WO2003055284A2

WO2003055284A2 - Electric fence energizing apparatus and method

Info

Publication number: WO2003055284A2
Application number: PCT/SE2002/002272
Authority: WO
Inventors: Göran ALMHAGEN; Staffan G. A. Nilsson
Original assignee: Delaval Holding Ab
Priority date: 2001-12-11
Filing date: 2002-12-10
Publication date: 2003-07-03
Also published as: SE0104163D0; WO2003055284A3; AU2002366834A8; AU2002366834A1

Abstract

An apparatus for supplying high-voltage pulses to an electric fence is disclosed, the apparatus comprising a rechargeable power supply (1); a voltage transformer device (3) to step up the voltage; a storage capacitor device (5) for repetitively being charged and discharged, the charging being performed by means of connecting the storage capacitor device to the voltage transformer device; and a discharge circuit (7) connectable to an electric fence and to ground, respectively, for repetitively delivering electric energy discharged from the storage capacitor device to the electric fence to thereby supply the electric fence with high-voltage pulses. The apparatus further includes a circuit (11) for measuring the voltage of the rechargeable power supply, and a control unit (9) adapted to control the repetitive charging of the storage capacitor device depending on the measured voltage of the rechargeable power supply to thereby save energy when the power supply runs down.

Description

ELECTRIC FENCE ENERGIZING APPARATUS AND METHOD

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of electric fences, and more specifically the invention relates to an apparatus and a method, respectively, for supplying high-voltage pulses to an electric fence.

DESCRIPTION OF RELATED ART AND BACKGROUND OF THE INVENTION

In conventional electric fence energizers a capacitor is repetitively charged to a predetermined voltage and discharged through an output transformer. Such an energizer consumes a constant amount of energy for each pulse produced and is also typically designed to accommodate for variations in the fence load caused by grass etc. For energizers powered by mains this is not a serious problem, but for locally driven fences located far from a source of mains power the available energy may be limited, and such fences may run out of power with a reduced operating time as a result.

US 6,020,658 issued to Woodhead et al. discloses an energy- efficient energizer for an electric fence for controlling livestock or the like, which includes an output voltage sensor. By switching to extra storage capacitance and/or altering the charge voltage the energizer varies the duration of the output pulse and perhaps also the pulse voltage according to the sensed output, thus maintaining an effective livestock barrier and consuming high power only when required. Output pulses are about 8 kV (no load) down to 4 kV (wide range of loads). SUMMARY OF THE INVENTION

However, the energizer described by Woodhead et al. only saves energy when the load of the fence is high. At low loads there is no reduction in the energy consumption. While the overall energy consumption is probably reduced there are no provisions whatsoever for saving energy when needed, i.e. when the amount of available energy is low.

It is therefore an object of the present invention to provide an apparatus for supplying high-voltage pulses to an electric fence, which has an overall reduced energy consumption and which saves energy particularly when needed.

It is a further object of the invention to provide such an apparatus, which adapts its operation dynamically depending on available energy.

It is still a further object to provide such an inventive apparatus, which is uncomplicated, reliable, cheap, and easy to install and use.

It is yet a further object of the present invention to provide a method for supplying high-voltage pulses to an electric fence, which saves energy particularly when needed.

These objects, among others, are according to the present invention attained by apparatus and methods as specified in the appended claims .

By the provision of an electric fence energizing apparatus, which lowers its energy consumption when the battery runs down, the apparatus will adapt to the long-term available energy. If for instance the apparatus is provided with a correctly dimensioned solar panel for recharging of the battery the electric fence energizing apparatus will adapt to the energy delivered by the solar panel. During sunny periods the battery voltage will increase and the apparatus will operate at full power, and during less sunny periods the apparatus will operate at reduced output power.

Further characteristics of the invention, and advantages thereof, will be evident from the following detailed description of preferred embodiments of the present invention given hereinafter and the accompanying Figs. 1-4, which are given by way of illustration only, and thus are not limitative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 displays schematically in a block diagram a preferred embodiment of an apparatus for supplying high-voltage pulses to an electric fence according to the present invention.

Fig. 2 displays schematically in a flowchart an operation scheme of the apparatus for supplying high-voltage pulses to an electric fence according to the present invention.

