Cummins/Onan MDGDB Generator Set

⚠ High voltage. Touching uninsulated high voltage components and terminals on the voltage regulator can result in severe personal injury or death.

⚠ The sealed adjustment pots on the voltage regulator board are factory preset. Attempts to adjust them can lead to serious voltage instability and overheating.

Tools: AC/DC multimeter

1. Use the voltage trimmer for small voltage adjustments; measure voltage across any line and neutral with the set at no load and nominal frequency.
2. If trimmer adjustment is insufficient, lock it at midpoint and turn the VOLTS pot fully counterclockwise and the STABILITY pot to its midpoint.
3. If the red LED lights, refer to Jumper Reconnections and UFRO Adjustment.
4. Turn the VOLTS pot clockwise until rated voltage is obtained.
5. If voltage becomes unstable with a large load, turn the STABILITY pot clockwise until stable; readjust the VOLTS pot each time.
6. Set the RESPONSE jumper A to C for rated output less than 90 kW or B to C for rated output greater than 90 kW.
7. Set frequency jumper connections to correspond to the application frequency.

1. Push both selector switches (S1, S2) on the controller to their OFF positions.
2. Set pots initially: Gain 20%, I 20%, D 30%, Droop 0%.
3. If a remote speed pot is used, set it at its midpoint.
4. Start the set and adjust the Speed pot for required frequency: 60 Hertz (1800 RPM) or 50 Hertz (1500 RPM); warm up under load.
5. Disconnect the load and turn the GAIN pot to 100 percent or until operation becomes unstable, then turn counterclockwise until stable.
6. Adjust the D pot as in Step 5.
7. Adjust the I pot as in Step 5.
8. Readjust Speed if necessary.
9. Manually push the throttle to minimum speed, hold until the engine reaches minimum speed, release and observe speed overshoot.

1. Push both selector switches (S1, S2) on the controller to their OFF positions.
2. Set the pots initially: Gain 20%, I 20%, D 30%, Droop 0%.
3. If a remote speed pot is used, set it at its midpoint.
4. Start the set and adjust the Speed pot to obtain the required output frequency: 60 Hertz (1800 RPM) or 50 Hertz (1500 RPM).
5. Warm up the set under load until it is up to normal operating temperature.
6. Disconnect the load and turn the GAIN pot to 100 percent or until operation becomes unstable, then turn it counterclockwise until stable.
7. Adjust D as in the GAIN step.
8. Adjust I as in the GAIN step.
9. Readjust Speed if necessary.
10. Push the throttle to minimum speed position and hold until minimum speed; release and observe overshoot (2 to 5 Hertz may be acceptable).
11. If overshoot is unacceptable, turn the I pot clockwise slightly to reduce overshoot.
12. If the set hunts during steady state, turn the I pot counterclockwise slightly until stable.

1. Turn the Start Fuel Limit pot fully clockwise; it requires no further adjustment.
2. Set the pots initially: Gain mid-position, Stability mid-position, Rated Speed fully counterclockwise.
3. If a remote speed pot is used, set to fully counterclockwise position.
4. Start the set and adjust the Rated Speed pot to obtain the required output frequency: 60 Hertz (1800 RPM) or 50 Hertz (1500 RPM).
5. Warm up the set under load until it is up to normal operating temperature.
6. Disconnect the load and turn the Gain pot fully clockwise or until unstable, then turn counterclockwise until stable.
7. Adjust Stability as in the Gain step.
8. Readjust Rated Speed if necessary.
9. Push the throttle to minimum speed and hold until minimum speed; release and observe overshoot (2 to 5 Hertz may be acceptable).
10. If overshoot is unacceptable, turn the Gain pot clockwise slightly to reduce overshoot.
11. If the set oscillates during steady state, turn the Stability pot counterclockwise slightly until stable.

1. Warm up the set under partial load (at least 1/4 rated load).
2. Turn the Speed potentiometer to obtain specified power supply frequency (60 Hertz - 1800 RPM or 50 Hertz - 1500 RPM).
3. Turn the Gain potentiometer clockwise until the governor begins to hunt, then turn it back until there is no audible hunting.
4. Connect 1/4 rated load and readjust the Gain potentiometer if necessary.
5. Connect rated load in one step. Shut down the set if it cannot pick up the load. Lengthen the governor rod by half turns of the swivel ends and repeat the test until the set picks up rated load in one
6. Check for stability (no audible hunting) under various loads.
7. Stop the set, wait 30 seconds for the turbo to coast down (if so equipped), restart and check for speed overshoot.

