On 06/15/2014 04:15 PM, Maynard A. Philbrook Jr. wrote:
In article ,
says...

MY friend would like me to help him build a cheap electric fence. I found lots of designs, and of course we could go solid state but the simplicity of this one really intrigues me.
I showed him the schematic and he questioned if the repeated opening and closing of the flasher points used in this application would quickly burn them out. I was thinking that in spite of the inductive component, the load of the coil would be much less than the load imposed by a lighting circuit. So I thought that combined with the correct capacitor and perhaps the addition of a small snubber circuit (a small resistor in series with the capacitor) would cut down on the
sparking. Perhaps I'm way off base here. Does anyone have any opinions on this or has anyone ever done this? This uses a standard automotive ignition coil. Thanks, Lenny

Make a capacitor discharge into a car coil via an scr.

Use a pulsed DC to charge the cap at a high rate so they'll be
a gap in the supply to the cap. Use a timer to trigger the
scr which shorts this cap to ground.

The pulse being in the DC to charge it up has a void of no current in
the off duty part of the pulse (Diode) and allows the SCR to turn off so
the cycle can repeat itself.

if you're doing all of this from low voltage you can use a 556 timer,
this would be the DUAL version. One timer is used as a pulse generator
to charge the cap while the other would be the long duration
pulse to supply a very short duty pulse with long off time.

Some designs use the falling edge of the charging pulse to charge up
a cap on for the trigger pulse to the scr so that it's asynchronous and
that circuit will discharge that cap for the next whack on the cattle's
body!


Have fun.

Jamie


Why not just use a flyback transformer? Do cars even have coils these
days? There are tiny flybacks on each sparkplug wire. Run by computers,
not distributors. More efficient. Babbling.