Allen-Bradley Drive Capacitor Replacement Guide: PowerFlex, 1336 & Legacy Drives
Last Updated: February 2026 | Reading Time: 18 minutes
Your Allen-Bradley drive just faulted. The display reads "DC Bus Undervoltage" or "Bus Fault," and resetting doesn't clear it. The drive has been running reliably for 12 years—until today. Production is down, and the clock is ticking.
The most likely cause? Failed DC bus capacitors.
Allen-Bradley drives from Rockwell Automation are installed in hundreds of thousands of industrial facilities worldwide. These drives depend on aluminum electrolytic capacitors for DC bus filtering, and those capacitors have a finite lifespan. After 7-15 years of continuous operation, capacitor failure isn't a question of if—it's when.
This guide covers every major Allen-Bradley drive platform, the capacitors inside them, how to diagnose failure, and how to source replacements—including obsolete and discontinued part numbers.
Every aluminum electrolytic capacitor contains a liquid or gel electrolyte that slowly evaporates through the rubber seal over time. This is a fundamental characteristic of the technology—not a defect. The evaporation rate depends on:
- Temperature — For every 10°C above 40°C, capacitor life roughly halves
- Ripple current — Higher ripple generates more internal heat
- Voltage stress — Operating near rated voltage accelerates aging
- Duty cycle — Continuous operation ages capacitors faster than intermittent use
In a typical Allen-Bradley VFD, the DC bus capacitors operate at 50-80% of their voltage rating while handling significant ripple currents from the rectifier input and inverter output. Combined with the heat inside an enclosed drive cabinet, these capacitors experience conditions that limit their life to 7-15 years.
Capacitor failure in drives is usually gradual:
| Stage | What Happens | Symptoms |
|---|
| Early degradation | Capacitance drops 10-20%, ESR rises | None visible—drive operates normally |
| Moderate degradation | Capacitance drops 20-40%, ESR doubles | Occasional DC bus ripple faults under heavy load |
| Advanced degradation | Capacitance drops 40%+, ESR triples or more | Frequent faults, reduced current capacity, drive trips at startup |
| Failure | Open circuit, short circuit, or electrolyte leak | Drive will not run, visible damage, blown fuses |
The dangerous part: by the time you see symptoms, the capacitors may already be well past their useful life.
When capacitors degrade, the drive's protection systems detect the resulting electrical problems. Knowing which fault codes point to capacitors saves diagnostic time.
| Fault Code | Description | Capacitor Connection |
|---|
| F002 | Aux Undervoltage | Control power supply capacitors degraded |
| F004 | Undervoltage | DC bus capacitors can't maintain voltage |
| F005 | Overvoltage | Failed capacitors cause voltage spikes during deceleration |
| F006 | Motor Stall | Insufficient bus capacitance to support motor current |
| F007 | Motor Overload | Drive derate due to bus voltage instability |
| F033 | Auto Rstrt Tries | Repeated attempts to clear bus faults |
| F034 | Heatsink OvrTmp | High-ESR capacitors add heat to the drive |
| F041 | Analog In Loss | Control board capacitor failure affects analog circuits |
| F070 | Power Unit | General power stage failure—often capacitor-related |
| F100 | IO Board Fail | I/O power supply capacitor degradation |
| Fault Code | Description | Capacitor Connection |
|---|
| 12 | HW Overcurrent | Insufficient bus capacitance causes current spikes |
| 13 | Ground Fault | Capacitor dielectric breakdown |
| 23 | DC Bus Overvoltage | Failed capacitors can't absorb regen energy |
| 24 | DC Bus Undervoltage | Direct symptom of capacitor failure |
| 29 | Analog Input Fault | Control board capacitor issues |
| 33 | Heatsink Overtemp | ESR-related heat generation |
| 63 | Power Unit Fault | Capacitor bank failure |
| Fault Code | Description | Capacitor Connection |
|---|
| UV Fault | Bus Undervoltage | Primary indicator of DC bus capacitor failure |
| OV Fault | Bus Overvoltage | Capacitors can't absorb energy |
| OC Fault | Overcurrent | Voltage sag from weak capacitors causes current surges |
| OH Fault | Overheating | High-ESR capacitors generating excess heat |
The PowerFlex 520 series uses compact electrolytic capacitors sized for the drive's power rating.
