04/ 1998

FORD  4G ALTERNATORS

Ford's latest addition to their charging systems line is the 4G alternator.This 150 ampere alternator has the rectifier diodes encased in a plastic assembly that is riveted to the rear of the alternator end frame. The rotor slip rings are smaller than the rear bearing and protrude through the rear frame similar to Nippondenso designs. The voltage regulator assembly houses the brushes that contact the slip rings and all electrical contacts are made to the rectifier assembly via surface contacts secured with screws. The voltage regulator-rectifier assembly is protected by a stamped steel cover and care must be used to clip the stator leads short to prevent short circuits. By removing six screws, you can replace the voltage regulator, but the rectifier requires the unsoldering of 12 leads (actually eight terminals as the stator is bifilar wound), pressing off  the rear frame and drilling out three rivets. The negative diodes are pressed-in the rear end frame.

Ford has maintained voltage regulator circuit continuity in the 4G as the terminals are nearly identical to the older 2G and 3G SERIES. The figure below shows the vehicle harness to regulator connections. The stator or "S" terminal which enables the voltage regulator to detect that  the alternator is operating, has been removed from the harness. It is now connected directly to the rectifier assembly through a regulator mounting screw. Like the 2 & 3G alternators, the 'A' terminal is directly connected to the positive side of the battery, the 'A' terminal provides voltage to operate the voltage regulator and field circuit. As the 4G employs a 6 ampere field coil, this current flows through the 'A' terminal, so this connection must be clean and tight. Also identical to the 2 & 3G series, the 4G uses the T terminal to both excite the regulator and drive a warning lamp. The Terminal should never be connected directly to the positive side of the battery

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as a lamp-on condition may damage the voltage regulator. Use at least a 60 ohm resistor or preferably, a #57 lamp connect in seriesbetween Terminal andbattery positive when testing.The 4G voltage regulator uses the same pulse width modulation as in the 2 & 3G series units, where a voltage change from 14.5 to about 14.8 volts causes the field duty cycle to decrease from 100 to 6%. Between 0 and 300 hertz stator frequencies, the 4G has load response control, where the rate of change of the duty cycle is controlled to take a full 10 seconds to reach a 100% duty cycle state. The rate of duty cycle rate of change is instantaneous whenever battery voltage increases. All units feature a high.

voltage warning lamp 'on' condition if the charging voltage increases beyond 16.5 volts. The warning lamp is also ignited if the stator signal is not present. Transpo is fully committed to learn of new automotive products and is conducting ongoing testing and evaluations to provide you with high quality components

April 1996 TRANSPO'S Rebuilder Forum

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