BATTERY CHARGE INDICATOR

摘要

An automotive battery charge indicator uses an algorithm expressed by fixed component values to determine if the remaining charge in the battery has fallen below a predetermined threshold. A current sensing resistor (8) (having a resistance of the same order of magnitude as the internal resistance of the battery (1) to be monitored), is connected in series with the positive battery terminal (2) of a lead acid battery (1) and the positive side of a non-critical load (4). A percentage of the voltage across the load detected as input (6) is compared by comparator (11) with a dynamic reference voltage at input (5). The dynamic reference voltage is made up of a fixed reference voltage (7) less the voltage drop through current sensing resistor (8). When the percentage of load voltage at (6) is less than the dynamic voltage at (5), the comparator provides a negative output at (12) indicating that the remaining charge in the battery has fallen below the preset threshold value. The output from the comparator can be used to operate an indicator such as an LED or it could be used to initiate circuit shutdown to protect the battery from being discharged excessively.