How to Correctly Select a Frequency Converter for a Motor

A frequency converter (FC) is the "brain" of an electric motor. For it to run efficiently and reliably, it's important to size it correctly for the load.

1. Determine the motor's power rating. Check the table on the nameplate (kW or HP). If the motor operates under variable load, take the rated power and add a 10–15% margin.
2. Account for the rated current. The FC must be able to handle the motor's rated current at full load. If the current is close to the FC's maximum limit, choose a higher-class model.
3. Margin for starting loads. Heavy machinery (crushers, presses, compressors) requires an FC with a 20–30% power margin.
4. Supply voltage. 220 V — low-power motors (up to 3 kW); 380 V — industrial equipment (3 kW and above).
5. Operating conditions. Dust, humidity, high temperature — requires an FC with an IP54 or higher protection rating; IP20 is sufficient for clean rooms.

Tip: don't skimp on the power margin — overload is the main enemy of a frequency converter. Dynamics Engineering specialists will select the optimal FC based on your site's parameters and help with commissioning, technical documentation, and integration with the process control system (APCS).