1. Turn the governor idle and speed adjusting screws while the engine runs at normal operating temperature under full load.
2. Adjust droop to within five percent of nominal frequency (3 Hertz for 60 Hertz sets and 2.5 Hertz for 50 Hertz sets).
3. Check operation under various loads and increase droop if the governor hunts.
4. Readjust full-load frequency if droop is adjusted.

⚠ Do not adjust the idle speed screw or break its wire seal. Doing so can void the generator set warranty.

1. Run engine at normal operating temperature under full load.
2. Turn the governor speed adjusting screw to adjust output frequency (50 Hz or 60 Hz).
3. Adjust droop to within five percent of nominal frequency.
4. Check operation under various loads; increase droop if the governor hunts.
5. Readjust full-load frequency if droop is adjusted.
6. Do not adjust the idle adjusting screw; it is factory set and sealed.

⚠ Do not make adjustments in the control panel or on engine with unit running.

1. Adjust the output voltage plus or minus five percent of nominal voltage using the adjustment screw on the back of the power supply outlet box.
2. Call your distributor if the required voltage cannot be obtained by this adjustment.

⚠ Do not adjust the idle speed screw or break its wire seal. Doing so can void the generator set warranty.

1. Operate the set and disconnect all loads after engine warms to normal operating temperature.
2. Loosen locknut on throttle lever speed adjusting screw; turn screw counterclockwise to 1980 RPM (66 Hz) for 60 Hz sets or 1650 RPM (55 Hz) for 50 Hz sets.
3. Set the locknut; leave the spring in place to maintain throttle lever position.
4. Move fuel pump stop lever (inboard lever) forward slowly until the engine stops; hold this stop position when linkage is connected.
5. Thread locknut onto male swivel-end link; thread female link five turns onto male link and set the locknut.
6. Secure male end of link to the injection pump lever on the engine side of the pump; tighten two nuts first.
7. Loosely thread the locknut and clevis onto the actuator shaft.
8. Rotate the injection pump lever to the established stop position; turn the clevis until the link swivel hole registers with the clevis holes; connect with screw, nut and lock washer.
9. Tighten the clevis locknut on the actuator shaft.

Tools: AC voltmeter (at least 5000 ohms/volt impedance)

1. Push the fuel injection pump lever to full power by hand; there should be no binding in the linkage.
2. If the actuator does not drive to full power, disconnect the two actuator leads and connect battery voltage across them; replace the actuator or control unit as indicated.
3. If speed is still unstable, reinstall the magnetic speed pickup: bar the engine until a gear tooth aligns, thread the unit in by hand, back out one quarter turn and set the locknut.
4. Measure speed pickup output voltage while cranking with leads reconnected via bare wire links and fuel solenoid disconnected.
5. Replace the speed pickup if the meter indicates less than 2.5 volts; replace the control unit if voltage is at least 2.5 volts.
6. Follow each lead out of the governor control unit to its connector; tighten or repair any loose, dirty or corroded connector and try to start.

⚠ Release the Start switch as soon as the engine fires to prevent damage to the starter. Because the PMG is disconnected there will be no generator voltage and the start disconnect relay will not function.

Tools: AC voltmeter, Wheatstone bridge

1. Remove the PMG cover and disconnect the leads at the connector.
2. Start the engine at the set and let the speed stabilize.
3. Measure voltage across leads P2-P3, P2-P4 and P3-P4 (at least 150 VAC for 50 Hz sets, 180 VAC for 60 Hz sets).
4. Push the control panel switch to STOP and let the set come to a complete stop.
5. Measure resistance across leads P2-P3, P2-P4 and P3-P4 with a Wheatstone bridge (approximately 4.4 ohms each).

⚠ Accidental starting of the generator set while working on it can cause severe injury or death. Disconnect the starting battery cables (negative first).

⚠ Always remove the negative (-) cable first and reconnect it last.

Tools: AC/DC multimeter, Ohmmeter, Wheatstone bridge (0.001 ohm precision), Frequency meter, Load test panel

1. Disconnect the starting battery cables (negative first) to prevent accidental starting.
2. Disconnect the applicable winding leads from their terminals.
3. Measure insulation resistance between a lead and the laminations (replace if less than 1 megohm).
4. Measure winding resistance with a Wheatstone bridge or ohmmeter having at least 0.001 ohm precision.
5. Compare winding resistance to Table 5-1 and replace the component if not as specified.