Note: Descriptions are shown in the official language in which they were submitted.
~ 96~
B KGROUND OE` THE INVENTIVN
This invention is directed to a system particularly
useful for measuring and indicating the state of charge of a
storage battery. The system may be fabricated using any of
the many devices which are capable of measuring and indicat-
ing the integral oE an electrical signal. Such devices
include electronic devices such as counters, electromechanical
devices such as stepper motors, and electrochemical devices
such as coulometers and the inventive system will be described -`
in circuits employing such devices. It is, however, contem-
plated that the inventive system may be used advantageously ;~
with any integrating device.
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1 SUMMI~Y OF T}IE INVENTION
2 The present invention is directed to a system for
3 measuring the state of charge of a battery. The invention is
4 especially use~ul for monitoring rechargeable storage batteries
such as those used in battery powered vehicles which may include
6 various battery p~owered tools, such as fork lifts or the like,
7 and it will be described in detail in this context. However,
8 the inventive system may be used with any battery powered system
9 using rechargeable or non-rechargeable batteries.
Circuitry is provided for integrating a signal related
11 to the magnitude and duration of fluctuations in the battery
12 terminal voltage and for displaying the state of charge of the
I3 battery in terms of percentage charge remaining in the battery~
14 The display is similar to a display showing the fuel remaining
in a conventional gasoline powered vehicle and is therefore quite
16 easy for an operator familiar only with gasoline powered vehicles
17 to read and understand. The system may also be provided with a
18 deep discharge detector which, when the remaining charge in the
19 battery has been depleted below a predetermined level, disables .-
the various tools on the vehicle, leaving only those systems that
; 21 are essential for the operator to be able to return to a battery
22 charging station.
?3 In tha preferred er~odiment, connection of the battery .~;
2 to the vehicle results in the actuation of a circuit which de-
2 tects whether the voltage present at the terminals of the battery
' 26 is above a certain threshold value. Insofar as a newly charged
; 2 battery has an output voltage which is significantly higher than
2 the nominal terminal voltage, the threshold value is picked to ,
2 be about 10 percent above the norninal terminal voltage. If this
3 threshold voltage is detected by the circuit, it furnishes a
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fairly reliable indication that the battery is freshly charged
and causes the state of charge monitoring circuitry to produce
an indication that the battery is fully charged.
As the battery is used, varying load conditions placed
across the battery cause the voltage to be reduced. The magni-
tude and duration of each of these voltage reductions is monitored
by a threshold circuit which produces an output whenever the term~
inal voltage falls below a predetermined threshold. In accord-
ance with one embodiment of the invention, the output of the
threshold circuit is connected to circuitry which generates a
train of pulses in response to reductions in voltage. The
number of pulses generated is a function of the time during which
the terminal voltage is below the threshold voltage. Illustrat-
ively, the pulse generating circuitry takes the form of either a
voltage controlled oscillator or a relaxation oscillator.
The pulse generating circuitry is in turn connected to
integrating means for counting the pulses and accumulating the
count, thus generating an integral which is proportional to the
total time that the terminal voltage is below the threshold
voltage. This counting means may take the form of an electronic
counter or a stepping motor.
The output of the integrating means furnishes an indi-
cation of the state of charge. This indication is more accurate
than prior art devices since the integrating means accumulates ;~
the count for each time the terminal voltage falls below the ;~
threshold value. In the case of the electronic counter, the out~
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put of the integrating means may be converted to an analogue
signal and used to drive a conventional electric meter; and in the
case of the stepping motor, the motor may be used to position
the needle of a gauge. The output of the integrating means may
also activate an alarm which warns the operator that the state
of charge of his
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1 vehicle battery is at a predetermined low sta~e of charge and,
2 at a lower level of charge, may disable auxiliary functions cn
3 the vehicle such as the fork lift, thereby forcing the operator
4 to return to the base station for a fresh battery.
In an alternative embodiment, the magnitude and
6 duration of voltage reductions caused by varying load conditions
7 placed across the battery are monitored by a multiple-threshold
8 circuit whose output signal is related to the magnitude and
9 duration of the voltage reductions. This signal is stored by
an integrator which drives a display. The output of the inte-
11 grator, which may be displayed by a simple display device such
12 as a d'Arsonval electric m~oter, furnishes an indication of the
13 state of charge. The output of the integrator may also activate
14 an alarm as in the first embodiment.
16
17
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1 BRIEF DESCRIPTION OF T~IE DRAWINGS
2 Figure 1 is a schematic diagram of the power system of
a battery powered vehicle incorporating an illustrative control
4 system for monitoring the state of charge of the batteryi
Figure 2 is an alternative embodiment of a control
6 system constructe~d in accordance with the present invention;
7 Figure 3 is a perspective view of an indicator for use
8 in conjunction with still another embodiment of the invention;
9 Figures 4-6 are plan views of the indicato~ illustrated
in Figure 3 in various positions corresponding to different
11 levels of charge; .
12 Figure 7 is a schematic diagram of a battery state ..
13 of charge monitoring system incorporating the indicator illus-
14 trated in Figures 3-6; .
