Abstract:
An electric storage device monitor includes a measurement unit detecting and obtaining a detected value, a power supply switch portion switching a power supply state of the monitor between a monitoring state and a low power consumption state, a wakeup timer to which an actuation time is set and starting counting time in response to switching to the low power consumption state and continuing counting time and outputting an actuation signal if reaching the actuation time, and a control unit. The switch portion switches from the low power consumption state to the monitoring state every time the wakeup timer outputs the actuation signal. The control unit controls the measurement unit to detect and obtain the detected value in the monitoring state, compares the detected value and a reference value, and changes the actuation time according to a comparison result of the detected value and the reference value.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application Nos. 2011-197077 filed on Sep. 9, 2011, 2012-176839 filed on Aug. 9, 2012, and 2012-197187 filed on Sep. 7, 2012. The entire contents of the priority applications are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a technology of monitoring a state of an electric storage device. 
     BACKGROUND OF THE INVENTION 
     A battery monitor executes a voltage measurement mode and a sleep mode alternately to reduce power consumption of a secondary battery. 
     While the secondary battery is used, the battery monitor that monitors the secondary battery usually receives an actuation signal from a load side and is actuated to be switched from the sleep mode to the voltage measurement mode. Therefore, the battery monitor continuously monitors the state of the secondary battery while the secondary battery is used. 
     However, if the secondary battery is separated from the load to be used or an error or a problem occurs in the communication between the secondary battery and the load, the battery monitor cannot receive the actuation signal from the load side. There has been no consideration for dealing with such a case. This kind of problem occurs in other elements than the secondary battery, for example, capacitors. 
     SUMMARY OF THE INVENTION 
     The present technology has been made in view of the above, and it is an object of the technology to deal with a state that a monitor cannot receive an actuation signal from the load side. 
     The present invention provides a monitor monitoring an electric storage device that includes a measurement unit, a power supply switch portion, a wakeup timer, and a control unit. The measurement unit is configured to detect a state of the electric storage device and obtain a detected value. The power supply switch portion is configured to switch a power supply state of the monitor between a monitoring state and a low power consumption state that requires lower power than the monitoring state. An actuation time is set to the wakeup timer and the wakeup timer is configured to start counting time in response to switching to the low power consumption state by the power supply switch portion and continue counting time until reaching the setting time and output an actuation signal if reaching the setting time. The power supply switch portion switches the power supply state of the monitor from the low power consumption state to the monitoring state every time the wakeup timer outputs the actuation signal. The control unit is configured to control the measurement unit to detect the state of the electric storage device and obtain the detected value when the power supply state of the monitor is set in the monitoring state by the power supply switch portion. The control unit is further configured to compare the detected value and a reference value and change the actuation time according to a comparison result of the detected value and the reference value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an electric configuration of a monitor according to a first embodiment; 
         FIG. 2  is a flowchart illustrating a flow of processing of an actuation period change sequence; 
         FIG. 3  is a graph illustrating an actuation period with which the monitor is actuated if a battery voltage is not changed; 
         FIG. 4  is a graph illustrating an actuation period with which the monitor is actuated if the battery voltage is changed; 
         FIG. 5  is a flowchart illustrating a flow of processing of an actuation period change sequence according to a second embodiment; 
         FIG. 6  is a graph illustrating an actuation period of a monitor; 
         FIG. 7  is a graph illustrating charging characteristics of an olivine iron-type lithium-ion secondary battery; 
         FIG. 8  is a flowchart illustrating a flow of processing of an actuation period change sequence according to a third embodiment; and 
         FIG. 9  is a flowchart illustrating a flow of processing of an actuation period change sequence according to another embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the present technology, if the detected value is changed, the actuation time is also changed. Thus, the monitor may monitor the electric storage device more frequently. Accordingly, it is promptly detected that the electric storage device such as a secondary battery is used in a condition that the monitor cannot receive an actuation signal from the load side. Further, even if the state of the electric storage device such as a secondary battery is changed, it is less likely to occur that the electric storage device is not monitored for a long time. Therefore, the electric storage device is less likely to be in an abnormal state such as an overcharged or over discharged state. In this description, when the detected value changes, it means that the detected value changes from an objective value such as a previous value that is detected prior to a detected value. 
