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°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.