Delco Remy CS130 & CS121 Series Alternator Repair Manual - Basic Operating Principles - Page 2

Alternator Service Manual
For Delco Remy CS130 and CS121 Series Alternators

  • Years Used: 1986-1996
  • Amperages: CS-130/85-105 amps CS-121/61-74 amps
  • Used as the most common standard unit on GM Cars & Light Trucks. Also used in Industrial, Marine, Agricultural and other applications.


Unlike other charging systems which have three wires connected to the alternator, the CS-121 and CS-130 may be used with only two wires connected to the alternator. The output wire to the battery positive, and an "L" terminal wire connected to the charge indicator bulb, or to the resistor, or to both. A basic wiring circuit is shown (Figure 3).

The charge indicator works in much the same way as on other charging systems-the indicator lights when the switch is closed, and then goes out when the engine is running. If the charge indicator is on with the engine running a charging system defect is indicated. For all kinds of defects, the indicator will glow at full brilliance. A new feature of this regulator is that it will cause the charge indicator to be on with the engine running if the system voltage is too high or too low. The regulator is temperature-compensated; that is, it's voltage setting varies with temperature.

As in other alternators, the regulator limits the system voltage by controlling the rotor field current. Unlike other regulators, this regulator switches the field current on and off at a fixed frequency of about 400 cycles per second. By varying the on-off time, the correct average field current for proper system voltage control is obtained. At high speeds, the on-time may be 10% and the off- time 90%. At low speeds with high electrical loads the on-off time may be 90% and 10% respectively.

The use of the "P", "F", and "S" terminals is optional. The "P" terminal is connected to the stator, and may be connected externally to a tachometer or other device. The "F" terminal is connected internally to field positive, and may be used as a fault indicator. The "S" terminal may be connected externally to a voltage, such as battery voltage, to sense the voltage to be controlled. For complete circuit, reference must be made to the vehicle manufacturer's wiring diagrams.

Where the regulator is identified with an "I" marking on the regulator case, the circuit in Figure 3A applies. In this circuit, both the "L" and "I" terminals serve to turn on the regulator and allow field current to flow when the switch is closed. The "I" terminal may be connected directly to the switch, or through a resistor. Both are illustrated. The "I" circuit may be used with or without the "L" circuit that is, with or without anything connected to the "L" circuit. The vehicle circuit can be identified, Figure 3 or Figure 3A, by observing the terminal marking on the regulator, which will be either an "F" (Figure 3) or "I" (Figure 3A).

Fig. 2 - Delco Remy CS130 Alternator Cross Section