     First Embodiment 
     A first embodiment will be described with reference to  FIGS. 1 to 4 . 
     A monitor  30  is connected to a secondary battery  10  and integrally provided therewith. The secondary battery  10  is an example of an electric storage device. The monitor  30  monitors a state of the secondary battery  10 , specifically, voltage, temperature, and current values of the battery. As illustrated in  FIG. 1 , the monitor  30  includes a CPU  31 , a clock signal oscillator  33 , a wakeup timer  35 , a watchdog timer  37 , a measurement unit  41 , an A/D converter  43 , a RAM  45 , a ROM  47 , and a communication interface  49  and a power supply switch portion  51 . The CPU  31  is an example of a control unit and the RAM  45  is an example of a memory. 
     The measurement unit  41  detects voltage (inter-terminal voltage), temperature, and current values of the secondary battery  10 . The A/D converter  43  converts detected values of the voltage, the temperature, and the current of the secondary battery  10  into digital values and outputs them to the CPU  31 . The CPU  31  receives information such as the voltage and the current of the secondary battery  10  via the A/D converter  43  and analyzes them to monitor the state of the secondary battery  10  and check if the battery is in an abnormal state or not. The RAM  45  is used as a working memory of the CPU  31  and the RAM  45  stores the detected values. The ROM  47  stores a program that performs an actuation period change sequence and data necessary for various calculations. 
     The power supply switch portion  51  receives an internal actuation signal S 1 , a sleep signal Sa and an external actuation signal Sb. Upon receiving one of the signals, the power supply switch portion  51  switches a power supply state of the monitor  30  between a monitoring state and a sleep state. The sleep state is an example of a low power consumption state. The monitor  30  has two modes including a measurement mode and a sleep mode that is a low power consumption mode. In the measurement mode, the power supply state of the monitor  30  is maintained in the monitoring state and the monitor  30  detects the voltage, temperature, and current values of the secondary battery  10  to continuously monitor the state of the battery and power is supplied to all components of the monitor  30 . 
     In the sleep mode, the monitor  30  is set to alternately in the monitoring state and the sleep state. In the sleep state, the monitor  30  is in a standby state. In the sleep mode, the power supply switch portion  51  temporally switches the power supply state of the monitor  30  from the sleep state to the monitoring state every actuation period T the power supply switch portion  51  receives the internal actuation signal S 1  from the wakeup timer  35 . The monitor  30  monitors the state of the battery only in the monitoring state, and thereafter, the monitor  30  is switched to be in the sleep state. The wakeup timer  35  counts time and if the time counted by the wakeup timer  35  reaches the actuation period T, the wakeup timer  35  outputs the internal actuation signal S 1  to the power supply switch portion  51 . Accordingly, the monitor  30  is switched from the sleep state to the monitoring state with the certain actuation period T. In the monitoring state, the measurement unit  41  of the monitor  30  detects a voltage, a current, and a temperature of the secondary battery  10 . 
     In the sleep state, only the clock signal oscillator  33 , the wakeup timer  35 , the communication interface  49 , and the power supply switch portion of the monitor  30  are supplied with power and supply of power to the other components is stopped, thereby reducing power consumption in the secondary battery  10 . The monitor  30  is supplied with power from the secondary battery  10  and therefore, if the monitor  30  is in the sleep state, the consumption power in the secondary battery  10  can be reduced. 