Fig. 3 illustrates in a circuit diagram a particular preferred embodiment of the inventive the apparatus for supplying high- voltage pulses to an electric fence. In the circuit diagram resistors are denoted by R, inductors are denoted by L, capacitors are denoted by C, and diodes, thyristors and transistors are denoted by V.

Fig. 4 is a diagram of energy need versus fence load for apparatuses for supplying high-voltage pulses to an electric fence according to the present invention as compared to a conventional electric fence energizer. DETAILED DESCRIPTION OF EMBODIMENTS

With reference to Fig. 1 a general ^• embodiment of an apparatus for supplying high-voltage pulses to an electric fence according to the present invention will be described. The main components of the apparatus comprise a rechargeable power supply 1, such as e.g. a car, tractor, or semi-traction battery, a voltage converter or transformer device 3, preferably a flyback type of DC-DC converter, to step up the voltage, a storage capacitor device 5, a discharge circuit 7, and a control unit 9, such as a microcontroller.

The power supply 1, which typically has an output voltage of 12 V, is used to repetitively charge the storage capacitor device 5 via the voltage converter 3 , and to power the control unit 9.

The control unit 9 is adapted to control the repetitive charging of the storage capacitor device 5 via the voltage converter 3 and repetitive discharging of the storage capacitor device 5 via a triggering circuit 11. The storage capacitor device 5 discharges through the discharge circuit 7, which is connected to the electric fence and to ground, respectively, and as a result the electric fence is repetitively supplied with high-voltage pulses, typically of 5-10 kV, with a duration of a couple of hundred microseconds , and at a frequency of about 1 Hz .

To achieve good electrical connection to ground the discharge circuit 7 is connected to grounding rods, which are driven into the soil, preferably at moist areas. If there are problems with frost in the ground or sandy soil the electric fence may be provided with a separate ground wire. Such a described electric fence energizer, however, consumes not insignificant amounts of energy, and as a consequence the rechargeable power supply 1, at least in some applications, runs down rather quickly. In order to overcome such a limitation and to thus provide an apparatus for supplying high- voltage pulses to an electric fence, which apparatus saves considerable amount of energy when needed, the present inventors suggest incorporating into the apparatus the following features .

A power supply voltage measuring circuit 13 for measuring the voltage of the rechargeable power supply 1 is provided, and the measured voltage is transferred to the control unit 9. This measuring circuit 13 may in an uncomplicated version be a voltage divider.

The control unit 9 is then adapted to control the repetitive charging of the storage capacitor device 5 depending on this measured voltage of the rechargeable power supply 1 to thereby save energy. Thus, the control unit 1 lowers the level, to which the storage capacitor device 5 is charged, as the rechargeable power supply 1 looses capacity.

It shall be appreciated that the capacitor device 5 may be comprised of a single capacitor, but nevertheless several individual capacitors may be connected in parallel to obtain pulses of suitable energy (not explicitly illustrated) . If the energy is to be decreased one or several capacitors may be disconnected by means of a switch to achieve a suitable charge level.

Preferably, the control unit 1 controls the repetitive charging such that the capacitor device 5 is charged to a first voltage when the measured voltage of the rechargeable power supply 1 is above a threshold voltage and to a second voltage when the measured voltage of the rechargeable power supply 1 is below the threshold voltage, where the second voltage is lower than said first voltage. For instance, the first voltage may be the maximum possible voltage obtainable using the rechargeable power supply 1, the voltage converter 3 and the capacitor device 5, which should be at least 5 kV, preferably at least 6 kV, more preferably between 6 and 10 kV, and most preferably about 7 kV. The second voltage is advantageously selected to obtain an output voltage to the electric fence of not more than 5 kV, preferably between 3 and 5 kV, more preferably between 4 and 5 kV, and most preferably about 4,5 kV. The threshold voltage may correspond to a level where the rechargeable power supply 1 is charged to between 30 and 70 % of its maximum capacity, preferably between 40 and 60 % of its maximum capacity, and most preferably about half of its maximum capacity.

In such a manner higher voltage pulses are supplied to the fence when the battery capacity is good to have a very disagreeable effect on animals coming into contact with the fence, and pulses of lower voltage, still disagreeable for the animals, are supplied when the battery capacity runs down in order to save battery capacity and prolong the time period, during which the apparatus is capable of delivering high-voltage pulses to the fence without supply of further energy.

