FIELD OF THE INVENTION
The present invention relates to a protection system for vehicle
storage batteries, and more particularly, concerns a system in which electrical
loads are disconnected if the battery voltage falls below a predetermined level,
and in which the vehicle can still be started without any operator action other
than normal operation of the ignition switch.
BACKGROUND OF THE INVENTION
Battery protection systems typically sense battery condition when
the battery is not being charged, as for example, when the engine of the vehicle
is off. Should a load remain on after the vehicle is turned off, the load will
be disconnected before the battery is completely discharged. However, when a partially
discharged battery is disconnected from its load, the voltage appearing across
the battery increases. Thus, measured voltage increases to an open circuit voltage,
which could cause the load to be reapplied, resulting in a cyclic disconnect and
reconnect operation. Further, during normal vehicle starting operations, sensed
battery voltage will drop substantially due to the large current drain of the
starting solenoid, but the system must not disconnect the loads.
In some prior systems, such as U.S. Patent No. 4,902,956, the system
must be manually reset by the operator in order to start the vehicle engine after
the loads have been disconnected Some of these systems such as U.S. Patent No.
4,493,001 which forms the basis for the generic portions of claim 1 also require
special connections to other elements of the vehicle in order to reconnect the
load. All of these special requirements and equipment are costly and inconvenient
to the vehicle operator, who preferably should be able to start the vehicle by
doing nothing more than inserting and turning the ignition.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
a battery protection system which automatically reconnects the battery to the load
upon operation of the vehicle ignition system.
This object is solved by devices with the features of claim 1.
A battery protection system is provided in which a low battery signal
is generated when voltage at the battery falls below a selected level. A normally
closed switch is then opened to disconnect the battery from the load. The selected
level is set at a voltage sufficient to restart the vehicle by normal operation
of the ignition switch.
Opening the switch in response to the low battery signal is delayed
to ensure that the battery voltage has remained below the selected level for a
sufficient time to ensure that a true low voltage condition exists and not simply
the result of normal starting operations. Hysteresis may also be provided to effectively
lower the sensed battery voltage so that the resultant rise in battery voltage
due to disconnection of the load will not cause the load to be reconnected. In
one preferred embodiment, low voltage disconnect operation may be inhibited while
the engine is running.
To restart the vehicle after the battery has been disconnected, a
reset pulse is provided in response to a change in voltage across the load to temporarily
disable the voltage sensing means and reconnect the battery to the load. The reset
pulse is generated in response to a change in voltage across the disconnected
load, but its operation is delayed for a short time to avoid a spurious reset during
proper disconnection of the load and resultant rise in battery voltage.
According to a preferred embodiment of the invention, the entire
battery protection system is integrated into one of the battery cables so that
the protection system can be installed merely by connecting the battery cable
in substantially the usual manner of a conventional cable. In another preferred
embodiment, the battery protection system is situated in a housing that connects
between the end of one battery cable and a battery terminal, and has dimensions
so as to be located on top of the battery between the terminals.
The features and advantages of the invention will be further understood
upon consideration of the following detailed description of the presently preferred
embodiments of the invention, taken in conjunction with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
- FIG. 1 is a block diagram of a preferred embodiment of a battery protection
system employing the principles of the present invention;
- FIG. 2 is a longitudinal, sectional view of a motor driven switch that may
be employed in the system of FIG. 1;
- FIG. 3 is a section taken along lines 3-3 of FIG. 2;
- FIGS. 4A and 4B together form a preferred embodiment of a circuit diagram of
the system of FIG. 1;
- FIG. 5 is a longitudinal view, partly in section, of a battery cable having
a built-in battery protection system according to the invention;
- FIG. 6 is a section taken along lines 6-6 of FIG. 5 showing the disconnect
switch of one preferred embodiment of the invention; and
- FIGS. 7A and 7B are two views of another presently preferred housing for the
battery protection system of the invention.
The battery protection system of the present invention provides protection
for a vehicle storage battery against discharge below a predetermined voltage
threshold while the engine is not running. The system protects against discharge
below a threshold greater than total discharge due to a current drawing condition
resulting from any load connected to the battery. The system operates automatically
without any additional action by the vehicle operator, or any noticeable effect,
other than normal starting operations.
The system monitors battery voltage while the vehicle is not in operation
and there are ostensibly no loads, or only minimal loads, drawing current from
the battery. However, should a load inadvertently remain across the battery, the
system will automatically disconnect all electrical loads from the battery after
the battery voltage has fallen to a predetermined level where sufficient power
remains to restart the vehicle. An example of one such condition would occur if
the vehicle headlights were to remain on after the vehicle is parked.