     The monitor  30  is switched between the measurement mode and the sleep mode according to two control signals including the sleep signal Sa and the external actuation signal Sb output from a control system of the load side. In a case that the secondary battery  10  is mounted to a vehicle, a vehicle-mounted ECU selectively outputs one of the two control signals Sa, Sb. If the secondary battery  10  is not used for a certain time period and the battery  10  is not required to be charged, the control system of the load side detects conditions for switching the monitor  30  to the sleep mode and determines that the monitor  30  is to be switched to the sleep mode. In such a case, the control system of the load side outputs the sleep signal Sa to the monitor  30  and the CPU  31  of the monitor  30  receives the sleep signal Sa via the communication interface  49 . Accordingly, the monitor  30  is switched to be in the sleep mode. Namely, the state of the battery  10  is basically not changed while the monitor  30  is in the sleep mode. 
     The load-side control system outputs the external actuation signal Sb to the monitor  30  to use the battery  10  and the monitor  30  receives the external actuation signal Sb via the communication interface  49 . Accordingly, the monitor  30  is switched to be in the measurement mode. Therefore, if the monitor  30  is properly connected to the load and can receive the external actuation signal Sb from the load, the monitor  30  monitors the state of the secondary battery  10  that is being used. 
     However, if the secondary battery  10  is separated from the load to be used or an error or a problem occurs in the communication between the monitor  30  and the load side, the monitor  30  does not receive the external actuation signal Sb from the load side. Therefore, the monitor  30  remains in the sleep mode and monitors the battery repeatedly with the certain period. If the secondary battery  10  is charged improperly, the battery  10  may be in an abnormal state such as overcharge or over discharge during a period between a current monitoring and a subsequent monitoring. 
     In the present embodiment, if determining that a current detected battery voltage of the secondary battery  10  is changed from a previous detected battery voltage in the sleep mode, the monitor  30  changes the actuation period T. Specifically, in response to such determination, the CPU  31  shortens the actuation period T so that the monitor  30  monitors the secondary battery  10  more frequently with a shorter period. Accordingly, it can be detected promptly that the secondary battery  10  is used in a condition that the monitor  30  cannot receive the external actuation signal Sb from the load side. Further, the voltage of the secondary battery  10  does not reach the prohibited level. 
     An actuation period change sequence will be explained with reference to  FIG. 2 . In the actuation period change sequence, the actuation period T of the monitor  30  is changed. It is assumed that the secondary battery  10 , the charger  20 , the relay R, and the monitor  30  are mounted to the load side and a time set to the wakeup timer  35 , that is, the initial value of the actuation period T is 60 seconds, for example. A number of continuous changes K that will be described later is zero. 
     The actuation period change sequence starts in response to detection of conditions for switching the monitor  30  from the measurement mode to the sleep mode and output of the sleep signal Sa from the load side to the monitor  30 . 
     If the CPU  31  receives the sleep signal Sa, the monitor  30  is switched to the sleep mode and set to be in the sleep state that reduces consumption power. In the sleep mode, only the clock signal oscillator  33 , the wakeup timer  35 , the communication interface  49 , and the power supply switch portion  51  are supplied with power to be operated and supply of power to the other components is stopped (S 10 ). 
     After the monitor  30  is switched to the sleep state, the wakeup timer  35  starts counting time and detects whether the counted time reaches the set time. If the time counted by the wakeup timer  35  reaches the set time (S 20 ), the wakeup timer  35  outputs the internal actuation signal S 1  to the power supply switch portion  51 . The initial value of the set time is 60 seconds. If 60 seconds passes after the monitor  30  becomes in the sleep state, the wakeup timer  35  outputs the internal actuation signal S 1  to the power supply switch portion  51 . 
     If receiving the internal actuation signal S 1 , the power supply switch portion  51  supplies power to each component of the monitor  30  to actuate the monitor  30  (S 20 , S 30 ). Then, the measurement unit  41  detects voltage, temperature, and current values of the secondary battery  10  (S 40 ). 
