How to Specify an AC Drive Based on Application

Specifying the right AC drive (also called VFD – Variable Frequency Drive) for your application is critical to achieving reliable performance, energy efficiency, and motor protection. Here’s a step-by-step guide to help you get it right:

  1.  

Know Your Motor

 

Collect basic motor nameplate data:

  • Horsepower (HP) or kilowatts (kW)
  • Voltage (V) – e.g., 230V, 460V, etc.
  • Full load current (FLA)
  • Frequency (Hz) – typically 50 or 60 Hz
  • Number of phases – usually 3-phase

 

Tip: Always size the drive by current, not just horsepower.

  1.  

Understand the Load Type

 

Different loads demand different drive characteristics:

Load Type

Example Applications

Drive Feature Needed

Constant Torque

Conveyors, crushers, compressors

High torque at low speed

Variable Torque

Fans, pumps, blowers

Energy-saving features, PID control

Constant Horsepower

Winders, spindles

Wide speed range, torque limiting

Tip: For fans/pumps, consider drives with built-in energy optimization and soft start.

  1.  

Match the Environment

 

Check the installation conditions:

  • Ambient temperature (e.g., derate if >40°C/104°F)
  • Dust/moisture → Need NEMA 12, IP54, or IP65 enclosure
  • Outdoor/explosive locations → Consider protective coatings or explosion-proof ratings
  1.  

Determine Control Requirements

 

What level of control or integration is needed?

Feature

Needed for…

PID Control

Pressure, flow, or temperature regulation

VFD/PLC Integration

Industrial automation

Analog & Digital I/O

Sensor/actuator feedback

Network Communication

BACnet, Modbus, Ethernet/IP, Profibus, etc.

Tip: If you’re replacing a drive, check existing communication protocols.

  1.  

Account for Duty Cycle and Overload

 

Drives are rated for different duty types:

  • Light-duty (110% overload for 60 sec) – for HVAC fans/pumps
  • Heavy-duty (150% overload for 60 sec) – for conveyors, crushers, etc.

 

Tip: Always check the drive’s current rating at your duty class.

  1.  

Select Key Features Based on Application

Application

Must-Have Features

HVAC Systems

PID control, sleep mode, BACnet

Pumps

Soft start, anti-ramp, underload detection

Conveyors

Torque boost, flying start, braking options

Cranes/Hoists

Dynamic braking, high overload capacity

Mixers/Agitators

Low-speed torque, stall prevention

  1.  

Plan for Future Needs

  • Consider expandable I/O or field-upgradable firmware
  • Choose drives that support energy logging, fault history, or remote monitoring
  1.  

Check for Local Standards & Certifications

  • UL, CE, RoHS compliance
  • IEEE 519 for harmonic mitigation (especially in large systems)
  • NEC/CEC for installation guidelines

Final Spec Checklist

 

✔ Motor HP/kW, voltage, FLA

✔ Load type (constant/variable torque)

✔ Duty cycle and overload rating

✔ Enclosure/environment rating

✔ Control & communication needs

✔ Application-specific features

✔ Compliance and safety requirements

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