Below, there will be described a number of more inventive aspects that may be added to the above described low-battery- energy-reduction feature or may each be used as a complement or an alternative to the feature described. Virtually any of the aspects may be combined to arrive at a respective inventive embodiment of the present invention. Thus, one inventive aspect is to adapt the control unit 1 to control the repetitive discharging such the capacitor device 5 is discharged at a decreased frequency as the rechargeable power supply 1 looses capacity. For instance, the capacitor device 5 may be discharged at a first frequency when the measured voltage of the rechargeable power supply 1 is above the threshold voltage and at a second frequency when the measured voltage of said rechargeable power supply 1 is below the second threshold voltage, where the second frequency is lower than the first frequency. A typical first frequency would be 1 Hz or close to such value, whether the second frequency may be lower to much lower.

The inventive apparatus for supplying high-voltage pulses to an electric fence may further comprise any of a load measuring circuit 15 for measuring the load of the electric fence-to- ground circuit, a charge voltage measuring unit 17 for measuring the charge voltage of the capacitor device 5, an energy recovery circuit 19 for recovering electric energy from the energy discharged through the discharge circuit 7, a charge control circuit 21 to prevent the rechargeable power supply 1 from being overcharged, a solar panel or similar for charging the rechargeable power supply 1, a mode indicator 25 for indicating to the user a mode of operation of the electric fence energizing apparatus, and a main switch or similar (not illustrated), which connects the rechargeable power supply 1 to the voltage converter 3 and powers the control unit 9 , such that the apparatus can start sending out high-voltage pulses on the electric fence.

According to a further aspect of the invention the control unit 9 receives from the load measuring circuit 15 once for each pulse supplied to the electric fence a value of the instantaneous load of the electric fence-to-ground circuit, and is adapted to control the subsequent charging of the capacitor device 5 depending on this received value of the load of the electric fence-to-ground circuit. If desired the charging may depend on an average value of loads as measured during several preceding discharges .

In a preferred version the control unit 9 is adapted to control the charging such that the capacitor device 5 is charged repetitively according to a first charge scheme when the measured load of the electric fence-to-ground circuit is below a threshold load and according to a second charge scheme when the measured load of the electric fence-to-ground circuit is above that threshold load, where the average charging of the capacitor device 5 is lower using the second charge scheme than what would have been obtained using the first charge scheme at that load. The threshold load may be between 0.5 and 6 kΩ, preferably between 1 and 4 kΩ, more preferably between 1.5 and 3 kΩ, and most preferably about 2 kΩ, see further the discussion below with reference to Fig. 4.

A particularly preferred implementation of a load measuring circuit as an aspect of the present invention will be depicted further below with reference to Fig. 3.

In order to accurately control the charging the charge voltage measuring circuit 17 is used to measure the charge voltage during charging of the storage capacitor device 5. The control unit 9 is receiving repetitively indications of the charge voltage level and when a suitable charge voltage level is indicated, the charging of the storage capacitor device is completed. The energy recovery circuit is used to recharge the rechargeable power supply 1 with electric energy from the energy discharged from the storage capacitor device 5, which is not actually transferred to the electric fence. Energy recovery will be further discussed below with reference to Figs. 3 and 4.

With reference next to the flowchart of Fig. 2 a particularly preferred embodiment of operation of the electric fence energizing apparatus will be depicted.

The apparatus is, in a step 31, switched on, and, in a step 33, the battery voltage is measured. The battery voltage as measured is, in a step 35, compared with a reference or threshold voltage, which may as an example be identical with any of the threshold voltages as indicated above. If the battery voltage is higher than the threshold voltage the apparatus is, in a step 37 employing an operation mode referred to as a high energy mode, and the algorithm is returned to the battery voltage measuring step 33. As long as the battery voltage is higher than the threshold the apparatus keeps operating in the high energy mode.