     The values detected by the measurement unit  41  are converted into digital values by the A/D converter  43  and transferred to the CPU  31  and stored in the RAM  45  (S 40 ). The CPU  31  determines whether the current detected value changes (S 50 ). Specifically, the CPU  31  compares the current detected value and a previous detected value stored in the RAM  45  and determines whether the current detected value of the secondary battery  10  changes from the previous detected value (S 50 ). If the current detected voltage of the secondary battery  10  changes from the previous detected voltage by at least a predetermined value (for example, 0.05 V), it is preferably determined that the detected battery value is changed. Accordingly, it is not erroneously determined that the battery value is changed according to very small change in the battery voltage that may be caused due to a situation or an environment in which the monitor  30  is used. Such a very small change in the battery voltage may be caused even if improper charging is not executed. 
     No previous detected value is stored in the RAM  45  in the first determination just after the monitor  30  is switched to the sleep mode. Therefore, the detected value that is most recently detected in the measurement mode immediately before the monitor  30  is switched to the sleep mode is used as the previous detected value. If the CPU  31  determines that the current detected value does not change from the previous detected value (S 50 ), the process proceeds to S 70 . 
     In S 70 , the set time of the wakeup timer  35  is maintained to be the initial value. Then, the process returns to S 10  and the monitor  30  is switched to the sleep state again. Then, if the wakeup timer  35  determines that the counted time reaches the set time, the timer  35  outputs the internal actuation signal S 1  to the power supply switch portion  51  and accordingly, the monitor  30  is actuated (S 20 , S 30 ). 
     In such a manner, the monitor  30  is actuated and detects the voltage, temperature, and current values of the secondary battery  10 . If no change is detected in voltage of the secondary battery  10 , a negative decision (NO) is made in S 50  and the number of continuous changes K is set to be zero (S 60 ). Therefore, the set time of the wakeup timer  35  is maintained to be the initial value (S 70 ). 
     Therefore, as long as the detected value of the battery voltage is not changed from the previous detected value, the monitor  30  is repeatedly actuated to monitor the state of the secondary battery  10  at the initial interval as illustrated in  FIG. 3 . 
     The secondary battery  10 , the charger  20 , the relay R and the monitor  30  may be removed and separated from the load, and the secondary battery  10  may be charged with power supplied from an external device or may be charged by a charger other than the built-in charger  20 . In such a case, even if the monitor  30  is in the sleep mode, the voltage of the secondary battery  10  rises as illustrated in  FIG. 4  and it is determined that the current detected voltage is changed from the previous detected voltage in S 50 . Accordingly, the number of continuous changes K is increased by one (S 80 ), and it is determined that the increased number of continuous changes K is less than a threshold number of changes Kth (for example two) in S 90 . Further, it is determined that the current detected value is equal to or less than the threshold voltage Vth (S 100 : No). Then, the CPU  31  changes the set time of the wakeup timer  35  to a first change value (for example, 30 seconds) and shortens the actuation period T of the monitor  30  in S 110 . For example, as illustrated in  FIG. 4 , the CPU  31  changes the set time of the wakeup timer  35  from 60 seconds to 30 seconds and changes the actuation period T of the monitor  30  from the initial value of 60 seconds to 30 seconds. 
     After changing the actuation period T to the first change value, the monitor  30  is actuated at an interval of the first change value in subsequent monitoring. After changing the actuation period T, the process returns to S 10 . Then, the process proceeds to S 20 , S 30  and S 40  and if it is determined that the battery voltage does not change (S 50 : No), the CPU  31  resets the number of continuous changes K to be zero (S 60 ) and also resets the set time period of the wakeup timer  35  to the initial value (S 70 ). If it is again determined that the current battery voltage changes from the previous detected value (S 50 : Yes), and it is determined that the current detected value detected in S 40  is equal to or less than the threshold voltage Vth (S 100 : No), the CPU  31  does not change the set time of the wakeup timer  35  and keeps the first change value (S 110 ). The threshold voltage Vth is preferably close to the full charge voltage of the secondary battery  10 . 
     If the battery voltage of the secondary battery  10  continuously changes with respect to a time axis as illustrated in  FIG. 4 , for example proportionally, the monitor  30  is repeatedly actuated at an interval of 30 seconds to monitor the secondary battery  10 . 
