Cummins/Onan 1750DQKB Generator Set

Tools: Dial indicator holding device, Magnetic base or clamp

1. Perform only when an objectionable vibration is present.
2. Fasten dial indicator holding device to skid base, engine block, or generator shell so the sensor rests on the generator shaft hub.
3. Bar the engine over clockwise through a couple of rotations and record readings in eight equally spaced points around the shaft diameter.
4. To correct out-of-tolerance T.I.R., remove the capscrews connecting drive discs and flywheel; mark drive discs and flywheel.
5. Rotate engine or generator so drive disc holes are repositioned 180 degrees from original location; retorque capscrews.
6. Re-check shaft alignment; if unchanged, rotate discs 30, 60, or 90 degrees from original location.
7. If T.I.R. still does not improve, inspect flywheel pilot and drive disc runouts.

Tools: Calibrated voltmeter

1. Display the Bus Voltage Calibration submenu.
2. With all gensets OFF, attach a calibrated voltmeter to TB1-A (L1) and TB1-B (L2) of the bus PT module.
3. Start another genset, allow it to reach normal speed and voltage, and connect operating genset to the bus.
4. Calibrate the Bus Volts L1 reading so the display matches the calibrated meter.
5. Shut the generator set OFF.
6. Repeat steps 2 through 5 for Bus Volts L2 and L3.
7. Exit menu to save changes.

⚠ Disconnect negative battery cable(s) before beginning; accidental starting presents hazard of severe personal injury or death.

Tools: Dial indicator, Shims

1. Disconnect the negative (–) battery cable(s) before beginning.
2. Fasten a dial indicator to the generator shaft or cooling fan with the sensing point on the capscrew head or flat of the drive disc at bolt circle diameter.
3. Bar the engine over clockwise (viewed from engine flywheel); do not allow it to roll back on compression.
4. Record T.I.R. as the sum of the maximum positive and negative readings over one revolution.
5. To correct, remove or add equal shims under the four generator mounting feet.
6. Approximate shim change: multiply (step 1 to step 2 distance ratio) by one half the T.I.R.

⚠ Accidental starting of the generator set during this procedure presents the hazard of severe personal injury or death.

Tools: two 1 3/4 inch T x 2 inch W x 6 inch L steel spacers, adequate lifting device

1. Turn off and disconnect battery charger (if equipped).
2. Disconnect the negative (-) battery cable(s) to prevent accidental starting.
3. Unscrew bolt (Item 2) from skid but do not remove it from either rear engine vibration isolator.
4. Loosen the three screws that secure the engine mount brackets to the engine.
5. Loosen but do not remove the hex nut (Item 1) from the M20 screw of the generator vibration isolators.
6. Lift the generator until the mounting feet brackets are high enough to insert a 1 3/4 inch steel spacer under both stator foot brackets.
7. Insert spacers and lower the generator so the full weight rests on the mounting foot brackets.
8. Make sure no gap is present between the skid and the lower mount of the rear engine vibration isolators; tighten the three screws to 190-200 ft-lbs.
9. Lift the generator to remove the two 1 3/4 inch steel spacers.
10. Before lowering, start the threads of the rear engine vibration isolator bolts (Item 2).
11. Lower the generator and tighten the two rear engine vibration isolator bolts to 270-330 ft-lbs.
12. Secure the generator foot brackets to the vibration isolators; tighten the fastener to 270-330 ft-lbs.

Tools: Calibrated ammeter

1. Display the Current Calibration submenu.
2. With the genset OFF, attach a calibrated ammeter to L1.
3. Start the genset and allow it to reach normal operating speed.
4. Load the genset to maximum rated kVA at rated voltage.
5. Calibrate the L1 current reading so the display agrees with the calibrated ammeter.
6. Repeat steps 2 through 5 for L2 and L3.
7. Exit menu to save changes.

⚠ Contacting high voltage components can cause electrocution; calibration must be performed by technically qualified personnel only.