. Figu~e 8 is a schematic illustration in block diagram
16 form of an alternative monitoring system constructed in accord-
17 ance with the present invention; and
18 Figure 9 is a schematic representation of an alterna-
19 tive threshold detection circuit which may be used in the circuit
20 of Figure 8. .
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1 ETAILED DESCRIPTION OF Tll~ PREFI~RRED EMBODIM13NTS
2 For c~nvenience the invention will be described in a
3 number of illustrative embodiments particularly useful for
measuring the state of charge of the rechargeable batteries
in a ba-ttery powered vehicle. However, it is noted that the
invention may be~applied to any battery powered system whether
7 the system employs rechargeable or nonrechargeable batteries.
8 Turning first to Figure l, power is supplied to the
9 system by a battery l via mating connectors 3 and 5. Connection
of the battery to the system couples power to the essential
ll circuits 7 in the system which include all the electrical sub-
12 systems in the vehicle that are not to be disabled in response
13 to the detection of a depleted state of charge in the battery.
14 Connection of the battery to the system also results in the
application of the battery terminal voltage to voltage-dividing
16 resistors 9, ll and 13 with the result that the magnitudes of
17 the voltages at points 15, 17 and l9 are functions of the
18 magnitude of the voltage present at the output terminals of .
l9 battery l. The appearance of a voltage at point 15 results in .
the application of that voltage to sequencer 21. In response,
21 the sequencer produces a logical "0" output which is coupled to
22 an AND gate 23 causing it to be disabled and producing a logical
23 "0" output. AND gate 23 is disabled in order to make it unrespon
24 sive to any transients which may pass through the state of charge -
2 detecting circuitry via connectors 3 and 5. After a fixed period
2 of time which may be typically in the order of one second, or
2 as long as is necessary for all transients to subside, the output
of the sequencer becomes logical "l".
2 The voltage at point 19 is coupled to a reset compara-
3 tor 25 which compares it with a reference voltage source 27
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powered by battery 1. Reference voltage source 27 may be any
of a number of known circuits which provide constant voltages
as outputs even though they may be powered by a source which
varies within certain limits. Such circuits are well known
and may typically compxise Zener diode regulated voltage
sources or the like.
For batteries of the lead acid variety, the voltage
sent by reference voltage source 27 to comparator 25 is selec-
ted to be equal in magnitude to the voltage present at point
19 when the output terminal voltage of battery 1 is on the
order of 10% higher than the nominal terminal voltage of the
battery. This 10% figure is selected because, for lead acid
batteries, the terminal voltage of the battery when it is fully
charged is usually about 10% higher than its nominal terminal
voltage. Thus, if the output terminal voltage of the battery
is about 10% higher than its nominal terminal voltage, compara-
tor 25 will detect this condition by comparing the voltage at
point lg to the voltage coupled to the comparator by source 27
and will produce a logical 1 output. It has been empirically
2Q shown that this technique is generally quite reliable. Of
course, the particular value of terminal voltage which one
wishes to test for varies as a function of the nominal terminal
voltage of the battery and the battery type.
The logical 1 output of comparator 25 dxives one of
the inputs of AND gate 23. The other input of AND gate 23 is
driven by sequencer 21. AS noted above, the sequencer changes
its output from logical 0 to logical 1 after transients in
the system have subsided. The presence at the input of AND
gate 23 of the logical '1 output of comparator 25, which indi-
cates that the battery is fully charged, and the logical 1
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output of se~uencer 21, which indicates that transients have
subsided, causes the output of AND gate 23 to produce a
logical "1" output. This logical 1' output is coupled to
and drives the "clear' input of a counter 29, thereby clearing
any signal that may be in the counter. Outputs 39a-g of
counter 29 have two digital states 0 and 1' and display the
output of counter 29 in binary code with output 39a being the
least significant digit and output 39g the most significant.
When the counter is cleared, all of its outputs 39a-g are
logical 0~, indicating that the battery is fully charged.
Outputs 39d and 39g are coupled to a NAND gate 41
whose output drives lockout circui-t 43. The two logical "0"s
at the input of NAND gate 41 cause it to have a logical "1"
output. This logica~ "1 output causes lockout circuit 43 to
close the contacts 45 of a relay 47 and couples power to the
nonessential electrical circuits 49, such as the power lift of
an electrical truck. Since output 39g is the most significant
output, it will not change to a '1' output until half the total
- capacity of counter 29 is counted. When this happens, the
logical '1' will actuate an alarm 57, notifying the operator~
The output of NAND gate 41 will not change until more than half
the total capacity of counter 29 has been counted when a digital
value which includes a logical "1' at outputs 39d and 39g is
first reached. At this time, lockout circuit 43 will open con-
tacts 45, which will remain open, thereby disabling nonessential
circuits 49. The operator of the vehicle is thus forced to
return to the charging station because the nonessential task
performing circuits such as the power lift of the vehlcle are
disabled while such nonessential circuits such as the traction
motor are still operable. As will be evident, the point at
8.
