Temperature sensor
Common error-code part. Confirm resistance and connector style.
Error Code: Danfoss W30 — Brake Resistor Overtemperature
What it means: Danfoss warning W30 (BRAKE RESISTOR OVERTEMPERATURE) indicates the brake resistor’s calculated thermal load has exceeded its rated duty cycle. Danfoss FC-series drives (FC301, FC302/VLT AutomationDrive) include an internal thermal model that estimates brake resistor temperature based on braking current and time. When the model calculates that the resistor has reached its thermal limit, the drive issues W30. If braking continues, it may escalate to a full trip (A30/ALARM 30) and disable braking.
Common Causes
- Undersized braking resistor — A resistor with insufficient power rating for the actual braking demand. This is a design error — the resistor is being asked to dissipate more energy per cycle than its wattage rating allows.
- Too frequent stopping — Applications with high stopping frequency (frequent reverse, fast positioning cycles) exceed the resistor’s thermal duty cycle even if each individual stop is within spec.
- Braking from too high a speed — Large speed drops (e.g., 60 Hz to 0 Hz) in short deceleration times produce peak braking power that can spike resistor temperature.
- High ambient temperature at resistor location — An inadequately ventilated resistor enclosure prevents the resistor from cooling between braking events.
- Incorrect Pr (resistor power) parameter set — If the drive’s braking resistor power parameter (parameter 2-16, Brake Resistor Power) is set lower than the actual installed resistor wattage, the thermal model will be overly conservative and trip W30 prematurely.
Diagnosis Steps
- Review the braking cycle: how often is the drive braking, and from what speed? High cycle rates with large speed drops confirm a thermal overload scenario.
- Check the braking resistor’s actual wattage rating vs. the cycle demand. Danfoss publishes a braking energy formula: E = ½ × J × (ω₁² - ω₂²), where J is load inertia. Compare calculated energy per cycle to the resistor’s rated energy capacity.
- Verify parameter 2-16 (Brake Resistor Power) in the drive matches the installed resistor’s rated wattage. A mismatch causes premature W30.
- Inspect the physical resistor location: is it mounted in a ventilated enclosure? Is there adequate airflow around it? Resistors in sealed enclosures with no airflow will overheat regardless of rating.
- Measure resistor temperature with an IR thermometer during braking. Compare to the resistor’s rated maximum temperature (typically 150–400°C depending on type).
Fix
Increase deceleration time (parameter 3-42) to reduce braking power per stop. This is the fastest fix if the application allows longer stopping times.
If the application requires fast, frequent stops: replace the braking resistor with a higher wattage unit or a peak-rated resistor with higher thermal mass. Contact Danfoss or the resistor manufacturer with application duty cycle data for a proper selection.
Correct parameter 2-16 to match the installed resistor’s actual rated wattage. This alone may resolve W30 if the parameter was set incorrectly.
Improve ventilation at the resistor location: mount the resistor where airflow can cool it between braking events.
Parts
| Part | Where to Buy |
|---|---|
| Danfoss braking resistor (size to application) | Grainger |
| Resistor enclosure with ventilation | Grainger |
Need Replacement Parts?
Before ordering, match the drive part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Technician
Braking resistor sizing for demanding applications (cranes, centrifuges, winding machines) requires detailed load inertia and cycle analysis. An incorrectly sized resistor is a fire hazard. Consult a Danfoss applications engineer or qualified drive integrator for high-duty-cycle applications.