U.S. patent number 3,655,995 [Application Number 05/113,480] was granted by the patent office on 1972-04-11 for automatic electric fence charging system.
This patent grant is currently assigned to Wire Sales Company. Invention is credited to Elmer K. Malme.
United States Patent |
3,655,995 |
Malme |
April 11, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
AUTOMATIC ELECTRIC FENCE CHARGING SYSTEM
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."
Inventors: |
Malme; Elmer K. (St. Charles,
IL) |
Assignee: |
Wire Sales Company (Chicago,
IL)
|
Family
ID: |
22349687 |
Appl.
No.: |
05/113,480 |
Filed: |
February 8, 1971 |
Current U.S.
Class: |
307/132R; 256/10;
340/564 |
Current CPC
Class: |
H05C
1/06 (20130101) |
Current International
Class: |
H05C
1/06 (20060101); H05C 1/00 (20060101); H01h
047/00 () |
Field of
Search: |
;307/132R,132M,132VR,132ER,96,106,112 ;256/10 ;340/253,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hohauser; Herman J.
Claims
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 IR 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 network for disabling said
capacitor charging system and preventing the potential across said
capacitor from reaching a breakdown value so long as said fence
remains "unloaded," 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.
Description
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 be true to some extent in connection with
chargers energized from a conventional power line such as a 60
cycle 120 volt line.
In my co-pending application filed 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 no possibility 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 10 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 11B through fuses from a
conventional 60 cycle power line.
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 21 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 1.2 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 transformer 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 50
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 for providing
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 55 will normally have substantial
capacitance (as an example 130 .mu.f.) but need only withstand a
relatively low voltage, such as, for example, 15 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 mf. 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 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-off 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 sufficiently 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 one-fourth 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 60 in 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 by-pass 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.
* * * * *