Technical Specifications

FAQ

1. What is the Allen-Bradley 1336-CAP-SP15A used for?

The Allen-Bradley 1336-CAP-SP15A is a DC-link bus capacitor designed for use with 1336STEF drives in the F-frame configuration. Its main function is to store electrical energy on the drive’s DC bus and help stabilize the DC-link voltage during normal drive operation. The capacitor also helps reduce voltage ripple produced by the rectifier and switching sections of the variable frequency drive. Stable DC-bus voltage is important because the inverter section relies on this intermediate DC supply to generate the controlled output waveform for the motor. The 1336-CAP-SP15A is therefore an important part of the drive’s power section rather than a control or communication component.

2. What are the main electrical specifications of the 1336-CAP-SP15A?

The 1336-CAP-SP15A is specified as a 480 V bus capacitor for the 1336STEF F-frame drive configuration, with a capacitance of 4600 µF. It is an aluminum electrolytic capacitor intended for DC-bus applications. The relatively high capacitance allows the component to store energy and smooth fluctuations on the DC link. In a variable frequency drive, the capacitor works together with the input rectifier and inverter power section to provide a more stable intermediate DC voltage. When selecting a replacement, technicians should verify the complete drive model, frame configuration, voltage requirements, capacitance, mounting arrangement, and electrical characteristics rather than selecting a capacitor based only on physical appearance.

3. Why is a DC-link capacitor important in a variable frequency drive?

The DC-link capacitor performs several important functions in a variable frequency drive. After the incoming AC supply is rectified, the resulting DC voltage contains ripple that needs to be reduced before it reaches the inverter section. The capacitor stores electrical energy and releases it when necessary, helping maintain a more stable DC-bus voltage during changes in load and switching conditions. This contributes to stable inverter operation and helps the drive generate the required motor output. A deteriorated capacitor can result in increased DC-bus ripple, unstable operation, excessive stress on other power components, and potentially drive faults. For this reason, the condition of the DC-link capacitor should be considered during preventive maintenance of older 1336 drive systems.

4. What are the common symptoms of a failing 1336-CAP-SP15A?

A deteriorating DC-link capacitor can produce several symptoms depending on the severity of the failure. Possible indications include increased DC-bus voltage ripple, unexpected drive trips, unstable operation, excessive electrical noise, overheating, or abnormal behavior during acceleration and deceleration. In severe cases, the capacitor may develop physical swelling, leakage, venting, or other visible signs of failure. However, not every capacitor problem is immediately visible, and a drive fault may also originate from the rectifier, inverter, braking circuit, wiring, or control electronics. Therefore, troubleshooting should include measurement of the DC-bus condition and review of the drive’s diagnostic information rather than relying only on visual inspection.

5. How can the condition of the 1336-CAP-SP15A be checked?

The capacitor should be checked using an appropriate electrical maintenance procedure and suitable test equipment. Before any inspection, the drive must be completely isolated from the incoming power supply and the DC bus must be allowed to discharge. The actual DC-bus voltage should be verified with an appropriate meter before accessing the capacitor because hazardous voltage can remain present after power has been removed. Technicians can then inspect the capacitor for swelling, leakage, damaged terminals, overheating, or other physical abnormalities. Where appropriate, capacitance and electrical leakage characteristics can be evaluated using suitable equipment. A comparison with the expected electrical behavior of the drive can also help determine whether the capacitor is contributing to a fault. Testing should only be performed by qualified personnel familiar with high-voltage drive systems.

6. Can the 1336-CAP-SP15A be replaced with any 480 V capacitor?

No. Although the 1336-CAP-SP15A is specified for a 480 V drive application, a replacement should not be selected based solely on voltage rating. The capacitance, capacitor technology, ripple-current capability, temperature characteristics, physical construction, terminals, mounting arrangement, and compatibility with the 1336STEF F-frame drive must also be considered. The DC-link capacitor operates under significant electrical and thermal stress, so an unsuitable replacement can cause excessive ripple current, overheating, reduced service life, or damage to other drive components. For maintenance work, the replacement should match the required electrical and mechanical characteristics of the original component and the specific 1336 drive configuration.

7. What precautions are required when replacing the 1336-CAP-SP15A?

Replacing a DC-link capacitor requires strict electrical safety precautions because the drive’s DC bus can retain hazardous energy even after the AC input has been disconnected. The drive should be isolated according to the applicable lockout/tagout procedure, and sufficient discharge time should be allowed before any internal components are accessed. The actual DC-bus voltage must be measured and confirmed to be at a safe level using appropriate equipment. Technicians should also record the existing wiring and terminal arrangement before removing the capacitor to prevent incorrect reconnection. The replacement component should be checked for correct voltage, capacitance, polarity, mounting, and electrical compatibility. After replacement, the drive should be inspected carefully before controlled re-energization and functional testing.

8. What can cause premature failure of the 1336-CAP-SP15A?

Premature DC-link capacitor failure can be caused by excessive operating temperature, high ripple current, repeated high-load operation, voltage stress, frequent charging and discharging cycles, inadequate cooling, aging, or abnormal conditions elsewhere in the drive’s power section. A capacitor installed in a drive operating continuously at high load or in a hot electrical cabinet may experience significantly greater thermal stress than one operating under lighter conditions. Poor ventilation can further increase internal temperature and accelerate capacitor aging. Problems in the input rectifier, inverter, braking circuit, or DC bus can also place additional stress on the capacitor. When a replacement capacitor fails again shortly after installation, technicians should investigate the operating environment and the complete drive power circuit rather than simply replacing the capacitor a second time.