However, when the battery voltage is not higher than the threshold voltage, the algorithm continues with a step 39, in which the load of the electric fence is measured, and thereafter, in a step 41, the load as measured is compared with a reference or threshold load, which may as an example be identical with any of the threshold loads as indicated above. If the load is not higher than the threshold load the apparatus is, in a step 43, employing an operation mode referred to as a normal mode, and if the load is higher than the threshold load the apparatus is, in a step 45, employing an operation mode referred to as a variable pulse mode. Subsequent to selection of operation mode the algorithm is again returned to the battery voltage measuring step 33. As a result the apparatus is employing any of the three operation modes at a time depending on available battery capacity and also when appropriate on the load as experienced from the electric fence.

The three operation modes are each depicted in the lower portion of Fig. 2. In the high energy mode, when the battery capacity is good, a suitable pulse frequency and a highest charging of the storage capacitor device is, in a step 51, adopted. In this mode the charge level has not really to be monitored if the apparatus is designed properly. Particularly during the high energy mode animals are taught to stay away from the fence as the high voltage energy of the pulses is experienced as strongly unpleasant by the animals .

In the normal mode, when the battery capacity is lower, but the load of the fence is low, the repetitive charging of the storage capacitor device is performed to obtain a fixed output voltage for the pulses supplied to the electric fence, which is lower than in the high energy mode. The storage capacitor device is, in a step 53, charged, preferably stepwise. During charging, preferably subsequent to each charging step, the charging level is, in a step 55, monitored. The charging of the storage capacitor device is then, in a step 57, completed when needed in order to obtain the fixed output voltage to the electric fence, and subsequently the storage capacitor device is discharged through the discharge circuit. In a final step 59, which is optional, the frequency, at which the storage capacitor device is discharged, is lowered as the battery voltage decreases.

Operation in the normal mode consumes less energy then when operating in the high energy mode, but still the high voltage energy of the pulses will have an unpleasant effect to animals coming into contact with the electric fence. In the variable pulse mode, when the battery capacity is low and the load of the fence is high, the repetitive charging of the storage capacitor device is performed to obtain a repeated cycle of pulses supplied to the electric fence, where the pulses in each cycle have different energy. For instance the pulses in a cycle may have a consecutively increasing energy. The average energy output to the electric fence in the variable pulse mode is lower than the average energy output obtained if the normal mode would have been employed at that load. The storage capacitor device is, in a step 61, charged, preferably stepwise. During charging, preferably subsequent to each charging step, the charging level is, in a step 63, monitored. The charging of the storage capacitor device is then, in a step 65, completed when needed in order to obtain a selected output voltage for the particular pulse in the cycle, and subsequently the storage capacitor device is discharged through the discharge circuit. In a final step 67, which is optional, the frequency, at which the storage capacitor device is discharged, is lowered as the battery voltage decreases . This frequency reduction may be identical with the frequency reduction in the normal mode, but alternatively the frequency reduction of the two modes may be performed differently.

Operation in the variable pulse mode consumes less energy then if operation in the normal mode had been employed at that load. Preferably, at least one pulse in the cycle has sufficiently high voltage to be unpleasant for the animals .

The control function described with reference to Fig. 2 as performed by the control unit is obtainable by designing or programming the control unit in a suitable manner.

In a practical environment with the solar panel connected and correctly dimensioned, the electric fence energizing apparatus will adapt to the long-term available energy, i.e. the energy delivered by the solar panel. During sunny periods the battery voltage will increase and the apparatus will operate in high energy mode, and during less sunny periods the apparatus will enter any of the normal and the variable pulse modes to save energy.

With reference, now to the circuit diagram of Fig. 3, a particular preferred embodiment of the inventive apparatus for supplying high-voltage pulses to an electric fence will be overviewed.

In the circuit diagram a connector is denoted by XI and has four terminals Xl-1, Xl-2, Xl-3 and Xl-4, to which the battery and solar panel (not illustrated in Fig. 3) should be connected. Suitably, the battery provides a voltage of 12 V and is connected with its positive pole to the terminal Xl-1 and its negative pole to the terminal Xl-2. The solar panel is connected with its positive pole to the terminal Xl-3 and its negative pole to the terminal Xl- .

The voltage converter is mainly comprised of a transformer TR1, a MOSFET transistor V8, and two diodes V4 and V3. The voltage converter is a DC-DC converter of the flyback type and steps up the 12 V battery output, such that the storage capacitor device, including a single storage capacitor denoted by C9, can be charged to several hundred volts .