DC Bus Capacitors:
| Drive HP (230V) | Capacitor Type | Typical Values | Quantity |
|---|
| 0.5-2 HP | Snap-in electrolytic | 390-820µF / 400V | 1-2 |
| 3-5 HP | Snap-in electrolytic | 1000-1500µF / 400V | 2 |
| 7.5-10 HP | Snap-in electrolytic | 1500-2200µF / 400V | 2-3 |
| 15-25 HP | Snap-in or screw terminal | 2200-3300µF / 400-450V | 2-4 |
Key specifications to match:
- Voltage: 400V or 450V DC
- Temperature: 105°C rated
- Ripple current: Match or exceed original rating
- Physical size: Must fit drive chassis
- Terminal type: Snap-in for smaller drives, screw terminal for larger
The PowerFlex 700 is the workhorse of the Allen-Bradley VFD lineup. Higher-power models use large computer grade capacitors.
DC Bus Capacitors:
| Drive HP (460V) | Capacitor Type | Typical Values | Quantity |
|---|
| 1-5 HP | Snap-in electrolytic | 470-1000µF / 450V | 2-3 |
| 7.5-15 HP | Snap-in electrolytic | 1000-2200µF / 450V | 2-4 |
| 20-40 HP | Screw terminal | 2200-4700µF / 450V | 2-4 |
| 50-100 HP | Screw terminal (computer grade) | 4700-6800µF / 450V | 4-6 |
| 125-250 HP | Screw terminal (computer grade) | 6800-10000µF / 450V | 4-8 |
| 300-600 HP | Screw terminal (computer grade) | 10000-15000µF / 450V | 6-12 |
Critical specifications:
- Voltage: 450V DC minimum (some use 500V for extra margin)
- Ripple current: 5-50A+ depending on drive size
- ESR: Low-ESR types required for high-frequency switching applications
- Life rating: 10,000+ hours at 105°C preferred
These are the premium drive platforms with advanced power stages.
DC Bus Capacitors:
| Frame Size | Capacitor Type | Typical Values | Bus Configuration |
|---|
| Frame 1-3 | Snap-in electrolytic | 1000-2200µF / 450V | Single bus |
| Frame 4-6 | Screw terminal | 3300-6800µF / 450V | Single bus |
| Frame 7-9 | Computer grade | 6800-15000µF / 450V | Parallel banks |
| Frame 10+ | Computer grade | 10000-22000µF / 450V | Multiple parallel banks |
Note: PowerFlex 755 drives use modular power cells. Each power cell contains its own capacitor bank. When one cell's capacitors fail, you typically need to replace all capacitors in that cell.
The 1336 platform is one of the most widely installed Allen-Bradley drive families. Many are now 15-25 years old, making capacitor replacement a frequent need.
1336 PLUS and PLUS II DC Bus Capacitors:
| Drive HP (460V) | Capacitor Type | Typical Values | Quantity |
|---|
| 1-5 HP | Snap-in electrolytic | 680-1500µF / 450V | 2 |
| 7.5-15 HP | Screw terminal | 1500-3300µF / 450V | 2-3 |
| 20-40 HP | Computer grade | 3300-6800µF / 450V | 2-4 |
| 50-100 HP | Computer grade | 5600-10000µF / 450V | 4-6 |
| 125-250 HP | Computer grade | 8200-15000µF / 450V | 6-8 |
| 300-500 HP | Computer grade | 10000-22000µF / 450V | 8-12 |
1336 IMPACT:
- Uses similar capacitor values to the PLUS series
- Power converter topology differs but DC bus capacitor requirements are similar
- Some models use proprietary capacitor mounting brackets—verify physical dimensions carefully
1336 Force:
- High-performance drives with stringent capacitor requirements
- Often specify low-ESR computer grade capacitors
- Original capacitors may be from Nippon Chemi-Con, Nichicon, or Cornell Dubilier
The 1305 is an older economy drive still found in many facilities.
DC Bus Capacitors:
| Drive HP (230V) | Capacitor Type | Typical Values | Quantity |
|---|
| 0.5-3 HP | Snap-in electrolytic | 470-1500µF / 400V | 1-2 |
| 5-10 HP | Snap-in electrolytic | 1500-3300µF / 400V | 2 |
DC Bus Capacitors:
| Drive HP (460V) | Capacitor Type | Typical Values | Quantity |
|---|
| 0.5-3 HP | Snap-in electrolytic | 330-680µF / 450V | 1-2 |
| 5-10 HP | Snap-in electrolytic | 680-1500µF / 450V | 2 |
The 1397 is a DC motor drive used with wound-field and permanent-magnet DC motors.