A preferred voltage level may be on the order of about seventy percent
of the full battery charge. For example, in a lead-acid battery that has a 12.68
volt fully charged output without load, an exemplary system embodying principles
of the present invention will disconnect the load when the battery voltage falls
to about 12.44 volts. Thus, all loads are disconnected well before the battery
has discharged below the point where it will no longer supply the desired rated
cold cranking current to restart the vehicle. Typically, a fully discharged lead-acid
battery possesses a voltage of about 11.89 volts.
Means are also provided which permit the battery to drop a predetermined
voltage caused by normal vehicle starting operations, without disconnecting the
Importantly, the existence and operation of the system is transparent
to the user. If a drain on the battery should occur such that the system disconnects
the load, enough voltage will remain in the battery to restart the vehicle upon
normal operation of the ignition switch. Operation of the ignition switch is sensed
by the system to automatically reconnect the battery to the load, and thus provide
the remaining power of the protected, partly discharged battery to the vehicle
As illustrated in FIG. 1, a vehicle battery 10 is connected through
a normally closed main switch 12 to an unswitched load 14, and to a switched load
16, which is under control of an ignition switch 18. Load 14 may include, for
example, headlights, radio, and the like. Load 16 may be, for example, the starter
motor and starter solenoid. The standard vehicle electrical system connects the
battery to loads 14 and 16 directly without interposition of the main switch 12.
To apply the system of the present invention in a conventional vehicle electrical
system, it is only necessary to connect the main switch 12 between one battery
terminal, such as the positive terminal, and the loads, as shown in FIG. 1.
The switch 12 connects or disconnects terminals 20 and 22 according
to the switch condition as determined by a switch driver 24. With the switch 12
in a closed position, the terminals 20, 22 are connected to one another, and the
battery is thus connected to the load. When the switch is driven to the open position,
the terminals 20, 22 are disconnected and the loads are disconnected from the
Battery voltage at the positive switch terminal 20 is sensed through
line 26 and is connected as a first input to a comparator 28. A second input to
the comparator 28 is provided from a reference or threshold voltage generator
30. The comparator 28 provides a low output 29 on line 31 when the sensed battery
voltage at terminal 20 falls below the threshold determined by the threshold voltage
The comparator output 29 is connected through a delay circuit 32,
which provides a fault signal 33 to the switch driver 24, to open the main switch
12 after the sensed voltage has remained below the threshold for the delay period.
Generation of the fault signal 33 will occur if the voltage drops below the threshold
for the duration of the delay period regardless of the size of the load causing
the condition. The comparator output 29 is thus a function of time alone, and is
independent of the size of the voltage drop below the threshold.
Delay Circuit 32
In normal operation when the vehicle is started by engaging the ignition
switch 18, the sensed voltage on line 26 will drop as the starter solenoid and
starter motor (not shown) draw current from the battery 10. This sensed voltage
drop would normally cause the main switch 12 to open. However, the delay circuit
32, which initiates its delay interval when the low battery output 29 occurs,
is interposed between the comparator 28 and the switch 12 to inhibit delivery of
the fault pulse 33 for the delay period. If the fault signal 33 was not delayed,
operation of the starter would result in a drop in voltage at the battery, and
the low battery voltage signal 29 would be provided at the output of comparison
A delay period of fifty-five to sixty seconds should be long enough
to cover the time normally required to start the vehicle by operation of the ignition
switch 18. Thus, a sensed voltage drop due to normal starting operation will not
inadvertently open the main switch 12. The output of the comparator 28 appearing
on line 31 will rise to disable the delay circuit 32 prior to the end of the delay
period. Accordingly, the delay circuit will not time out, and the disconnect signal
will not be transmitted to the switch driver 24. On completion of the starting
operation, the starter motor is disconnected so the battery voltage will return
to its normally higher level.
Should the low voltage sensed on line 26 result from a drain on the
battery so that the battery voltage remains in a lowered condition for longer than
the delay period, the delay circuit 32 will time out and provide the fault signal
33 to the switch driver 24. This operation causes the main switch 12 to open and
disconnect the loads from the battery. When the loads are disconnected, there
is no further drain on the battery.
Upon disconnection, voltage across the terminals 20, 22 will begin
to increase, and within several minutes will attain the open circuit voltage of
the battery. The open circuit voltage, however, may be above the threshold voltage
of circuit 30. Thus, this increase in voltage may cause the output 29 of the comparator
28 to rise and result in reapplication of the loads. In order to prevent such
cyclical operation, a hysteresis feedback signal is provided on line 34 to the
voltage sensing input of the comparator 28 to maintain the input at a value below
the threshold. This feedback prevents closing the main switch 12 and thus avoids
repetitive off and on cycling.