     If the detected battery voltage changes consecutively several times, the CPU  31  determines that the secondary battery  10  is used in condition where the monitor cannot receive the external actuation signal Sb from the load side. If determining that the number of continuous changes K is over the threshold number Kth (S 90 : No), the CPU  31  changes the set time of the wakeup timer  35  to be a second change value that is shorter than the first change value (for example, 20 seconds) in S 120 . Accordingly, the actuation period T of the monitor  30  is further shortened. Therefore, the voltage is detected for several times at a shortened actuation period T. This reduces time required to determine that the secondary battery  10  is used in an improper state. 
     In the present embodiment, the actuation period T is changed to be shortened if the secondary battery  10  is improperly used. Therefore, compared to a case where the actuation period T of the monitor  30  is not changed from the initial value even if the secondary battery  10  is improperly used, it is promptly detected that the secondary battery  10  is used in an improper state that the monitor  30  cannot receive the external actuation signal Sb from the load side. If detecting that the secondary battery  10  is used in an improper condition that the monitor  30  cannot receive the external actuation signal Sb from the load side, the CPU  31  of the monitor  30  performs an informing process that informs an error using an error notification lamp or a buzzer for example (S 130 ). 
     If the actuation period T is kept to be long, the secondary battery  10  is not monitored by the monitor  30  for a long time. Thus, if the secondary battery  10  is charged for a long time without monitoring and the battery voltage reaches a prohibited level, overcharge or over discharge may be caused in the secondary battery  10  and the secondary battery  10  may become in an abnormal state. However, in the present embodiment, the actuation period T of the monitor  30  is shortened and this shortens a monitoring interval of the secondary battery  10 . Therefore, the CPU  31  may disconnect the relay R (S 130 ) to stop charging before the secondary battery  10  is overcharged. Therefore, the secondary battery  10  is not overcharged. 
     In determining that the number of continuous changes K is less than the threshold number Kth (S 90 : Yes) and determining that the current detected value that is detected in S 40  is greater than the threshold voltage Vth (S 100 : Yes), the CPU  31  changes the set time of the wakeup timer  35  to the second change value (S 120 ). Accordingly, as illustrated in  FIG. 4 , the CPU  31  may further shorten the actuation period T of the monitor  30 , and the secondary battery  10  is not overcharged. 
     Second Embodiment 
     Next, a second embodiment will be described with reference to  FIGS. 5 to 7 . In the first embodiment, the voltage of the secondary battery  10  proportionally changes with respect to the time axis and changes the actuation period T of the monitor  30  from 60 seconds to 30 seconds. 
     In the second embodiment, the CPU  31  compares the current detected voltage and the previous detected voltage and obtains a change amount of the battery voltage every time determining that the current voltage changes from the previous voltage. Specifically, if determining that the current detected voltage changes from the previous detected voltage (S 50 : Yes), the CPU  31  computes a change amount between the previous detected voltage and the current detected voltage (S 210 ). As the change amount becomes greater, the CPU  31  changes the set time of the wakeup timer  35  to be a shorter value (S 220 ). Accordingly, the greater the change amount of the detected battery voltage values is, the shorter the actuation period T becomes. For example, if the battery voltage changes along a substantially quadratic curve with respect to the time axis as illustrated in  FIG. 6 , the actuation period T of the monitor  30  is changed to be shorter as time passes. 
