US 3655995 A
A fence charging system includes a sensing circuit connected to a fence to be charged. The sensing circuit applies a harmless low voltage which normally maintains a fence charger below operating level so long as the fence is "unloaded" (has a high resistance in the absence of at least one animal grounding the fence). When the fence becomes "loaded," the current drawn by the fence sensing system changes potential distribution in the fence charging system and permits the charger to operate normally, the fence charging system under such conditions impressing high voltage pulses on the fence at predetermined intervals so long as the fence remains "loaded.
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Description (OCR text may contain errors)
United States Patent Malme  AUTOMATIC ELECTRIC FENCE Assignee:
US. Cl. ..307/132 R, 256/ 10, 340/254 Int. Cl. ..H0lh 47/00 Field ofSearch ..307/l32 R, 132 M, 132 VR, I32 ER,
References Cited UNITED STATES PATENTS 3,581,299 5/1971 Schmit ..307/l32 R [151 3,655,995 [4 1 Apr. 11, 1972 Primary Examiner-Herman J. Hohauser Attorney-Robert L. Kahn  ABSTRACT A fence charging system includes a sensing circuit connected to a fence to be charged. The sensing circuit applies a harmless low voltage which normally maintains a fence charger below operating level so long as the fence is unloaded (has a high resistance in the absence of at least one animal grounding the fence). When the fence becomes loaded, the current drawn by the fence sensing system changes potential distribution in the fence charging system and permits the charger to operate normally, the fence charging system under such conditions impressing high voltage pulses on the fence at predetermined intervals so long as the fence remains loaded.
3 Claims, 1 Drawing Figure FENCE Patented April 11 1972 Inventor ELMER K. MALME ATTY.
AUTOMATIC ELECTRIC FENCE CHARGING SYSTEM This invention relates to an electric fence charger for intermittently charging a fence to train cattle or animals from pressing against such fence. As is well known, such chargers are designed to impress an electric charge on a fence containing a metal wire usually of iron, such charge lasting only a few milliseconds and at spaced time intervals. It is desirable to minimize the actual time during which a fence is charged in comparison to times when a fence is not charged so that consumption of power for the charger is minimized. This is particularly true where chargers are designed for battery operation although such considerations may betrue to some extent in connection with chargers energized from a conventional power line such as a 60 cycle l2O volt line.
In my co-pending applicationfrled of even date with the present application, I have disclosed a fence charger system wherein a sensing action of fence conditions'is provided to reduce the fence charger power input when fence conditions are appropriate. As is true with the present invention, the fence charger described in the companion application referred to above has a mode of operation which is based upon the electrical condition of a fence when loaded" (where an animal is contacting the metal of the fence) and where a fence is unloaded" (when no animal is touching the fence metal or where no low resistance grounds such as water, snow or certain weeds are at the fence metal). The present invention improves upon the invention disclosed in the aforementioned application by continuously impressing sensing low voltage on the fence to be charged and maintaining such charger in what might be designated as a relatively inactive stand-by condition so long as the fence remains unloaded. The new fence charger will condition the circuitry so that normal fence charging potentials are impressed upon the fence at appropriate intervals when such fence is loaded. The sensing potential impressed upon the fence has a low value in the general order of about 50 volts or less and the voltage regulation and resistance of the circuit supplying such sensing potential is such that there is nopossibility of a dangerous or damaging current that can be drawn, irrespective of fence conditions.
For a full-understanding or the invention reference will now be made to the drawing wherein the single FIGURE shows a wiring diagram of the new fence charger.
Referring now to the drawing, transformer is a conventional iron core transformer having primary winding 11 and secondary winding 12. Preferably an electrostatic shield is disposed around primary winding 11 to prevent the possibility of high potentials being impressed or appearing in secondary winding 12. Such electrostatic shielding is old and well known.
Primary winding 11 is adapted to be supplied from line wires 11A and 118 through fuses from a conventional 60 cycle power line. 1
Instead of primary winding 11 being energized from a power line, a battery may be used as a source of power, the battery current being interrupted by suitable means such as a blocking oscillator, chopper or the like.
