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A Homemade Fence Charger, Energizer Circuit

A Homemade Fence Charger, Energizer Circuit

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.


Homemade Fence Charger, Energizer Circuit
Homemade Fence Charger, Energizer Circuit with IC 555 oscillator

Let’s diagnose the proposed electric fence charger circuit more deeply.

 Circuit Operation

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,


C4 = 105/400V PPC,


IC = 555

TR1 = 0-12V/3Amp (120 or 230V)

TR2 = 0-12V/1Amp (120 or 230V)




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 how an Ignition Coil could be applied for producing high voltage

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.

Circuit Operation

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

Transformer Specs

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.

Circuit Diagram

Simplest Fence Charge using Just a Couple of Capacitors

If you have an access to a 220V AC or 120V AC mains input within reach, then perhaps the following simple capacitor based AC fence energizer circuit could be used for the purpose without incorporating any kind of complex circuitry.

The capacitor may be selected depending on the level of electric shock needed for the application.

Note: Although capacitors are used for dropping the input current to significantly lower levels, still the output from this system may be large enough to kill any living thing if it happens to get stuck or entangled in the fence and is subjected to the current for a longer duration of time.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

85 thoughts on “A Homemade Fence Charger, Energizer Circuit”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Hello, I need your help
    I have assembled an Electric fence energizer from a commercial kit and it works perfectly with an old car ignition coil.
    The problem is that it ends with a 12V-7.2Ah / 20hr battery in less than 24 hours.
    And it is the same battery that feeds another Electric fence energizer of industrial manufacture for 3 weeks.
    Can any of you tell me how to reduce the consumption of this assembly?

    • Hi, you can try increasing R2, R4 to 470 ohms, or upto 1K.

      and decrease the value of the 33uF to 22uF or 10uF.

      Please check the results and let me know!

      • Hello, I appreciate your quick response.
        Now I am traveling, when I return I will make the changes you recommend.
        I will expose the results in this way

          • Hello again,
            I have made the changes you suggested and the results have not been as expected.
            When I decrease the value of 33uF, electric discharges are accelerated and consumption increases. I have tried to increase the capacity to 100uF and the electric shocks decelerate a bit, but the consumption does not decrease much.
            With the resistors I have increased its value up to 1K and, contrary to expectations, the electrical impulses have increased a lot.
            I do not understand the behavior of the circuit.
            I do not know what else to do
            Anticipated thanks

            • Hello,
              referring to this diagram:
              the circuit is a simple transistorized astable multivibrator where the two transistor sides oscillate alternately with a delay time determined by the values of R1/R3, and C1, C2, …or simply all the 4 components combined decide the ON/OFF intervals. Higher values will give higher pulse delays and vice versa.

              To avoid confusion it is better either to change C1/C2 or R1/R3.

              When the values of these components are equal on both sides then the pulse delay time is equal on both sides meaning we get 50% ON/OFF timing across the two transistor collectors.
              But suppose if you increase or decrease either C1 or C2 will result in the pulse delay across the transistor collectors to change and become un-uniform.

              In other words one of the transistors will produce narrow pulses while the other transistor will produce wider pulses.

              Narrow pulse will allow short switching time of the transformer and therefore low battery consumption and also weaker sparks, while the wider pulses will cause higher consumption and stronger pulses.
              So you have to identify with trial and error reducing which capacitor reduces the pulse intensity. Keep testing with reduced values until you identify the right consumption value.

              And increasing R2/R4/R5 values will definitely help to reduce the overall consumption because in doing so the switching current through T1, T2, T3 will reduce proportionately.

              Since T3 inverts T2 pulses, adjust one of the capacitors such that T2 gives wider pulses, this wll cause cause T3 to conduct more and reduce T4 conduction and help to reduce the battery consumption.

          • If someone had a circuit that does the same functions but with a reduced battery consumption, I would appreciate it very much.
            Greetings and thanks again

  3. Hallo sir, i want to make a flying insect killer from your mini fence charger circuit. so please suggest me which type /model/number ferrite core transformer should i use in that circuit ,instead of iron core transformer?? what are the values of c2,c3, c4 and c5 . does the c4 and c5 are ppc one ? thanks in advance

  4. Hi Swagatam,
    In my country we have a huge problem with armed car hijackers. I want to know if I can install your unit in a car so that it can be activated when you are high jacked. I want to connect it to the chassis of the car so that when the hijackers touch the car they will be shocked by the high voltage. Hopefully this will deter them and they will seek easier targets.
    Do you think this can work? I am especially concerned that high voltage can cause a spark in the fuel tank of the car.
    Kind regards

    • Hi Jan,

      I am afraid that may not be possible, because the car body is huge and this might make the impact very weak, and even if it was made strong it can't affect the intruder since the intruder would be wearing shoes, and without an earthing the shock would become ineffective, so the concept won't work as assumed by you.

      and yes the fuel tank is another crucial thing which might need to be considered…

  5. The charger design discussed here is not considered low-impedance output is it? If I understand correctly, a low impedance current would have a final transformer with a low ratio winding.