     In the second embodiment, if the change amount of the battery voltages becomes larger and the current detected voltage is close to the full-charge voltage, the actuation period T is further shortened. Therefore, the monitor  30  monitors the secondary battery  10  more frequently. Therefore, the secondary battery  10  is not overcharged. An olivine-type lithium-ion iron second battery has characteristics as illustrated in  FIG. 6 , and in the olivine-type lithium-ion iron second battery, the voltage rises drastically at a terminal stage of charging. The olivine-type iron battery is a kind of lithium-ion batteries and has a positive electrode made of olivine-type iron phosphate, that is, lithium iron phosphate (LiFePO4) and a negative electrode made of, for example, carbon. The olivine-type lithium-ion iron secondary battery has a full-charge voltage of about 3.5 V as illustrated in  FIG. 7 . Therefore, if the olivine-type lithium-ion iron secondary battery is set such that the voltage drastically rises in a range between 3.45 V and 3.5 V that is close to the full-charge voltage, the actuation period T is also shortened at the voltage between 3.45 V and 3.5 V. Accordingly, the olivine-type lithium-ion iron secondary battery  10  can be monitored more frequently at the voltage close to the full-charge voltage. Therefore, the olivine-type lithium-ion iron secondary battery is not overcharged. 
     Third Embodiment 
     Next, a third embodiment will be described with reference to  FIG. 8 . An actuation period change sequence of the third embodiment is substantially same as the sequence of the second embodiment including steps S 10  to S 220  and additionally includes processing of S 3  and S 5  in  FIG. 7 . Therefore, the processing of S 3  and S 5  will be explained. 
     As shown in  FIG. 8 , in the third embodiment, if the CPU  31  detects that the conditions for switching the monitor  30  to the sleep mode are satisfied and receives the sleep signal Sa output from the load side, the CPU  31  of the monitor  30  determines whether the most recent battery voltage of the secondary battery  10  detected in the measurement mode is close to a full-charge voltage or not (S 3 ). Specifically, the CPU  31  compares the most recent battery voltage to a threshold voltage Vth that is previously set (a value close to the full-charge voltage). If determining that the most recent battery voltage is higher than the threshold voltage Vth, the CPU  31  determines that the most recent battery voltage is close to the full-charge voltage (S 3 : Yes). If determining that the most recent battery voltage is less than the threshold voltage, the CPU  31  determines that the most recent battery voltage Vth is not close to the full-charge voltage (S 3 : No). 
     If the CPU  31  determines that the most recent battery voltage is not close to the full-charge voltage (NO: S 3 ), the process proceeds to S 10 . Processing executed after S 10  is same as that in the second embodiment. In the sleep state, if the detected voltage of the secondary battery  10  is not changed from the previous detected value (S 50 : No), the monitor  30  is actuated with an actuation period T of 60 seconds to monitor the secondary battery  10  (S 70 ). If the current detected voltage is changed from the previous detected value (S 50 : Yes), the actuation period T is changed (S 60 ). 
     Next, if the CPU  31  determines that the most recent battery voltage is close to the full-charge voltage (YES: S 3 ), the process proceeds to S 5 . In S 5 , the CPU  31  changes the set time of the wakeup timer  35  to a time shorter than an initial value. The initial value of the set time of the wakeup timer  35  is 60 seconds, and the set time is changed to a time shorter than that. For example, 30 seconds is set to the wakeup timer  35  in S 5 . Accordingly, immediately after being switched to the sleep mode, the monitor  30  is actuated with an actuation period T that is shorter than the initial setting and monitors the secondary battery  10 . 
     In such a manner, if the voltage of the secondary battery  10  is close to the full-charge voltage before the monitor  30  being switched from the measurement mode to the sleep mode, the actuation period T of the monitor  30  is set to a small value. Therefore, the secondary battery is not overcharged. 
     Other Embodiments 
     The present invention is not limited to the above description and the drawings. For example, the following embodiments are covered by the technological scope of the invention. 
     (1) In the above embodiments, the monitor  30  monitors the state of the secondary battery  10 . However, the target to be monitored by the monitor  30  is necessarily a storage element (electricity storing element), and the state of a capacitor may be monitored by the monitor  30 . Further, in the above embodiments, the control device is the CPU  31 . However, the control device may be a hardware circuit. 