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which loc]cout circuit 43 is activated, can be modified simply
by selectiny the appropriate output leads 39a-g to control NAND
gate 41.
- It has been found experimentally that the time that the
voltage is below threshold is a measure of the state of charge
of the battery. Thus, as the battery is used, a picture of its
sta-te of charge can be continuously constructed by cumulatively
storing the periods of time that the terminal voltage remains
below a given threshold.
Reductions in the terminal voltage are detected by a
tracking comparator 35 which compares the voltage present at
point 17 to the voltage provided to comparator 35 by reference
voltage source 27. The voltage coupled by reference voltage
source 27 to comparator 35 is selected to be approximately equal
to the voltage at point 17 when the output terminal voltage of
the battery is at the desired threshold. The voltage at point ~ ~
17 is coupled to comparator 35 by a tracking filter 36 which ~ ;
prevents transients and other signals unrelated to depletion
in the state of charge in the battery from being registered in
the monitoring circuitry. Setting the response of filter 36
to eliminate transients faster than 10 milliseconds to
;~ 100 milliseconds has been found to give excellent results, as this
effectively eliminates microsecond and millisecond transients
which are not related to charge depletion.
AND gate 37, which is coupled to the clocking input
of counter 29, is responsive to the output of tracking comparator
35, to a free-running oscillator 39 and to the output of NAND gate `
41. When counter 29 is cleared by the pulse from AND gate
indicative of full charge, all of its outputs become logical "0",
and outputs 39d and 39g cause NAND gate 41 to produce a logical "1"
at its output.
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If there is then a drop in battery voltage below
threshold, this drop will be detected by comparator 35 which
will in turn apply a logical 1 to the input of AND gate 37.
With the output of comparator 35 and NAND gate 41 logical 1 ,
the periodic pulsed application of a logical 1 signal to AND
gate 37 from oscillator 39 will result in the periodic appli-
cation of a pulsed logical 1 signal from AND gate 37 to the
clocking input of counter 29. This advances the count of the
counter which accumulates the number of pulses applied from
gate 37, said number being proportional to the total time that
the terminal voltage has been below the threshold value. In
ordinary usage, the terminal voltage will have to fall below
the threshold value several times before the count in counter
29 becomes high enough to trigger alarm 57.
The output of counter 29 is converted to an analogue
signal by summing resistors 51a-g. Resistors Sla-g have success-
ively lower values, each resistor having a value of resistance one
half that of the previous resistor. Thus, resistor 51a has a value
of R ohms, resistor 51b a value of R/2 ohms, resistor 51c a value
of R/4 ohms and so forth. ~he current output from resistor 51b is
thus twice the current output from resistor 51a, while the current
output from resistor 51c is four times the output current from re-
sistor 51a, etc. The outputs of the resistors are coupled together
and sent to an inverting amplifier 53 which sums them, Because
amplifier 53 is an inverting amplifier it has a maximum output
when outputs 39a-g are all logical 0 . This results in a full
scale deflection of meter 31 which is gradually decreased to zero
as pulses are stored in counter 29. Because these pulses are peri-
; odic and are only coupled from the oscillator during the time that
the tracking comparator senses a voltage below threshold, the num-
ber of pulses stored is proportional to the total amount of time that
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1 trclcking compara~or 35 has detec~cd a voltage below threshold.
2 Thus, the display on panel meter 31 reveals the state of charge
3 of the battcry. -
4 ~ Depletion of the state of charge in a battery powered
~ system results in longer and deeper transient voltage reductions
6 in rcsponse to transien-t load condi-tions. It may therefore be
7 desirable to vary the threshold of comparator 35 in response to
8 the integral stored in counter 29. Specifically, because of the
9 increasing magnitude of voltage reductions with decreasing state
of charge, it may be desirable to be able to lower the threshold
11 value in response to a lower level of charge in the battery.
12 This may be done by connecting a resistor 53' from the output of
13 amplifier 53 to the input of tracking comparator 35, as is
14 illustrated in phantom lines.
16 The longer and deeper transients in output terminal
16 voltage which occur in response to increasingly lower states of
17 charge in a battery may also be compensated for by making the
18 response of trac~ing filter 36 a function of the integral stored
19 in counter 29. This may be done using the feedback path, shown
in phantom lines in Figure 1, extending between amplifier 53 and
21 filter 36. -
22 Under various circumstances, battery 1 may be~ dis-
23 connected from the system and then reconnected. In order to
2 prevent counter 29 from losing the count stored in it, it is
2 necessary to provide the system with a memory battery 79 which
supplies power to counter 29 during the interval that the battery
2 1 is disconnected. Memory battery 79 is coupled to counter 29
2 by diode 81 which i5 biased into the nonconductiny region by
2 diode 83 when battery 1 is connected in the circuit.
