MOONEY INTERNATIONAL CORPORATION
M20V SERVICE AND MAINTENANCE MANUAL
Page
Date
6
MAR 2017
Rev Date
(1) Turn Master Switch OFF. Disconnect alterna-
tor wiring.
(2) Remove attaching hardware and pull alterna-
tor drive gear from engine pad.
B. Alternator Installation
(1) Be sure Master Switch is turned - OFF. Do
not turn Master Switch ON until all wiring connections
have been secured.
(2) Insert alternator into engine accessory drive
pad. Install attaching hardware.
(3) Connect alternator wiring and check wiring
connectors throughout system.
24- 31- 02 - ZEFTRONICS (A25EAM) 28V AUTO-
PARALLEL CONTROLLER (APAC)
MAIN ALTERNATOR
The Zeftronics (A25EAM) is an electronic Auto- Paral-
lel Alternator Controller (APAC) designed for use with
24VDC aircraft alternator system. This system pro-
vides the following:
Voltage Regulation - The voltage regulator keeps the
Buss voltage constant by increasing the current to the
alternators field with a system load increase, decreas-
ing it with a load decrease. The Pulse Width Modulation
(PMW) function allows the field current to increase or
decrease with an increase or decrease in the system
load demand at a fixed frequency.
Battery Off- Line Failure Recognition (BOLR) - Regu-
lates the Buss voltage with the battery off- line. This al-
lows the system to carry electrical load if the battery
fails or the battery relay fails to open. The APAC pro-
vides RVP (Remote Voltage Sensor/Protection) and
GFP (Field- to- Ground Short protection) functions
while the system operates in the BOLF mode.
Over Voltage (OV) Protection – The OV protector turns
off the Voltage Regulator and the Alternator if the Buss
voltage exceeds the OV set point, thus protecting sen-
sitive avionics equipment and the battery. The OV trip is
time delayed to prevent nuisance tripping.
Remote Voltage Sensor & Protection (RVP) – The RVP
senses the voltage at the battery terminal of the alter-
nator or the Buss to provide better voltage regulation
and eliminate flickering charge- meter and panel light
problems. Losing or opening the RS wire will turn off the
APAC, taking the alternator offline.
Alternator Off- Line Sensor (AOS) & Indicator (AOI) –
The AOI will come on under these conditions:
- The ALT switch is OFF/OPEN while battery
switch is ON
- The field- to- ground short protection (GFP) func-
tion or open field
- OV protection turns off the alternator due to OV
fault or RS loss
- Loss or opening of the Alternator Off Sense wire
or voltage
Whenever the TSL on the unit is Red, the AOI is on.
Field- to- Ground Short Protection (GFP) – If the alter-
nator’s field becomes shorted to ground (the reason
most ACU/Voltage Regulators fail), the field- to-
ground short protector will deactivate the Voltage Reg-
ulator, and switch on the unit’s Red Troubleshooting
light, and the OV or Low Voltage indicator on the instru-
ment panel.
Troubleshooting Light (TSL) – The TSL on the APAC
unit alerts the user to the condition of the Alternator/
APAC system (Refer to Fig. 24- 1).
ZEFTRONICS (A25EAM) Specifications
Voltage Regulation, PWM 28.5 0.4V
Field Current, Max 5A DC
Battery Off- Line Regulation,
BOLR
Yes, VR
1.0V
Remote Voltage Sensor/Protec-
tion
Yes
RVP & GFP Protection with Bat-
tery Off
Yes
Parallel (Load Share) Yes
Over Voltage Protection/Warning 32.0 0.8V
Alternator Off- Line Sense/Indica-
tion
Yes
Field- to- ground Short Fault Yes
Troubleshooting Light Yes
Weight 0.40 Lb.
HOW THE SYSTEM WORKS (refer to Fig. 24- 2)
Closing the Bat switch applies battery power to the air-
craft Buss. The APAC is powered through the 5 Amp
Circuit Breaker. The APAC controls the alternator’s
field current to regulate the Buss voltage.
The Voltage Regulator (VR) - To control Buss voltage,
the VR of the APAC monitors the alternator output volt-
age through the remote sense input (pin 8) and
compares it to an internal reference. The VR regulates
the Buss voltage by increasing or decreasing the field
current at a fixed frequency with automatically adjusted
length of it’s on and off time; this is called pulse width
modulated (PWM) voltage regulation. The VR in-
creases the field current if the Buss voltage drops be-
low a preset level, and decreases the field current if the
voltage exceeds the preset level. The power to control
the field comes into the APAC from pin 5, while its out-
put is from pin 7.
24-31-02
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