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The significance of this is that the energy of the pulse cannot be controlled by varying the size of the capacitor feeding the primary, since the energy is fixed by the degree of magnetization of the core at the instant the "points" open, not in the capacitor feeding the primary. Pulse energy level can, however, be controlled by varying the voltage (and, therefore, the steady-state current) in the primary prior to opening of the primary circuit.
The circuit I posted uses PWM to control the output power of the ignition coil. The switch does not control frequency but pulse width. Frequency (1.5Hz) is controlled by R4, R5 and C4. For a higher frequency (pulse repetition frequency) R5 might be shorted or omitted.
Output pulse duration can be varied in three steps: 16.5, 24 and 32ms, hence controlling the strength of the magetic field in the ignition coil resulting in different high voltages with engery levels of 250, 400 and 450mJ.
We had one of those old style weed burner electric fencers when I was growing up.
It did not use a induction coil. It used a step up transformer and just put about 1500 volts AC on the fence! 5 seconds On 5 seconds off.
I could take the pulse fencers but not that one!
the easiest and cheapest way to check if high voltage is generated is a piece of isolated wire wound in several turns (4 to 6) around the HV-cable and connected to a neon-lamp (the same type which is used as signal lamp in rice cookers or other household appliances). Don't disconnect or omit the current limiting resistor (neon-lamps generally operate at 50VAC)
There is no current flow as long as nothing is being zapped, hence there is no voltage drop. So the wire length is of minor importance.
Electric fences are mandatory close to highways (Autobahn) in Germany to avoid cattle endangering road traffic. For a fence of a total length of 4km there is only one HV-generating circuit necessary. Normall the cirucuit feeds HV into two sides of a rectangle parallel.
Please refer to the sketch.
For a quick check you might also "P" on the fence.
I haven't read all the posts on here but here is some information and a true story that may interest.
I worked for an industrial electronics company in the 1960's that developed an "unshortable" fence controller. The secret to it was a very low source impedance, something in the order of a fraction of an ohm. This in-itelf meant that it was virtually "shorted-out" already (if you can get your head around that) and that putting anything else across the line would had virtually no-effect on performance. The output spike was in the order of 5kV, at around 100 amps per pulse, but the duration of the pulse was extremely short, in the order of microseconds, so as not to be lethal to humans. Any grass that came across the line was instantly vaporised! It could feed 100km's wire without appreciable loss at the far end. It found wide use where it was too expensive to install conventional fencing on large outback farms.
I know it wasn't lethal (and yes, it was legally compliant) as I took a "dare" from my boss (the designer) to actually take some pulses from it to see how it felt! I hesitated at first but when baited with an offer of $10 per pulse (a lot of money in those days), I eagerly took up the dare! I sat at a big table with the alligator clamps neatly laid out before me in two parallel rows. Grabbing them impulsively (pun intended), it seemed to take an eternity for the first pulse to arrive, as did the next one and finally the one after that. Although they were actually one second apart, it seemed more like ten seconds between each pulse - time definately did slow down. The shocks were like being hit in the chest by a train at 100kms/hr! The "slams" were massive and deeply felt, but being only 16 years old at the time I was able to withstand the energy and not have my heart stop, but my forearms were sore for days afterward. I wouldn't recommend anything as powerful as this really (we were all a bit silly in the 1960's), and suggest you seek out a ready-made and authority-approved unit in your area to avoid the possibilty of risk of injury to yourself or other persons.
Hello sir, can i use transformer for this fencer circuit,if yes can u tell me the no. of turns for primary and secondary.If no can i use ignition coil.
The CORRECTED, New Link is: http://chemelec.com/Projects/Fencer-1/Fencer-1.htm
The Transformer MUST be a CAR IGNITION COIL.
And it Must be the OLDER STYLE as used in Older Cars.
Not the Newer Electronic Ignition Types of coils.
Hello sir, can i use transformer for this fencer circuit,if yes can u tell me the no. of turns for primary and secondary.If no can i use ignition coil.
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