GB2213600A

GB2213600A - Testing batteries

Info

Publication number: GB2213600A
Application number: GB8904528A
Authority: GB
Inventors: Eiji Ohnari
Original assignee: EIKOH GIKEN CO Ltd
Current assignee: EIKOH GIKEN CO Ltd
Priority date: 1986-01-14
Filing date: 1989-02-28
Publication date: 1989-08-16
Anticipated expiration: 2006-10-07
Also published as: GB8904528D0; GB8904527D0; GB2213599A; GB2213599B; GB2213600B

Abstract

In an arrangement for judging the lifetime of a battery B in a no-break power supply system a switch DS is changed from a position a to a position b whereby to allow the battery to discharge through a dummy load DL. The time taken for the output voltage VD of the battery to drop to a predetermined level is measured (TA) and the result gives an indication of the battery lifetime. During this test an engine generator EG provides a back-up to an AC power source P for supplying power to a real load L by way of two rectifiers (Recl, 2) and an invertor (IV). <IMAGE>

Description

"A CIRCUIT ARRANGEMENT FOR JUDGING THE LIFETIME OF A BATTERY IN A NO-BREAK POWER SUPPLY SYSTEM" The present invention relates to a circuit arrangement for judging the lifetime of a battery in a no-break power supply system. This application has been divided out from our application 2185326.

In a conventional no-break power supply system, as shown in Figure 1, the AC power of an AC power supply source P (for example, a commercial power source) is converted into DC power through a rectifier Rec and a smoothing capacitor C and the DC power thus obtained is again inverted by an inverter IV including an automatic voltage regulating means into AC power having a constant voltage and constant frequency, which is supplied to a load L such as a computer or the like so that the load L is operated with such AC power under normal conditions of the AC power source.

Under such conditions, the AC power source P charges through a charging means CH under a floating charge condition a battery B having one electrode connected to ground and the other electrode connected to the input of the inverter IV through a diode D, so that the battery B compensates by supplying power to the inverter IV when a service interruption occurs or the output voltage of the rectifier Rec becomes lowered by some failure. This floating charge system is suitable for a no-break power supply system comprising a battery having a comparatively small capacity.

In another conventional -no-break power supply system, as shown in Figure 2, the AC power of an AC power supply source P (such as a commercial power source) is converted into a DC power through an rectifier Rec such as a thyristor and a smoothing capacitor C and the DC power thus obtained is again inverted by an inverter IV including an automatic voltage regulating means into AC power having a constant voltage and constant frequency, which is supplied to a load L such as a computer or the like.

In this case, the rectifier Rec has to charge under a floating charge condition a battery B connected between the input of the inverter IV and ground in order to compensate for the DC power in the case of service interruption, so that the conducting phase of the rectifier Rec is controlled by a thyristor control circuit CN so as to adjust the DC power finely. This floating charge system is suitable for a no-break power supply system comprising a battery having a comparatively large capacity.

In comparatively large scale no-break power supply systems using a stationary battery, even in the circuit arrangement shown in Figures 1 and 2, ordinary maintenance personnel may judge the lifetime of the respective batteries with ease by regularly checking the voltage, the specific gravity or the like cf the batteries. In recent spread small no-break power supply system with easy maintenance and small capacity, a small enclosed lead storage battery is actively used.

When such an enclosed type battery is used, it is difficult to judge the performance or lifetime of the battery because of the enclosed structure. Particularly, as the lifetime of the battery approaches its end, it is necessary to try the discharging test to decide when the battery should be exchanged. Even if the battery is approaching the end of its lifetime, when one of the cells or batteries fails (since the number of series connected cells is usually several tens), the discharging property deteriorates and in the extreme case the no-break power supply system does not actuate, so that the voltage across the load decreases rapidly with service interruption of the commercial power supply source resulting in a perturbation on the load being the computer. In order to avoid such a condition, the battery must be actually discharged to check such a condition.

In the conventional system shown in Figures 1 and 2 generally, the service interrupting condition is forcedly generated during operation of the no-break power supply system to discharge the battery thereby performing such a check. If at such a checking, failure of the battery occurs, the output voltage of the no-break power supply system is abnormally decreased, thereby causing a perturbation on the load such as a computer close down. Actually, the discharging test of the battery is difficult under the forced service interrupting condition during operation of the no-break power supply system.

The present invention seeks to overcome the above mentioned disadvantages of the conventional circuit arrangement for judging the lifetime of a battery in a no-break power sup1y system.