Secondary winding 12 has terminals 13, 14 and 15. In the case of a 120 volt power line for energizing the system, secondary winding 12 would normally step up the voltage between terminals 13 and 15 by a ratio of about 2 to 1. Connected across terminals 13 and 15 are ballast resistors 17 and 18 between which are connected neon glow lamp 20. Terminal 13 is connected to wire 2l which is used as a ground for the entire system.
Terminal 15 of the secondary winding is connected to the positive terminal of rectifier 25, the negative terminal of which is'connected through resistor 26 to wire 27. Connected to wire 27 is high resistance 28 as about l.2 megohms going to junction point 29. Wire 30 goes from junction point 29 to junction point 32. Connected to junction point 32 is terminal 33 of secondary winding 34 of step-up pulse transfonner 35. The remaining terminal of secondary winding 34 is connected to one terminal 37 of capacitor 38 whose other terminal is connected to ground wire 21. Shunting capacitor 38 is spark gap 40 adapted with regard to spacing and electrode shape and gas environment to spark-over at about 300 volts.
Junction point 32 is connected to one terminal of choke winding 41, the other terminal of which is connected to a fence to be charged. Across the fence to be charged and ground is spark-gap 43 adapted to break down at about 8,000 volts. Connected across choke 41 and spark-gap 43 in series is ballast resistor 45 and neon lamp 46. Ballast resistor 45 has a high enough value (almost a megohm) so that there is no danger of the fence system appearing as loaded" to the charger output terminals 32 and ground.
Connected between wire 27 and ground wire 21 is capacitor normally having substantial capacitance (such as about 16 mf.) and capable of withstanding the full potential across secondary winding 12.
Terminal 14 of secondary winding 12 is connected to such a point on the secondary winding as to provide for a suitable voltage for operating transistors. This voltage will depend .upon' the types of transistors used and, as an example, may be suitable forproviding a DC voltage of about 12. Secondary winding terminal 14 is connected to the positive or anode electrode of rectifier 52, the negative electrode of which is connected to wire 53. Connected between the negative electrode of rectifier 52 and ground 21 is capacitor 55. Capacitor will normally have substantial capacitance (as an example 130 pf.) but need only withstand a relatively low voltage, such as, for example, l5 volts if wire 53 carries 12 volts. Thus capacitor 55 acts as a filter.
Wire 53 is connected to the collector electrode of NPN- transistor 57. Transistor 57 has its base connected through bias resistor 58 to ground wire 21, the latter being shunted by diode 60 having the anode grounded and the cathode connected to the base of transistor 57. Power supply wire 53 is also connected to the collector of transistor 62 whose base is directly connected to the emitter of transistor 57. The emitter of transistor 62 is connected through bias resistor 63 to junction point 64. The latter junction point 64 is grounded through bias resistor 65 and is also connected to the base of transistor 67. All the transistors are of the same type, in this instance being NPN. Transistor 67 has its emitter directly grounded and has its collector connected through load resistor 69 to junction point 70. Between junction point 70 and ground, capacitor 71 is connected. This capacitor has a substantial value of the order of about 22 mi. as an example but normally need not withstand any voltage greater than about 35 volts in an exemplary system having resistors whose values are hereinafter given. Junction point 70 is connected through four resistors 72A to D inclusive to wire 27. The four resistors each have substantial value of the order of about 360 k ohms and are normally required by Underwriters Laboratories to minimize the possibility of damage because of failure of a resistor. In any event the total value of the resistor network will run in the general order of about 1.5 megohms, as an example.