The discharge circuit is mainly comprised of an output transformer TR2 having a core and primary and secondary windings, the primary winding being connected to the storage capacitor C9 and the secondary winding being connected to the electric fence and to ground. Further the discharge circuit includes a thyristor V5 for switching the discharge circuit to repetitively discharge the storage capacitor C9 over the output transformer and to thus supply the electric fence with high voltage pulses, which are stepped by means of the output transformer TR2 up to several kilovolts.

The discharge circuit further includes a low pass filter Ll, CI including an inductor Ll coupled in series with the transformer TR2 and a capacitor CI coupled in parallel with the transformer TR2 to reduce any occurring radio frequency interferences .

The triggering circuit includes a transistor VlO, a capacitor C5, resistors R8, R7 and R12, and diodes 9-1 and 9-2 and the battery voltage measuring circuit is comprised of a voltage divider including resistors R14 and R16.

The charge voltage measuring circuit is comprised of a voltage divider including resistors R1-R6, and R21.

The load measuring circuit includes a capacitor C3 and a diode V6 having an anode and a cathode, where the diode anode is connected to the capacitor C3 and the diode cathode is connected to the low pass filter Ll, Cl of the discharge circuit, and a voltage divider including resistors R4-R6 and R21.

Soon after the start of the discharging of the storage capacitor C9 a negative pulse is obtained in the low-pass filter Ll, Cl node connected to the cathode of the diode V6, the amplitude of which depends on the connected load at the secondary winding of the transformer TR2. The negative voltage is stored in the capacitor C3 by means of the diode V6. The voltage of the capacitor C3 is then read via the voltage divider R4-R6 and R21. The load measuring circuit as described is uncomplicated and inexpensive and no complex circuitry is needed. Thus, this circuit is considered to be inventive and is in fact a particular aspect of the present invention.

The energy recovery circuit includes the circuit from the output transformer TR2, via the inductor Ll, the thyristor V5, the battery, a diode VI, and back to the output transformer TR2.

This energy recovery circuit is closed during discharge of the storage capacitor C9 and when the storage capacitor no longer has sufficient charge to drive a current in the secondary winding of the output transformer TR2, whereby the remaining energy stored in the core of the output transformer TR2 is directed back to the battery in the form of a current to recharge the battery.

Note that the storage capacitor C9 is connected galvanically to the positive pole of the battery to provide for the energy recovery. This is in sharp contrast to conventional apparatus wherein the storage capacitor C9 is connected to 0 V.

By means of the energy recovery circuit energy not fed to the electric fence is brought back to the battery, and heat dissipation within the apparatus is to a large extent avoided.

The control unit is a microcontroller D2 and is powered by the battery via a serial, regulator Dl provided with filtering circuitry including inductors L2 and L3, a zener diode Vll, and two capacitors C6 and C7 to achieve the common 5 V input.

The microcontroller reads the battery voltage at terminal 18 and the load and the charge voltage at terminal 11 with the pulsref at terminal 11 held at +5 V when measuring the load and at 0 V when measuring the charge voltage. Thus, the pulsref should be held at +5 V at least during the initial phase of the discharging of the storage capacitor C9 and held at 0 V at least during the charging of the storage capacitor C9.

Further, the microcontroller D2 controls the charging of the storage capacitor C9 by means of a switch at microcontroller terminal 6, which connects the DC-DC converter to the storage capacitor C9. Typically, the switch is turned on repeatedly a short period, after each of which the charge voltage is read. Such a stepwise charging is continued until the charge voltage as read corresponds to the desired voltage.

Triggering of the thyristor V5 to initiate discharging of the storage capacitor is controlled from the microcontroller D2 via trigger terminal 7. When triggering is to be performed the output of the microcontroller trigger terminal 7 is set to +5 V to charge the capacitor C5 via the diode V9-2, where the current is determined by the resistance of the resistor R7. When the microcontroller resets the trigger output to 0 V, the transistor VlO is switched off and the capacitor C5 is discharged through the gate of the thyristor V5 and the resistor R8, and thus the thyristor V5 ignites and the discharging of the storage capacitor C9 begins .

If the thyristor ignites erroneously during charging of the storage capacitor C9 the microcontroller D2 will note this as the repetitive reading of the charge voltage during charging would indicate a decrease, and as a consequence the charging is interrupted and the storage capacitor is allowed to discharge, wherafter a delay may be introduced before next charging is performed.

