Piper Arrow IV Turbo Maintenance Manual page 199

CHECKING ALTERNATOR SYSTEM.
With all electrical equipment off (except master switch) the ammeter will indicate the amount of charging
current demanded by the battery. This amount will vary, depending on the percentage of charge in the battery
at the time. As the battery becomes charged, the amount of current displayed on the ammeter will reduce to
approximately two amperes. The amount of current shown on the ammeter will tell immediately whether or
not the alternator system is operating normally, if the following principles are kept in mind.
The amount of current shown on the ammeter is the load in
amperes that is demanded by the electrical system from the
a l t e r n a t o r. As a check, take for example a condition where the
battery is demanding 10 amperes charging current, then switch
on the landing light. Note the value in amperes placarded on the
circuit breaker panel for the landing light circuit breaker (10
amps) and multiply this by 80 percent, you will arrive at a current
of 8 amperes. This is the approximate current drawn by the light.
Therefore, when the light is switched on, there will be an increase
of current from 10 to 18 amperes displayed on the ammeter. As
each unit of electrical equipment is switched on, the current will
add up and the total, including the battery, will appear on the
ammeter.
Using the example that the airplane's maximum continuous load with all equipment on is approximately
48 amperes for the 60 ampere alternator. This approximate 48 ampere value, plus approximately two amperes
for a fully charged battery, will appear continuously under these flight conditions. If the ammeter reading were
to go much below this value, under the aforementioned conditions, trouble with the alternator system would be
indicated and corrective action should be taken by switching off the least essential equipment.
The following test procedure could be helpful in locating faulty components:
1. Ascertain that the airplane is positioned so that the prop blast will not interfere with other operations
going on near by. Start engine and set throttle for 1000 to 1200 RPM.
2. Switch on the following loads and observe the ammeter output increase as indicated:
A. Rotating beacon - 3 to 6 amps.
B. Navigation and instrument lights (bright position) - 4 to 6 amps.
C. Landing light - 7 to 9 amps.
If alternator does not meet above indications, refer to troubleshooting chart. Follow troubleshooting
procedure outlined on the chart in a step by step fashion checking each cause and isolation procedure under a
given trouble before proceeding to the next.
On airplanes without night-flying equipment, load required by test can be simulated by connecting a lamp-
bank load consisting of 8 landing lights wired in parallel from main bus (+) to airframe ground (-). (Refer to
Figure 24-1), or use fourteen 3 ohm, 100 watt resistors.
On air-conditioned aircraft, full alternator output on ground
must be limited to not more than 10 minutes. Refer to Pilot's
Operating Handbook.
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL
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1I7
24-31-01
Page 24-12
Added: August 17, 1982