, ending the latch and compelling the transistor to commence the conduction sequence afresh.
R1 that may be a 1K resistor is installed to restrict the base gain for T1 to secure inhibits whereas VR1 that could be a 22k preset could very well be tweaked for acquiring an effectively pulsating T1 rate.
C2 could be additionally fine tuned by attempting supplementary values until the maximum output is accomplished at the trafo output
The transformer could possibly be any iron-cored step down transformer (500mA) commonly employed in transformer version AC/DC power supply devices.
The output immediately across the transformer output may be at the evaluated secondary level, for instance whether it is a 220V secondary, in that case the output could possibly be anticipated to be with this levels.
The above degree could possibly be even more heightened or stepped up by means of the connected diode, capacitor charge pump set-up corresponding to cockroft-walton power generator system.
The set-up boosts the 220V level to scores of volts that could be compelled to spark across an accordingly deployed finish terminals of the charge pump circuit.
The above end high tension end terminals could be appropriately wired up across the whole length of the area which needs to be guarded from the bugs and for implementing the intended fencing charging operations.
The fence charger wires must be separated by some minimum distance so that the sparks do no keep flying of even in the absence of any external intrusion from the insects.
The explained mini fence charger circuit concept could be furthermore utilized in mosquito swatter bat purpose by swapping the iron cored transformer with a ferrite core counterpart.