Piper COMANCHE PA-24-180 Service Manual page 553

PIPER COMANCHE SERVICE MANUAL
9-42. Alternator System.
9-43. General. The alternator output circuit is connected by means of a 90 ampere circuit breaker. a filter in
the line to eliminate radio interference and an ammeter to monitor alternator output
The field circuit consists of a 5 ampere thermal circuit breaker. a voltage regulator. overvoltage relay.
radio noise filter. voltage regulator and a special switch ganged to the 90 ampere circuit breaker to remove
field voltage from the alternator should the circuit breaker open
The field and output circuit of the alternator is joined by a bus bar which directs current to the batters
An ammeter is installed between the battery and bus to measure current flow to and from the battery The
field circuit is combined with the master switch to turn off the alternator when the master switch is turned off
Should it be necessary to turn the alternator "on" and "off" for any reason. the field breaker can safely
be used for this purpose. The 90 ampere breaker should be actuated from "on" to "off" only when the engine
is stopped. when the master switch is "off" or after the field breaker has first been opened. It may be actuated
from "off" to "on" at any time. A guard has been provided to prevent inadvertent tripping in flight.
9-44. Checking Alternator System. The ammeter is equipped to check the electrical output-input of the
battery. Should the alternator show no output on the ammeter. check the appropriate circuit breakers If a
further check of the ammeter shows no output from the alternator. check the alternator system. (Refer to
Figure 9-15.)
a. Ascertain that the ammeter is operating properly
b. Disconnect the battery and field leads at the alternator
c. Ascertain that all electrical units are off and the battery is fully charged
d Turn on the master switch.
e.
To check the alternator output circuit. connect a voltmeter or 12 volt test light to the battery lead
and to ground. If a reading of approximately 12 volts registers on the voltmeter or test light lights. the battery
circuit is operational
f Should there be no indication of voltage. trace back through the output circuit until voltage is
indicated. (Refer to Figure 9-15.) A component that allows no voltage to pass through it should be replaced.
g.
To check the field circuit. connect a voltmeter or 12 volt test light to the field lead and to ground.
Test the field circuit using the same procedure as in Steps e and f.
h. If indication shows a possible malfunction of the voltage regulator and before installing a new
regulator. refer to Paragraph 9-58 For the relay, refer to Paragraph 9-60.
i.
If voltage is indicated at both the battery lead and field lead. the alternator should be checked for
possible malfunction. (Refer to Paragraph 9-46.)
945 Adjustments. The only adjustments necessary to maintain the alternator system is the adjustment of
the voltage control on the voltage regulator. A voltage of 14 volts is maintained. All other control adjustments
are made at time of installation and need not be reset.
IMPORTANT
Since the alternator and regulator are designed for use on only one
polarity system. the following precautions must be observed when
working on the charging unit. Failure to observe these precautions
will result in serious damage to the electrical equipment.
ISSUED: 8/18/72
3B7
ELECTRICAL SYSTEM
3B7