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Static Phase Converter [Pros and Cons]


The difference between Static and Rotary Phase Converter is that Rotary Phase Converter uses an idler motor to give you a continuous third phase, while Static Phase Converter just gives you a third phase for a startup boost. This means that if your 3-phase motor does not require full nameplate HP to operate on, you will be able to start your motor and use it at 2/3 of its horsepower.

If you are like many small shop owners, you probably don’t have a three-phase power supply readily available to use. So how does a brand new entrepreneur sets up and operates his 3-phase machines?

The solution is to use a phase converter to operate any 3-phase equipment from a single-phase power source. Phase converters can be easily installed by a licensed electrician and you have one less thing to worry about besides just running your production.

There are several phase converters available on the market right now and of course, many people trying to build their own variations of it. A Static phase converter is a device similar to a Rotary phase converter, only without an idler motor-generator.

A typical 3-phase induction motor has three windings and if you are trying to start it on a single-phase power current, it will lack the needed third phase to start itself. Static Phase Converter will create an additional phase in order for you to be able to start your motor, but then it drops out and your motor will continue to run on single-phase power (2 legs).

If you are just starting a project or you have this fancy hobby of creating wonderful things, you will have the following phase conversion systems to choose from:

  • Rotary Phase Converter (RPC). Idler motor generates the third leg and keeps on running to give you stable, but rough (if not balanced properly) three-phase power.
  • Static Phase Converter (SPC). It will start up your 3-phase motor and disconnect itself, leaving your machine with 2 legs of power to use.
  • Variable Frequency Drive (VFD). This device uses inverter technology to give you a varied frequency and could be used as a Phase Converter.
  • Electronic or Digital Phase Converter (DPC). It uses inverter technology to give you a third leg of power. These converters will provide the most balanced and regulated three-phase power, similar to the one that would come from utilities.

Static Phase Converters -vs- Rotary Phase Converters -vs- Variable Frequency Drives

In this document, I will be talking about the Static Phase Converters (SPC). A Static Phase Converter is the least expensive out of them and very popular for that reason.

Since the choice of machines that operate on single-phase power above 5HP is limited, the workshop owner has the following options to consider:

  1. Local power. Ask your utility company to install one for you. This is very expensive and usually not an option for most people unless you are trying to power an industrial building or a factory.
  2. Single-phase machinery. Do not purchase 3-phase machines. This would work for some people, but if you already have some three-phase production machinery in your shop, it is not an option for you.
  3. Convert three-phase machines into using 1-phase power.
  4. Convert single-phase power into a three-phase power supply.

What is a Static Phase Converter?

Static Phase Converter uses capacitors to start your 3-phase motor and then it falls out of the circuit. After that, your motor will run on a single-phase power supply.

It is designed for light and medium 3-phase motors. Static Phase Converters work best with single motor applications with constant and automated operation.

Static Phase Converter is only a starting device for your motor and it does not produce a true three-phase power. Your motor should be capable of running on a single phase after it gets activated.

If you don’t really need a full-rated power out of your motor, then Static Phase Converter is probably right for you! Here is an interesting video on how to build a Static Phase Converter, but besides that, you will find out how it compares to VFD and Rotary Phase Converter:

DIY Static Phase Converter


Static Phase Converter wiring diagrams

Here is a basic wiring Static Phase Converter diagram:

There is an interesting document that includes a detailed explanation of how to add run capacitors to your Static Phase Converter. Click here (external link) to check it out and here are some more wiring diagrams (that include run capacitors):

Here is the wiring explanation from TEMCo (video):

TEMCo How to Wire a Static Phase Converter

Here is a Static Phase Converter (Phase-A-Matic) installation video:

How to Install a Static Phase Converter

Pros and cons of Static Phase Converters

Even though this type of converter doesn’t produce three-phase power all the time, this is a very popular device due to the following:

  • It costs less.
  • You will still be able to start your three-phase motors (as long as they don’t exceed 2/3 of the nameplate HP).

There are also limitations to using Static Phase Converters:

  • Not all motors support this kind of startup.
  • You will lose about 1/3 in horsepower.
  • Your motor will not run smoothly, because it is designed to run on 3-phase power.

** Important! You should NOT try starting machines that work on full-rated horsepower with Static Phase Converter!

Since only two winding of your 3-phase load will be getting power (after startup), your HP will be greatly reduced. Meaning that if you have a 10 HP motor (for example), it will startup as a 10 HP motor and run only as a 5 HP motor.

 Feel free to save this infographic on static phase converters for future reference .

How does a Static Phase Converter work?

A Static Phase Converter is made up of a voltage-sensitive relay and a start capacitor, which is connected to the motor application. This capacitor (or capacitors) delays some of the current and therefore shifts the phase (which means it creates a third leg of power).

After the motor reaches its full RPM, the relay disconnects the start capacitor and the motor continues to run on two single-phase lines. With this type of converter, you will get approximately 50-60% of its full-rated horsepower.

What you CAN and what you CAN’T run on the Static Phase Converter

Following loads are known to work well with Static Phase Converters:

  • Horizontal conveyor belts
  • Washing machines (industrial size)
  • Sewing machines
  • Milling Machines
  • Drill press
  • Table saw
  • Chop saw 
  • Lathe (below 2 HP)

Do NOT try to start up the following loads with Static Phase Converter:

  • CNC Machines
  • Plasma Cutters
  • Air Compressors
  • Refrigeration Trucks
  • Water pumps
  • Vacuum pumps
  • Hydraulic car lift
  • Band saw
  • Granite saw
  • Dust collection blower
  • Heaters
  • Welders
  • Bailers
  • Lathe (above 2 HP)
  • Fans & Blowers
  • Large Flywheels
  • Two Speed Motors
  • Motors made before 1965

** Important! Consult the Static Phase Converter manufacturer for more information on what you can run and how to size it.

Static Phase Converters manufacturers

Popular Static Phase Converter brands include:

In conclusion, I would like to note that a Static Phase Converter has a price advantage over the other phase converters. Considering that phase converters are expensive devices, this is what they are most useful for:

  • Static Phase Converter. If you need to power something that you are not using very heavily, you could probably get the most use out of Static Phase Converter (cheaper solution and less complicated).
  • Other Phase Converters. If you need to power the whole shop that uses equipment constantly or needs a full-rated HP, you may want to look at other Phase Converters. For example, a Rotary Phase Converter (a link to another article).

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1 Comment

  1. james holland

    hey hey
    my name is Jim Holland i am here in Washington state and i have a milling machine that I installed a 3phase shifter on it
    it get very hot and it starts to smoke after a little while this machine was built in the early 1960’s
    i was reading that the insulation on the windings may be not able to handle the heat generated by the motor
    if this is true….. is it possable to have the motor dipped at the rewind shop or do i need to have the motors rewound

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