Charging apparatus

Abstract: A charging apparatus for charging a secondary battery arranged in such a manner that the interterminal voltage of the battery, which is being charged, is measured so that the charging status of the battery is detected in accordance with the measured interterminal voltage of the battery which is being charged and the charging/discharging characteristics with respect to the interterminal voltage of the battery. As a result, the charging status of the battery can accurately be detected.

Description: Background of the Invention: Field of the Invention: This invention relates to a charging apparatus for charging a secondary battery. Description of the Related Art: A conventional charging apparatus comprises a display means for informing a user of the fact that the charging of the secondary battery has been completed. Usually, the information system is arranged in such a manner that the interterminal voltage of the secondary battery to be charged is observed and a determination is made such that the charging of the secondary battery has been completed when the interterminal voltage of the secondary battery to be charged has been raised to a predetermined level. In accordance with the determination made as described above, the display means is caused to display a predetermined information. However, the conventional charging apparatus has not been able to inform the user of the specific time taken to completely charge the battery during the charging operation. Furthermore, the time, in which the apparatus loaded with the battery which has not completely been charged can be used, cannot be informed to the user. In addition, the degree of the charging of the battery which has not been completely charged cannot also be informed to the user. From DE-A-3440430 is known a battery charging apparatus, in which the electromotive force of the battery to be charged is detected and the charging status is determined on the basis of the detected electromotive force. Another charging apparatus is known from WO-A-89/08940 wherein the charging state of a 100% charged accumulator is determined by measuring the extreme value of the variation of a charging parameter. The time at which this extreme value is reached can be used to control the charging operation. One of the charging parameters suggested by this document is the electromotive force calculated from the equivalent electrical circuit of the battery. From US-A-4644245 is known a battery state-of-charge measuring method wherein the terminal voltage is measured while the battery is placed under a heavy discharge load during a predetermined short interval. It is the object of the present invention to further develop a charging apparatus according to the preamble of Claim 1 that it is able to detect the charging state of the battery in an easy way. This object is achieved by a charging apparatus having the features of Claim 1. The invention is further developed by the features mentioned in the dependent claims. Other and further objects, features and advantages of the invention will appear more fully from the following description. Brief Description of the Drawings: Fig. 1 is a graph which illustrates the discharging characteristics displayed when a predetermined load is connected to an Ni-Cd secondary battery; Fig. 2 is a graph which illustrates the charging characteristics displayed when the Ni-Cd secondary battery is charged with a predetermined electric current; Fig. 3 is a graph which illustrates the time sequential change in the charging characteristics shown in Fig. 2; Fig. 4 is a block diagram which illustrates the structure of an embodiment of the charging apparatus according to the present invention; Fig. 5 is an operation flow chart of a calculation control circuit 222 shown in Fig. 4; Detailed Description of the Preferred Embodiments: First, an embodiment of the present invention will be described with reference to the drawings. Fig. 4 is a block diagram which illustrates the structure of an embodiment of a charging apparatus according to the present invention. Fig. 1 is a graph which illustrates the discharging characteristics displayed when a predetermined load is connected to an Ni-Cd secondary battery, wherein the axis of ordinate stands for the interterminal voltage of the battery and the axis of abscissa stands for the elapsed time. As can be seen from Fig. 1, the interterminal voltage is monotonously lowered in accordance with a lapse of time. Referring to Fig. 1, symbol T E denotes the time in which the battery, which has been completely charged, can be used. Fig. 2 is a graph which illustrates the charging characteristics displayed when the Ni-Cd secondary battery is charged with a predetermined electric current, wherein the axis of ordinate stands for the interterminal voltage of the battery and the axis of abscissa stands for the time. As shown in Fig. 2, the interterminal voltage of the battery is slightly lowered when the battery has been completely charged. Therefore, whether or not the battery has been completely charged can be determined by detecting the fact that the interterminal voltage of the battery has been lowered. Symbol T F denotes the time necessary to completely charge the battery 210 which has been completely discharged assuming that the symbol V E denotes the lowest interterminal voltage capable of operating the subject apparatus. Table 1 shows data of the discharging characteristics shown in Fig. 1 and data of the charging characteristics shown in Fig. 2, the table 1 being stored in the memory 228. Referring to Table 1, item A numerically shows the degree of charging in a range from 100 to 