Reset Circuit 40
System reset circuitry 40 is preferably provided to continuously
test the disconnected load and sense a change in load caused by an attempted restart
of the vehicle. A test voltage generator 44 is connected across the main switch
12 and is supplied with power from the positive terminal 20. The test voltage generator
44 employs a closed loop, negative feedback arrangement to establish a small test
voltage at its output on line 46. A preferred value for such test voltage is about
The closed loop arrangement maintains a relatively stable voltage
on line 46 over a wide range of loads. The voltage on line 46 is connected through
an amplifier 50 to a comparison circuit 52. The comparison circuit 52 compares
the amplified voltage on line 46 to a reference voltage established by a reference
circuit 54. The difference between the feedback voltage on line 46 and the reference
voltage appears as an output on line 55 from the comparison circuit 52. The output
on line 55 serves as an input to the test voltage generator 44 to vary the value
of the voltage generated by minimizing changes in the voltage on line 46. This
negative feedback stabilizes the test voltage at a small value over a wide range
The test voltage on line 46 is applied to both loads 14, 16 through
line 56 and through terminal 22 of the main switch 12. This small voltage is applied
to the loads 14, 16 while they are disconnected from the battery 10 and after
the main switch 12 has been opened due to an inadvertent battery drain.
Operation of the ignition to start the vehicle will close ignition
switch 18 and will connect the starter solenoid (load circuit 16) momentarily in
parallel with the small cold resistance of load 14. Closing ignition switch 18,
therefore, causes a very small change in resistance across load 14, which changes
the voltage seen on line 46. This change in voltage causes an output to appear
on line 55 from comparison circuit 52. This output is coupled through line 62 to
a reset pulse generator 60. The reset pulse generator 60 provides a reset signal
to the threshold circuit 30. The reset signal operates to lower the threshold voltage
at the second input of comparator 28, and as a result resets the delay circuit
32, thus removing the fault pulse. Removal of the fault pulse causes driver 24
to close the disconnected main switch 12.
Operation of the ignition switch 18 is sensed by the reset circuit
40, which engages the switch driver 24 to substantially immediately close main
switch 12. Closing switch 12 is preferably accomplished in less than one second.
The operation is such that the vehicle driver is not aware of any delay or difference
in operation, and is able to start the vehicle in a normal manner.
Disconnect Delay Circuit 66
When a low battery voltage has been detected and has remained in
excess of the delay period, switch 12 is opened and the voltage at terminal 22
begins to decay rapidly. The reset circuit 40 would normally sense this drop in
voltage and generate a reset pulse to immediately close switch 12. If this were
allowed to happen, the system would repetitively cycle on and off. To avoid such
recycling, the reset pulse generator 60 must be inhibited for a selected period
of time (on the order of several seconds) by means of a disconnect delay circuit
66 triggered by the occurrence of the fault signal 33. Thus, the reset circuit
is effectively isolated from the threshold circuit for a short period of time
after the main switch 12 is opened.
After the main switch 12 has remained open for several seconds, the
voltage at terminal 22 becomes relatively stable, and the reset pulse generator
15 is again allowed to operate until the ignition switch is reengaged. Thereafter,
a valid reset pulse quickly closes switch 12 and allows current from the battery
to be supplied to the starter solenoid.
Engine Running Circuit 61
The protection circuitry discussed so far will operate whenever the
battery voltage falls below the predetermined threshold, whether this occurs while
the vehicle is parked or while the engine is running. However, for most applications
it is not desirable to disconnect the loads from the battery while the engine is
running. If the battery voltage should drop below the threshold while the engine
is running, the main switch 12 will open. If the alternator is not operating to
provide electrical power during such occurrence, the vehicle engine would simply
stop. Accordingly, an engine running signal is preferably provided by means of
an engine running circuit 61, which raises the sensed battery signal and prevents
generation of the fault signal.
The engine running circuit 61 operates by sensing a ripple or slight
variation in current through the load due to either alternator or ignition operation,
and raises the sensed battery signal at the input to comparator 28. The ripple
from the alternator or ignition is amplified through a high gain amplifier consisting
of a series of operational amplifiers. The high gain amplifier magnifies this ripple
into approximately a 12 volt square wave. The square wave is then connected to
a pulse pump circuit that serves to maintain a voltage above the threshold level
at the input to the comparator 28.
