U.S. patent number 3,867,681 [Application Number 05/452,804] was granted by the patent office on 1975-02-18 for battery charging circuit.
This patent grant is currently assigned to General Electric Company. Invention is credited to Larry D. Bishop, William R. Smith.
United States Patent |
3,867,681 |
Bishop , et al. |
February 18, 1975 |
BATTERY CHARGING CIRCUIT
Abstract
Batteries in locations such as unattended telephone buildings
are kept in a good and reliable condition by a circuit which
provides a normal charge periodically, which provides a normal
charge each time the primary electrical power fails and is
restored, and which provides an equalizing charge for a
predetermined length of time in response to a manual or automatic
operation.
Inventors: |
Bishop; Larry D. (Lynchburg,
VA), Smith; William R. (Lynchburg, VA) |
Assignee: |
General Electric Company
(Lynchburg, VA)
|
Family
ID: |
23798005 |
Appl.
No.: |
05/452,804 |
Filed: |
March 20, 1974 |
Current U.S.
Class: |
320/158 |
Current CPC
Class: |
H02J
7/0069 (20200101); H04M 19/06 (20130101) |
Current International
Class: |
H02J
7/00 (20060101); H04M 19/00 (20060101); H04M
19/06 (20060101); H02j 007/04 () |
Field of
Search: |
;320/29-34,37,38,39,40,21,22,14,19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; J. D.
Assistant Examiner: Hickey; Robert J.
Claims
What we claim as new and desire to secure by Letters Patent of the
United
1. An improved circuit for charging a battery from a charging
source, comprising:
a. a voltage regulator adapted to be connected to the charging
source, said voltage regulator having a control input for
selectively causing said voltage regulator to produce an upper
regulated voltage and a lower regulated voltage at its output;
b. a current regulator connected to said voltage regulator
circuit;
c. a normally open charging path having an input connected to said
current regulator, having an output, and having a control
input;
d. means connected to said charging path output and adapted to be
connected to the battery to be charged;
e. a voltage comparator having an input adapted to be connected to
said battery to be charged for producing a first charging signal in
response to a battery voltage below a selected voltage reference
level;
f. a first timer for producing a second charging signal at selected
predetermined intervals;
g. a power fail and restore circuit for producing a third charging
signal in response to failure and subsequent restoral of primary
power;
h. a second timer for producing a fourth charging signal of a
selected duration in response to a selected operation;
i. means connected between said voltage comparator, said first
timer, said power fail and restore circuit, and said second timer
and between said charging path control input for closing said
charging path in response to the simultaneous presence of said
first charging signal and either of said second and third charging
signals, and in response to said fourth charging signal;
j. and means connected between said second timer and said voltage
regulator control input for causing said voltage regulator to
produce said upper regulated voltage in the presence of said fourth
charging signal and for causing said voltage regulator to produce
said lower regulated voltage in
2. The improved circuit of claim 1 wherein said selected voltage
reference level varies inversely as a function of the ambient
temperature
3. The improved circuit of claim 1, and further comprising a latch
circuit connected to said first timer and to said power fail and
restore circuit for producing a continuous second charging signal
and a continuous third charging signal in response to said second
charging signal and said third charging signal respectively, and
means connected between said voltage comparator and said latch
circuit for disabling said latch circuit and stopping said second
and third continuous charging signals in response to
4. The improved circuit of claim 1, and further comprising means
connected to said second timer for causing said second timer to
produce said fourth charging signal in response to a battery
discharge of selected duration.
5. The improved circuit of claim 1, and further comprising a latch
circuit connected to said first timer and to said power fail and
restore circuit for producing a continuous second charging signal
and a continuous third charging signal in response to said second
charging signal and said third charging signal respectively, means
connected between said voltage comparator and said latch circuit
for disabling said latch circuit and stopping said second and third
continous charging signals in response to the absence of said first
charging signal, and means connected to said second timer for
causing said second timer to produce said fourth charging signal in
response to a battery discharge of selected duration.