0, B shows time 0 to T F taken to completely charge the battery and C shows time T E to 0 taken to completely discharge the battery. Assuming that the interterminal voltage of a battery which has been used to a certain degree is V O , the time in which the battery can be used becomes, from Fig. 1, T E - T O (minute) which is, as C O , then stored in variable C of the memory 228. At this time, an assumption can be made that the battery has been used by T O /T E x 100 (%) which is, as A O , then stored in variable A of the memory 228. Furthermore, an estimation can be made that the battery can be completely charged in T F x T O /T E (minute), which is, as B O , then stored in variable B of the memory 228. Electromotive force A B C V F 100 0 T E ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ V O A O B O C O ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ ˙ 0 0 T F 0 Fig. 3 is a graph which illustrates the time sequential change in the charging characteristics shown in Fig. 2. The degree of the charging can further accurately be determined by observing the characteristics about the change in the interterminal voltage shown in Fig. 3 as well as the charging characteristics shown in Fig. 2. Referring to Fig. 4, reference numeral 210 represents a battery to be charged and 212 represents a voltage measuring circuit for measuring the interterminal voltage of the battery 210. Reference numeral 214 represents a charging circuit for charging the battery 210, and 216 and 218 represent resistors for measuring the degree of the charging of the battery 210. Reference numeral 220 represents a switch for selectively connecting the charging circuit 214, the resistor 216 or the resistor 218 to the battery 210 in order to select the charging with the charging circuit 214 or the discharging with the resistor 216 or the resistor 218. Reference numeral 222 represents a calculation control circuit comprising a microcomputer for controlling the operation of the charging circuit 214 and the switching action of the switch 220 and obtaining the degree of the charging of the battery 210 in accordance with the output of the voltage measuring circuit 212. Reference numeral 224 represents a display for displaying the result of the calculation performed by the calculation control circuit 222 and the state of the control. Reference numeral 226 represents an instruction switch for instructing the calculation control circuit 222 to measure the degree of the charging of the battery 210. Reference numeral 228 represents a memory for storing the characteristics data such as the charging/discharging characteristics of the open-circuit voltage of the battery 210 to be charged or measured. The calculation control circuit 222 causes the switch 220 to be connected to the contact "a" when the battery 210 is charged and operates the charging circuit 214. The interterminal voltage of the battery, which is being charged, is measured by the voltage measuring circuit 212 by connecting the switch 220 to the contact "b" or "c" at a predetermined time interval, at a time interval which corresponds to the interterminal voltage of the battery 210, at an optional time interval, or in accordance with the action of the switch 226. The interterminal voltage thus measured by the voltage measuring circuit 212 is supplied to the calculation control circuit 222. The calculation control circuit 222 calculates electromotive force v of the battery 210 from interterminal V1 displayed when the resistor 216 is connected to the battery 210 and interterminal voltage V2 displayed when the resistor 218 is connected to the same. Since the resistance value of each of the resistors 216 and 218 is a known value, the following relationships can be obtained assuming that the electric currents are respectively I1 and I2, the internal resistance of the battery 210 is R and the electromotive force (open-circuit voltage) is v: R = (V1 - V2) / (I2 - I1) v = V1 + I1 · R = V2 + I2 · R = (I2 · V1 - I1 · V2) / (I2 - I1) The electromotive force v is not influenced by external factors such as the internal resistance R and the resistances of the connecting lead wires. Therefore, the degree of charging/discharging of the battery 210 can accurately be determined by utilizing the electromotive force. The data shown in Table 1 being stored in the memory 228. Referring to Table 1, item A numerically shows the degree of charging in a range from 100 to 0, B shows time 0 to T F taken to completely charge the battery and C shows time T E to 0 taken to show the lowest voltage V E at which the battery can be used. Assuming that the interterminal voltage of a battery which has been used to a certain degree is V O , the time in which the battery can be used becomes, from Fig. 1, T E -T O (minute) which is, as C O , then stored in variable C of the memory 228. At this time, an assumption can be made that the battery has been used by T O /T E x 100 (%) which is, as A O , then stored in variable A of the memory 228. Furthermore, an estimation can be made that the battery can be completely charged in T E x T O /T E (minute), which is, as B O , then stored in variable B of the memory 228. Fig. 5 is an operation flow chart of a calculation control circuit 222 shown in Fig. 4. The calculation control circuit 222 first operates the charging circuit 214 so that the charging operation is started (S201). Then, the switch 220 is connected to the contact "b" (S202) so that the interterminal voltage V1 of the battery'210 due to the resistor 216 is measured by the voltage measuring circuit 212 (S203). Then, the switch 220 is connected to the contact "c" (S204) so that the interterminal voltage