Motor Driven Switch
A presently preferred embodiment of the invention employs a motor
and gear driven switch of the type illustrated in FIGS. 2 and 3. The motor driver
24 (shown in FIG. 1) includes circuitry that operates a small bi-directional DC
motor 70. Due to its small size, the bi-directional DC motor 70 can be easily located
anywhere on the vehicle body. Moreover, the motor 70 can be preferably operated
with small currents on the order of 250 milliamperes. A further advantage of the
bi-directional DC motor 70 is its lack of susceptibility to inadvertent operation.
Unlike the uni-directional relays of the prior art, since the bi-directional motor
70 requires a positive voltage to drive it in either direction, inadvertent operation
due to noise is unlikely.
The motor 70 has a gear box 72, which drives an output shaft 74.
A housing 76 is provided around the motor 70 that includes a cap 78 having an internally
threaded bore 80, which rotatably and threadedly receives an externally threaded
stub shaft 82. The threaded stub shaft 82 has a noncircular axial bore 84, which
receives a mated noncircular end 86 of the motor driven shaft 74. Thus, rotation
of the motor 70 and shafts 74 and 86 will rotate the stub shaft 82 and drive it
axially of the motor in either direction.
The outermost end of the stub shaft 82 has a fixed rotary contact
ring 90 arranged to alternatively contact or be displaced from a pair of switch
contacts 92, 94 mounted to the switch cap 78 between the cap and the cap cover
79. The contacts 92, 94 are electrically insulated from one another and are of
generally semicircular configuration (FIG. 3). The contacts cooperate with the
bi-directional, axially driven contact ring 90 to electrically connect or disconnect
the switch terminals 20 and 22 to or from the loads 14, 16.
In a preferred embodiment, the 12 volt bi-directional DC motor 70
(part no. LA16g-324, manufactured by Copal) is about 16 millimeters in diameter,
and is about 59 millimeters in length. The gear box, in an exemplary embodiment,
has a ratio of 1:120 and a nominal speed of 60 rpm, providing high torque and sufficient
speed of operation to pull the rotary contact ring 90 into proper electrical contact
with contacts 92, and 94, and to hold such contact. The cap 78 and the shaft 82
are preferably composed of nonconductive material such as nylon. The contacts
92, 94 and the contact ring 90 are preferably made of brass and may be cadmium
plated if necessary or desirable.
An additional advantage of the high speed miniature motor 70 is its
polar moment of inertia, which will result in as much as a one-half additional
revolution after its drive power has been removed. This additional one-half revolution
creates an over-travel in both directions of motion to ensure positive contact
or positive contact clearance. The motor drive circuitry is arranged to disconnect
the electrical drive for the motor immediately upon opening or closing of the contacts.
Only one quarter turn of the contact ring 90 is therefore required to open or
close the switch, and the switching action is completed with just a few revolutions
of the motor.
Detailed Circuit Diagram
Referring to the detailed circuit diagram shown in FIGS. 4a and 4b
(with FIG. 4b placed to the right of FIG. 4a to form a complete diagram), the battery
voltage appearing at the positive terminal 20 (FIG. 4b) is sensed on line 26 and
is connected through a diode 100 (FIG. 4a) to the upper end of a voltage divider
formed of resistors 102 and 104. The junction between resistors 102 and 104 is
the battery voltage sensing node 105, and is connected to ground through capacitor
106. The voltage sensing node 105 is also connected to the noninverting input of
operational amplifier 108 (corresponding to the comparator 28 of FIG. 1).
Attached to the inverting input of operational amplifier 108 is a
threshold or reference voltage provided at the cathode of a zener reference diode
110 connected between ground and the positive battery terminal through a resistor
112 and diode 100. The threshold voltage provided by the zener diode 110 is established
at a value, preferably 6.2 volts, such that amplifier 108 will provide a normally
high output on line 114 when the battery voltage is above seventy percent of its
The threshold voltage provided by the zener diode 110 is preferably
chosen at 6.2 volts since it is the most stable voltage for most zener diodes across
a wide variation of temperature. A voltage divider, composed of resistors 102,
103 and 112, are configured such that when the voltage at the battery terminals
drops to its predetermined level (approximately 70% of the fully charged voltage)
the voltage provided at the inverting input to amplifier 108 equals 6.2 volts.
The voltage divider network, therefore, scales down the threshold voltage to the
optimal range of operation for the zener diode 110. The parallel combination of
resistors 102 and 103 allows precise calibration of the voltage divider network
to achieve the 6.2 volt threshold.
