Figure 4-16.-Ripple pattern of alternator output.
CHARGING CIRCUIT DIODES
When an alternator fully produces, each of its diodes
conducts an equal share of the current. This condition is
indicated by a ripple pattern that appears on the screen
of the engine analyzer. (See fig. 4-16.) But a single
nonconducting diode places a strain on the charging
circuit which causes a decrease in the output of the
alternator. Whereas an ammeter or voltmeter may not
detect this strain, the analyzer can do so easily. The strain
brought on by an open field condition, for example, will
stop the alternator output ripple entirely. See the screen
display of figure 4-17.
A likely result of decreased alternator output is an
undercharged battery, and without a fully charged
battery, there may not be enough current available to
start the engine or meet the demands of the electrical
circuits. When a good battery cannot be fully charged,
the fault is usually in the alternator or voltage regulator.
The engine analyzer can help you determine which is at
fault. However, the regulator has to be bypassed
altogether and battery voltage applied to the field
terminal of the alternator. Not all alternators can be full
fielded. Refer to the manufacturers fieldtest procedure.
Figure 4-17.-Open file stops the ripple.
Figure 4-18.Bypass adapter.
The first step in the procedure for bypassing the
voltage regulator is for you to turn OFF the engine.
Next, disconnect the regulator and place a jumper wire
between the positive (+) battery terminal and the field
terminal of the alternator. You can also use the bypass
adapter hooked up as shown in figure 4-18. Again start
the engine and slowly increase its speed until the rated
alternator output is reached. DO NOT RUN THE
ENGINE FOR MORE THAN 20 SECONDS.
If the ripple pattern now appears on the screen of
the engine analyzer, the regulator is faulty. No change
in the screen pattern means the alternator or output
wiring is at fault. Stop the engine, disconnect the jumper
wire or bypass adapter, and reconnect the voltage
OPEN AND SHORTED DIODES
A shorted diode or shorted winding will usually
burn itself open. The pattern on the screen will show a
shorted diode (fig. 4-19) or open diode (fig. 4-20).
Notice the similarity in the patterns. At any rate, the
alternator will require service or replacement even
Figure 4-19.-Shorted diode pattern.