According to the invention there is provided a circuit arrangement for judging the lifetime of a battery in a no-break power supply system comprising a first rectifier connected to an AC power source, an inverter connected to the first rectifier, a load connected to the inverter, a second rectifier having an input connected to an engine-generator and an output connected to an input of the inverter, a diode having a cathode connected to the inverter, a battery having one electrode connected to an anode of the diode and the other electrode connected to ground, a voltage detector connected to the one electrode of the battery, a time counting means connected to the voltage detector, a change-over switching means connected across the diode and for short-circuiting the diode, a dummy load connected to the battery by the change-over switching means, and a switch connected to the time counting means and interlocked with the change-over switching means.

The change-over switching means short-circuits the diode as well as supplies an operation stop signal to the voltage detector in one switching state, and supplies the power of the battery to the dummy load as well as closes the switch which supplies a count starting signal to the time counting means, in the other switching state.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram showing a conventional no-break power supply system; Figure 2 is a block diagram showing another conventional no-break power supply system; Figure 3 is a block diagram showing a first embodiment of a circuit arrangement for judging the lifetime of a battery used in a no-break power supply system according to the present invention; Figure 4 is an explanatory view showing a discharge characteristic of a battery for explaining the operation of the circuit arrangement according to the present invention; ; Figure 5 is a block diagram showing a second embodiment of a circuit arrangement for judging the lifetime of a battery used in a no-break power supply system according to the present invention; Figure 6 is a block diagram showing a third embodiment of a circuit arrangement for judging the lifetime of a battery used in a no-break power supply system according to the present invention; and Figure 7 is an explanatory view showing a discharge characteristic of a battery for explaining the operation of the circuit arrangement according to the present invention.

Referring now to the drawings, there are shown some embodiments of circuit arrangements for judging the lifetime of a battery used in a no-break power supply system according to the present invention.

Figure 3 shows an electrical connection of the circuit arrangement according to the present invention.

Figure 4 shows the discharging characteristic of the battery for explaining the operation of the circuit arrangement according to the present invention. The same reference numerals and letters are used for corresponding components in Figures 1 and 3. In Figure 4, the time T is plotted on the abscissa and the voltage of the battery B (input voltage of the inverter, hereinafter referred to as point P voltage) is plotted on the ordinate. Reference T is a stepdown transformer connected to a commercial power source P and set in such a manner that when a switch S, is changed to a contact b the DC output voltage is chanted from a normal value VN to a reduced value, thereby reducing the AC input voltage to the no-break power supply system temporarily in order to perform the discharge test for the battery B.

Reference VD is a voltage detector connected to one electrode of the battery B. The voltage detector VD monitors the voltage Vb of the battery B and is set to generate an output signal when the voltage Vb reaches the voltage point b.

An autotimer TA is connected to receive the output signal of the voltage detector VD and for automatically counting and measuring the time duration from the discharge starting instant to the instant that the voltage point b of the battery B is reached. An analog counter and an automatic digital voltage meter may be utilised as the autotimer.

Reference S, is a switch interlocked to the switch S, and for commencing the operation of the timer TA.

The operation and the advantageous effect of this embodiment is described as follows. In the discharge characteristic of the voltage Vb of the battery B shown in Figure 4, point a shows the input voltage of the inverter IV at the commencement of discharge (normal voltage VN), Tj shows the instant when the input voltage is applied to a point p shown in Figure 3, and a point d shows the discharge final voltage VS of the battery B which also shows the lowest voltage for automatically stopping the system itself when the voltage of the battery becomes lower than the discharge final voltage VS.

A point c shows a change-over voltage when the switch S is changed to the contact b of the stepdown transformer T, a point b shows the voltage when the voltage-detector VD generates an output signal, and thus T shows an instant when the output signal of the 2 voltage detector VD is generated. The voltages of respective points are different according to the characteristic of the battery B to be used. When the upper limit voltage per one cell or battery is 2.2 Volt and the lower limit voltage (discharge final voltage) is 1.8 Volt, respective points are set as follows: the point a is 2.2V, the point b is 1.85V, the point c is 1.83V and the point d is 1.8V.

When the AC power source is operating normally, the system maintains the condition shown in Figure 3, so that the DC power is supplied to the inverter IV through the rectifier Rec, thereby supplying the load L normally.

Under such a condition, in order to test the battery B by discharging, the switch S is changed to the contact b of the step-down transformer T to decrease the voltage of the AC power source, so that the output of the rectifier Rec becomes decreased and thus the voltage at the point p is changed to the change-over voltage VR, that is, the voltage at the point c by the transformer T. This voltage VR is lower than the battery voltage so that the battery begins to discharge through the diode D (normal voltage VN, that is, the voltage at the point a).

The switch S is closed at the same time the 2 switch S is changed, to the contact b of the transformer T so that the auto-timer TA is actuated to record the starting instant T, and count the duration of discharge.