3 ~eferring to Figure 2, an alternative embodiment of the
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1 apparatus of the present invention is illustrated. The operation
2 of this system is largely identical to that of the system illus-
3 trated in Figure 1. The primary difference is that oscillator
4 39, tracking comparator 35 and AND gate 37 have been replaced by
tracking comparator 35', self-resetting integrator 39' and ~ND
6 gate 37'~ When a`voltage bclow the threshold value is detected
7 by comparator 35', it produces an output current which is fed
8 via diode 61 and resistor 63 to capacitor 65. The voltage pre-
9 sent across the capacitor is applied to terminal 67 of a uni-
junction transistor 69. Terminal 71 of the unijunction transisto
11 is provided with a bias voltage by a voltage divider comprising
12 resistors 73 and 75 which are connected to a source of DC power.
13 Whenever the output of tracking comparator 35' becomes active,
14 it sends current into capacitor 65, thereby raising the voltage
at terminal 67. This ~oltage is stored in capacitor 65 after the
16 tracking comparator returns to its unactivated state, and it
17 resumes increasing as soon as tracking comparator 35' is again
18 actuated. .
lg When the voltage at terminal 67 becomes high enough,
unijunction transistor 69 is driven into conduction, thereby
21 producing an output at its terminal 77. This signal is coupled
22 to AND gate 37' and, when NAND gate 41 is active, results in
23 the passing of a pulse to counter 29 and advancement of the
2 counter. During the course of completely discharging a battery,
capacitor 65 is charged and discharged a great number of times
X6 with the resultant application of a pulse from terminal 77 and
2 AND gate 37' every time the capacitor is discharged. It is thus
seen that self-resetting integrator 39' produces a train of
2 pulses in response to tracking comparator 35' in place of oscilla
3 tor 39 of Fig. 1.
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~n alternative embodiment of the present invention is
illustrated in Figures 3-7. Referring to Figure 3, an indicator
100 comprising a stepping motor (not shown in this ~igure) that
drives a disk 103 via shaft 101 replaces the counter, memory
battery and display unit in the other embodiments. The stepping
motor is advanced an increment every time it receives an elec-
trical pulse. I'his advances disk 103 which includes an indicator
tab 105 indicating the state of charge of the battery on a cali-
brated scale 107. The angular position of the disk 103 serves
as an indication of the state of charge of the battery. Disk
103 includes four tracks 104, 111, 113, and 115 which contain
information cutouts 117, 119, 121 and 123, respectively. Cutout
117 serves to indicate when the indicator is in the full position.
Cutout 119 serves as a warning slot indicating that the battery
has been seriously discharged and that lift lockout will soon
occur. Cutout 121 provides a control signal for the lift lockout `-
and finally, cutout 123 provides control information for pre-
venting further advancement of the disk when discharge is complete.
This particular information is especially important if the indi-
cator is so constructed that the scale takes up a major portion ~
of the angle through which the disk moves and further advancement ~;
of the disk is likely to advance the tab 105 to the full position
though the battery is depleted. It is also noted that, if desired,
some economy may be obtained by using cutout 121 to perform the
function of hole 123, thus eliminating the need for one of the
tracks with its associated circuitry. In this case, cutout 121
would be shaped like hole 123.
The information-contained in the cutouts is read by
~ . .
four light emitting diodes 125, 127, 129 and 131 and correspond-
ing photocells 133, 135, 137 and 139. Initially, the disk is
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at the Eull position where light is allowed to pass only from
light emitter 125 to its associated photocell 133, as illustra-
ted in Figures 3 and ~. As the battery is depleted and the disk
advances in response theeeto, the light from diode 127 begins
to pass through cutout 119 onto photocell 135, activating appro-
priate warning circuitry and indicating that lift lockout will
soon follow. This condition is illustrated in Figure 5. The
disk next passes to the position shown in Figure 6, where light
also begins to pass from light emitting diode 129 to photocell
137. This causes the actuation of the lift lockout circuitry.
Finally, as the battery continues to be discharged and the disk
continues to rotate, light from light emitting diode 131 begins
to pass through cutout 123 and impinge upon photocell 139. This
prohibits further rotation of disk 103 and thus prevents it from
continuing to rotate until it again reaches the full position.
A typical control circuit for use with indicator 100
is shown in Figure 7. Power to the system is supplied by a
battery 201 via mating connectors 203 and 205. Connection of
the battery to the system couples power to essential circuits
207 which include all the systems in the vehicle that are not
to be disabled in response to the indication of a depleted state
of charge in the battery. Connection of the battery to the sys-
tem also results in application of the battery terminal voltage
to voltage-dividing resistors 209, 211 and 213, with the result
that the magnitudes of the voltages at points 215, 217 and 219
are functions of the magnitude of the voltage present at the
output terminals of battery 201.
The appearance of a voltage at point 215 results in
the application of that voltage to a sequencer 221. In response ~ -
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~ L0~9614
1 the sequ~ncer produc~s a logical "0" output, which is coupled to
2 an AND gate 223, causing it to be disabled and producing a logica
3 "0" output. AND gate 223 is disabled in order to cause it to be
4 unresponsive to any transients which may pass through the system
during connection o~ the battery via connectors 203 and 205.
6 After a fixed period of time which may typically be in the order
7 of one second, or as long as is necessary for all transients to
8 subside, the output of the sequencer becomes logical "1".