Description
BACKGROUND OF THE INVENTION
Our invention relates to a battery charging circuit, and
particularly to a charging circuit for maintaining batteries in
good condition and in a reliable state of charge but with
relatively little detriment to battery life or loss of water from
the battery.
Electrical storage batteries, such as the nickel-cadmium lead-acid
type, are frequently used for providing electrical power to
electronic equipment at remote or typically unattended locations.
Previously, alternating current electrical power supplied to the
location was rectified to direct current, and the batteries were
floated across the direct current so that they would receive an
almost constant trickle charge. While such an arrangement kept the
batteries at a high level of capacity or state of charge, it also
reduced the life of the battery, and caused loss of water from the
battery. Hence, the batteries had to be frequently serviced, and in
the case of lead-acid, frequently replaced.
Accordingly, a primary object of our invention is to provide a new
and improved charging circuit which keeps storage batteries in a
reliable state of charge with relatively little detriment to the
life of the battery and with very little loss of water.
Another object of our invention is to provide a new and improved
charging circuit which automatically provides a charge to a storage
battery at selected, periodic times, for example weekly, and which
also provides a charge to the battery each time the alternating
current electrical power fails and is restored.
Another object of our invention is to provide a new and improved
battery charging circuit which automatically provides a storage
battery with a normal charge, and which also provides a storage
battery with an equalizing or heavy charge in response to a desired
operation.
Another object of our invention is to provide a new and improved
battery charging circuit which automatically provides a normal
charge to a storage battery at selected periodic intervals; which
provides a normal charge to the battery each time the alternating
current electrical power fails and is restored; and which provides
an equalizing charge to the battery in response to a manual
operation or other condition.
SUMMARY OF THE INVENTION
Briefly, these and other objects are achieved in accordance with
our invention by a voltage regulator and current regulator
connected from the charging source through a normally open charging
path to the battery to be charged. The actual battery voltage is
compared with a reference voltage to provide a first charging
signal in response to the battery voltage being below the reference
voltage. A first timer for producing a second charging signal at
selected predetermined intervals is provided, and a power fail and
restore circuit for producing a third charging signal in response
to failure and subsequent restoral of electrical power is provided.
A second timer for producing a fourth charging signal of selected
duration is provided to respond to a manual operation or other
condition. A logic circuit is connected to the voltage comparator,
the first timer, the power fail and restore circuit, and the second
timer for producing a charge signal in response to the simultaneous
presence of the first charging signal and either of the second or
third charging signals, and further in response to the presence of
only the fourth charging signal. This charge signal is applied to
the charging path for closing the path when the charge signal is
present. Thus, the charging path is closed to provide a normal
charge to the battery when either the first timer operates or when
power is restored and the battery voltage is below the referencce
voltage. The logic circuit also responds to operation of the second
timer to cause the battery to receive a high or equalizing charge
in response to the fourth charging signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which we regard as our invention is particularly
pointed out and distinctly claimed in the claims. The structure and
operation of our invention, together with further objects and
advantages, may be better understood from the following description
given in connection with the accompanying drawing, in which:
The single FIGURE shows an electrical block diagram of a preferred
embodiment of a battery charging circuit in accordance with our
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated earlier, we contemplate that our battery charging
circuit will typically be used in remote or unattended locations,
although it is to be understood that our circuit can be used in any
location. Such locations typically are supplied with alternating
current electrical power which is applied to a charging source 10
for rectification to direct current at the proper voltage for the
storage battery to be charged. This direct current is applied to
the input of a voltage regulator 11 which has a control for setting
the regulated voltage at either the normal battery charging voltage
or at a higher or equalizing charging voltage. This regulated
voltage is applied to a current regulator 12 which regulates the
current to some specified magnitude. The regulated charging current
is applied to a normally open charging or switch path SP,
represented as a single pole, single throw switch. This path in
turn is completed to a storage battery 13 which is to be charged.