A small amount of positive feedback is provided to the noninverting
input of amplifier 108 through the parallel combination of resistor 115 and resistor
116 to minimize any noise on the output of amplifier 108. This output is provided
as the triggering input to a programmable and resettable counter/timer 120 (corresponding
to delay circuit 32 in FIG. 1). A second input to the counter/timer 120 is provided
from the junction of a capacitor 122 and resistor 124 connected between the positive
battery voltage and ground. This input establishes the counting frequency for the
timer 120. The timer 120 is reset to zero upon receiving a high output from amplifier
108, and is triggered to count by a low output from amplifier 108.
In its counting state the timer counts on from zero to a predetermined
count, representative of the desired delay, before disconnecting the main switch
12. When the predetermined count is reached, the normally low output of the counter
on line 126 rises to drive an NPN emitter-follower transistor 128, which provides
a high signal to the inverting input of a motor drive control. The motor drive
control comprises an operational amplifier 130 having its inverting input connected
to the emitter of transistor 128.
The counter/timer 120 continues to count as long as the output 114
from amplifier 108 remains low. Should the output 114 return to its normally high
condition after the counter has commenced counting, but before it has reached
its full preprogrammed count, the timer 120 is reset to zero. A high signal at
timer output 126 will not occur unless the output from amplifier 108 remains low
for the full duration of the count programmed into timer 120. As previously mentioned,
this time period is preferably about fifty-five to sixty seconds, and will prevent
the battery protection circuit from disconnecting the battery when the battery
voltage experiences a momentary drop.
A reference voltage is applied to the noninverting input of amplifier
130 from the cathode of a zener diode 132 connected between ground and the positive
battery voltage through a resistor 134 and diode 100. A high signal connected
to the inverting input of amplifier 130, when compared to the reference voltage,
will provide a low signal at the output 137 of amplifier 130. This low output
137 comprises the fault signal discussed above, which operates the drive circuit
of motor 70 to open the main switch 12.
A feedback loop is provided from the output of amplifier 130, over
line 131, through resistor 133 and diode 139, to the noninverting input of amplifier
108. The fault signal is thereby fed back to the noninverting input of amplifier
108 to maintain this input sufficiently low to ensure retention of the fault output.
This feedback loop is required, as explained above, since the battery voltage
will tend to rise when the main switch 12 opens, which might reset the system.
While the main switch 12 is closed, a high voltage appears at the
output of amplifier 130, which is connected through line 135 and resistor 136 to
NPN transistor 138. Transistor 138 drives PNP transistor 140, which has its emitter
coupled to the battery and its collector connected through line 142, resistor 144
and diode 146 to the base of PNP transistor 148. Transistor 148 has its emitter
connected to the base of a PNP power transistor 150. The collector of transistor
148 is connected through line 149 and resistor 151 to the base of a second PNP
power transistor 152, which has its emitter connected to the positive battery terminal
A high signal at the output of amplifier 130 turns on transistor
138, which activates transistors 140, 148, 150 and 152. When transistors 140, 148,
150 and 152 conduct, current flows from the battery terminal 20 through transistor
152 to a first motor terminal 154. The path continues through the motor, through
a second motor terminal 156, and then through power transistor 150 to ground.
This flow of current causes the motor 70 to operate in the direction to close the
main switch 12. With the main switch 12 closed, terminal 22 receives the battery
voltage transmitted through diode 158 to the emitter of transistor 138, cutting
off transistor 138, as well as transistors 152 and 150 of the motor drive circuit.
While the main switch 12 is closed, the protection system is in a
steady state condition. In this condition, the vehicle electrical system will
operate as if the protection system were absent. Battery loads, lights, ignition
and the like can be applied with no effect on the protection system since the alternator
will provide power to these loads. However, if the vehicle engine is off, and
an electrical load is connected between the battery terminals such as when the
headlights are left on, or there is a short circuit or another fault occurs that
causes a drain on the battery, the battery output voltage will begin to decay.
With continued decay, the voltage at the sensing node 105 will eventually
fall below the threshold established by zener diode 110 and will cause the output
of amplifier 108 to drop and trigger operation of the timer 120. If the low battery
condition remains for a time period longer than the predetermine count, the output
of the timer 120 will rise and drive the output of amplifier 130 low. This low
output is connected to the base of PNP transistor 170, which begins to conduct,
thus turning on NPN transistor 172.
The collector of transistor 172 is connected through resistor 174
and diode 176 to the base of PNP transistor 178, which has its emitter connected
to the base of a PNP power transistor 180. The collector of transistor 180 is
connected to motor terminal 156. The collector of transistor 178 is connected through
line 177 and resistor 179 to the base of an NPN power transistor 182. The collector
of power transistor 182 is connected to motor terminal 154.