Junction 70 is connected through current limiting resistor I 74 to one terminal of a diac 75 whose other terminal is connected to the gate electrode of SCR 76 (silicon controlled rectifier). Diac 75 (conduction in only one direction is involved and hence could be replaced by a diode having desired discharge barrier characteristics) normally will conduct at about 29-35 volts. Shunted across SCR 76 is rectifier 78 reversely poled to protect SCR 76 against reverse voltage. High potential wire 27 is connected to one terminal of primary winding 80 of pulse transformer 35, the remaining terminal of this winding being connected to the positive electrode of SCR 76. Referring to junction point 29, a wire goes to one terminal of resistor 82, the other terminal of which is connected by wire to the base of transistor 57 The operation of this system is as follows:
Capacitor 50 is charged to the maximum voltage of power supply transformer 10. In an assumed example, capacitor 50 may be charged to about 350 volts DC. Resistor 26 normally has a low enough value (as an example, about 1,500 ohms) so that capacitor 50 becomes charged fully within a small fraction of a second. Wire 27 will therefore have a DC potential normally at about 350 volts. The resistance network from wire 27 through resistors 28,- 82 and 58 will normally be such that in stand-by position a sensing potential of the order of less than 50 volts, such as 35 volts, will be applied to the fence. Due to poor voltage regulation of the charger system, this sensing voltage may drop considerably when the charger system is impressing high potentials on the fence.
During stand-by, the potential at junction 29 will be such that transistor 57 will have its base potential maintained so that transistor 57 will be conducting. The conducting condition of transistor 57 (in the configuration illustrated) will cause transistor 62 to be conducting. Transistor 67 will also be conducting. In a system embodying the present invention, the various resistors are so arranged that the potential of junction point 70 will normally be somewhat lower than is required for fence charger operation when a fence is loaded." As an example, the voltage at junction point 70 may be 25 volts so that timing capacitor 71 becomes partially charged. The potential at junction point 70 will be somewhat lower than the breakdown voltage of barrier trigger device 75. Under stand-by conditions, SCR 76 will not discharge and no current will flow through primary winding 80 of pulse transformer 35.
As soon as the resistance facing transformer secondary winding 34 drops below a desired high value so that the pulse transformer faces a loaded fence, then the sensing current drawn by the fence from junction point 32 becomes greater. This increased current flow through resistor 28 drops the potential at junction point 29, dropping the potential of the base of transistor 57 and cutting off current flow through transistor 57. This is followed by transistor 62 cutting off and in turn by transistor 67 cutting off. As a result, the current through resistor 69 normally drawn by transistor 67 is cut-H and the potential of junction point 70 rises.
As an example, the normal voltage of junction point 70 in stand-by may be 25 volts but will now rise to a value between about 29 and about 35 volts, depending upon the values of various resistors. Barrier trigger device 75 is adapted to break down at a voltage between say 29 and 35 so that SCR 76 will conduct. The breakdown permits a rush of current from capacitor 50 to flow through primary winding 80 of the pulse transformer. The duration of such discharge is extremely short and results in a steep pulse created in the secondary of the pulse transformer. A high voltage pulse will thus be impressed upon the fence. When capacitor 50 is discharged, SCR 76 stops conducting. When SCR 76 breaks down, timing capacitor 71 will also discharge, the drop in voltage at junction point 70 being limited by the duration of conduction through SCR 76 between gate and negative electrodes. In the meantime, after SCR 76 cuts off, the potential at junction point 70 begins to rise as capacitor 71 charges.
Thus the potential at junction point 70 has a generally sawtooth shape with the maximum voltage of a sawtooth being about 35 or so volts and suddenly dropping to a lower voltage, depending upon how completely timing capacitor 71 discharges. Capacitor 55 will filter and thus maintain the stability of the transistors. Once the load on the fence is removed, the potential at junction point 32 tends to rise due to reduced IR drop and the system assumes normal standby. Thus the potential at junction point 70 will be stabilized at a stand-by value such as 25 volts and will be prevented from rising. This stabilization will prevent SCR 76 from operating.
