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Your Most Common Questions Answered When it Comes to Three-Phase Power

Recently, Jim out of California called us and inquired about who exactly American Rotary is and why we do what we do. He was starting up a shop in his pole barn behind his house and had acquired a few solid pieces of three-phase equipment but only had single-phase power.  It was a great conversation had by all. From the viewpoint of American Rotary, we were excited to be part of another customer following their American Dream. From Jim’s standpoint, he was very educated about what he needed, to begin with. However, he did have some very good questions we find others ask as well and wanted to share them with you.

How do I size a Rotary Phase Converter and what information is needed to have someone help me size?

To size a rotary phase converter, you want to look at the type of machine you are running and the power requirements the machine needs. Typically, the power requirements are listed in a few different types of measurements; HP, AMPs, kW, or KVA. You will also want to verify the voltage the machine requires. These numbers are typically listed at 208-250v, 380v, or 480v. Once you know this information you can reference one of our load charts at or call one of our Application Engineers to help size a phase converter for your needs.

How does American Rotary stand apart from the competition?

American Rotary features a number of industry-leading benefits and patented technology.  With all American Rotary rotary phase converters, we utilize a custom-designed induction generator as our idler. This features our VIT Generator which is a true soft start idler that uses 1/3 of the inrush current of a comparable three-phase motor. This technology also allows you to run the phase converter 24/7 a little to no load without any negative effects. Our idlers run very smoothly, quietly, and efficiently.

Within our Digital Rotary phase converter line (AD, ADX, and AI) we feature our Patented Microsmart Controller. This digital controller monitors and controls your voltages across the three legs of power providing precise voltage balance to your equipment and adding additional fail-safe features to your phase converter operation. By monitoring your voltage every 50 Milliseconds and providing better voltage control, this helps prolong the life of your converter, allows significantly more load capacity (ADX and AI), and will run your equipment more efficiently.

In addition to industry-leading technology, American Rotary also offers industry-leading support. When you purchase an American Rotary phase converter you become part of the American Rotary family.  We will support you with the best tech support in the industry and back you with the best warranties in the industry. The American Rotary Digital Series (AD, ADX, AI) panels are backed by a Lifetime Warranty.

I’ve read on forums to stay away from rotary phase converters, is this true?

Depending on the technology behind the rotary phase converter this can be true.  Phase converter companies that are using old technology, can produce imbalanced power which can have a negative effect on your equipment. This is not the case with an American Rotary phase converter. American Rotary has a lot of patented technology standing behind it. With our Patented VIT Generator producing a true three-phase sine wave and our patented Microsmart controller monitoring and controlling your voltages, your equipment is receiving very clean balanced power. To give an example, typical utility three-phase power is balanced around 10%. With a Digital Series phase converter, you will get roughly 2-5% balance. This means with a Digital Series phase converter, you are providing your equipment with cleaner power than utility three-phase.

I do not want a loud motor running in my shop.  How loud is the rotary converter?

This is another advantage of using a phase converter that utilizes the custom-designed VIT generator versus a standard three-phase motor as the idler. Our Induction Generator runs much smoother and quieter than a typical three-phase motor. The idler will operate less than 60 Db which is comparable to a box fan running. In most cases, your three-phase machine will drown out the sound of the phase converter.  There are also options available for outdoor-rated phase converters if that is desired.

Are rotary phase converters safe to run on CNC machines?

The simple answer is YES! When running a CNC or other computer-controlled machine we recommend going with one of the Digital Series (AD, ADX, AI) converters since they are going to produce the tightest voltage balance. The digital phase converter produces power well within a CNC voltage tolerances. Running a CNC machine off of one of American Rotary’s phase converters is a common practice.

I have many different three-phase machines I wish to run; do I need a separate phase converter for each individual machine? 

When you are running a rotary phase converter you can tie in multiple three-phase machines. When going through the sizing process it is a good idea to know which machines will be starting at the same time and which machines may possibly run at the same time if started separately. This is important to know so you can get a phase converter that is going to be large enough to allow for current and future use. Typically, when multiple machines are in use a three-phase load center is added. In this setup, you would come out of your phase converter and feed the three-phase load center which would work as a distribution panel to each machine.  When sized properly, we have customers who power their whole shop off the phase converter.

We hope this helps answer some of your questions when it comes to three-phase power and using a phase converter. Please feel free to contact us should you have any additional questions. One of our Applications Engineers will be happy to go over your plans to ensure you are getting the phase converter that will work best for your needs.  All of us at American Rotary are proud to be part of making your American Dream a Reality!

13 thoughts on “Your Most Common Questions Answered When it Comes to Three-Phase Power

  • Arthur

    March 17, 2017 at 6:58 pm

    Can I run welding and plasma cutter with rotary converter?

  • Darren

    April 8, 2017 at 2:29 am

    this article is pretty much the exact same as me love it

    • admin

      April 19, 2017 at 3:06 pm

      Hi, Darren. Glad you enjoyed it!

  • Joe

    April 15, 2017 at 9:28 am

    How much more amperage would I need, over the requirements of the machine, to run it with a phase converter?

  • Marty Escarcega

    May 31, 2017 at 12:41 pm

    Will there be any difference in power quality using a standard quality (Baldor/Leeson etc.)3 phase motor vs. your VIT generator as the idler?

    • admin

      June 20, 2017 at 2:49 pm

      Hi Marty,

      Please give us a call at 262-402-6400 and one of our application engineers will be glad to get you exactly what you need!

  • Lenze/AC Tech Variable frequency drives

    September 19, 2018 at 4:36 am

    While dealing with new equipment and machines, there are many questions that arise in mind. There is always a need to know more about that. Thanks, really many questions and doubts have been cleared after reading this. Keep up the good work!
    Lenze/AC Tech Variable frequency drives


    January 4, 2020 at 7:49 pm

    I have an old 3hp 3 phase brake press, can I use a 10 hp converter?
    I plan on adding more equipment.

    • Sarah

      May 26, 2020 at 6:01 pm

      Yes our 10hp converter is capable of starting up to a 5hp load! So that would even give you some extra cushion for growth as well. Based off of your current type of load I would recommend taking a look into our ADX10! It will also give you flexibility on the types of loads you can run off of the converter as it is designed to run any type of load. It comes with heavier duty capacitors, CTR technology and booster coils that will provide extra torque, voltage monitoring and a life time warranty on the control panel!

  • James Metzler

    June 1, 2020 at 9:59 pm

    I have a water source heat pump 208V 3ph 13amps. I want to convert my 1 ph 208V circuit to 3 phase. Please provide the following information:
    1. Size and model number of recommended unit.
    2. Noise rating in db’s. I need the quietest unit available.
    3. Cost of unit.
    4. How to purchase and delivery time

    Jim Metzler

    • Sarah

      June 2, 2020 at 4:12 pm

      Hi Jim, Thanks for reaching out! Based off of the information you have provided for me I would recommend our model AI-20. This is our one piece Nema 3R unit which helps sound proof the idler to be rated less than 60 db. This unit is built to order but feel free to call our office at 888-743-6832 and they would be happy to give you a more definite answer on delivery time. This unit is currently listed for $2,799.00 includes a life time warranty on the control panel/enclosure, 2 year warranty on the idler, wash down filters, easy installation, plus is completely outdoor rated and can handle starting up to a 28 amp load!

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