The voltage of the battery 13 is applied to the negative input
(indicated by a minus sign) of an operational amplifier OA. The
operational amplifier OA is connected as a voltage comparator, and
produces a relatively high voltage (or a logic 1) at its output if
the voltage at its positive input exceeds the voltage at its
negative input, and produces a relatively low voltage (or a logic
0) at its output if the voltage at the negative input exceeds the
voltage at the positive input. The positive input is connected to a
temperature sensing voltage divider comprising a negative
coefficient, temperature sensitive resistor RT, a normal charging
voltage resistor R1, and a heavy or equalizing charging resistor R2
connected to a suitable voltage source indicated as B+. The
temperature sensitive resistor RT is located so as to sense the
ambient temperature at the batteries. As this ambient temperature
increases, the voltage V1 at the junction of the resistors R1, RT
and the voltage V2 at the junction of the resistors R2, R1
decrease. As this ambient temperature decreases, the voltages V1,
V2 increase. The as the ambient temperature rises, a smaller
voltage at the negative input of the operational amplifier OA is
required to produce a low or logic 0 output, and as the ambient
temperature falls, a greater voltage is required at the negative
input of the operational amplifier OA to produce a low or logic 0
output. As known, a temperature dependent voltage reference is
desirable for storage batteries, as such batteries should be
charged to a lower voltage as the ambient temperature
increases.
The output of the operational amplifier OA is applied to one of two
inputs of an OR logic gate 16 and is also applied to a latching
circuit 17. The latch circuit 17 is arranged so that when the
operational amplifier OA produces a logic 0, as it will when the
voltage on the storage battery 13 exceeds the reference voltage V1,
the latch circuit 17 will be opened and will remove the logic 1
being supplied to the OR gate 24. The output from the OR gate 16 is
applied to one of two inputs of an AND logic gate 18, and the
output of the AND gate 18 is applied to a driver 19. When the AND
gate 18 produces a logic 1, it causes the driver 19 to close the
switch path SP.
A first timer 20 is provided to produce a pulse or signal once for
every selected time interval, in a preferred embodiment this being
once every seven days. An AC fail and restore circuit 21 is
provided in order to sense when alternating current power to the
charging circuit has been interrupted and is then restored, and
this is indicated by a signal or pulse. The signals from the timer
20 and the AC fail and restore circuit 21 are applied to the
latching circuit 17 which, upon receipt of either of these signals,
latches to a condition to supply a logic 1 to one of two inputs of
an OR gate 24. The output of the OR gate 24 is applied to the other
input of the AND gate 18. We also provide a periodic timer 22
which, in a preferred embodiment, provides a logic 1 signal for a
20 hour period when activated. This activation is typically a
manual one, but it may also be provided by other features, such as
any alternating current power failure which exceeds a selected
number of hours. The output of the timer 22 is applied to the other
input of the OR gate 24 and also to the other input of the OR gate
16. The output of the timer 22 is also applied to a driver circuit
23. When the driver circuit 23 receives a logic 1 from the timer
22, it causes the switch S1 to move from the lower contact as shown
to the upper contact. The lower contact is connected to the
junction of the resistors R1, RT, and the upper contact is
connected to the junction of the resistors R2, R1. The movable
element of the switch S1 is connected to the control input of the
voltage regulator 11. When switch S1 is in the lower position, the
voltage V1 causes the voltage regulator 11 to provide a normal
charging voltage, and when the switch S1 is in the upper position
in response to activation of the driver 23, the voltage V2 causes
the voltage regulator 11 to supply a higher or equalizing charging
voltage.