Under such a discharging condition, when. the battery voltage Vb is gradually decreased along the downward curve to reach the point b, the voltage detector VD connected to the battery B generates an output signal which is supplied to the auto-timer TA, thereby recording the instant T2, so that the autotimer TA may detect the duration T -T 21 By performing such a discharging test pericdic- ally, the lifetime of the battery B may be judged precisely, since the power consumption of the load L is substantially constant.

Even if a part (one cell) of the battery B fails or contact failure of the battery terminals occurs, thereby decreasing the voltage at the point p rapidly as shown by the broken line e, substantially constant voltage is supplied to the load L continuously by the automatic voltage regulating function of the inverter IV since the change-over voltage VR (the voltage at the point e) of the transformer T is set higher than the discharge final voltage VS (the voltage at the point d), so that the load L is not subjected to any harm. Moreover, the auto-timer TA records the instant T ' thereby detecting the shortening of the 2 time duration so that the occurrence of the battery failure may be easily judged.

Figure 5 shows a second embodiment of the circuit arrangement according to the present invention.

In this embodiment, the rectifier Rec is formed by a thyristor, and a thyristor control circuit or unit CN is connected to the rectifier Rec. The control circuit CN comprises a change-over mechanism (not shown) constructed to obtain a predetermined voltage (change-over voltage) by short-circuiting the incorporated voltage dividing resistor. The control unit CN controls the conducting phase of the thyristor Rec by supplying a trigger pulse to its gate. When the change-over mechanism is operated, the DC output voltage of the rectifier is set in such a manner that the normal value VN is changed to the change-over value VR.

This change-over mechanism is used to perform the discharging test of the battery B as shown in the first embodiment.

An interlocked switch S is connected to an auto-timer TA to commence the operation thereof autor-- atically when the change-over mechanism is operated.

The other construction of this embodiment is the same as that of the first embodiment so that the detailed explanation thereof is omitted.

The operation of the circuit arrangement is described as follows: A substantial part of the operation of this embodiment is the same as that of the first embodiment so that only the operational differences are described.

In the present embodiment a point c shown in Figure 4 designates the change-over voltage when the change-over mechanism is operated.

When the AC power source is operating normally, the system maintains the condition shown in Figure 5, so that the DC power is supplied to the inverter IV through the rectifier Rec, thereby supplying the load L normally.

Under such a condition, in order to test the battery B with discharging, the change-over mechanism (not shown) of the thyristor control circuit CN is operated to decrease the output of the rectifier Rec to the change-over voltage VR, that is, the voltage at the point c shown in Figure 4, so that this voltage VR is lower than the battery voltage, thereby commencing the discharging of the battery (normal voltage VN, that is, the voltage at the point a).

While the above change-over operation closes the switch S which is interlocked therewith so that the auto-timer TA is operated to record the starting instant T , and count the duration of discharge.

Under such a discharging condition, when the battery voltage Vb is gradually decreased along the downward curve to reach the point b, the voltage detector FC connected to the battery B generates an output signal which is supplied to the auto-timer TA, thereby recording the instant T2, se that the auto- timer TA may detect the duration T -T 21 By performing such a discharging test periodically, the lifetime of the battery B may be judged precisely, since the power consumption of the load L is substantially constant.

Even if a part (one cell) of the battery B fails or contact failure of the battery terminals occurs, thereby decreasing the voltage at the point p rapidly as shown by the broken line e, substantially constant voltage is supplied to the load L continuously by the automatic voltage regulating function of the inverter IV since the change-over voltage VR (the voltage at the point e) of the transformer T is set higher than the discharge final voltage VS (the voltage at the point d), so that the load L, or the computer is not subjected to any harm. Moreover, the auto-timer TA records the instant T ' thereby detecting the 2 shortening of the time duration so that the occurrence of battery failure may be easily judged.

Figure 6 shows a third embodiment of the circuit arrangement for judging the lifetime of a battery used in a no-break power supply system.

In Figure 6, reference S is a normally open switch for generating an engine start signal to an engine-generator E-G. Reference S is a normallyclosed switch for generating an engine start signal to the engine-generator. The switches Sj and S are 3 connected to an engine operating unit or block PC which is connected to the engine-generator E-G. The enginegenerator E-G is connected, through a rectifier Rec 2, to an inverter IV for supplying AC power to a load L and having an automatic voltage regulating function.

The load L may be a computer. The input of the inverter IV is also connected to a rectifier Rec 1 through a commercial power source P, on the one hand, and to a battery B through a diode D, on the other hand. The battery B has one electrode connected to the anode of the diode D and the other electrode connected to ground. A change-over switch DS is connected across the diode D and connected to a dummy load DL. The switch DS comprises three contacts a, b and c. The common contact c is connected to a junction point of the anode of the diode D and the positive electrode of the battery B. When the common contact c is connected to the contact a, the diode D is short-circuited so that the outputs of the rectifiers Rec 1 and Rec 2 are charged on the battery B in a floating manner.

