24-00-00 Page 24-12 Revised: February 28, 2002
1J22
D.C. GENERATION.
ALTERNATOR SYSTEM.
Each alternator is located on the front lower right side of the engine and utilizes a belt drive from the engine crankshaft. The alternating current is converted to direct current by diodes pressed into the end bell housing of the alternator. The diodes are highly reliable solid state devices, but are easily damaged if current flow is reversed through them.
Each alternator system has an independent ON-OFF rocker swicth and a solid state voltage regulator that automatically regulates alternator field current. When selected ON, the positive output of each alternator is fed through individual shunts to the main tie bus. Overcurrent protection is provided by the 70 amp L ALT and R ALT main tie bus circuit breakers. Additionally, each alternator field is protected by a 5 amp circuit breaker marked L ALT FIELD or R ALT FIELD, as appropriate. If this breaker trips, it will result in a complete shutdown of power from the respective generating system. After a one or two minute cool down period, the breaker can be reset manually. If tripping occurs again, this indicates a short in the respective alternator circuit.
Two annunciator lights are located at the upper right of the pilots panel. When either alternator fails, or is selected OFF, the amber ALT annunciator light will illuminate. A low voltage monitor, also connected to the tie bus will illuminate the red LO BUS annunciator light when the system drops from bus voltage (14 Vdc) to battery voltage (approx. 12 Vdc). A fuse provides overvoltage protection for the low voltage monitor.
The dual ammeters do not indicate battery discharge, but display the load in amperes placed on the individual generating systems. With all electrical equipment off, except the master switch, the ammeters will indicate the amount of charging current demanded by the battery. This amount will vary depending on the percent of charge in the battery at the time. As the battery becomes charged the amount of current displayed on the ammeters will reduce to approximately two amperes. The amount of current shown on the ammeters will tell immediately whether or not the alternator system is operating normally, if the following principles are kept in mind.
— Note —
The amount of current shown on the ammeter is the total load, in amperes, that is demanded by the electrical system from the alternator. 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 arrived 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.
A simulated load can be made by connecting 8 landing lights wired in parallel from the main bus to air-frame ground or fourteen 3 ohm, 100 watt resistors. (See Figure 24-1)
24-30-00 Page 24-13 Revised: February 28, 2002
PRECAUTIONS.
The following precautions are to be observed when testing or servicing the electrical system.
1.
Disconnect the battery before connecting or disconnecting test instruments, except voltmeter, or before removing or replacing any unit or wiring. Accidental grounding or shorting at the regulator, alternator, ammeter or accessories, will cause severe damage to the units and/or wiring.
2.
The alternator must not be operated on an open circuit with the rotor winding energized.
3.
Do not attempt to polarize the alternator. No polarization is required. Any attempt to do so may result in damage to the alternator, regulator or circuits.
4.
Grounding of the alternator output terminal may damage the alternator and~or circuit and components.
5.
Reversed battery connections may damage the rectifiers, wiring or other components of the charging system. Battery polarity should be checked with a voltmeter before connecting the battery. This aircraft is negative ground.
6.
If a booster battery or fast charger is used, its polarity must be connected correctly to prevent damage to the electrical system components.
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