Filter Capacitors:
- Input/output filter sections use high-voltage electrolytics
- Typical values: 1000-4700µF at 350-500V DC
- Snubber circuits may use film capacitors (not electrolytic)
- Commutation capacitors are high-current film types
Soft starters and smart motor controllers with electrolytic capacitors in control and power sections.
Common capacitor locations:
- Control power supply: Small snap-in electrolytics (100-470µF, 25-63V)
- Thyristor snubber circuits: Film capacitors (0.1-1µF, 600-1000V)
- DC bus filtering (in SSC drives): Snap-in electrolytics (470-2200µF, 400-450V)
- Insulated screwdrivers (Phillips and flat)
- Torque wrench (for screw terminal capacitors)
- Digital multimeter with capacitance function
- ESR meter (recommended)
- Discharge resistor (100 ohm, 25W minimum for 450V bus)
- Insulated gloves (Class 00 minimum)
- Safety glasses
- Camera or phone for documentation
- Labels and markers for wire identification
This is the most important step. DC bus capacitors can hold lethal voltages for hours after power is removed.
- Disconnect the drive from AC power at the branch circuit breaker
- Lock out / tag out per your facility's LOTO procedure
- Disconnect motor leads (prevents back-feed from spinning motor)
- Wait a minimum of 5 minutes — Longer for larger drives
- Open the drive front panel or cover
- Using the multimeter set to DC voltage (600V range), measure across the DC bus terminals (typically marked DC+ and DC-, or + and -)
- Voltage must read below 50V before proceeding
- If voltage is higher, wait longer or use the discharge resistor connected between DC+ and DC-
- Verify zero voltage a second time before touching any internal components
Before removing anything:
- Photograph the entire capacitor bank — Multiple angles
- Photograph each capacitor's label — Part number, specs, date code
- Note the wiring connections — Which terminal goes where
- Record polarity — Positive (+) and negative (-) markings
- Measure and record — Physical dimensions of each capacitor (diameter, height)
- Note the mounting — How capacitors are secured (clamps, brackets, adhesive)
- Disconnect wiring from capacitor terminals (note: screw terminals may have specific torque requirements)
- Remove mounting hardware (clamps, brackets, straps)
- Extract capacitors from the drive chassis
- Inspect the removed capacitors — Look for bulging tops, electrolyte leakage, corroded terminals, or discoloration
- Place old capacitors aside for proper disposal
Before installing new capacitors:
| Parameter | Requirement |
|---|
| Capacitance (µF) | Match within ±20% of original |
| Voltage rating (V DC) | Equal to or higher than original |
| Temperature rating (°C) | Equal to or higher than original (105°C preferred) |
| Ripple current (A) | Equal to or higher than original |
| ESR (mΩ) | Equal to or lower than original |
| Diameter (mm) | Must fit mounting location |
| Height (mm) | Must fit drive enclosure |
| Terminal type | Must match (screw terminal pitch, snap-in pin spacing) |
- Verify polarity orientation matches original — Reversed polarity will cause immediate catastrophic failure
- Seat capacitors in mounting positions
- Secure with mounting hardware — Use original clamps or brackets
- Connect wiring to correct terminals — Match documentation from Step 2
- Torque screw terminals to manufacturer specification (typically 2-3 N·m for M4, 4-5 N·m for M5, 8-10 N·m for M6)
- Verify all connections are tight — Loose connections cause arcing and failure
If replacement capacitors have been stored for more than 2 years, they should be reformed before full-voltage operation:
- Apply 10% of rated voltage through a current-limiting resistor (1K ohm, 10W)
- Hold for 30 minutes, monitoring leakage current
- Increase to 25% of rated voltage for 30 minutes
- Increase to 50% for 30 minutes
- Increase to 75% for 30 minutes
- Apply full rated voltage for 60 minutes
- Leakage current should decrease to rated specification at each step
Skip this step if using newly manufactured capacitors from a reputable source.