As an example for explaining the operation of our invention, we
have assumed that an 80 ampere-hour, lead-acid storage battery
having a nominal voltage of 48 volts is the battery 13 in our
charging circuit. The actual terminal voltage of such a battery at
a typical temperature of 77.degree.F is 50.4 volts. We have also
assumed a normal charge voltage of 55.4 volts at 4 amperes and a
heavy or equalizing charge of 56.8 volts at 4 amperes are to be
provided. With such a battery in place, the switch path SP is
normally open. Unless the battery is supplying power to the
equipment, it is losing its charge at a rate dependent upon the
internal leakage of the battery. At the time determined by the
timer 20, a pulse is produced to cause the latching circuit 17 to
supply a logic 1 to the OR gate 24. This logic 1 is supplied to the
ANd gate 18. However, the AND gate 18 does not produce a logic 1 to
the driver 19 unles the operational amplifier OA supplies a logic
1. The operational amplifier OA will produce a logic 1 only if the
voltage V1 at the divider exceeds the voltage of the battery 13
being charged. If the battery voltage is sufficiently low, a logic
1 will be supplied by the amplifier OA and passed through the OR
gate 16 so that the AND gate 18 provides a logic 1 to the driver
19. This causes the switch path SP to close so that the battery 13
receives a charge. At this point, it should be pointed out that if
the AC fail and restore circuit 21 had produced a logic 1 in
response to a power failure and subsequent restoral, then the
operation just described would occur. In either case, if the
battery voltage is sufficiently low, it receives a charge. As the
battery becomes charged, its terminal voltage rises until, at some
point determined by the voltage V1, the voltage at the negative
input of the operational amplifier OA exceeds the voltage at the
positive input so that the operational amplifier OA produces a
logic 0. This causes the OR gate 16 to produce a logic 0. The AND
gate produces a logic 0 so that the driver 19 opens the switch path
SP. At this time, the same logic 0 from the operational amplifier
OA opens the latch 17 and resets it so that a subsequent logic 1
from the timer 20 or the AC fail restore circuit 21 can cause the
latch 17 to close again. Thus, our circuit as described thus far
provides a normal or lower charging voltage in response to the
timer 20 or the AC failure and restore circuit 21. And, this charge
is at the lower voltage because of the voltage V1 supplied by the
switch S1 to the voltage regulator 11.
Persons familiar with storage batteries recognize that such
batteries receive severe or deep discharges under extended load
periods. Even though a normal charge brings the battery terminal
voltage back to its rated magnitude, such batteries are not fully
charged to their complete ampere hour capacity. In order to bring
such batteries back to their full capacity, it is necessary that an
equalizing or heavy charge be provided. In accordance with our
invention, such an equalizing charge is provided by the 20 hour
timer 22 which, when manually operated either at or remotely from
the charging circuit or in response to a discharge of selected
minimum time, produces a logic 1. This logic 1 is applied to both
OR gates 24, 16 which cause the AND gate 18 and the driver 19 to
close the switch path SP. This same logic 1 causes the driver 23 to
operate the switch S1 to its upper position so that the higher
voltage V2 is supplied to the voltage regulator 11. This causes the
voltage regulator 11 to supply the higher equalizing charging
voltage of 56.8 volts and the battery 13 receives this equalizing
charging voltage. This charge continues regardless of the battery
terminal voltage, since the logic 1 supplied by the timer 22
insures that the driver 19 remains operative. The timer 22
continues for the selected duration, this being 20 hours in the
assumed example. After this time, the timer 22 is deenergized and
produces a logic 0 so that the normal condition of charge can take
place either in response to the 7 day timer 20 or the AC fail and
restore circuit 21.
It will thus be seen that we have provided a new and improved
charging circuit which provides many desired charging
characteristics not previously found in charging circuits, namely:
a normal charge at fixed intervals, regardless of whether the
battery has been discharged by a load or not; a normal charge in
response to a power failure and restoral; and an equalizing charge
when desired or in response to a selected condition. While we have
shown only one embodiment, persons skilled in the art will
appreciate that modifications may be made. For example, the switch
path SP may, in actuality, be a feature that renders either the
current regulator 12 or the voltage regulator 11 inoperative or
operative in response to the driver 19. Another feature is, of
course, that the timer 20 and the timer 22 may be varied in their
timing intervals. Another feature is that the operational amplifier
OA may have a fixed reference voltage rather than a temperature
sensing voltage. The latch 17 may be omitted, and the timer 20 and
the AC fail and restore circuit 21 may provide fixed duration
output signals to the OR gate 24 so that these signals determine
the maximum length of time a battery will receive a charge, rather
than the operational amplifier OA determining the amount of charge.
And finally, our circuit can provide visual or audible indications
of the charging state at any time. Therefore, while our invention
has been described with reference to a particular embodiment, it is
to be understood that modifications may be made without departing
from the spirit of our invention or from the scope of the
claims.
* * * * *