A battery state detection apparatus (battery sensor) that detects the state of a battery has been conventionally known. Such a battery state detection apparatus is disclosed in, for example, Patent Documents 1 and 2.
This type of battery state detection apparatus includes a circuit board and a shunt resistor for detecting a current. Referring to FIG. 9, a shunt resistor 7 is configured such that a resistor element 10 (made of Manganin, for example) whose resistance value is known is arranged between a first conductor part 11 and a second conductor part 12.
Each of the first conductor part 11 and the second conductor part 12 is provided with a board connection terminal 15. The board connection terminal 15 includes a connecting part 30 to be connected to a circuit board (not shown).
In the conventional battery state detection apparatus, as shown in FIG. 9, the board connection terminal 15 is mounted to the shunt resistor 7 with a mounting screw. This structure, which enables the board connection terminal 15 to be electrically and mechanically connected to the shunt resistor 7 with reliability, can ensure a high degree of accuracy of sensing.
The circuit board is configured to apply pulse discharge so that a pulse current flows through the shunt resistor 7, and also to detect, for example, the intensity of a current having flowed through the resistor element 10 at a time of the pulse discharge. The state of a battery can be determined based on, for example, a current value detected at this time. Since a method for determining the battery state through pulse discharge is known, a detailed description thereof is omitted.
Conventionally, the battery state detection apparatus has adopted the known four-terminal method for the detection of a current. As well known, adoption of the four-terminal method enables accurate measurement of a current. FIG. 10(b) shows an equivalent circuit that detects a current having flowed through the resistor element 10 by means of the four-terminal method.
As shown in FIG. 9, the conventional board connection terminal 15 is configured to have a slit formed therein so that two connecting parts 30 are provided. More specifically, the board connection terminal 15 arranged at the first conductor part 11 side is provided with two connecting parts 30c and 30d. On the other hand, the board connection terminal 15 arranged at the second conductor part 12 side is provided with two connecting parts 30a and 30b. Thus, four connecting part 30 in total are arranged on the shunt resistor 7, which enables a current having flowed through the resistor element 10 to be measured by using the four-terminal method.
In the conventional battery state detection apparatus, to achieve the equivalent circuit shown in FIG. 10(b), the four connecting parts 30 (30a, 30b, 30c, 30d) are arranged in a straight line (FIG. 10(a)).