UPS 120, UPS 150, UPS 250, UPS 300, UPS 301, UPS 500, UPS 600, UPS 750 and UPS 900 Uninterruptible Power Supplies Caterpillar

DC Bus Capacitor Remove/Replace Procedure

Prior to conducting any work, ensure the following:

• The MMU is de-energized

• The flywheel is at 0 RPM

• The DC bus has discharged and is at 0 VDC

1. Remove the field coil driver module. Refer to Systems Operation Testing and Adjusting, RENR9988, "Field Coil Driver " for the removal procedure for the field coil driver.

2. Remove the phase "A" and "B" flywheel inverters. Refer to Systems Operation Testing and Adjusting, RENR9988, "Flywheel Inverter Assembly" for the removal procedure for the flywheel inverter assembly.

   Note: Remove capacitors front-to-back and install back-to-front, to have more room to work and to have greater visibility of the work being done.

   Show/hide table

   Illustration 1	g03392358

3. Remove the 12 "HI/LOW DC" bus fuses from the left-hand side of the DC bus.
   Show/hide table

   Illustration 2	g03393019

4. Remove "#6 HI/LOW" neutral leads from the DC bus capacitors, using a 4 mm (5/32 inch) Allen wrench.

5. Remove the "#6 HI/LOW" resistor from the DC bus capacitor, using a 4 mm (5/32 inch) Allen wrench.

6. Remove the "#6 HI/LOW" fuse holders from the DC bus capacitors, using a 4 mm (5/32 inch) Allen wrench.
   Show/hide table

   Illustration 3	g03390957

7. Remove the "#6 HI/LOW" nylon mounting nuts from the right-hand side of the DC capacitors using a 3/4 inch socket. Set the nylon nut aside. The nylon nut will be used for installation.

8. Slide out the "#6 HI/LOW" capacitors along the diagonal mounting track.

Illustration 4	g03387642

Note: Capacitor specifications are 20093 CAP, ALUM, 7200 uf, 500 VDC, 20%.

Illustration 5	g03392378

Capacitor orientation is positive on top.

Illustration 6	g03387644
DC capacitor insulator is 78.0 mm (3.07 inch)

Note: Remove capacitors front-to-back and install back-to-front to have more room to work and to have greater visibility of the work being done.

1. Install "#6 CAP, ALUM 7200uf LOW" capacitor and capacitor insulator along the bottom of the capacitor bank. The capacitor insulator will be placed between the capacitor and the mounting bracket.

   Note: Reuse the original 40243 insulator.

2. Tighten, but do not torque, the nylon mounting nut on the right-hand side of the capacitor. Not tightening the nut will assist in aligning the left-hand mounting hardware.

3. Install the "#6 LOW" resistor lower 14 mm bolt using a flat washer and split washer. Torque prior to installing the remaining hardware.

4. Tighten the 14 mm hex bolt to a torque of 21 N·m (186 lb in).

5. Install "#6 LOW" fuse holder 14 mm bolt using a flat washer and a split washer. The bolt must pass through the neutral lead, the resistor, and then the fuse holder.

6. Install "#6 LOW" fuse holder upper 14 mm bolt using a flat washer and a split washer.

7. Tighten the 14 mm bolts mentioned in Steps 4 and 5 to a torque of 21 N·m (186 lb in).

8. Tighten the 3/4 inches nylon mounting nut to a torque of 15 N·m (133 lb in).
   Show/hide table

   Illustration 7	g03392379

9. Install the "#6 CAP, ALUM 7200uf HI" capacitor. Install the capacitor insulator, 40243, along the top of the capacitor bank.

10. Tighten, but do not torque, the nylon mounting nut on the right-hand side of the capacitor. Not tightening the nut will assist in aligning the left-hand mounting hardware.

11. Install "#6 HI" resistor upper 14 mm bolt using a flat washer and split washer.

12. Install "#6 HI" fuse holder upper 14 mm bolt using a flat washer and a split washer. The bolt must pass through the neutral lead, the resistor, and then the fuse holder.

13. Install the "#6 HI" fuse holder lower 14 mm bolt using a flat washer and a split washer.

14. Tighten the 14 mm hex bolts to a torque of 21 N·m (186 lb in).

15. Tighten 3/4 inches nylon mounting nut to a torque of 15 N·m (133 lb in).
    Show/hide table

    Illustration 8	g03391759

16. Repeat the installation procedure Steps 1through 15 for the remaining "#1-5 HI/LOW" capacitors, working from back to front.

17. Install the field coil driver (FCD) module. Refer to Systems Operation Testing and Adjusting, RENR9988, "Field Coil Driver " for the installation procedure for the field coil driver.

18. Install the AØ and BØ flywheel inverters, as per the installation procedure given under the topic "Flywheel Inverter Assembly" in this manual.

19. Initialize power to the system in "Bypass" as per the instructions given in this manual.

20. Calibrate the DC bus. Refer to Systems Operation Testing and Adjusting, RENR9988, "DC Bus Voltage - Calibrate" for the procedure to calibrate the DC bus.