58 SENR9977 Testing and Adjusting Section When it is possible, make a test of the charging unit and voltage regulator on the engine, and use wiring and components that are a permanent part of the system. Off-engine testing or bench testing will give a test of the charging unit and voltage regulator operation. This testing will give an indication of needed repair. After repairs are made, perform a test in order to prove that the units have been repaired to the original condition of operation. When the magnetic force increases in both coils, the pinion gear moves toward the ring gear of the flywheel. Then, the solenoid contacts close in order to provide power to the starting motor.
When the solenoid contacts close, the ground is temporarily removed from the pull-in coil. Battery voltage is supplied on both ends of the pull-in coil while the starting motor cranks. During this period, the pull-in coil is out of the circuit. Cranking of the engine continues until current to the solenoid is stopped by releasing the ignition switch. Alternator Regulator The charging rate of the alternator should be checked when an alternator is charging the battery too much or not charging the battery enough. Power which is available during cranking varies according to the temperature and condition of the batteries.
The following chart shows the voltages which are expected from a battery at the various temperature ranges. Alternator output should be 28 ± 1 volt on a 24 volt system and 14 ± 0.5 volt on a 12 volt system. No adjustment can be made in order to change the rate of charge on the alternator regulators. If the rate of charge is not correct, a replacement of the regulator is necessary. For individual alternator output, refer to Specification, “Alternator and Regulator”. Table 9 i01945632 Electric Starting System - Test General Information All electrical starting systems have four elements: The following table shows the maximum acceptable loss of voltage in the battery circuit.
The battery circuit supplies high current to the starting motor. The values in the table are for engines which have service of 2000 hours or more. Ignition switch Start relay Starting motor solenoid Table 10 Starting motor Start switches have a capacity of 5 to 20 amperes. The coil of a start relay draws about 1 ampere between test points. The switch contacts of the start relay for the starting motor are rated between 100 and 300 amperes. The start relay can easily switch the load of 5 to 50 amperes for the starting motor solenoid. The starting motor solenoid is a switch with a capacity of about 1000 amperes. The starting motor solenoid supplies power to the starter drive.
The starting motor solenoid also engages the pinion to the flywheel. The starting motor solenoid has two coils. The pull-in coil draws about 40 amperes. The hold-in coil requires about 5 amperes.
Typical Voltage Of Electrical System During Cranking At Various Ambient Temperatures Temperature 12 Volt System 24 Volt System −23 to −7°C (−10 to 20°F) 6 to 8 volts 12 to 16 volts −7 to 10°C (20 to 50°F) 7 to 9 volts 14 to 18 volts 10 to 27°C (50 to 80°F) 8 to 10 volts 16 to 24 volts Maximum Acceptable Voltage Drop In The Starting Motor Circuit During Cranking Circuit 12 Volt System 24 Volt System Battery post “-” to the starting motor terminal “-” 0.7 volts 1.4 volts Drop across the disconnect switch 0.5 volts 1.0 volts Battery post “+” to the terminal of the starting motor solenoid “+” 0.5 volts 1.0 volts Solenoid terminal “Bat” to the solenoid terminal “Mtr” 0.4 volts 0.8 volts