  6. Hello Swagatam,

    The circuit works,But,
    1)The output pulse length is short,if adjust the 1M pot.
    2)Not work with 12v Dc Battery.
    Pls help me.

    • Hello Thushara, the circuit will definitely work with a 12V battery but make sure it's rated at, at least 7 ah

      for increasing the pulse length you can try increasing the 1uF capacitor to 10uF and see the difference…and also replace the 22K resistor with a 100K pot so that you get an additional option for optimizing the PWMs

    • Hello Sanjay, the siren will need to be configured separately by using some other concept such as through an IR based alarm system or a vibration detector etc…It cannot be done within the above explained circuit…

  7. Thanks Swagatam, one more question, the high voltage bobbin I have has primary with marks 15 and -. The secondary of Tr2 going to one primary of the bobbin I suppose to + (15). From SCR , end going to minus (-) and earth of fence. End of C4 going to bobbin secondary. The other end of secondary bobbin going to fence(high voltage). My bobbin is from a car, and has short with one end of primary and one end of secondary. Will this work in this way?

  8. Ok, I will make my own. Can I use for example Myrra transformers to montage to pcb? The second Tr I have is 2×1.25A, is it sufficient or it has to be just 3A?

    • The transformers are ordinary step-down iron core type since these are supposed to be used with the 50/60Hz from the mains, ferrite versions will not work

    • Gom, 20kV can be difficult to measure with ordinary DMM….but it's not required…you can judge it visually…if the spark is able to fly across a 1cm gap or more then it's well over 20KV

  9. Sir, I have read your home made electric fence energizer and found very simple designed and cost effective. So m also planning to design one electric fence energizer with following parameters;
    Input 12v DC
    Pulse width 100micro secs
    Maximum output is 2joules
    working length is 200m to 40km.
    Therefore can you kindly advice me.

    • Gom, pulse width can be set by adjusting the 22k resistor value appropriately.
      however I am not sure about the joule calculation,, you can probably do it by yourself.

      for 40km length you may have to install many such circuits at appropriate intervals for enabling an effective outcome from the units.

  10. hi Swagatam
    i made this fence circuit but its working fine for 1 minutes
    after 1 minutes traic BT136 getting hot and spark stops
    whats cause for that ?

    • thanks for reply
      now am changing from 230 ac to 12 dc power supply options
      for that i am going to replace bt136 with tip122 and 1k resistor with 100 Ohms that connects to tip122 Base
      but i not sure with 3 legs of tip122
      1st leg of tip122 connect with output from timer 555
      2nd leg with TR2 and 3rd with ground wire
      is that correct ?

    • I can specify the leg orientation here, but it would be better if you check it through an image.

      just type and search TIP122 datasheet and you'll be able to get the complete info regarding the device, or you can click the "images" option in Google search for getting an instant view of the same

    • it will get hot, you will need to add a heatsink to it…..also try increasing its base resistance from 1K to may be 22k or even higher.

    • can tip122 replace with MOSFET irfz44 in 12v dc model or BT136 replace with MOSFET irfz44 in AC230 model to solve hitting problem ?

    • hello vikas, it could be implemented using a current sensor stage…..if possible I'll try to update it in the above article.

  11. Hy Swagatam

    i like your ckt but have some questions

    there is some difference in the part list and fig -2 also some parts from fig 1 also differ from fig-2
    so which is completely write part list or fig-1 or fig2


  12. dear sir
    i want to make solar fence enegiser. i m from chemical field so don't have technical info.so plz guide me for the same. can we have ready made circuit for energiser?

    • Hi Abu-Hafss,

      It's correct, the resistor can be any value between 2k and 10k as the triac would require just 15mA or even less to trigger fully.

  13. Hi Swagatam

    1) According to the circuit description, the right transfo should be labelled TR2 and the the left one as TR1.

    2) What is the purpose of the diode in the lower right corner, next to the capacitor?

    3) Is it important to connect one lead of the primary to one lead of the secondary, of the 2nd transformer?

    • Hi Abu-Hafs,
      2)the diode is for grounding the negative spikes.
      3) yes it's very important for providing the ground to the scr with reference to its gate voltage.

  14. a simpler solution is to pulse TR2 directly with the IC555 via a transistor or a mosfet and eliminate TR1 entirely from the CDI circuit.

  15. The capacitor accepts and stores the 220V input, and in the process when the firing limit of the SCr is crossed, the SCR fires and shorts the capacitor leads across the connected winding of the coil discharging the cap voltage into the coil. This discharge is stepped-up by the coil to the specified levels at the high tension output….so this is how it works.

  16. the negative terminal is the ground point.

    the positive terminal goes to C4.

    the central top cap is the high tension terminal.

    you may refer to this diagram


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