Accordingly, a low signal at the output of amplifier 130 will turn
on transistors 170, 172, 178, 180 and 182. Turning on these transistors causes
current to flow from the positive side of the battery through terminal 22 and
power transistor 180, through the motor from terminal 156 to 154 (which is opposite
the direction of current flow when the main switch 12 is open), and then through
transistor 182 to ground. This flow of current reverses the direction of motor
operation to drive the switch contact ring 90 away from the contacts 92, 94 and
disconnect the loads from the battery.
While the main switch 12 is open, battery voltage no longer appears
at terminal 22, and there is no drive current through transistor 180 to the remainder
of the circuit. Further energization of the motor is stopped as soon as the main
switch 12 is opened. Resistor 186, connected between the base of transistor 178
and terminal 22, and resistor 188 connected between ground and the base of transistor
148, provide bypass paths to ensure that the power transistors are cut off in their
non-operative states. This precludes the possibility of simultaneously engaging
opposite sets of transistors to drive the motor 70 in opposite directions.
Preferably, transistors 138 and 170 are back biased by a circuit
including resistors 160, 162, 164 and 166 connected to provide a positive potential
from the battery to the emitters of these transistors. This back bias circuit
prevents any ambiguous states for amplifier 130, which might otherwise engage both
transistor 138 and transistor 170 at the same time.
While the main switch 12 is open, after a fault has been sensed,
the reset circuit provides a relatively small but stable test current to the loads
(now disconnected from the battery). The test current will remain at its stabilized
value over a wide range of load resistances. The reset test current is generated
by PNP transistor 200 (corresponding to test voltage generator 44 of FIG. 1),
which has its emitter connected through resistor 202, line 26 and diode 100 to
the positive terminal of the battery. This transistor is not disabled by opening
of the main switch 12. The collector of transistor 200 is connected through diode
204 and test line 206 to terminal 22 of the main switch 12. Effectively, this
test current generating transistor 200 is connected in parallel with the main switch
12 to connect the battery directly to the load through transistor 200, diode 204,
resistor 202 and diode 100.
Current traveling through transistor 200 is stabilized at a very
small value so that a stable voltage of three millivolts is maintained at the cathode
of diode 204 at test point 48. The voltage at test point 48 is controlled and
stabilized by a closed loop control circuit including a first operational amplifier
210, having its noninverting input connected to test point 48 and its output connected
to the noninverting input of a second operational amplifier 212. Amplifier 212
has its output connected to the base of transistor 200. A test reference potential
is established at point 214 between resistor 216, connected to the positive terminal
of the battery, and diode 218 connected to ground. The test reference potential
is connected through resistor 220 to the inverting input of amplifier 212. This
arrangement provides a closed loop stabilization of the test current and voltage
at test point 48 in order to accommodate a wide dynamic range of load resistances.
The circuit will maintain a constant voltage at test point 48 whether
the load inadvertently left on (and causing the sensed fault) comprises small lights,
such as glove compartment or trunk lights, or headlights. However, when a second
predetermined load, such as the starter solenoid, is momentarily connected across
the small cold resistance of this load, a minor change in the load resistance
occurs that causes a small but sharp decrease in the test signal at point 48. In
the preferred embodiment described above, the second predetermined load comprises
the starter solenoid. It will however, be recognized by those skilled in the art
that the second load may comprise other suitable loads connected in a similar
This change is amplified by amplifiers 210 and 212 to provide a negative
pulse at the output of amplifier 212. This negative pulse is connected through
capacitor 222 to the noninverting input of operational amplifier 224. Operational
amplifier 224 has a reference voltage, established at its inverting input, between
the cathode of diode 205 and zener diode 228. Resistor 226, diode 205 and zener
diode 228 are positioned between the positive battery terminal and ground. The
negative pulse from amplifier 212 also provides a negative pulse at the output
of amplifier 224 connected to the base of NPN transistor 230, which cuts off this
normally conducting transistor 230.
Cutting off transistor 230 provides base drive for NPN transistor
232, which is driven into conduction. Transistor 232 is normally cut off by connection
of its emitter to the positive battery terminal through resistor 236. Turning
on transistor 232 places a low voltage across diode 240 and at the threshold voltage
reference point between the anode of zener diode 110 and the noninverting sensing
amplifier 108. Thus, during an attempted restart of the vehicle the threshold voltage
to amplifier 108 is lowered and the system is reset.
