Are you looking for reliable equipment to power your next heavy-duty project? Phase converters and variable frequency drives (VFDs) are two great options. While both devices convert power from one phase to another, the way they operate and the results they produce aren’t quite the same. Keep reading to learn more about each type of system and how to choose which one is a better fit for your power needs.

Table of Contents

What is a Phase Converter?

A phase converter converts utility single-phase power into three-phase power. Rather than changing voltage frequency or motor speed, phase converters simply change the type of voltage from one form to another.

While single-phase power travels through two power lines, three-phase power travels through three power lines. Because of this, phase converters require an additional power line to operate. This enables them to provide a stronger, steadier stream of power for larger loads.

What is a Variable Frequency Drive (VFD)?

A variable frequency drive (VFD) is a type of motor controller that converts single-phase power into three-phase power in addition to changing the speed of a motor from constant to variable form. The VFD controls the speed of the machine being powered by varying the frequency and voltage of the power supplied to it. Unlike digital phase converters, VFDs can change voltage frequency, motor speed, and voltage direction. While phase converters are designed to power larger loads, VFDs are designed to power smaller loads.

2 Types of Phase Converters

Selecting the correct phase converter type for your power needs is crucial to getting every job done right the first time. Check out this breakdown to determine which type is right for you.

1. Rotary Phase Converter

Rotary phase converters transform alternating current (AC) power into direct current (DC) power. These systems are designed to power large machines that carry heavy loads and consist of a rotor and a stator.

  • Rotor: The rotor is an electromechanical device that contains coils and converts electrical power into mechanical power.
  • Stator: The stator is a stationary electromechanical device that converts mechanical power into electrical power. This device usually consists of coils that are wound around an iron core.

Rotary phase converters are more popular than digital phase converters because they:

  • Are more affordable
  • Are more user-friendly
  • Are more efficient
  • Have a faster response time

Tips and Insights: What Is a NEMA 4 Enclosure and Why Do Phase Converters Use Them?

2. Digital Phase Converter

Digital phase converters consist of an inverter, a rectifier, a filter, and a transformer:

  • Inverter: The inverter, which is usually located on or near the compressor, converts the power supply’s digital signal to a signal that the compressor’s motor can use.
  • Rectifier: The rectifier is the component that converts AC power to DC power and vice versa.
  • Filter: The filter removes noise from the power supply, resulting in a quieter operation.
  • Transformer: The transformer can be used for voltage conversion and power factor correction.

While rotary phase converters use an analog control system, digital phase converters use a digital control system. Because they are generally more expensive than rotary phase converters, digital phase converters are a less popular option among users.

Phase Converters vs. Variable Frequency Drives (VFD)

Variable Frequency Drive Features & Uses


VFDs are characterized by an interface, a bridge rectifier, a capacitor bank, and an inverter. Here’s what each of those components does during the phase conversion process:

  • Interface: The interface is where all the controls are located for system operation.
  • Bridge rectifier: The bridge rectifier is the part that starts the AC to DC voltage conversion process.
  • Capacitor bank: The capacitor bank is a filter that smooths the DC voltage output, making it more stable.
  • Inverter: The inverter is what converts the single-phase AC voltage into three-phase DC voltage.


VFDs are most frequently used in these four industries:

  • Manufacturing
  • Automotive industry
  • Petrochemical industry
  • Electrical power generation and distribution

VFDs are used to power the following equipment:

  • Drill presses
  • Large mills & pumps
  • CNC
  • Cranes
  • Automation & lathes

Tips and Insights: What Is Three-Phase Power Used For? Benefits and Applications

Which Is Better: Phase Converter or VFD?

While VFDs serve a similar purpose to phase converters, they operate differently. They also differ in a few other ways. Here are four factors to consider when choosing between a phase converter and a VFD to power your heavy-duty projects:

1. Number of Machines

How many machines you plan to run will determine which system to choose. If you just need to run one machine, a VFD will get the job done. But if you need to run two or more machines, a phase converter is the better choice. Phase converters can power multiple machines simultaneously and provide smoother, more reliable power.

2. Space

If you don’t have much space to work with or are looking to downsize your workshop, a phase converter is more effective because they’re more compact.

3. Installation & Operation

Stuck in a time crunch? Go with a phase converter. Equipped with less wiring, these devices are easier to set up and operate with the press of a button.

4. Budget

Phase converters are cheaper to purchase and install than VFDs. If you lack wiggle room in your budget, we suggest going with a phase converter.

Rotary Phase Converters

View Our Selection Of Phase Converters

Do you need a rotary phase converter you can count on to provide reliable three-phase power for every project? We manufacture the highest-quality, most affordable rotary phase converters on the market. We also offer free product estimates and 24/7 emergency services. Shop our collection of expert-built rotary phase converters to find the one that’s right for you. Give our team a call by phone at (866) 418-9060 to receive assistance choosing a phase converters for your unique application.