Sveba-Dahlen oHF

What does Sveba-Dahlen oHF mean?

The SD-180's Schneider frequency converter has detected that its internal temperature has exceeded the safe operating threshold. An internal thermal sensor monitors the drive's heatsink or power module temperature. When the measured temperature rises beyond the permissible limit, the drive triggers the oHF fault and shuts down to prevent permanent damage to the converter's power electronics.

Symptoms

• Drive trips with oHF displayed on the touchscreen, typically after a period of operation rather than at cold startup
• Converter enclosure or heatsink is noticeably hot to the touch
• Fault recurs after the drive cools down and is restarted, indicating a persistent thermal management problem
• Cooling fan on the converter is absent, running slowly, or making abnormal noise
• Ambient temperature around the drive installation is elevated or ventilation openings are blocked

Common causes

• Converter internal temperature exceeding safe limits (primary cause per manual)
• Blocked or restricted airflow through the converter's ventilation slots or cooling ducts
• Failed or seized internal cooling fan on the drive
• Excessive ambient temperature in the electrical enclosure or installation environment
• Drive operating at sustained high output current beyond its thermal rating for the duty cycle
• Accumulation of dust, grease, or debris on the heatsink fins reducing thermal dissipation

Diagnostic steps

1. 01

   Check and clean ventilation openings

   Inspect all ventilation slots and airflow paths on the SD-180 converter enclosure. Remove any dust, grease buildup, or physical obstructions using compressed air or a soft brush, following appropriate lockout/tagout procedures.

2. 02

   Inspect and test the cooling fan

   Visually inspect the converter's internal cooling fan for damage, seized bearings, or foreign material. With the drive powered, verify the fan spins freely at the correct speed; replace the fan if it is slow, noisy, or inoperative.

3. 03

   Measure ambient temperature at the installation

   Use a calibrated thermometer to measure the air temperature at the drive's air intake. Confirm it is within the converter's specified operating ambient temperature range as stated in the SD-180 manual; improve enclosure ventilation or add forced cooling if the ambient is too high.

4. 04

   Review drive load and duty cycle

   Check the drive's output current in the diagnostics menu during operation and compare against the converter's continuous current rating. If the drive is consistently running near or at its thermal limit, evaluate derating or upgrading to a higher-rated drive.

5. 05

   Allow the drive to cool and clear the fault

   After addressing the root cause, allow the converter to cool to a safe temperature, then clear the oHF fault via the touchscreen. Perform a monitored test run and observe temperature readings in the diagnostics to confirm the thermal issue is resolved.

When to call a professional

Escalate to a licensed technician or Sveba-Dahlen-authorized engineer if the fault persists after cleaning, fan replacement, and environmental corrections, as this may indicate a failing internal thermal sensor, damaged power module, or a thermal design issue requiring drive replacement. Repeated thermal trips without clear cause can indicate imminent power stage failure and should not be left uninvestigated.