     (2) In the above embodiments, if the voltage of the secondary battery  10  is changed from the previous detected value, the actuation period T of the monitor  30  is changed. For example, the CPU  31  may detect a temperature of the secondary battery  10  and determine whether the detected temperature of the secondary battery  10  is changed from the previous detected value. If determining that the detected temperature is changed from the previous value, the CPU  31  may change the actuation period T of the monitor  30 . 
     Besides the battery temperature, the information denoting the state of the secondary battery  10  may include any information from which the CPU  31  can detect the possibility of occurring abnormality of the battery such as a state of charge (SOC), a current value, or an internal pressure of the battery. 
     A current of the secondary battery  10  may be detected to detect the state of the battery  10 . A dark current dissipated by the battery  10  while a vehicle being parked may be detected to determine whether the actuation period T may be changed or not. Specifically, in a system in which the dark current dissipated by the secondary battery  10  while a vehicle being parked is 100 mA or less, if determining that the dark current is a normal value and is less than 100 mA, the CPU  31  sets the actuation period T of the monitor  30  to 60 seconds that is an initial value. 
     If determining that the dark current is 100 mA or higher, the CPU  31  may change the actuation period T of the monitor  30  from 60 seconds to 30 seconds or may shorten the actuation period T in a stepwise manner according to the level of the dark current. For example, in the secondary battery  10  having a capacity of 60 Ah, the actuation period T is changed according to the level of the dark current as follows. If the dark current is from 100 mA to 0.1 CA (6 A), the actuation period T is set to 30 seconds. If the dark current is from 0.1 CA (6 A) to 0.5 CA (30 A), the actuation period T is set to 20 seconds. If the dark current is 0.5 CA (30 A) or greater, the actuation period T is set to 10 seconds. 
     The actuation period T may be determined based on a plurality of detected values. For example, a current and a battery voltage may be detected and the CPU  31  may detect whether each of the values of the current and the battery voltage is equal to or greater than a corresponding certain level. If both of the detected values of the current and the battery voltage are the certain level or greater, the actuation period T may be further shortened as compared to a case in which only one of them is greater than the corresponding certain level. In such a case, the measurement unit  41  is a current sensor that detects a current flowing through the secondary battery  10 , and a current is detected by the current sensor and the detected value corresponds to a detected current. 
     (3) In the above embodiments, the actuation period T of the monitor  30  is changed if the detected value of the secondary battery  10  is changed from the previous detected value. The target value to be compared with the current detected value of the secondary battery  10  may be a value that is detected prior to the last value that is detected at last or a reference value that is previously stored in the RAM  45 . Therefore, if the current detected value of the secondary battery  10  is changed from the value detected prior to the last value or the reference value, the actuation period T of the monitor  30  may be changed. 
     (4) In the above embodiments, the voltage of the secondary battery  10  is increased from the previous detected value (charging). However, the voltage of the secondary battery  10  may be decreased from the previous detected value (discharging). Also in the case where the voltage of the secondary battery  10  is decreased from the previous detected value, the actuation period T may be shortened to shorten the monitoring interval at which the monitor  30  is monitored. 
     (5) In the above embodiments, the monitor  30  is switched from the measurement mode to the sleep mode if the CPU  31  of the monitor  30  receives the sleep signal Sa output from the side of load. However, the monitor  30  may detect the conditions for switching to the sleep mode without receiving any signal from the external device and if detecting the conditions, the monitor  30  may be switched to the sleep mode. 
     (6) In the above embodiments, each of the sleep signal Sa and the external actuation signal Sb is an independent signal. However, the two signals Sa and Sb may be configured with a single signal. The single signal may be set to a high level or a low level to control switching the mode of the monitor  30 . 
     (7) In the above embodiments, the actuation period T of the monitor  30  is changed if the voltage of the secondary battery  10  is changed from the previous detected value. In addition to this, the CPU  31  may further detects if a current is flowing through the secondary battery  10  to determine whether to change the actuation period T or not. The CPU  31  changes the actuation period T of the monitor  30  if detecting that the current detected voltage of the secondary battery  10  is changed from the previous detected value and a current is flowing through the secondary battery  10 . 
