AU2005100855A4 - More Efficient Operation of an Electric Fence Energiser - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 INNOVATION PATENT SPECIFICATION Name of Applicant: Pakton Developments Pty Ltd Actual Inventor: Paul Thompson Address for Service: Pakton Developments Pty Ltd PO 1068 Burpengary Q4505 16 Ferrier Rd Narrangba, Q4504 Invention Title: More Efficient Operation of an Electric Fence Energiser Details of Associated provisional Application: 2004905876 filed 13 October 2004 This invention is described in the following statement: n MORE EFFICIENT OPERATION OF AN ELECTRIC FENCE

SENERGISER

O FIELD OF THE INVENTION The present invention relates to electric fences and, in particular, to energisers for electric fences. Although the invention will be described with In In particular reference to energisers that are used in farm fencing applications, it oO 00 will be appreciated that the invention may be employed with energisers that are used in other fencing applications.

In c BRIEF DISCUSSION OF THE PRIOR ART Electric fences are widely used on farms to restrict the movement of both farm and feral animals. Such fences normally include a number of uninsulated wire conductors strung on supporting posts from which they are insulated. The conductors are coupled to an energiser that periodically outputs a high voltage pulse to energise the conductors so that an animal will receive a small electric shock if it contacts the energised conductors. Electric fences are also used as a perimeter security system for industrial premises and detention centres.

Energisers that are used to energise electric fences may be mains or battery powered. Most modern energisers include a discharge capacitor, a capacitor charging circuit for charging the capacitor to a high potential (e.g.

several hundred volts), and a capacitor discharging circuit for discharging the capacitor to produce a very high potential output pulse several thousand volts) that is used to energise the fence conductors.

The capacitor charging circuit is typically a voltage converter circuit that converts the relatively low supply voltage powering the energiser to the high voltage required to charge the capacitor.

The capacitor discharging circuit typically includes a semiconductor switch and a step-up output transformer that are both coupled to the capacitor such that the capacitor is able to be discharged through the transformer's primary winding by closing the switch to thereby produce a high voltage pulse across the transformer's secondary winding that can be used to energise the

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O fence conductors.

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Due to the very rapid rate of rise of voltage of the energiser output O pulse, electric fences can be the source of electrical interference in N 5 telephones, televisions, radios and other communications equipment. Also it is known that to best energise to the end of very long electric fences, a longer smoother pulse shape is better than a shorter sharper pulse.

00 In order to prevent large amounts of electrical noise being emitted, and Oto produce an output pulse shape suitably matched to the electrical S io characteristics of the typical fence load applied to it, energisers often include Scomponents to change the shape of the output pulse. These components are placed in the primary discharge circuit. These are usually a series inductor and a parallel capacitor across the transformer primary. These components form a resonant circuit and a low pass filter. This filter removes undesirable and unproductive high frequency components from the output pulse.

To withstand the high voltage and very high currents present in the capacitor discharge circuit, these components must be physically large and relatively expensive, therefore the inclusion of these pulse-shaping components can significantly increase the cost to manufacture these energisers. They may also reduce the efficiency of energy transfer from the main capacitor through the transformer due to the energy dissipated in the resistance of the inductors windings.

It is an object of the present invention to provide an electric fence energiser that overcomes, or at least ameliorates, one or more of the deficiencies of the prior art electric fence energisers mentioned above, or that provides the consumer with a useful or commercial choice.

SUMMARY OF THE INVENTION According to an aspect of the present invention there is provided an electric fence energiser for energising the conductors of an electric fence, the energiser including a pulse shaping circuit, a discharge capacitor, and a capacitor discharging circuit for discharging the capacitor to energise the fence conductors, wherein the discharging circuit includes an output transformer having a primary winding which the capacitor is discharged 0 through, the energiser being characterised in that the capacitance of the pulse

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Oshaping circuit is on the secondary of the transformer rather than the primary.

Leakage inductance in a transformer comes about due to an imperfect O coupling of the primary to secondary windings and is usually considered to be a parasitic and detrimental effect. The use of the capacitance on the secondary of the transformer allows the leakage inductance of the transformer to act as part of the tuned circuit, instead of being merely a parasitic element.

00 The value of typical leakage inductance of transformers (measured in micro Ohenries) used in medium to large energisers, is of the same order of S1io magnitude as that of the series inductance usually chosen for the tuned circuit Sof the pulse shaping components.

This effect reduces the size of, or eliminates entirely, the required value of the series inductor. This, in turn, reduces resistance in the primary circuit and increases the efficiency of transfer of energy from the main discharge capacitor to the energiser output.

Since the value of a capacitor on the output is multiplied by the step up ratio of the output transformer when viewed from the primary side, the value of the pulse shaping capacitance may be reduced by this ratio. However a capacitor on the output must have a higher voltage rating. This is easily achieved by using a series connected bank of inexpensive 240Vac mains capacitors. A further benefit is that by moving this capacitance to the output it improves the resilience of the product to lightning surges that may be conducted into the unit from the fence terminal. To protect the capacitor from excessive rate of rise of current (first derivative with respect to time) a series resistor may be added.

BRIEF DESCRIPTION OF FIGURES In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate typical preferred embodiments of the invention and wherein: Figure 1 is a schematic circuit of a prior art electric fence energiser; Figure 2 is a schematic diagram of an electric fence energiser according to a first embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS c Referring to Fig. 2, an electric fence energiser 10 according to an O embodiment of the present invention includes a charging circuit 1, a discharge S 5 capacitor 2, and a discharge circuit 11. The capacitor charging circuit 1 charges the discharge capacitor 2 to a predetermined voltage. The timing In circuit 3 then gates the semiconductor switch 5 on, in this case an SCR, to 00 discharge the capacitor through the series inductor 7 and the primary of the Sstep up transformer 4. The series inductor, plus the leakage inductance of the I io transformer act together with the capacitor on the secondary 6 to form a low Spass inductor capacitor filter which acts to remove the unwanted higher frequency components from the output waveform. The cut off frequency of the low pass filter is described by the equation: 1 f= f 2 -L C Where C the capacitance on the secondary multiplied by the turns ratio of the output transformer and L is the combination of the leakage inductance of the transformer referred to the primary plus the inductance of series inductor 7. The inductor 7 may be smaller then for the prior art circuit due to the additive effect of the leakage inductance of the primary winding.

The above represents only one embodiment of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the invention. For example the series elements, the inductor, primary of the output transformer and the SCR in the discharge circuit may be arranged in a different order. Also the shape of the output pulse can be further modified by the addition of diodes in the discharge circuit.

Claims (7)

1. An electric fence energiser for energising the conductors c of an electric fence, the energiser including a discharge capacitor, a O capacitor charging circuit for charging the capacitor, and a discharging circuit for discharging the capacitor through the primary winding of a step up transformer to energise the fence conductors, the energiser In being characterised by a pulse shaping low pass filter circuit whose In oO capacitance is on the secondary side of the transformer.

2. The energiser of claim 1, wherein there is placed a In resistor in series with the pulse shaping capacitor.

3. The energiser of claim 1, wherein the capacitor discharging circuit includes an inductor in the discharge circuit.

4. The energiser of claim 1, wherein the capacitor discharging circuit includes a diode across the primary of the transformer.

The energiser of claim 1, wherein the capacitor discharging circuit includes a diode across the discharge capacitor.

6. The energiser of claim 1, wherein the capacitor discharging circuit includes an inductor-capacitor tuned circuit in the discharge circuit.

7. An electric fence energiser substantially as herein described with reference to Fig 2 of the drawings. DATED this 1 1 th day of October 2005 Pakton Developments Pty Ltd By PaulThompson