During the attempted restart, the reset system lowers the threshold
value to a point below the voltage of the battery at the time it was disconnected
from the load. As a result, the output of the sensing amplifier 108 rises, providing
a low output at the timer and a high signal at the output of amplifier 130. This
high from amplifier 130, as previously described, will energize the motor in the
switch closing direction and effect closing of the main switch 12. With the main
switch 12 closed, the battery power is again available to start the vehicle engine.
A disconnect delay circuit (element 66 of FIG. 1) is provided to
prevent the reset circuit from reconnecting the battery after the load is first
disconnected and a rapid decay of voltage at terminal 22 occurs. The disconnect
delay circuit comprises an operational amplifier 118 connected to a pair of resistors
244, 246. The non-inverting input to amplifier 118 is connected between resistor
117, which is connected to the emitter of transistor 128, and capacitor 119, which
is connected to ground. The inverting input to operational amplifier 118 is connected
to the cathode of diode 225. The resistors 244, 246 are connected between the output
of amplifier 118, and the base of transistor 232 and the collector of transistor
230. A diode 248 is connected across resistor 244 and its anode is connected to
ground through a relatively large capacitor 250.
Capacitor 250 in normal condition (the main switch 12 is closed)
is discharged, being connected to the normally low output of amplifier 118. Base
drive for transistor 232 is derived from the charge on this capacitor through
resistor 246. Thus, transistor 232 is normally off.
When the main switch 12 opens, the emitter of transistor 128 is pulled
high, which causes the output of amplifier 118 to rise. As this output rises, capacitor
250 begins to slowly charge through resistor 244. However, the charge on the capacitor
will remain at a relatively low value for several seconds because of the large
time constant of capacitor 250 and resistor 244. Therefore, transistor 232 will
not conduct for several seconds after the main switch 12 opens. The system reset
circuit is thus inhibited for a time, preferably on the order of several seconds,
immediately after the opening of the main switch 12. After the main switch 12 has
remained open for a sufficient time to allow capacitor 250 to become fully charged,
transistor 232 is turned on by the negative reset pulse provided from amplifier
224, which shuts off transistor 230.
While the engine is running, electrical noise from operation of the
alternator or the ignition appears at test point 48. This noise is amplified into
a series of square waves of approximately 12 volt amplitude at the output of amplifier
224. The noise signal, which appears on line 206 at point 48, is connected to a
pair of operational amplifiers 210, 212 that function as a high gain amplifier.
In a preferred embodiment, the gain of this high gain amplifier is about 44,000.
The output from the high gain amplifier is connected to the non-inverting input
of amplifier 224 through capacitor 222.
The engine running circuit, which is driven by the output of amplifier
224, includes a capacitor 225 and a pair of oppositely poled diodes 227, 229. Diodes
227 and 229 are connected to opposite sides of capacitor 106, which itself is
connected between ground and the non-inverting input of comparator amplifier 108.
The engine running circuit is, therefore, a pulse pump, which ensures that capacitor
106 remains charged above a certain voltage level.
On the rising edge of each of the square waves provided at the output
of amplifier 224, a small voltage increment is added to capacitor 225. This incremental
voltage is inversely proportional to the ratio of capacitor 225 to capacitor 106.
For example, with a ratio of 0.01:2, each square wave adds 1/200ths of the square
wave amplitude to capacitor 106. On each falling edge of the square wave, capacitor
225 discharges through diode 229. Capacitor 106, however, continuously discharges
through resistor 104. Thus, under engine running conditions, this circuit operates
to maintain a relatively high potential at the non-inverting input of comparator
amplifier 108, which prevents a drop in sensed battery voltage as long as the engine
is operating. Because the drop in sensed battery voltage is masked by the engine
running signal, opening of the main switch 12 is prevented.
Table 1 below includes a list of suitable components for some of
the elements described above.
BATTERY CABLE HOUSING
LS7210 Programmable Digital Delay Timer, Manufactured by LSI
Computer Systems, Inc.
Amplifier 108, 130, 118, 210, 212 and 224
LM358 Operational Amplifier
Transistor 128, 230, 232, 138, 172 and 148
2N3904 NPN Transistor
Transistor 200, 140, 170 and 178
2N3906 PNP Transistor
Transistor 152 and 180
2N5401 PNP Transistor
Transistor 150 and 182
2N5551 NPN Transistor
The battery protection system may be retrofitted to any existing
vehicle merely by inserting the system between the loads and the positive terminal
of the battery. It is also contemplated that this system may be incorporated as
part of the battery, or provided in a separate housing mounted directly upon the
battery or immediately adjacent the battery. The system may also be physically
and electrically incorporated into the battery itself so that the system can be
sold or installed in a vehicle together with, and as a part of, the battery.
