Picture of Reverse Engineering an Electric Fence Charger
Reverse engineering something can be a great form of both entertainment and education.  I’ve often purchased items just for the satisfaction of disassembling them to determine how they function and how they are designed.  Along the way you can learn a great deal, improving your own design and debugging skills.

The unit that will be investigated and described herein is what is called an electric fence charger.  It is the unit that generates the high voltage used to drive an electric fence for containing pets or livestock.

Personally, I find anything that generates high voltage is inherently interesting.  This applies to all high voltage items in general, be they Tesla coils, stun guns, automobile ignition systems, or whatever.  Hopefully you will find this investigation interesting and educational.

Of couse, since this also means that a safety disclaimer is in order:

The device described here is powered by 120 VAC.  Excercise caution when working with 120 VAC, as contact with it can be lethal!  Unplug any 120 VAC device from power when investigating it!

The output side of this device is used to drive an electric fence, and  can generate kilovolt pulses causing pain when contacted!

Exercise extreme caution when working with any high voltage device or 120 VAC powered device! Experiment at your own risk!
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alemail1231 year ago
excellent post and education, I thank you
That was most interesting, thanks! I am as well intrigued by the capacitive divider on the high voltage side, something to remember. But no, i am ignorant of the crescent shape reasons...

Another use of the circuit might be a power supply for Geiger tube circuit? You would run the input at a lower AC voltage, and rectify and regulate the secondary voltage to what is needed ( in this case, I am thinking of the 900Vdc or so tubes), and since they require very little current, Bob's your uncle. You might be able to control the dc voltage on the secondary by pre-loading the pulse counter on the primary as well, if this particular counter accept such operation.
jukees2 years ago
How can it be that there is a 16 electrolytic cap in mains, and also led's, i think your schematic is wrong
LargeMouthBass (author)  jukees2 years ago
Diode D2 rectifies the 120VAC input. Resistors R1 and R2, which total about 5k, are in series with the electrolytic cap, and limit to the current considerably. D1 is a 15V zener across the electrolytic cap, so it never sees a voltage greater than 15 V across it.
The LED is protected from reverse breakdown by D2, and the current is limited by R1 adn R2. (Refer to step 3 for details).

As I mention elsewhere, it is odd to see logic powered without any transformer isolation, but from the description I gave you can see how the circuit would in fact work. Its not the way I would design it, but it would be very cost effective.
if you dumped that huge voltage through a coil of wire you could probably make a coil/rail gun.
deaks3 years ago
When looking for datasheets in Google, I find it helpful to type the part number I'm searching for, the word datasheet, then "filetype:pdf" so that it will ONLY return direct links to pdf's.

It saves a lot of time searching through those datasheet linking websites looking for the link where you can download. It has a secondary benefit of sometimes taking you directly to the datasheet on the manufacturer's website.
LargeMouthBass (author)  deaks3 years ago
Thanks for the tip! I'll definitely try that next time I make a general google search for a part datasheet.
Sharp_Tack3 years ago
Well done. Interesting design uncovered.
TABULLO3 years ago
Ever tried to reverse engineer one of those inversors that activate the laptop backlight? Good instructable, souds ike you have fun doing it and that's great.
Fantastic post! I've had an accoutn on the site for a couple of years and have never commented. This was a wonderful, extremely well explained instructable. I've tried what you've done here with dollar store electronics for fun but this is well beyond any level of detail I've applied to reverse engineering those items.
Very good stuff, I am inspired.