9 Connection of the battery to
the system also results in the presence at point 219 of a voltage
11 whose magnitude is proportional to the voltage present at the
12 output terminals of battery 201. This voltage is coupled to a
13 reset comparator 225 which compares it with a reference voltage
14 supplied by a reference voltage source 227 which is powered by
battery 201. If comparator 225 detects that the voltage present
16 at the output terminals of battery 201 i5 abovP a threshold which
i7 may typically be in the order of 10 percent higher than the
18 nominal terminal voltage of the battery for batteries of the lead .
19 acid variety, comparator 225 will produce a logical "1" output.
This output, together with the logical "1" output of the se-
21 quencer, will actuate AND gate 223 causing a logical "1" pulse
22 to appear at its output.
23 This logical "1" pulse is then coupled to a bistable
reset circuit 229, thereby setting the circuit and coupliny a
2 relatively large voltage via diode ~31 and resistor 233 to a
2 voltage controlled oscillator 235. This voltage controlled
2 oscillator has a characteristic that when no signal is coupled
2 to it, it produces an extremely low frequency oscillation having
2 a frequency essentially equal to zero. When a relatively small
3 voltage siynal
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is coupled to it, it has a relatively low Ere~uency signal at its
output; and when a relatively large voltage signal is coupled to
it, it has a relatively high freguency signal at its output. Thus,
the relatively large voltage signal coupled to osciallator 235 re-
sults in a relatively high frequency signal which is coupled to
stepping motor driver amplifier 237. This amplifier dr~ves coil
239 oE the stepping motor that drives disk 103 relatively quickly
until pointing tab 105 reaches the position indicative of full
charge. This condition is detected by photocell 133 when light
10 from light emitting diode 125 falls upon it in this position
through cutout 117. This condition is sensed by full charge sens-
ing circuit 140 which resets the output of bistable flip-flop 229,
thus removing voltage from voltage controlled osciallator 235.
The terminal voltage is monitored by a comparator 241
which compares the voltage present at point 217 to a voltage which
is a function of one of the outputs of reference voltage 227. The
voltage present at point 217 is coupled by filter 242 whose func-
tion is identical to filter 36 in Figures 1 and 2. The output oE
comparator 241 is coupled to voltage controlled oscillator 235
20 via AND gate 246, diode 245 and resistor 243.
AND gate 246 is controlled by detector 248. When there
is no light impinging on photocell 139, as in the case of the full
charge position, detector 248 produces a logical 1 , enabling AND
gate 246. Thus, after indicator 100 has been set to a full indi- ~ -i7
cation, the detection by comparator 241 of a drop in voltage below
the predetermined threshold results in the application of a logi-
cal 1 input to AND gate 246 which is enabled by the output of
detector 248. The output of AND gate 246 is a relatively low
voltage signal which is applied through diode 245 and resistor
243 to oscillator 235 to produce a relatively low fre~uency
signal and thus advance the stepping motor at a relatively low
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rate in response to the reduction of the battery' 5 terminal
voltage below the threshold value. It is thus seen that the
display on indicator 100 is advanced relatively quickly during
reset and relatively slowly during operation.
As the stepping motor is advanced, light Erom light
emitter 127 is caused to impinge upon photocell 135 through
cutout slot 119. Actuation of photocell 135 results in the
detection of this condition by warning lamp circuit 247 which
in turn illuminates a warning lamp advising the operator that
lift lockout is about to occur.
Further advancement of the motor results in further ;~
rotation of disk 103, causing cutout slot 121 to align with light
emitting diode 129 and photocell 137, thus actuating photocell 137
and coupling a signal to lift lockout lamp circuit 249 which in
turn actuates a lift lockout lamp to advise the operator of the
fact that the lift has been locked out. Lockout of the lift is
accomplished by coupling a signal from photocell 137 to lift lock-
out circuit 251 to actuate the lockout circuit, thereby opening the
contacts 253 of a relay 255 and disconnecting power from nonessen-
20 tial electrical circuits 257. It is noted that relay 255 may be re-
placed by any well known equivalent such as an SCR or triac. As in
the case of the apparatus disclosed in Figures 1 and 2 when a full
charge is detected, the lockout circuit may be reset to connect
power to the nonessential circuits 257. In the interest of sim- ~
plicity, this resetting apparatus is not shown in Figure 7. ~ .
Still further rotation of disk 103 results in aligning
circuit 123 with light emitting diode 131 and photocell 139. This
results in a logical 0 at the output of detector 248. This log-
ical 0 disables further advancement of indicator 100.
Another alternative embodiment of the invention is illus-
; trated in Figure 8. When lt is desired to put a vehicle into
17.
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service, a battery 310 i5 connected via connectors 312 ancl 314into the vehicle s monitoring system. This causes actuation of
a timing circuit 316 which, after a delay typically in the order
of one second, actuates comparator 318 for a period also typi-
cally in the order of one second. If the voltage present at the
output terminals of battery 310 is unusually high in comparison
to the nominal terminal voltage, comparator 318 produces a pulse
at its output. This pulse serves as an indication to the remain-
ing circuitry in the system that the battery is sufficiently
10 charged. The function of comparator 318 and timing circuit 316
is similar to that of sequencer 21 and reset comparator 25 of
Fig. 1 and will not be discussed further.
