VFD’S for Single Phase Motors?
Posted by Morgan Spano on Dec 8th 2021
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 motors we tend to see are 3-phase, but that doesn’t cover all the single-phase applications we’re dealing with. The solution? There are single-phase VFDs! While there are a limited number of manufacturers that offer single-phase output VFD, this is one potential solution. At points where three-phase power is unavailable or impractical, correctly fitted single-phase motors can potentially be a great option. 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. When working with a single-phase application, the next step is to determine whether a single-phase input drive the right option or if oversizing a three-phase drive is preferable.
Single-phase input drives 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/incompatible with single-phase designed drives:
Compatible
Permanent Split Capacitor (PSC)
Shade Pole Induction Motor
AC Synchronous
Incompatible
Split Case
Capacitor Start
Repulsion Induction
Series Universal (AC/DC)
Any motor with starting switch (centrifugal or relay)
Any motor with separate starting winding
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
Potential Single-Phase Applications
- Drill Press
- Refrigerators
- Mixers
- Heavy Duty Conveyors
- Hoists
- Lathes
- Freezers
- Grinders
- Air Compressors
- Submersible pumps
- Iron Works
- Sheers
- Presses
- Sanders
- Saws
- Fans
- Centrifugal Pumps
- Air Flow Controls
- Blowers
- Fume Exhausters
In summary, the technology is available, but it might not be your only option. First it’s important carefully review the pros and cons of benefits of purchasing single-phase drive. When in doubt, it might be best consider a 3-phase VFD or phase converter and determine the proper size drive for your application.
Check out our blog ‘How to run a 3-Phase Machine with 1-Phase Power?‘ to learn more how Fuji Electric’s handy guides make finding the right drive a snap.
Still have questions about VFDs? Check out out resource section for blogs such as “Resetting VFD's to Factory Default Parameters,” “How to Program a VFD,” and “What are the Benefits of a VFD?“