- Remove LOTO, reconnect AC power
- Do not start the motor yet — Let the drive power up and charge the bus
- Monitor for any unusual sounds, smells, or visual problems during the first 60 seconds
- Check the drive display for fault codes
- If no faults, run the motor at low speed under light load
- Gradually increase to full speed and full load
- Monitor DC bus voltage stability using the drive's parameter display
- Run for at least 30 minutes while monitoring drive temperature
Many original capacitors installed in Allen-Bradley drives are now discontinued. Cross-referencing to current-production equivalents is often necessary.
Allen-Bradley drives have historically used capacitors from:
| Original Manufacturer | Status | Cross-Reference To |
|---|
| Nippon Chemi-Con | Active | Direct equivalent often available |
| Nichicon | Active | Direct equivalent often available |
| Cornell Dubilier (CDE) | Active | Wide range of industrial capacitors |
| Rubycon | Active | Good cross-reference availability |
| Illinois Capacitor | Active (now part of Cornell Dubilier) | Check CDE catalog |
| Panasonic (Matsushita) | Active | Industrial series available |
| Sprague | Discontinued | Cross-reference to CDE or Nichicon |
| Mallory | Discontinued | Cross-reference to CDE or Nichicon |
| Philips/BC Components | Discontinued | Cross-reference to Vishay or Nichicon |
When cross-referencing, match these parameters in order of priority:
- Voltage rating — Must meet or exceed original
- Capacitance — Within ±20% of original
- Ripple current at 105°C — Must meet or exceed original
- Physical dimensions — Must physically fit
- Terminal configuration — Must match mounting
- Temperature rating — Must meet or exceed (105°C preferred)
- ESR — Should meet or beat original specification
- Life rating — Higher is better (5,000, 10,000, or 12,000 hours)
These are the capacitor values we source most frequently for Allen-Bradley drive repairs:
| Application | Typical Spec | Common Replacements |
|---|
| PowerFlex 700 (50-100HP, 460V) | 4700µF 450V 105°C screw terminal | Nichicon LGU, CDE 381LR, Nippon Chemi-Con LXS |
| PowerFlex 700 (125-250HP, 460V) | 6800-10000µF 450V 105°C screw terminal | Nichicon LGU, CDE 382LX, Rubycon MXG |
| 1336 PLUS (20-60HP, 460V) | 3300-5600µF 450V screw terminal | CDE 381LR, Nichicon LGG, Nippon Chemi-Con KMH |
| 1336 PLUS (100-250HP, 460V) | 6800-15000µF 450V computer grade | CDE 520C, Nichicon LQR, Illinois Capacitor 107 series |
| 1336 Force (all sizes) | Various 400-450V computer grade | Application-specific—contact us with drive model |
| 1305 (all sizes) | 330-1500µF 400-450V snap-in | Nichicon LGU, Panasonic EE, CDE 380LX |
| 1397 DC Drive | 1000-4700µF 350-500V | CDE 520C, Nichicon LQR, application-specific |
- Drive is less than 20 years old and otherwise functioning well
- Replacement parts are available at reasonable cost
- Process doesn't justify new drive cost — Capacitor replacement is typically 10-25% of new drive cost
- Application hasn't changed — Motor and load are the same as original design
- Spare drives aren't available — Faster to repair than procure a new drive
- Drive has specialized programming — Reprogram cost adds to replacement cost
- Drive is 20+ years old with multiple component failures
- Energy efficiency savings justify the upgrade (modern drives are 2-5% more efficient)
- Motor has been replaced — New motor may benefit from updated drive features
- Application requirements have changed — Need more speed range, better control
- Parts are truly unavailable — All capacitor sources exhausted
- Multiple drives in the facility are the same model and age — Plan phased replacement
| Scenario | Capacitor Repair | New Drive |
|---|
| 25HP PowerFlex 700 | $200-600 in parts | $3,000-5,000 |
| 100HP 1336 PLUS | $400-1,200 in parts | $8,000-15,000 |
| 250HP 1336 PLUS II | $800-2,000 in parts | $15,000-30,000 |
| 500HP PowerFlex 755 | $1,500-4,000 in parts | $30,000-60,000 |
Parts cost only. Labor is additional. Costs are approximate and vary by availability.
