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Is it true? There are actually single-phase output inverters for certain single-phase motors? I thought that VFD’S were only for 3-phase motors?

The bulk of the industrial market is flooded with 3-phase motors, but yes; there are single-phase VFDs! There are a limited number of manufacturers, including Leeson, that offer single-phase output VFD. At points where three-phase powerCentrifugal motor is unavailable or impractical, correctly fitted single-phase motors can potentially be a great solution. It is important to note that while using single phase output, your motor may run hot at full load and may need to be de-rated.

“Though they lack the higher efficiencies of their three-phase siblings, single-phase motors – correctly sized and rated – can last a lifetime with little maintenance” (Kevin Heinecke, Leeson Electric).

As our tech support will readily tell you, incorrectly fitting a motor can cause repeated motor failure and equipment downtime costing you in the long run. This is why it’s most important to initially size the motor based on your application. Knowing that your application has a single-phase motor opens you up to the option of using a single-phase VFD for control; even if this technology comes with some limitations.

These devices are typically horsepower (output amps limited) and have very specific compatibility options when it comes to pairing with different types of single-phase motors.

Here’s the list of what motor applications would be considered compatible and not compatible.

Compatible

Incompatible

 Permanent Split Capacitor (PSC) Split Case
Shade Pole Induction Motor Capacitor Start
AC Synchronous  Repulsion Induction
Series Universal (AC/DC)
Any motor with starting switch (centrifugal or relay)
Any motor with separate starting winding

Leeson FHP Series VFD

See our selection of Leeson single-phase VFDs here!

Wondering how these types of drives are designed? Similar to design on the board level, some drives are available in an open chassis design (see image to the left) meaning they need to be housed in an electrical enclosure. Other drives are available in NEMA 1 (IP20) enclosure or even NEMA 4X (IP66) configurations. Features and performance are dependent upon various manufacturers.

Output performance in HP (horsepower) rating and amps are relegated to input voltage.

 

Example: a 115V input will output 115V and may have a maximum HP rating of ¼ to 1/2HP and amps to 2.4 – 4.0 amps.

Higher HP models are available if your supply side voltage is 200-240V/1PH/60HZ.  Some manufactures limit their models to one HP while others may go to 5HP.  Horsepower and output current (amps) are going to be the limiting factors with this style for single phase input to single phase output type of VFD.

When trying to decide whether your application would be a good fit for a single-phase option, it’s always good to remember just about every manufacturer has designed this style of VFD around a specific duty load.

Below are some examples of applications that can incorporate single-phase motors and some that would be better off as three-phase.

Three-Phase Applications

  • Drill Press
  • Lathes
  • Iron works
  • Refrigerators
  • Freezers
  • Sheers
  • Mixers
  • Grinders
  • Presses
  • Heavy Duty Conveyors
  • Air Compressors
  • Sanders
  • Hoists
  • Submersible pumps
  • Saws

Potential Single-Phase Applications

  • Fans
  • Blowers
  • Centrifugal Pump Motors
  • Fume Exhausters
  • Air Flow Controls

In summary, the technology is available, but one must always carefully review the pros and cons of benefits of a single phase motor and controller. When in doubt, change it out to 3 phase and your door of opportunities for options increases.

Still have questions about VFDs? Check out out resource section for blogs such as “Basic Single-Phase VFD Sizing,” “VFD Tips & Tricks,” and “What are the Benefits of a VFD?

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