DIY Electric Fence Engergizer

Discussion in 'The Projects Forum' started by jgporteous, Mar 24, 2014.

  1. jgporteous

    Thread Starter New Member

    Feb 2, 2014
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    Hi everyone,

    I do volunteer work for the a local game reserve and with recent flood damages we have had some of our electric fence energizers submerged in water.

    I was hoping to build a low cost, simple 12V DC powered, Solar backed-up, Electric Fence energizer. I'm looking for a low AMP and high Voltage output which is pulsed, something that will NOT kill a human but will help deter animals.

    I need to be able to source the components locally and will etch the pcb board myself.

    I've done some google'ing and found many that use automotive coils, but I would like to try build a capacitor and transformer based solution.

    Would anyone be able to assist me with getting a template circuit/schematics I could create it from?

    The current fences give out from 2000V to 6000V. I would prefer around 6KV or a little higher :)

    Thanks,
    J
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a transformer from 12v to 6kv would be rare ad expensive. automotive ignition coils are available almost everywhere. if you were thinking of making up a tesla coil type, they dont shock much, not very much current and the high frequency flows on the surface of he skin (skin effect) .
     
  3. jgporteous

    Thread Starter New Member

    Feb 2, 2014
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    Hi,

    thanks for the reply.

    are you saying that a coil is the most inexpensive and safest option?

    J
     
  4. wayneh

    Expert

    Sep 9, 2010
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    I think you will be challenged to accomplish this for less cost than just buying an off-the-shelf commercial product.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    An ignition coil isn't just a coil, it's a transformer. True, it's a flyback transformer rather than a traditional, continuous conduction type, but it will give you 6 kV with way less effort than a traditional ps design. What is the peak current requirement and period? For example, 6 kV @ 1 amp for 10 milliseconds out of every 5 seconds, or something like that.

    ak
     
  6. jgporteous

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    Feb 2, 2014
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  7. wayneh

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    I prefer the first one because of the better documentation.

    If it was capable of unsafe operation, and I'm not saying it is or is not, you could always tone it down by limiting current through the primary coil. I believe you would do this by increasing the resistance of the 20Ω resistor. You have to assume some knucklehead will come along and turn up the dial to see what happens.

    Also, check out figure 10.4 of Bill's blog. It shows a similar circuit but simpler because it uses a MOSFET for switching the coil. This would be more efficient, and could be used for that circuit you've already found.
     
    Last edited: Mar 24, 2014
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Ibtl :)........
     
  9. crutschow

    Expert

    Mar 14, 2008
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    An ignition coil is safe because it generates a short, low current pulse. If it were dangerous there would be a lot of dead auto mechanics. :rolleyes: The output voltage can be adjusted by the value of primary current (controlled by the 20Ω resistor in the first referenced circuit by jgporteous). Too high a voltage will tend to jump the insulators, particularly when the insulator is dirty and moist. Note that the capacitance of a long fence will tend to reduce the peak voltage.

    To minimize power consumption use CMOS type LMC555's for timing, set the pulse rate to no more than 1pps and the ON pulse time as short as will still give a good output spark. The minimum should be around a ms for typical ignition coils. If you do all that, the average current draw should only be a few mA. Thus it wouldn't take a very large solar cell to keep the battery charged. 10AA NiMH batteries could provide 12V and power the system for at least 10 days without charging. Add at least 500μF across the circuit power rails to help provide the high current pulse when the coil is turned on.
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I have built the one using the two 555 timers, and using a mosfet to drive a car ignition coil, works a treat on horses, runs from a 12v batt.
     
    Last edited: Mar 24, 2014
    wayneh likes this.
  11. jgporteous

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    Feb 2, 2014
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  12. AnalogKid

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    This is a very different animal from the earlier parts of this thread. It runs continuously rahter than making a series of pulses, and it runs at a much lower power. If you are thinking of using this to drive a long fence wire, it probably will not make much of a shock over long distances.

    Back to your question. Image c3 tells the tale. In something like this, very low cost for high volume offshore manufacturing, the transformer is almost certainly custom designed for this specific circuit. With just one active component, this probably is a blocking oscillator driving the primary. The secondary drives a Cockroft-Walton voltage multiplier that ends in the big cap.

    http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator

    ak
     
  13. jgporteous

    Thread Starter New Member

    Feb 2, 2014
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    Hi AnalogKid,
    Thanks for that.

    I am aware this circuit doesn't pulse, I thought I could start simple, get the concept of HV working, then upgrade the components and put in a 555 timer to get the pulsing.

    I just googled blocking oscillator, this is interesting, if I built a small circuit with this and an LED, should I see it flash?

    Do you think the "Cockroft-Walton voltage multiplier" is used to charge the big cap, and the big cap give the HV, or it is responsible for the HV with the output of the CAP?

    I've tried contacting local suppliers to ask for help in getting a circuit and components to build an electric fence energizer (one without a motor coil and with components they supply), but they all recommend buying a ready built unit - where is the fun in that?

    J
     
  14. wayneh

    Expert

    Sep 9, 2010
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    As did I. The fun is in having a couple beers with your friends with all the time and money you saved by not trying to do it yourself!

    But I understand the urge to create. I'm building myself a router table right now, and I'd have a hard time justifying not just buying one. ;)

    I'd go back to the circuit you identified earlier. Tried and true, and easy to build.
     
  15. jgporteous

    Thread Starter New Member

    Feb 2, 2014
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    mmmm, if I was to use the first circuit, as posted, what transformer could I use instead of a car coil?
     
  16. crutschow

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    Mar 14, 2008
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    What's wrong with a car coil? Their relatively cheap and readily available.
     
  17. jgporteous

    Thread Starter New Member

    Feb 2, 2014
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    I'd like something that looks a little more professional :)
     
  18. AnalogKid

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    Aug 1, 2013
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    A CRT TV or monitor flyback transformer might have more of the electronic component look you want.

    ak
     
  19. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The old style, round coils really shouldn't be used at ~12V anyway. They are really 6V coils, 12V was only on them during engine starting/cranking. When the key went to "run", a ballast resistor is put in the circuit to supply ~6V.

    If you want a "more professional looking" coil, get one from a 'high energy' HEI type ignition. They ARE made to run at 12V.
     
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