Initial experimentation with external shunt ammeter
A few posts requested more technical information on what this thread is all about. Here is my attempt at shedding some light. The concept stems from Ohm's Law where V=I/R; V=Volts, I=Current, and R=Resistance. Shunts are highly accurate small value resistors, often <1 Ohm in resistance. Using V=I/R, a 1 Ohm resistor conducting 1 amp of current will have a voltage drop of 1 volt. A 0.2 Ohm resistor will have a voltage drop of 0.200 volts (200 mV).
With that said, factory amp gauges that used the wiring harness as the resistance source are doomed to inevitable calibration drift, as connections corrode and the wire degrades. They should comfortably make it through the warranty period, though. Digi-Key has a supply of shunt resistors in the micro-ohm range (designated UOHM).
Displaying the amperage was done with an analog volt meter in the older Mopars. Instead of reading volts, it approximated amps. If the alternator is charging, the voltage is positive and swings the needle to the right. If engine is not running & headlights are on, the voltage is negative, pulling the needle to the left. A digital VOM could also be used to calculate amps across a shunt. I hope this helped some.
A few posts requested more technical information on what this thread is all about. Here is my attempt at shedding some light. The concept stems from Ohm's Law where V=I/R; V=Volts, I=Current, and R=Resistance. Shunts are highly accurate small value resistors, often <1 Ohm in resistance. Using V=I/R, a 1 Ohm resistor conducting 1 amp of current will have a voltage drop of 1 volt. A 0.2 Ohm resistor will have a voltage drop of 0.200 volts (200 mV).
With that said, factory amp gauges that used the wiring harness as the resistance source are doomed to inevitable calibration drift, as connections corrode and the wire degrades. They should comfortably make it through the warranty period, though. Digi-Key has a supply of shunt resistors in the micro-ohm range (designated UOHM).
Displaying the amperage was done with an analog volt meter in the older Mopars. Instead of reading volts, it approximated amps. If the alternator is charging, the voltage is positive and swings the needle to the right. If engine is not running & headlights are on, the voltage is negative, pulling the needle to the left. A digital VOM could also be used to calculate amps across a shunt. I hope this helped some.