Reference voltages are provided for comparator 318 and
several other elements of the system by a reference voltage cir-
cuit 315 that produces reference voltages A, B, C and D using
conventional circuitry. As shown reference voltage A is applied
to comparator 318.
An integrator 328 is used to store a signal that is
representative of state of charge. Initially, integrator 328 in -~
the vehicle monitoring circuit has an integral stored in it which
represents the state of charge of the last battery used in the
vehicle. When a new battery is placed into the vehicle, it thus
becomes necessary to reset the integrating device. When compara-
tor 318 senses that an unusually high voltage is present across
its input and hence that a new battery has been connected to the
system, it sets a bistable circuit (e.g. a flip-flop) 320, whose
output is used to set integrating device 328 to zero as will be
explained below. Bistable 320 also actuates clamp circuit 322
which, through unity gain amplifier 324, cause the display of a
~i 30 full charge indication on meter 326. The clamp circuit thus `
!' ' causes the display of the full charge condition detected by
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comparator 318 regardles~ of the integral stored in the inte-
qrator. This is necessitat~d due to the act that the integrator
may ~ake several minutes to reset, bu~ it is desired to display
the fully charged condition of the battery ~unediately.
Integrator 328 may comprise any circuit which is cap-
able of integrating electrical info~mation and providing an out-
put signal which is propor~ional to the integral, Such an
integrator circuit is shown in Eugene P. Finger and Edward M.
Marwell's Uniked States Patent No. 4,012,681 entitled "Battery
10 Control Syste3n For Battery Operated Vehicles" filed January 3,
1975 and issued March 15, 1977, Edward M. Marwell and Curtis
Busman's United States Patent No. 3,255,413 ~ssued June 7, 1977
and entitled "Elec~ro-Chemical Coulometer Including Differential
Capacitor Measuring Elemen~s" and Eugene P. Fingeris United
States Patent Nos. 3,704,431 and 3,704,432 both issued No~ember
- 28, 1972 and entitled Coulometer Controlled Variable ~requency
Generator" and "Capacitive Coulcaneter Improvements".
In such integrator circuits, integration is performed ;
by an electrochemical coulometer which receives curren~ from an
- 20 electrical signal source, the integral of whose output is indica-
tive of the parameter which one wished to monitor. Advancement
of the coulo~neter results in changing the l~ngth of the mercury
columns in the coulometer and consequently the capacitive coupling
between one of the mercury columns and a metallic plate disposed
around the body of the coulometer. An oscillator in series with
a capacitor is put in parallel with the coulometer, thereby
causing an AC voltage to appear on the plate. This electrical
voltage is proportional to the capacitance between the column of
mercury in electrical contact with the capacitor and the plate
30 disposed around the coulometer bo~ly. This AC voltage present
- on the plate is then amplified and sent to a simple amplitude
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detector which produces a DC output proportional to the peak-
to-peak value of the AC voltage coupled to the plate. In the
circuit of Figure 8, ~his DC voltage is the output of integrator
328. As will be explained below, it is representative of the
state of charge of the battery and is coupled to amplifier 324.
In such a system, resetting of the integrator is accom-
plished by passing a current through the coulometer. This cur-
rent is in a direction opposite that of the signal source which
advances the coulGmeter and has a magnitude relatively large
compared to the magnitude of the current produced by that signal
source. This may most conveniently be done by incorporating an
SCR in bistable 320 and passing the output of bistable 320
through the coulometer.
The value of the integral stored in integrator 328 is
sensed by comparator 330 and compared with a value corresponding
to full charge voltage as determined by reference voltage B.
When the integrator reaches full charge, the comparator resets
bistable 320 which, in turn, disables clamp circuit 322. The
output of integrator circuit 328 is then free to drive amplifier
324, thereby displaying on meter 326 the integral representative
of the state of charge of battery 310 which is stored in the
integrator.
As the charge stored in battery 310 is depleted, the
- placement of varying load conditions across the battery results
in a corresponding fluctuation in the voltage present at the
battery terminals. The present invention obtains a signal indica-
tive of the state of charge of a battery by monitoring the magni-
tude and duration of drops in terminal voltage. The magnitude
and duration of the decrease in terminal voltage is detected by ~ -
circuit 332 and sent to the integrator 328. Circuit 332 is a
:
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1~3614
1 circuit which will produce a cuxrent at its output which is
responsive to the voltage at the battery terminals. Thus, in
3 the preferred embodiment, as the voltage at the output of
battery terminal 310 drops below a threshold, circuit 332 is
actuated to feed a current to integrator 328, thereby advancing
6 integrator 328 so~that the voltage level displayed on meter 326
7 decreases from that indicative of full charge. The output of
8 circuit 332 is active only for the time when the voltage is
9 below its threshold value and returns to its inactive state in
response to a rise in terminal voltage above that threshold value.