A voltage detector VD is connected to the positive electrode of the battery B to monitor the battery voltage. When the battery voltage becomes a preset voltage at the point c shown in Figure 4, the voltage detector VD generates and supplies a stop signal to a time counting block or auto-timer TA.

The auto-timer TA is operated by the signal from the voltage detector VD to count the time duration between the discharge starting instant T of the battery B and the instant at which the battery voltage reaches the predetermined value. When the switch DS is changed to the contact b to connect the battery B to the dummy load DL, the switch S is closed to supply 2 the count starting signal to the time counting block TA.

The operation of the circuit arrangement shown in this embodiment is described as follows. The circuit arrangement is supplied by the commercial power source P so that the DC output of the rectifier Rec 1 is supplied to the inverter IV which supplies AC power with a constant voltage and constant frequency to the load. At the same time the output voltage of the rectifier Rec 1 is passed to the battery B through the contacts a and c of the switch DS in the floating manner.

Under such a condition, in order to commence the discharging test of the battery, it is necessary to prevent the load L from being subjected to a perturbation even in the event of service interruption of the commercial power supply source P. To this end, the switch S is closed to generate the engine starting signal which is supplied to the engine-generator E-G.

The AC output of the engine-generator E-G is converted into DC output power through the rectifier Rec 2.

That is the DC power obtained through the rectifier Rec 2 is supplied to the inverter in parallel with the DC power obtained through the rectifier Rec 1 from the commercial power source P, so that the inverter IV operates continuously, without any effect, by the DC power obtained through the rectifier Rec 2 even in the event of service interruption of the commercial power source.

Under such a condition, when the switch DS is changed to the contact b to connect the battery B to the dummy load DL, the interlocked switch S generates 2 and supplies the count starting signal to the time counting block or the auto-timer TA.

The discharge characteristic of the voltage V of the battery B is shown in Figure 7. The voltage V of the battery B is plotted on the ordinate and the time T is plotted on the abscissa. A point b on the discharge characteristic curve shows the voltage Vb when the switch DS is changed to the contact b. At this instant T1, the switch S is closed by the 2 interlock action at the time the current flows through the dummy load DL from the battery, thereby supplying the count starting signal to the auto-timer TA which records this instant T . A point c on the discharge characteristic curve shows the voltage Vc when the voltage detector VD generates and supplies its tut signal to the time counting block TA thereby stopping the counting action. The auto-timer TA also records the instant T at which the voltage Vc is generated.

2 The time counting block TA may record the discharge start instant T1 of the battery B and the instant T2 at which the discharge voltage reaches at the predetermined point c along the downward curve of the discharge characteristic, so that the time duration T2-T1 may be ascertained easily. The shape of the downward curve is previously known as the discharge characteristic to the predetermined load of the battery to be used.

If the switch DS is changed to the contact b and its discharge characteristic curve follows on the downward curve from the point b to the point c, it is decided that the battery B operates normally. This decision may easily be obtained from the time duration T -T by the characteristic or discharge test. When 21 the voltage detector VD generates and supplies the action stopping signal to the auto-timer TA by changing the switch DS to the contact a to open the switch S so 2 that the auto-timer TA stops its counting action. The switch S3 is then closed to stop the operation of the engine-generator E-G.

If the voltage of the battery B is rapidly decreased to the voltage Vc or the point c' as shown in Figure 7 by a broken line during the discharge characteristic test, the voltage detector VD generates and supplies the action stopping signal to the time counting block TA as in the same manner as the above, thereby detecting the instant T ' so that it is decided 2 that the battery B is defective.

If the dummy load DL is heated during the discharge test of the battery B, it may be force cooled by a radiator fan (not shown) of the engine-generator E-G.

Claims

1. A circuit arrangement for judging the lifetime of a battery in a no-break power supply system comprising a first rectifier for connection to an AC power source, an inverter connected to the first rectifier, a load connected to the inverter, a second rectifier having an input connected to an enginegenerator and an output connected to an input of the inverter, a diode having a cathode connected to the inverter, a battery having one electrode connected to an anode of the diode and the other electrode connected to ground, a voltage detector connected to the one electrode of the battery, a time counting means connected to the voltage detector, a change-over switching means connected across the diode and for short-circuiting the diode, a dummy load connected to the battery by the change-over switching means, and a switch connected to the time counting means and interlocked with the change-over switching means.

2. A circuit arrangement as claimed in Claim 1, wherein the change-over switching means short-circuits the diode as well as supplies an operation stop signal to the voltage detector, in one switching state, and supplies the power of the battery to the dummy load as well as closes the switch which supplies a count starting signal to the time counting means, in the other switching state.