The charge control circuit is comprised mainly of a MOSFET transistor V13, a Schottky diode V7, a transistor V12, and resistors R17-20, and is connected to the microcontroller via terminal 3.

Further components illustrated in the Fig. 3 circuit comprise a mode indicator including light emitting diodes V2 connected to the microcontroller via resistors RIO and Rll for indicating whether the battery is being charged or not, a clock circuit Yl for timing purposes and an error control circuit including a resistor R15 and a capacitor C8. Finally, polarity reversal protection is achieved by means of a PTC resistor Fl and the MOSFET V8.

The apparatus thus described is extremely user-friendly and cost-effective. There are no switches or regulators for altering operation mode or parameters and thus the operation is fully automatic .

Fig. 4 a is a diagram of energy need versus fence load for the apparatus for supplying high-voltage pulses to an electric fence according to the Fig. 3 embodiment as compared to a conventional electric fence energizer. The energy need of a conventional energizer is set to 100 % as shown by the solid curve, whereas the energy need for only, i.e. with the energy recovery circuit, in operation is shown by the dash-dotted curve. It can be seen that an energy saving of about 15 % at lower loads may be obtained, while the energy saving at higher loads decreases.

Finally, the energy saving using the energizer of Fig. 3 with energy feedback and operating in normal mode (as described above with reference to Fig. 2) is illustrated by the dotted line. As indicated the energy saving at low loads can be as high as 60 %, whereas at loads of approximately 3-4 kΩ to 500 Ω the energy saving is heavily reduced. For that reason the variable pulse mode, as described above with reference to Fig. 2, is introduced to be capable of saving energy also when the load is high. The load intervals when to switch operation mode as indicated above, i.e. 0.5-6 kΩ, 1-4 kΩ, and 1.5-3 kΩ, are selected with Fig. 4 in mind. Using variable pulse mode considerable energy saving is achievable also at higher loads .

It will be obvious that the invention may be varied in a plurality of ways . Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the appended claims.

Claims

1. An apparatus for supplying high-voltage pulses to an electric fence comprising:

- a rechargeable power supply (1) providing an output voltage;

- a voltage transformer device (3; TRl, V8, V4, V3) for transforming the output voltage of the rechargeable power supply to high voltage;

- a storage capacitor device (5; C9) for repetitively being charged and discharged, the charging being performed by means of connecting said storage capacitor device to said high voltage; and

- a discharge circuit (7; TR2, Cl, Ll, V5 ) connectable to said electric fence and to ground, respectively, for repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high-voltage pulses, wherein said discharge circuitry includes an output transformer (TR2) and a low pass filter (Ll, Cl) including an inductor (Ll) coupled in series with said transformer and a capacitor (Cl) coupled in parallel with said transformer,

characterized in

- a load measuring circuit including a capacitor (C3) and a diode (V6) having an anode and a cathode, the diode anode being connected to the load measuring circuit capacitor and the diode cathode being connected to said low pass filter of the discharge circuit, wherein a negative charge is stored in the capacitor, the negative charge resulting from a negative pulse obtained during an initial phase of a discharge of said storage capacitor device and the amplitude of which being indicative of the load of the electric fence-to-ground circuit.

2. The apparatus as claimed in claim 1 comprising a control unit (9, D2 ) adapted to control said repetitive charging of said storage capacitor device depending on the measured negative charge, of which the amplitude is indicative of the load of the electric fence-to-ground circuit.

3. The apparatus as claimed in claim 2 comprising a power supply voltage measuring circuit (13; R14, R16) for measuring the voltage of said rechargeable power supply, wherein said control unit ( 9 , D2 ) is adapted to control said repetitive charging of said storage capacitor device depending on the measured voltage of said rechargeable power supply.