Although there are many different ways in which the battery protection
system may actually be incorporated into the vehicle electrical system, in one
preferred embodiment the system is incorporated into the battery cable. Installing
this system merely requires replacing an existing battery cable with the new battery
cable. Such a battery cable is shown in FIGS. 5 and 6.
A modified battery cable including a first cable section 300, having
a connector 302, is adapted to be connected to a battery terminal. A second battery
cable section 304, having a connector 306, is adapted to be connected to vehicle
loads. Interposed between the two sections is the battery circuit protection system
308, which includes a housing molded or otherwise manufactured of suitable strong,
protective and non-electrically conductive plastic 310. The motor and switch assembly
illustrated in FIG. 2 are mounted (and may be potted) within the housing 310, and
are shown in FIG. 5 as a motor 370, a gear box 372 and the main switch 318.
The switch 318 has first and second sides or terminals 320 and 322,
respectively, which are electrically connected or insulated from each other upon
operation of the switch. One end of battery cable section 300 extends through
(and is fixedly connected to) one side of housing 310 and connects to switch terminal
320. Similarly, one end of battery cable section 304 extends partly through (and
is fixedly connected to) the other side of housing 310 and connects to switch terminal
A circuit board 350 is securely mounted (and may be potted) within
the housing 310 and connected through lines 352 and 354 to the switch terminals
320, 322, and through lines 356, 358 to the motor 370. The circuit 350 is also
connected through line 360 to the exterior of the housing 310 for connection to
Although the housing 310 may take many different forms, it preferably
comprises a nearly solid plastic body, which effectively encapsulates all of the
parts shown, and thus becomes a mere enlargement of an intermediate portion of
the common battery cable.
In another preferred embodiment shown in FIGS. 7A and 7B the battery
protection system can be situated directly on top of the battery between the terminals.
In this embodiment, the battery terminals are of a standard size according to the
Battery Council International and/or Society of Automotive Engineers. These terminals
may be tapered terminal posts where the negative terminal has a small diameter
of 12,7/20,3 cm (5/8") and the positive terminal has a small diameter of 27,9/40,6
cm (11/16"); both terminals possess a 1-1/3 taper per 30 cm (1 foot) and a 12,7/20,3
cm (5/8") minimum length of taper. In a fashion similar to that described above
in connection with FIGS. 5 and 6, the battery protection system of this invention
is enclosed in a housing 400 molded or otherwise manufactured of suitable strong,
protective and non-electrically conductive plastic.
Connected to the housing 400 is a battery terminal connector 402
which attaches to preferably the positive battery terminal 420. This connector
402 has the appropriate dimensions described above to connect to such terminal
420. Also connected to the housing 400 is a terminal 404. The terminal 404 is advantageously
configured such that a normal battery cable 424 may be connected to it. As such,
terminal 404 has the same dimensions described above for a positive battery terminal.
Also provided is a connector 406 coupled to the housing 400, which attaches to
the battery cable 426 preferably at the negative battery terminal 422. The connector
406 need not be a battery terminal connector such as battery terminal connector
402. Since the battery cable itself attaches to the negative terminal in the embodiment
shown in FIG. 7B, the connector 406 can simply be a washer or "C" connector that
fits within the battery terminal connector as shown.
In the manner illustrated in FIG. 7B, the battery protection system
is easily retrofitted to existing batteries. Instead of attaching the positive
battery cable 424 to the positive terminal of the battery 420, the cable is attached
to terminal 404. In the normal fashion, the negative battery cable 426 is attached
to the negative terminal 422. The battery protection system simply connects to
the battery at positive terminal 420 through connector 402, and at the negative
terminal 422 through connector 406. The dimensions of the housing 400 are such
that the battery protection system does not extend above the normal height of the
battery terminals 420, 422, nor beyond the top surface area of the battery.
There has been described a system that prevents discharge of a battery
to a predetermined point beyond which it cannot be used to start the vehicle engine
by sensing partial discharge of the battery and disconnecting all loads while
the battery still has sufficient energy to restart the vehicle engine. The system
ensures that the vehicle may be restarted simply by the normal operation of the
ignition switch. Such operation causes the protective system to generate a reset
pulse that immediately closes the main switch and provides battery power to the
starter and other loads.
It is to be understood that a wide range of changes and modifications
to the embodiments described above will be apparent to those skilled in the art,
and are contemplated. It is, therefore, intended that the foregoing detailed description
be regarded as illustrative rather than limiting, and that it be understood that
it is the following claims that are intended to define the scope of this invention.