11 In most batteries, the terminal voltage will drop below
12 the thre~hold more frequently and for longer periods of time as
13 the battery charge is increasingly depleted, but the relationship
14 between time below threshold and state of charge is not linear.
-15 This non-linear relationship is compensated for through the non-
16 linear action of circuit 332.
17 A particularly advantageous non-linear circuit 332 is
18 illustrated in Figure 8. This device comprises a threshold
1~ detector 334 which, when the voltage at the terminals of battery
20 310 drops below its threshold, produces an electrical signal
21 which advances integrator 328. ~urther reductions in terminal
22 voltage below successively lower thresholds results in actuation
23 of successive threshold detectors 336 and 338. Detectors 334,
24 336 and 338 are se~uentially and individually actuated (i.e.,
; 25 non-cumulatively) in response to voltage reductions with detectors
.26 334, 336 and 338 having, respectively, high, medium and low thres-
27 holds and, respectively, high, medium and low outputs. This
28 results in successively reducing the effect on integrator 328 of
~ successively greater reductions in terminal voltage. Thus, as
: 50 the frequency, duration and magnlt~de of voltage reductions
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increase, their increasing magnitude results in a successively
decreasing effect on integrator 328.
~ lternatively, detector 334 may produce a constant
output once it is actuated, and detectors 336 and 338 may be
successively and cumulatively actuated to produce outputs having
opposite sense to and lesser but fixed magnitude in comparison
to the output of detector 334. Detectors 336 and 338 would thus
have the effect of reducing the output of circuit 332 as the
magnitude of voltage reductions increases. In the alternative,
the use of a non-linear display device will also serve the func-
tion of linearizing the display.
When the output of integrator 328 reaches a value
corresponding to a first predetermined low state of charge in
battery 310 as determined by reference voltage C, it triggers
threshold circuit 340 which actuates a low capacity warning light
in order to warn the operator of the battery's condition. Fur-
ther use of the battery with corresponding further reductions
in the output of integrator 328 results in the actuation of
threshold circuit 342 when the output of the integrator reaches
a still lower value determined by reference voltage D. Actuation
of circuit 342 removes electricity from nonessential systems on
a vehicle such as the lift, thereby leaving the vehicle with
power applied only to such essential functions as the traction
motor and forcing the operator to return to a central station
for a newly charged battery.
Insofar as certain integrating devices such as electro-
chemical integrators may be damaged if they are driven beyond
their limits of integration, deep discharge rejector 344 and
over charge rejector 346 will be responsive to the output of the
integrator to prevent further integration at a point before the
22.
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1 limits o~ integration of in~ecJratOr 328 are exceeded. ~ejector
2 circuits 3~4 and 3~6 will thus protect inteyrator 328, during
3 discharge of the battery and resetting of integrator 328,
respectively. In the case of a system using an electrochemical
coulometer as an integrator, rejectors 344 and 346 may simply
6 take of the form of current sources which are activated by
7 threshold circuits to produce at the limits of integration a
8 current opposite in direction to the current which is advancing
g the electrochemical coulometer.
~0 Referring to Figure 9, an alternate threshold detection ~ ~
11 circuit 332' is illustrated that can be used in place of the -
circuit 332. ~hreshold circuit 332' comprises thxeshold detectors
13 350a-n that are triggered at a voltage level responsive not only
14 to the voltage present at the output of battery 310 but also to
a feedback voltage coupled by resistors 352a-n from the output
la of integrator 328. Threshold detectors 350a-n advance integrator
17 328 at a rate proportional to the value of their respective out-
1~ put resistors P~a-n. Threshold detectors 350a-n may simply be
1~ comparators which change their output at different threshold
20 values which are a function of the voltage fed back from integra-
21 tor 328 by resistors 352a-n and reference voltages coupled from
2~ reference voltage source 315' by resistors 356a-n. For the
23 circuit shown in Figure 9, detectors 350a-n are successively
24 and cumulatively actuated at dif~erent threshold values determined
~5 by reference voltage source 315' in a similar fashion as the
alternative non-linear circuits 332 of Figure 8 discussed three
27 paragraphs above. Thus, comparator 350b couples a current through
28 resistor Rb which is oppositP in sense and lower in magnitude
~ than the output of compara~or 350a so that as the voltage at the
50 battery terminal becomes lower and comparator 350b is actuated,
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1 the output of circuit 332' is reduced and causes a reduction in
2 the rate at which the int~rator advanccs. Comparators 350c-n
3 operate in similar fashion with the limitation that the cumula-
tive e~fect of operation of comparators 350b-n does not exceed
the effect of operation of comparator 350a to which they are
~ opposed.