Preventive Maintenance: Extending Capacitor Life#
Temperature is the single biggest factor in capacitor longevity.
| Action | Expected Life Extension |
|---|
| Reduce ambient by 10°C | Approximately 2x life |
| Improve cabinet ventilation | 1.5-2x life |
| Replace cabinet filters regularly | 1.3-1.5x life |
| Add cabinet cooling (AC or heat exchanger) | 2-3x life |
| Move drive to cooler location | Up to 2x life |
| Interval | Actions |
|---|
| Monthly | Check drive for fault history, monitor operating temperature |
| Quarterly | Visual inspection of capacitors through viewing window (if equipped) |
| Annually | Open drive, inspect capacitors for bulging/leaking, check ventilation |
| 5 years | Consider ESR testing of DC bus capacitors |
| 7-10 years | Plan capacitor replacement, source parts proactively |
| 10-15 years | Replace DC bus capacitors (don't wait for failure) |
The smartest approach is planned replacement before failure:
- Identify all Allen-Bradley drives in your facility with their installation dates
- Prioritize by criticality — Which drives cause the most downtime if they fail?
- Source capacitors in advance — Especially for older/obsolete drives
- Schedule replacement during planned downtime — Maintenance windows, shutdowns
- Replace all capacitors in a drive at once — They've all aged together
- Keep spare capacitor kits for critical drives
Replace the entire bank. All capacitors in a DC bus bank experience the same operating conditions and age at similar rates. A new capacitor paired with degraded ones will carry a disproportionate share of the ripple current, shortening its life and potentially causing it to fail prematurely. The cost difference between replacing one and replacing all is small compared to the cost of a second drive failure.
Three approaches: (1) Open the drive and read the part number directly from the capacitor label. (2) Look up the drive's service manual—Rockwell publishes parts lists for most drives. (3) Contact a capacitor specialist with your drive catalog number (e.g., "20F-11-080" for a PowerFlex 753, 80HP, 460V)—they can cross-reference to the correct capacitor specifications.
If the drive is otherwise functioning well and meets your application needs, capacitor replacement at $400-2,000 in parts is far more economical than a $10,000-30,000+ new drive. Many 1336 drives with fresh capacitors continue to operate reliably for another 10+ years. Replace if you need features the 1336 doesn't offer (like Safe Torque Off, Ethernet/IP, or advanced motion control).
Yes. A higher voltage rating provides additional margin and often results in longer life. The key constraint is physical size—a 450V capacitor may be slightly larger than a 400V unit of the same capacitance. Verify that the replacement fits the drive chassis before purchasing.
Several causes, but degraded DC bus capacitors are among the most common in drives over 7-10 years old. The capacitors can no longer maintain stable bus voltage during load transients. Other causes include incoming power problems, loose wiring, and failed rectifier diodes. Test capacitors with an ESR meter to confirm.
For a technician familiar with the drive: 1-4 hours depending on drive size and accessibility. Larger drives with 8-12 computer grade capacitors take longer. Add time for safety procedures, documentation, and post-replacement testing. Budget a full shift for large drive capacitor replacements.
No. Capacitor replacement is a hardware change that doesn't affect drive parameters or programming. The drive should power up and run with its existing configuration. However, if you cleared faults or reset the drive during troubleshooting, verify that all parameters are correct before returning to production.
Specialist capacitor distributors maintain inventory of obsolete and hard-to-find capacitors specifically for this purpose. General electronics distributors typically don't stock the large-format, high-voltage capacitors used in older drives. Provide the capacitor part number, or the drive model and HP rating, and a specialist can cross-reference to available equivalents.
- Capacitor failure is the #1 cause of Allen-Bradley drive failures in units over 7 years old—plan for it
- DC bus undervoltage faults are the primary symptom — Don't keep resetting; diagnose the root cause
- Match specifications carefully — Voltage, capacitance, ripple current, temperature, and physical size all matter
- Replace the entire capacitor bank — Mixed old and new capacitors cause problems
- Proactive replacement saves money — Planned replacement during downtime costs far less than emergency repairs
- Most obsolete A-B capacitors have current equivalents — A specialist distributor can cross-reference
- Capacitor repair is 10-25% the cost of a new drive — Almost always worth doing for drives under 20 years old
Need capacitors for your Allen-Bradley drive? We stock DC bus capacitors for PowerFlex, 1336, 1305, 1397, and legacy Allen-Bradley drives—including obsolete part numbers that other suppliers can't find. Tell us your drive catalog number or the capacitor part number from the label, and we'll identify the right replacement. Most in-stock orders ship same day.