     Accordingly, the following effects are obtained. Generally, the battery voltage changes for a while after completion of charging or discharging. Therefore, if the actuation period T is changed only based on a change in the battery voltage, the actuation period T may be changed even in an ordinary state where the battery is not charged improperly. However, if the actuation period is changed based on a change in the battery voltage and detection that the current is flowing through the battery, the actuation period T is not changed in the ordinary state. Thus, the actuation period T is changed only when the battery is used (charged) improperly. 
     (8) In the second embodiment, the larger the change amount of the measured battery voltage value is, the more the actuation period T is shortened. The actuation period T may be changed in any other methods according to the change amount of the detected value. For example, the actuation period T of the monitor  30  may be changed in accordance with any one of the following patterns. 
     As illustrated in  FIG. 7 , in the olivine-type lithium ion iron secondary battery, the full-charge voltage is about 3.5 V, and the battery is preferably used with the charged voltage being between 3.3 V and 3.5 V. In this case, a range of use E of the battery is 200 mV from 3.3 V to 3.5 V and the battery can be preferably used in this range, and 10% thereof is 20 mV. If the detected value is not changed from the previous value and the actuation period T is set to the initial value of 60 seconds, the actuation period T may be changed in the following methods. 
     Pattern 1: If the detected value is changed from the previous detected value by 20 mV that is 10% of the range of use, the actuation period T is changed from 60 seconds to 30 seconds that is a half of the initial value. 
     Pattern 2: If the detected value is changed from the previous detected value by 40 mV that is 20% of the range of use, the actuation period T is changed from 60 seconds to 15 seconds that is a quarter of the initial value. 
     Pattern 3: If the detected value is changed from the previous detected value by 20 mV and the actuation period T is changed from the initial value of 60 seconds to 30 seconds and then the subsequent detected value is changed from the previous value by 40 mV, the actuation period T is changed from 30 seconds to 15 seconds that is a half of 30 seconds. If the detected value is changed by the change amount same as the previous change amount of 20 mV, the actuation period T is not changed and maintained to be 30 seconds. 
     The actuation period T may be changed by multiplying the actuation period T by a constant (½ or ¼) corresponding to the change amount of the detected value as described above, and further, the actuation period T may be changed by subtracting a constant (20 seconds or 40 seconds) that is determined corresponding to the change amount of the detected value from the current actuation period T. 
     (9) In the above embodiments, the actuation period T of the monitor  30  is changed if the battery voltage of the secondary battery  10  is changed from the previous detected value. However, the actuation period T may be changed if the CPU  31  detects that the battery voltage of the secondary battery  10  is not changed from the previous detected value or a reference value. 
     Specifically, if the current detected value is not changed from the previous detected value, it is unlikely that the secondary battery  10  is used improperly. Thus, even if the actuation period of the monitor  30  is extended, it is unlikely that any error is caused in the secondary battery  10 . The actuation period T is 60 seconds that is the initial value and if the current detected value is not changed from the previous value, the actuation period T may preferably be set to 90 seconds or 120 seconds that is longer than the initial value. The actuation period T becomes longer and this reduces the power consumption of the monitor  30 . 
     The actuation period T may be changed if the battery voltage of the secondary battery  10  is not changed from the previous detected value or the reference value, and also the actuation period T may be changed if the current detected value is changed from the previous detected value. 
     As illustrated in  FIG. 9 , if determining that the current detected voltage changes (S 50 : Yes), the CPU  31  computes a change amount between the previous detected value and the current detected value (S 210 ), and the CPU  31  changes the set time of the wakeup timer  35  to be a shorter value as the computed change amount is greater (S 220 ). If determining that the current detected voltage does not change (s 50 : No), the CPU  31  may change the set time of the wakeup timer  35  to be a value that is longer than the initial value. 
     According to the present technology, the monitor can deal with a case that the monitor cannot receive an actuation signal from the load side.