Ranger 4WD V6-183 3.0L (1993)
Ammeter Gauge: Description and Operation
OPERATION
The ammeter is an instrument used to indicate current flow into and out of the battery. When electrical accessories in the vehicle draw more
current than the alternator can supply, current flows from the battery and the ammeter indicates a discharge (-) condition. When electrical loads of
the vehicle are less than alternator output, current is available to charge the battery, and the ammeter indicates a charge (+) condition. If battery is
fully charged, the voltage regulator reduces alternator output to meet only immediate vehicle electrical loads. When this happens, ammeter reads
zero.
TYPES OF AMMETERS
Fig. 1 Conventional Type Ammeter
Conventional Ammeter
A conventional ammeter must be connected between battery and alternator in order to indicate current flow. This type ammeter consists of a frame
to which a permanent magnet is attached. The frame also supports an armature and pointer assembly.
Current in this system flows from the alternator through the ammeter, then to the battery or from the battery through the ammeter into the vehicle
electrical system, depending on vehicle operating conditions.
When no current flows through the ammeter, the magnet holds the pointer armature so that the pointer stands at the center of the dial.
When current passes in either direction through the ammeter, the resulting magnetic field attracts the armature away from the effect of the
permanent magnet, thus giving a reading proportional to the strength of the current flowing.
Shunt Type Ammeter
The shunt type ammeter is actually a specifically calibrated voltmeter. It is connected to read voltage drop across a resistance wire (shunt) between
the battery and the alternator.
The shunt is located either in the vehicle wiring or within the ammeter itself.
When voltage is higher at the alternator end of the shunt, the meter indicates a charge (+) condition. When voltage is higher at the battery end of
the shunt, the meter indicates a discharge (-) condition. When voltage is equal at both ends of the shunt, the meter reads zero.
