Voltmeter vs ammeter
Originally submitted by T:
Voltmeter vs Ammeter:
The trouble with an Ammeter is that it reads 0 when the electrical system is working perfectly, 0 when all the electrical load is turned off and 0 when the Ammeter is busted.
Since an Ammeter can only report that the Battery is discharging, being recharged or having the same Voltage on each side of it (balanced situation) it can also read 0 when both the Battery Voltage and Alternator Voltages are low.
A Voltmeter reports the Car's System Voltage which will ideally be 14 Volts at all times. If the Alternator fails, the Voltmeter will drop fast. If the Alternator or Regulator goes overvolt, you will immediately see the Voltmeter's needle hit a danger area on the Gauge.
Because a Voltmeter only places a tiny load on the Electrical System it can be placed quite a distance from the Battery or Alternator and still give an accurate reading.
You can determine the Battery's state of charge by lowering the Engine RPM when the car is in Neutral. If the Voltage drops rapidly the Battery is undercharged. If the Voltage remains high for a lengthy period, the Battery has been recharged.
A Voltmeter tells the whole story, whereas an Ammeter at best can only tell half the story,
that is when it isn't being completely misleading.