Piper Aircraft Corporation Malibu Mirage PA-46-350P, Airplane Maintenance Manual

Page: 424 / 1956

PAGE 8
Feb 28/07
2I2
24-30-00
PIPER AIRCRAFT, INC.
PA-46-350P, MALIBU MIRAGE
MAINTENANCE MANUAL
7. Alternators
Electrical power for the 28 Vdc, negative ground, dual fed split bus electrical system is supplied by two
belt driven, parallel connected 28Vdc: 70-amp Prestolite alternators, No. ALV-8421-LS (
S/N’s 4636001
thru 4636131 ); or, 75-amp Electrosystems alternators, No. ES4039-LS ( S/N’s 4636132 and up ).
Voltage regulation is provided by a solid state voltage regulator, which automatically monitors and
controls alternator output by controlling the alternator field winding current. Also, an overvoltage control
is provided to shut down alternator output should an overvoltage condition occur. The alternator’s output
can also be shut off manually by individual alternator ON-OFF switches, which interrupts field winding
voltage to the voltage regulator.
CAUTION: DO NOT MANUALLY OPERATE (PULL) THE ALTR1 OR ALTR2 CIRCUIT BREAKER
WHEN THE ENGINE IS RUNNING AND THE ALTERNATOR IS OPERATING PROPERLY.
Over current protection is provided by the 70-amp ( S/N’s 4636001 thru 4636131 ) or, 80-amp ( S/N’s
4636132 and up ) tie bus ALTR 1 and ALTR 2 circuit breakers. Two ammeters. located on the lower center
section of the instrument panel, are fed from taps an each shunt resistor , and indicate the individual
electrical load of each alternator. Should an overvoltage condition occur in either alternator, its voltage
regulator will shut off the field winding voltage of that alternator, thus overvoltage relays are not required.
When either alternator fails, or is selected OFF, the appropriate ALTERNATOR INOP annunciator light
will illuminate.
A. Alternator Belt Tension
(1) If properly installed, tensioned, and checked periodically, the alternator drive belt will give very
satisfactory service. However, an improperly tensioned belt will wear rapidly and may slip and
reduce alternator output. Consequently, a belt should be checked for proper tension at the time
it is installed, again after 25 hours operation and each 100 hours thereafter, or whenever any
work is performed that would affect belt tension.
(2) Adjust the alternator belt tension as follows:
(a) Adjust the belt to obtain a tension of 45 pounds for a new belt or 23 to 34 lbs for an old
belt.
NOTE: The higher tension specified for a new belt is to compensate for the initial stretch
that takes place as soon as it is operated. These higher tension values should not
be applied to previously used .
(b) Run the engine for a 15 minute period at idle.
(c) Shut down engine and recheck the belt tension. New belt tension should fall back to
desired tension of 23 to 34 lbs. Old belts reinstalled should retain the 23 to 34 lbs tension.
(d) This tension check should be made at every 100 hours or annual inspection, whichever
occurs first.