V1 of the battery 210 due to the resistor 218 is measured by the voltage measuring circuit 212 (S205). The voltages V1 and V2 measured in steps S203 and 205 and their electric currents I1 and I2 are substituted into Equation (1) so that the electromotive force v of the battery 210 is calculated (S206). The obtained electromotive force v is collated with data table 2 stored in the memory 228 so that the corresponding data A, B and C shown in Table 1 are read (S207). The thus-read data is transferred to the display 224 so that the data is displayed (S208). Since the battery 210 has not been completely charged if the value of the data A is less than "100" (S209), the switch 220 is connected to the contact "a" (S210), so that the battery 210 is charged for a predetermined time set by a timer (omitted from illustration) (S211 and S212). As an alternative to this, the flow returns to step S202 in response to the action of the switch 226 so that the interterminal voltage is measured. If the terminal voltage of the battery 210 has been lowered (S214), the electromotive force v stored in the memory 228 is rewritten to the electromotive force v F for the completely charged state before the flow returns to step S207 (S215). In step S207, data A expressing "100" is read from the memory 228. Since the battery 210 has been completely charged if the data A is equal to "100 in step S209, the operation of the charging circuit 214 is stopped (S216) and the charging operation is ended. According to the above-described embodiment, the charging/discharging degree is estimated in accordance with the electromotive force of the battery. Furthermore, another structure may be employed in which the two resistance values may be obtained by realizing a partial short circuit of one resistor as an alternative to the above-described structure in which the two resistors 216 and 218 are switched. As described above, according to the present invention, the degree of charging/discharging of the battery, the time necessary to be taken to completely charge the battery and the time in which the battery can be used can accurately be known. Furthermore, since the degree of the charging is determined in accordance with the open-circuit voltage, the degree of the charging can be uniformed in a plurality of batteries. As described above, according to this embodiment, the degree of charging/discharging of the battery, factors of the status of the charging, discharging of the battery, such as the time necessary to be taken to completely charge the battery and the time in which the battery can be used can accurately be known. Although the invention has been described in this preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction, and the combination and arrangement of parts may be modified without departing from the scope of the invention as hereinafter claimed.

Claims: A charging apparatus for charging a secondary battery, comprising: (A) an electromotive force detecting means (212, 222) for detecting an electromotive force of the battery (210) which is being charged; and (B) detection means (222, 228) for detecting a charging / discharging status of the battery in accordance with the electromotive force detected by said electromotive force detecting means, characterized in (C) that the detection means takes into account charging / discharging characteristics with respect to the electromotive force of the battery, and (D) that said electromotive force detecting means is arranged to measure, during short time interruptions of the charging at predetermined intervals, each of the interterminal voltages obtained in cases where a respective one of a plurality of different predetermined loads (216, 218) resulting in different interterminal voltages is sequentially connected to the battery, and to calculate the electromotive force of the battery from the interterminal voltages thus measured. A charging apparatus according to Claim 1, wherein said detection means is further arranged to detect a quantity of change in the interterminal voltage of the battery and to stop a charging operation when the interterminal voltage has been lowered. A charging apparatus according to Claims 1 or 2 wherein said detection means includes: (A) data holding means (228) for holding data indicative of the charging/discharging characteristics with respect to the electromotive force of the battery; and (B) comparison detection means (22) for detecting a charging status of the battery by comparing the electromotive force of the battery measured by said electromotive force detecting means and the data stored in said data holding means. A charging apparatus according to Claim 1, further comprising display means (224) for displaying the charging/ discharging status of the battery detected by said detection means. A charging apparatus according to Claim 4, wherein said display means is arranged to display a quantity of charging of the battery. A charging apparatus according to Claim 4, wherein said display means is arranged to display the residual charge time of the battery. A charging apparatus according to Claim 4, wherein said display means is arranged to display the time during which the battery can be used.

Inventors: HARIGAYA ISAO, SAEKI TAKAYUKI, TAKAHASHI KOJI, TAKIMOTO HIROYUKI, TOBE KAZUMITSU, HARIGAYA, ISAO, SAEKI, TAKAYUKI, TAKAHASHI, KOJI, TAKIMOTO, HIROYUKI, TOBE, KAZUMITSU, HARIGAYA, ISAO, C/O TAMAGAWA JIGYOSHO, SAEKI, TAKAYUKI, C/O TAMAGAWA JIGYOSHO, TAKAHASHI, KOJI, C/O TAMAGAWA JIGYOSHO, TAKIMOTO, HIROYUKI, C/O TAMAGAWA JIGYOSHO, TOBE, KAZUMITSU, C/O TAMAGAWA JIGYOSHO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: H02J7
IPC codes: H02J7