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So you need to run a three phase motor but you only have single phase power?

A common enough problem we hear at Marshall Wolf and we wanted to take some time out to explain the basics between two of our American Rotary productsDigital Static Phase Converters and Rotary Phase Converters.

Digital Static Phase Converters

These straightforward units start your application with a 3 phase load but then switch to single phase power.

This is done through circuitry disconnecting after start-up and subsequently limits the load to about 2/3 of its rated capacity. This does effect your selection depending on how you intend on running your motor. Applications which require a high torque start-ups but not consistently high HP, such as drill presses, milling machines, and table saws, work best with Digital Static Phase Converters.

Rotary Phase Converters

A much more sophisticated solution, these units create true three phase power supply; often more precise than utility-supplied three phase power.

The function of the R.P.C. type unit is to transform single phase power to three phase power, vs static which provides discharge of its capacitor system to manage the start of the electric motor. Unlike the static converter which only supplies three phase power through start-up, the rotary converter is assisting running the machine continuously. Applications which require constant high use of their motors, such as pumping systems or hydraulics, are great candidates for Rotary Phase Converters.

Power Distribution

Static Phase Converters (SPC) do not produce continuous three phase power and not capable of running full loads continuously. This is due to the fact that once the motor has been started up the SPC will disconnect its internal circuitry in order to power two of the three windings.  A rotary phase converter produces a true sinewave of 3 phase power and can run the machinery at full horsepower.

Potential of Control

What we mean by this is the ability to control or manage more than one device at a time.  A static only has the ability to be single minded.  A rotary, with the correct sizing, can run multiple machines at a given point. What this means is static converters cannot function on more than one piece of equipment at time and typically are used on lower horsepower applications. Rotary type converters, on the other hand, can manage more difficult load types for all three phase and can feed a distribution panel to then feed all the needed machinery.


Rotary Phase Converter are very efficient in being a provider of balanced power which make them superior in motors that are controlling machinery loads.  If you have any real continuous duty conditions it is always better to use a rotary vs a static converter, especially with higher machine loads. If you happen to only need a strong start up to your motor with derated use afterwards, a static phase converter may be all you need.

Still have questions in regards to which converters is best for you? Feel free to reach out to us today at (847) 658-8130 or email us directly and we’d be happy to help!

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