Measurement of current in a vehicle using battery cable as a shunt

Apparatus for monitoring current flow to a battery installed in a vehicle, said battery having positive and negative terminals, and said apparatus comprising:

• a cable having a resistance value and connected from one of the battery terminals to a point of the vehicle electrical system;
• voltage measuring means connected to measure the voltage across said cable only, said voltage measuring means comprising
• a reference current source for producing a voltage corresponding to a reference current of a predetermined value,
• a first amplifier having an output voltage that varies over a range corresponding to the voltage measured across said cable;
• control means for adjusting the input to said amplifier of said voltage measured across said cable only so that its output voltage substantially matches the reference current of predetermined value, and
• second and third amplifiers receiving the output of aid first amplifier, each of said second and third amplifiers having a different gain to correspond to a different range of current values flowing through said cable;
• and
• a computing device for computing the current flow based on the voltage measured across said cable only.

Apparatus for monitoring current flow to a battery installed in a vehicle, said battery having positive and negative terminals, said apparatus comprising

• a cable having a resistance value and connected from one of the battery terminals to a point of the vehicle electrical system;
• voltage measuring means connected to measure the voltage variation across said cable only;
• a computing device for computing the current flow based on the voltage measured across said cable only;
• and
• wherein said measuring means comprises a differential current sensor including an amplifier producing an output voltage in response to said measured voltage across said cable only, said output voltage varying over a range corresponding to the range of current flowing through said cable.

Apparatus for monitoring current flow to a battery installed in a vehicle, said battery having positive and negative terminals, and said apparatus comprising:

• a cable having a resistance value and connected from one of the battery terminals to a point of the vehicle electrical system;
• voltage measuring means connected to measure the voltage variations across said cable only, said voltage measuring means comprising
• a reference current source for producing a voltage corresponding to a reference current of a predetermined value,
• an amplifier having an output voltage that varies over a range corresponding to the voltage measured across only said cable, and
• control means for adjusting the input to said amplifier of said voltage variation measured across said cable only so that its output voltage substantially matches the reference current of predetermined value;
• and
• a computing device for computing the current flow based on the voltage measured across said cable only.