Piper Comanche PA-24 Service Manual page 711

•
PIPER COMANCHE SERVICE MANUAL
--
FJ
a
9-68. H .. Load Te.t Check. (Refer to Figure
~27t.) CODDect
the
cranking motor in senes
with • fully charged battery of the specified
voltase. an ammeter capable of reedina several
hundred amperes. and a variable resistance.
Also connect a voltmeter as ilLustrated. from
- the motor terminal to the !Dotor frame. Ar!" r.p.r:t.
indicator is necessary to measure armature
speed. Obtain the specified yoltage
by
varying
the :esistanee uai t. Then read the cunent
drn!
and armature speed and compare these readings
with the valu.es listed ill the published specI-
fications. Interpret the test results as follows:
•. Rated current draw and no-load speed
indicate normal condition of the cracking motor.
b. Low free speed and high current draw
indicate:
FIGURE 9-27t. NO-LOAD TEST l. Too much fnction-tight. dirty. or
loose pole shoes allowing armature to drag.
2. Shorted armature. This can be further checked. on a vowler after disassembly.
3. Grounded armature or fields. Check further Ifter disassembly.
c. Failure to operate with high. current draw indicates:
1. A direct ground in the terminal or Helds.
2. "Frozen" bearings (th1s should have been determined by
~uming
the armature by hand).
d. Failure to operate with no current draw indicates:
1. Open held Circuit. This can be check.ed after disassembly by inspecting internal con-
nections and tracing Clrcuit with a test lamp.
2. Open armature coils. Inspect the commutator for badly burned bars after disassembly.
J.
Broken brush springs, worn brushes, bigh insulation between the commutator bars or
other causes wh1ch would prevent good contact between the brushes and commutator.
e. Low
n~load
speed and low current draw indicate:
L High internal resistance due to poor connections, defective leads, dirty commutator and
causes listed under (d).
f. High
free
speed and high current draw indicate shorted fields. If shorted fields are sus-
pected, replace the field coil assembly and check for improved performance.
9-69. Lock. T o.que T ... Check. (Refer to Fisure 9-27u.) The lock-torque test requires the eqUip-
ment illustrated. A variable resistance with a high current capacity should
be
used. The cranking
motor should
be
securely :Daunted and a brake arm hooked to the drive pinion. Use extreme cauuon
dunng this test to make sure the end of the brake am: does not Slip off of the ptnion when current
is applied. When specified
curre~1t
is ap'plied. the torque can
be
computed from the reading on the
scale. A one foot brake arm will directly indicate pound. feet. Compare the pound·(eet of torque
. as read on the scale with that listed in the published specifications. If the torque is tow, the
motor :nust be
d~assembled
for further tests and repair.
9-70. DilGslernbly. If the motor does n.ot perform in accordance with published specifications.
it may need to be disassembled for further testing of the components.
~ormal1y
the cranking motor
3
ell
ELECTRICAL SYSTEM
ISSUED: 8118n2