MEASUREMENT OF CURRENT IN A VEHICLE USING BATTERY CABLE AS A SHUNT

摘要

Current flowing into and out of a battery (1) installed in a vehicle (V) with the required cable (3) between one of the battery terminals and a reference point (8) on the vehicle is determined by measuring the voltage across the cable (3) and computing (22) the current from the digital value of the measured current. The resistance value of the cable can be known in which case the current is computed using Ohms low and a differential current sensor (30) can be used to respond to the voltage measured across the cable to accommodate for different ranges of current. In an embodiment where the cable (3) resistance is unknown, a reference current source (125) produces a known voltage (128) that is used to set the input value to an amplifier (111) of fixed gain for the voltage measured across the cable by controlling the output of a potentiometer (106) so that the amplifier output voltage can be set to match the reference current generator output voltage, thereby establishing the voltage output of the amplifier as a measurement of the current flow in the cable.