The resistor network bypass from junction point 29 to ground wire 21 through resistors 82 and 58 should have sulficiently high resistance to permit the potential of point 29 to vary with fence conditions. Thus, as long as the fence part of the system has an unloaded resistance of at least about onefourth megohms then resistor 82, as an example, could be about 1 megohm and resistor 58 could be about 1.5 megohms with resistor 28 being about 1.2 megohms. These values are illustrative only. The fence resistance can go down to about 100,000 ohms for "loading." In fact, "loading" may bring the fence resistance down to a few thousand ohms.
Diode m the system protects against voltage reversal on the base of transistor 57 when the voltage at junction point 32 goes negative during the end of a fence charging cycle. This negative voltage would be fed back to junction point 29 and then through resistor 83 in the absence of diode 60.
Capacitor 38 prevents the sensing voltage from being shorted to ground. Capacitor 38 should be large enough to bypass the pulse output from transformer secondary 34. Choke 41 and spark gap 43 may be used where lightning protection is desired. Spark gap 40 may function as a voltage barrier device to protect capacitor 38 against breakdown.
The sensing portion of the system may be applied to various kinds of fence chargers.
What is claimed is:
1. A fence charging system for impressing a shocking potential upon a loaded fence at predetermined time intervals, said fence being adapted to be loaded or unloaded" depending upon whether the electric resistance presented by the fence is below or above an arbitrary voltage, said fence charger system including a capacitor, means for charging the same to a predetermined maximum potential and thereafter discharging the same after said potential has reached a predetermined value, said fence charger including means for utilizing said discharge in generating a high shocking potential, said system including sensing means for connection to a fence load, said sensing means impressing a low direct voltage of the general order of about 50 volts continuously on said fence durint the time that said fence is unloaded," and means controlled by normal sensing voltage conditions in said sensing system for disabling said fence charging system so long as said fence is unloaded," said means becoming inoperative when the voltage conditions in said sensing system charge in response to fence loading, whereby said fence charger operates to impress high potentials at time intervals on said loaded" fence.
2. An automatic electric fence charging system comprising a sensing system including a resistance network, said sensing system being adapted to be connected to a fence to be charged, means for energizing said sensing system so that a maximum voltage of no more than about 50 volts can normally be impressed upon said fence, said fence load normally being adapted to permit a minute current to flow from said sensing system to ground with the [R drop being such as to maintain said sensing voltage, electric fence charging means including a relaxation type oscillator having a capacitor and a capacitor discharge circuit for permitting pulse discharge of said capacitor when the capacitor potential reaches a predetermined value, said capacitor thereafter being charged relatively slowly to repeat the discharge cycle, and means responsive to the voltage conditions in said sensing resistor I the loading on said fence reducing the fence load and increasing the current from said sensing system whereby said means responsive to the voltage conditions operates to permit said capacitor to reach a pulse discharge value and operate the fence charging system in a normal fashion.
3. The system according to claim 2 wherein said sensing portion of the system includes at least one resistor whose value is in the megohm range, said resistor having one end for direct connection to a fence, and voltage dividing means connected to said high resistance and transistorized means connected to said voltage dividing means, said transistorized means functioning as a switch to control a circuit to said capacitor for controlling the potential level to which said capacitor is charged, said transistorized means itself being controlled by the potential level at said voltage dividing means.
UNITED STATES PATENT OFFICE v CERTIFICATE CF CORRECTION PatentNo. 3,655,995 Dated April 11, 1 72 I Inventor(s) Elmer K. Malme 7 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 4, line 22, "voltage" should read value ----3 line 31, "durint" should read during;
Signed and sealed this 31st day of October 1972 (SEAL) Attest:
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents "ORM PO-105O (10-69) USCOMM-DC 603764 69 a u.s. GOVERNMENT PRINTING OFFICE: 1909 o-aas-ssl.
UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3,655,995 Dated pri 97 Inventor 5) Elmer K .Malme It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:
' Column l; line 22, "voltage" shcuid read value line 31, "durint" should read during Signed and sealed this 31st day of October 1972.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM USCOMM-DC 6OB76-P69 k U.s. GOVERNMENT PRINTING OFFICE I969 '356-33,