Danfoss FC302 ALARM 35 — What It Means
ALARM 35 on a Danfoss VLT FC302 indicates an option fault, meaning the drive has detected a problem with an installed accessory module or option card, not a motor or mains power issue. This fault is tied specifically to optional add-on components such as the Sensor Input Option, Programmable I/O Option, or other interface modules fitted to the drive’s control section.
The alarm typically appears when the drive cannot communicate with the option module during power-up, detects an initialization failure, or finds incompatibility between the option and the drive configuration. Because this is an option-specific fault, the motor and process equipment are usually not the root cause unless the option itself is a sensor interface monitoring that process.
Common Causes
- Incorrectly seated or loose option module The accessory card is not fully inserted into its slot, or the connector is partially detached, preventing communication with the drive.
- Failed or damaged option card The option module itself has failed due to age, electrical stress, or physical damage such as bent pins or corrosion on the connector.
- Power-up or initialization problem The option module does not initialize correctly when the drive powers on, often due to intermittent supply voltage or internal option firmware issues.
- Communication fault between option and drive The internal data bus or wiring between the option card and the drive’s control board is interrupted or corrupted.
- Incompatible or misconfigured option The installed option module is not compatible with the FC302 model or firmware version, or drive parameters are set incorrectly for the installed option type.
Step-by-Step Fix
- Safely power down the FC302 drive following lockout/tagout procedures and allow at least five minutes for internal capacitors to discharge before opening the drive enclosure.
- Identify the installed option module by inspecting the control section and recording the option card part number and type (such as Sensor Input Option or Programmable I/O Option).
- Remove and reseat the option module by carefully pulling it from its slot, inspecting the connector for bent pins, corrosion, or debris, then firmly reinserting it until it locks into place.
- Inspect all cables and connectors associated with the option card, checking for loose wiring, damaged insulation, or poor terminal connections, and tighten or replace as needed.
- Restore power and clear the alarm through the drive’s control panel, then monitor the display during startup to see if ALARM 35 reappears immediately or after a delay.
- Verify option compatibility by cross-referencing the option card part number with the FC302 model and firmware version in the Danfoss instruction manual or programming guide.
- Swap in a known-good option module if the alarm persists after reseating and inspection, or contact Danfoss technical support if no spare module is available for testing.
Parts Often Needed
| Part | Notes |
|---|---|
| Danfoss VLT Sensor Input Option module | Amazon | Replacement option card for sensor interface functions, verify part number matches your FC302 model. |
| Danfoss VLT Programmable I/O Option module | Amazon | Replacement programmable input/output option card, confirm compatibility with drive firmware version. |
| FC302 control board assembly | Amazon | Required only if the option interface circuitry on the main control board is damaged, confirm by substitution testing first. |
When to Call a Pro
Call a qualified VFD technician or Danfoss-authorized service provider if reseating the option module and inspecting connectors does not clear ALARM 35, if you do not have a spare option card for substitution testing, or if the alarm returns immediately after each power cycle. Also seek professional help if you are not trained in lockout/tagout procedures or working inside energized VFD enclosures, or if the drive shows additional alarms or erratic behavior that suggests damage to the control board or internal data bus.