Tools: Calibrated RMS multimeter (Fluke 87 or 8060A)

1. Display the Voltage Calibration submenu.
2. With the genset OFF, attach a calibrated voltmeter to the AC output from L1 to L2.
3. Start the genset and allow it to reach normal operating speed.
4. Calibrate voltage reading for L1 so the display agrees with the calibrated voltmeter.
5. Shut the generator set OFF.
6. Repeat steps 2 through 5 for L2 and L3.
7. Exit menu to save changes.

⚠ HIGH VOLTAGE. Touching uninsulated high voltage parts inside the control box can result in severe personal injury or death.

Tools: Jumper leads, 12 volt battery, Voltmeter

1. Throw line circuit breaker OFF and shut down the set.
2. Remove electronics box cover; remove connector 10 from regulator output module.
3. Prepare to measure output voltage across generator terminals while set is running.
4. Bring jumpers from a 12 volt battery to X (Field +, red wire 10-6) and XX (Field –, brown wire 10-3) pins of plug P10.
5. Check polarity again; polarity must be correct or test is inconclusive.
6. Start the set and connect the jumper from battery negative terminal to the XX lead.
7. If rated voltage or higher and phases balanced, generator circuitry is probably okay; otherwise troubleshoot.
8. If voltages unbalanced, troubleshoot main stator first; if uniformly low, troubleshoot exciter and field circuits first.

⚠ Medium-voltage 601-15,000 volts present special hazards; windings must be dry before operation.

Tools: Megger, Insulation Resistance Meter

1. Perform the Generator Set Grounding Procedure.
2. Remove electronics box cover; remove connector 10 from regulator output module.
3. Disconnect AC control input leads (marked 5, 6, 7, 8) from generator output terminals.
4. If RTD option installed, ground all six RTD temperature leads (18 leads total).
5. Perform the Winding Resistance Test for the desired windings.
6. Perform the Insulation Resistance and PI Test for the desired windings.
7. If low readings, investigate and correct cause before returning to service; dry windings if moisture is the cause.

⚠ Layers of dust can cause diodes to overheat and fail. Brush dust off regularly.

Tools: Ohmmeter

1. Disconnect the diode pigtails from the terminal posts.
2. Using an ohmmeter, measure resistance between each diode pigtail and the plate on which it is mounted.
3. Reverse meter test probes and repeat; resistance should be high in one direction and low in the other.
4. If resistance is high or low in both directions, replace the diode.

Tools: Wheatstone bridge, Megger

1. Disconnect the six rotor winding leads from the terminal posts on the rectifier assembly.
2. With a Wheatstone bridge, measure resistance across each pair of windings: U-V, V-W, W-U.
3. Replace the whole rotor shaft assembly if resistance of any winding is not as specified in Tables 4-2/4-3.
4. Disconnect all six exciter rotor leads from diode terminals CR1 through CR6 and isolate from ground.
5. Connect the megger between one lead and ground and conduct the test per Table 4-1.

Tools: Wheatstone bridge or digital ohmmeter, Megger

1. Measure winding resistance between the two stator leads, F1 (X) and F2 (XX), with a Wheatstone bridge or digital ohmmeter.
2. Replace the stator if winding resistance is not as specified in Tables 4-2/4-3.
3. Disconnect exciter stator leads F1 and F2 from connectors and isolate from ground.
4. Connect the megger between one lead and ground and conduct the test per Table 4-1.

Tools: Wheatstone bridge or digital ohmmeter, Megger

1. Disconnect the two leads of the main rotor from the terminals on the rotating rectifier assembly.
2. Measure resistance between the two leads with a Wheatstone bridge or digital ohmmeter.
3. Replace the rotor if the resistance is not as specified in Tables 4-2/4-3.
4. Torque the terminals to 24 in-lbs (2.6 N•m) when reassembling.
5. Disconnect main rotor and voltage suppressor leads from terminals F1+ and F2– and isolate from ground; tag each lead.
6. Connect the megger between one rotor lead and ground and conduct the test per Table 4-1.