4. A method for measuring a load of an electric fence-to-ground circuit in an apparatus for supplying high-voltage pulses to an electric fence comprising a rechargeable power supply (1) providing an output voltage; a voltage transformer device (3; TRl, V8, V4, V3) for transforming the output voltage of the rechargeable power supply to high voltage; a storage capacitor device (5; C9) for repetitively being charged and discharged, the charging being performed by means of connecting said storage capacitor device to said high voltage; and a discharge circuit (7; TR2, Cl, Ll, V5 ) connectable to said electric fence and to ground, respectively, for repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high- voltage pulses, wherein said discharge circuitry includes an output transformer (TR2) and a low pass filter (Ll, Cl) including an inductor (Ll) coupled in series with said transformer and a capacitor (Cl) coupled in parallel with said transformer, said method being c h a r a c t e r i z e d b y the steps of :

- connecting the cathode of a diode (V6) to said low pass filter of the discharge circuit;

- connecting the anode to a load measuring capacitor (C3);

- storing a negative charge in the load measuring capacitor, the negative charge resulting from a negative pulse obtained during an initial phase of a discharge of said storage capacitor device and the amplitude of which being indicative of the load of the electric fence-to-ground circuit.

5. An apparatus for supplying high-voltage pulses to an electric fence comprising:

- a rechargeable power supply (1) providing an output voltage;

a voltage transformer device (3; TRl, V8, V4, V3) for transforming the output voltage of the rechargeable power supply to high voltage;

- a storage capacitor device (5; C9) for repetitively being charged and discharged, the charging being performed by means of connecting said storage capacitor device to said high voltage;

- a discharge circuit (7; TR2, Cl, Ll, V5 ) connectable to said electric fence and to ground, respectively, for repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high-voltage pulses;

- a power supply voltage measuring circuit (13; R14, R16) for measuring the voltage of said rechargeable power supply; and - a control unit (9, D2 ) adapted to control said repetitive charging of said storage capacitor device depending on the measured voltage of said rechargeable power supply,

characterized in

- a load measuring circuit (15; C3, V6, R4-R6, R21) for measuring the load of the electric fence-to-ground circuit, wherein

- said control unit is adapted to control said repetitive charging of said storage capacitor device depending on the measured load of the electric fence-to-ground circuit.

6. The apparatus as claimed in claim 5 wherein said control unit is adapted to control said repetitive charging such that said storage capacitor device is charged repetitively according to a first charge scheme when the measured load of the electric fence-to-ground circuit is below a threshold load and according to a second charge scheme when the measured load of the electric fence-to-ground circuit is above said threshold load, said first and second charge schemes being different.

7. The apparatus as claimed in claim 6 wherein said first charge scheme includes a repetitive charging of said storage capacitor device to obtain a fixed output voltage to the electric fence.

8. The apparatus as claimed in claim 7 wherein said second charge scheme includes a repetitive charging of said storage capacitor device to obtain an output voltage to the electric fence, which varies on a pulse-to-pulse basis in a cyclic manner, wherein the average energy output to the electric fence is lower than the average energy output that would have been obtained using said first charge scheme.

9. The apparatus as claimed in any of claims 6-8 wherein said threshold load is between 0.5 and 6 kΩ, preferably between 1 and 4 kΩ, more preferably between 1.5 and 3 kΩ, and most preferably about 2 kΩ.

10. The apparatus as claimed in any of claims 5-9 wherein

- said discharge circuitry includes an output transformer (TR2) and a low pass filter (Ll, Cl) including an inductor (Ll) coupled in series with said transformer and a capacitor (Cl) coupled in parallel with said transformer; and

- said load measuring circuit includes a load measuring capacitor (C3) and a diode (V6) having an anode and a cathode, the diode anode being connected to the load measuring capacitor and the diode cathode being connected to said low pass filter of the discharge circuit, wherein a negative charge is stored in the load measuring capacitor, the negative charge resulting from a negative pulse obtained during an initial phase of a discharge of said storage capacitor device and the amplitude of which being indicative of the load of the electric fence-to-ground circuit.

11. The apparatus as claimed in claim 10 wherein said load measuring circuit includes a voltage divider (R4-R6, R21), which is connected to said control unit, and through which said control unit is capable of reading the negative charge indicative of the load of the electric fence-to-ground circuit.

12. The apparatus as claimed in any of claims 5-11 comprising a charge voltage measuring unit (17; R1-R6, R21) for measuring the charge voltage of the storage capacitor device .

13. The apparatus as claimed in any of claims 5-12 comprising an energy recovery circuit (19; TR2, Ll, V5, VI) for recharging the rechargeable power supply with electric energy from said discharged energy, which is not transferred to said electric fence .

