Komatsu 830E-AC Shop Manual page 260

PROBLEM
5. What is an alternator field coil, and how can the coil be
tested?
Refer to the Field Coil tests section for additional testing
information.
6. What is the function of the R terminal on the regulator
and what can be measured there?
7. An alternator is being tested on a test bench and it does
not reach its full-rated output. What could be wrong?
D10-30
The alternator field coil acts as an electromagnet
when field current is applied. The stronger the mag-
netic field, the higher the alternator output when the
shaft is turned. The strength of the magnetic field is
dependent on the resistance of the field coil winding
(which determines the amperes of current the field
coil draws) and the number of wire turns in the field
coil. The most common symptoms associated with
alternator field coil failure are a no output condition,
reduced output, and sometimes an over-charge con-
dition.
The field coil can be tested for resistance value or
short to ground using an ordinary multi-meter. To test
the alternator's field coil resistance, refer to the Field
Coil Tests for additional testing information.
The R terminal represents a tap or direct connection
to the alternator stator that has electric power only
when the alternator is turning and producing power.
The terminal output is utilized on some applications
for rpm or tachometer function. This requires a cali-
bration circuit that relates the alternator shaft speed
to the engine speed. The output at the R terminal is
AC voltage. The average voltage output can be mea-
sured with an ordinary multi-meter. The R terminal
output, depending on the electrical load, will be equiv-
alent to approximately one-half of the alternator regu-
lated voltage output. In other words, on the 28-Volt
system, the average voltage reading will be about 14-
Volts.
The maximum alternator output is dependent on the
alternator shaft speed. If the test bench motor is not
properly rated, the alternator shaft will turn too slowly.
The alternator will not reach its rated output. When
testing an alternator on a test bench, ensure the test
bench motor is powerful enough to drive the alterna-
tor shaft at full load. To properly test the alternator
rated at 28-Volts and more than 200 amps, a bench
motor rated at 30 hp is required. Testing an alternator
using an underrated bench motor can lead to misdi-
agnosis and unnecessary component replacement.
Battery Charging Alternator
CAUSE/SOLUTION
D10003 07/06