7 The operation of this circuit iis such that as the out-
8 put of the integrator indicates the storage of an increasingly
9 large integral (and therefore greater depletion of the battery),
the output voltage that is fed back by resistor 352a serves to
11 effectively lower the threshold values of the terminal voltage
12 of battery 310 which will cause actuation of threshold detectors
13 350a-n. Thus, as the battery is depleted and the frequency and
-14 duration of the battery's tendency to drop below any given fixed
threshold increases, the thresholds are lowered in order to
16 require greater and greater reductions in terminal voltage to
17 actuate comparators 350a-n. This feedback arrangement thus
18 reduces or nullifies the relatively rapid advancement of the -~-
19 integrator that would occur as the battery's charge is increas-
ingly depleted if the threshold of the detector circuit were not
21 varied. At the same time it permits relatively rapid advancement
22 of the integrator if the battery terminal voltage should go
23 below threshold early in the operating cycle when the output
24 of integrator 328 indicates a full charge or a value close theretc .
This has the advantage of permitting the integrator to "catch
26 up" if a partially charged battery has been connected by mistake
27 to the monitoring system. If such a battery has been given a
28 short high charge, its terminal voltage initially may be high
29 enough to be accepted by comparator 318~ T~ereafter, however,
the terminal voltage falls off quickly permikting relatively
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rapid advancement of the integratorV signifying that the
battery has not been properly charged.
Further variations in the feedback circuit may be ob-
tained by making resistors 352a-n non linear resistive elements.
This may also result in improving the linearity of the output of
integrators 328 as an indication of the state of charge.
Although the circuit has been described using a plur-
ality of comparators 350a-n, it will also work well with just a
single comparator 350a. It should also be noted that just as
10 the threshold of the threshold circuit may be varied in response ; ;
to the value stored in the integrator as is done in the embod-
iment illustrated in Figure 9 so also may the output of the
threshold circuit be varied in response to the output of the
integrator. For example, this may be done by using in place of
resistors Ra-n photoresistive devices whose resistance changes
in response to incident light. The output of integrator 328 may
then be made to drive a light source whose light would be made
to fall upon the photoresistive devices and thus vary their
resistance as the autput of integrator 328 is varied. Variation
; 20 of the resistance of the photoresistive devices results in vary-
ing the current output of comparators 350a-n, thereby varying
the output of the threshold circuit.
As will be apparent, a plurality of threshold detectors
~; may also be used in the circuits illustrated in Figures 1 - 7
to synthesize any desired response by the selection of various
thresholds and various electrical outputs for each of the plur-
ality of threshold detectors. For example, a synthesized re-
- sponse can readily be used to charge capacitor 65 of Figure 2;
or apparatus could be provided to apply clocking pulses to the
30 digital counter of Eigure 1 at different rates depending on which
threshold detector was activated. The feedback circuits shown in
Figures 8 and 9 can likewise be implemented in the apparatus for
25.
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Figures 1-7 as is indicated by resistor 53~ of E`igures 1 and 2.
With respect to the embodiment of ~igures 3-7, feedback may also
be provided by the use of additional light emitting diode (LED)
and photocell combinations.
The embodiments in Figures 1-9 disclose a system in which
a threshold circuit produces an intermediate output signal during
the time in which the magnitude of the battery terminal voltage is
below a threshold value. This signal is then integrated to provide
a first output signal and in typical operation is accumulated over
several different intervals in which the magnitude of the battery
terminal voltage is reduced below the threshold value. It should be
noted that the threshold value need not remain constant during the
period that integration is taking place. For example, in those de-
vices in which there is feedback from the integrator the threshold
value may vary during the period of time the battery terminal volt-
age is below it. It may also be advantageous to produce an inter-
mediate output signal which continues for a fixed period of time
after the voltage rises above the threshold. Finally, it should be
recognized that transient excursions below the threshold value will
not be integrated in those circuits that use a filter to eliminate
such transients.
Since the threshold circuit is not activated until the
magnitude of the terminal voltage is below a threshold value, the
first output signal may also be described as a function of the
magnitude of the terminal voltage. In the embodiments shown in
Figs. 1-7, the magnitude of the intermediate output signal does
not vary with the magnitude of the battery terminal voltage pro- `~
vided that magnitude is less than the threshold value. Where a
plurality of threshold detectors are used, however, the magni-
tude of the intermediate output signal does vary as a func-
tion of the magnitude of the battery terminal voltage even
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26.
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1 I when the batt~ry terminal volta~e is below the first threshold
2 ¦ value. In the embodiments shown in Figures 8 and 9, this
3 ¦ variation is in discrete steps. ~ppropriate circuitry for
4 ¦ providing an analogue intermediate output signal will also be
5 ¦ evident to those skilled in the art.
6 ¦ The intermediate output signal from each of the thres-
7 ¦ hold detectors shown in Figure 9 will be recognized as a
8 ¦ function of the difference between the battery terminal voltage
9 ¦ and a reference voltage that is a function o~ the output o~
10¦ integrator 328 and the output of reference source 315'. As will
11¦ be evident, various transfer functions can be synthesized
12¦ depending on the particular feedback circuitry used. All these
13¦ modi~ications are contemplated to be within the scope of the
1~¦ invention. In addition, since the invention can be practiced
15¦ using either a positive voltage polarity or a negative voltage
16¦ polarity, it will be recognized that either one is fully the
17¦ equivalent of the other and both are within the intended scope
18¦ of the claims.
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