14. The apparatus as claimed in claim 13 wherein

- said storage capacitor device is galvanically connected to the positive pole of the rechargeable power supply;

- said discharge circuitry includes an output transformer (TR2) having a core and primary and secondary windings, the primary winding being connected to said storage capacitor device and the secondary winding being connected to said electric fence and ground; and

- said discharge circuitry and said energy recovery circuit comprise jointly a switch (V5), preferably a thyristor, controlled by said control unit for

repetitively closing a circuit including said storage capacitor device (C9) and said primary winding of the output transformer (TR2) to discharge said storage capacitor device over the output transformer to thereby, via said secondary winding, output high-voltage pulses on the electric fence-to-ground circuit; and

repetitively closing a circuit from said primary winding of the output transformer (TR2) to said positive pole of the rechargeable power supply (1) to recharge said rechargeable power supply with energy stored in the core of the output transformer during discharges of said storage capacitor device, which does not give rise to currents in the secondary winding of the output transformer.

15. The apparatus as claimed in any of claims 5-14 comprising a solar panel (23) for charging said rechargeable power supply and a charge control circuit (21; V13, V7, V12, R17-20) to prevent said rechargeable power supply from being overcharged.

16. A method for supplying high-voltage pulses to an electric fence comprising the steps of:

- transforming the output voltage of a rechargeable power supply (1) to high voltage;

- repetitively charging and discharging a storage capacitor device (5; C9), the charging being performed by means of connecting said storage capacitor device to said high voltage;

- repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high-voltage pulses;

- measuring the voltage of said rechargeable power supply; and

controlling said repetitive charging of said storage capacitor device depending on the measured voltage of said rechargeable power supply, characterized by the steps of:

- measuring the load of the electric fence; and

- controlling said repetitive charging of said storage capacitor device depending on the measured load of the electric fence-to- ground circuit.

17. The method as claimed in claim 16 wherein said repetitive charging is controlled such that said storage capacitor device is charged repetitively according to a first charge scheme when the measured load of the electric fence is below a threshold load and according to a second charge scheme when the measured load of the electric fence is above said threshold load, said first and second charge schemes being different.

18. The method as claimed in claim 17 wherein said first charge scheme includes to repetitively charge said storage capacitor device to obtain a fixed output voltage to the electric fence; and said second charge scheme includes to repetitively charge said storage capacitor device to obtain an output voltage to the electric fence, which varies on a pulse-to-pulse basis in a cyclic manner, wherein the average energy output to the electric fence is lower than the average energy output that would have been obtained using said first charge scheme.

19. An apparatus for supplying high-voltage pulses to an electric fence comprising:

- a rechargeable power supply (1) providing an output voltage;

- a discharge circuit (7; TR2, Cl, Ll, V5) connectable to said electric fence and to ground, respectively, for repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high-voltage pulses, characterized in

an energy recovery circuit (19; TR2, Ll, V5, VI) for recharging the rechargeable power supply with electric energy from said discharged energy, which is not transferred to said electric fence.

20. The apparatus as claimed in claim 19 wherein

- said discharge circuitry and said energy recovery circuit comprise jointly a switch (V5), preferably a thyristor, for

- repetitively closing a circuit from said primary winding of the output transformer (TR2) to said positive pole of the rechargeable power supply (1) to recharge said rechargeable power supply with energy stored in the core of the output transformer during discharges of said storage capacitor device, which does not give rise to currents in the secondary winding of the output transformer.

21. A method for supplying high-voltage pulses to an electric fence comprising:

- transforming the output voltage of a rechargeable power supply to high voltage;

- repetitively delivering electric energy discharged from said storage capacitor device to said electric fence to thereby supply said electric fence with high-voltage pulses,

c h a r a c t e r i z e d b y the step of :

- recharging the rechargeable power supply with electric energy from said discharged energy, which is not transferred to said electric fence.

22. The method as claimed in claim 21 wherein

- repetitively closing a circuit including said storage capacitor device (C9) and the primary winding of an output transformer (TR2) to discharge said storage capacitor device over the output transformer to thereby, via the secondary winding of the output transformer, output high-voltage pulses on the electric fence-to-ground circuit; and