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What You Need to Know When Buying a Transformer

Buying a transformer can be stressful and confusing, so American Rotary would like to help you better understand what transformers are right for you. Some things to consider when buying a transformer are:

Why do I even need a transformer?

What type of environment am I putting it in?

How do I size a transformer?

Should I buy an auto or isolation transformer?

WYE or Delta?

Why do I even need a transformer?

A transformer is needed anytime you want to raise or lower your supplied voltage. An example of this would be when you have 240v power available, but you have a machine that requires 480v power. American Rotary offers a number of solutions that will allow you to go up or down in voltage as needed.

What type of environment am I putting it in?

There are a number of different enclosure types that you may want to consider when ordering a transformer. You will want to determine if it will be going indoors or outdoors. You may also want to consider things such as corrosion, noise, or if it will be in a hazardous location. Common enclosure types are:

Type 1 – These enclosures are constructed for indoor use to provide a degree of protection against access to hazardous parts and to provide a degree of protection of the equipment inside the enclosure against the entry of solid foreign objects (falling dirt).

Another very common type of enclosure is Type 3R – These enclosures are constructed for either indoor or outdoor use to provide a degree of protection against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against the entry of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the entry of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.

American Rotary can help to determine the best NEMA rated enclosure for your situation as there are a number of other less common types that we offer by special order only.

How do I size a transformer?

Sizing a transformer can seem quite complex at first, but in reality, it is quite easy if you understand the terms and abbreviations that are used. The following will help ensure you are successful in your quest for the properly sized converter.

1. The transformer size is determined by the KVA of the load.

2. Load voltage, or secondary voltage, is the voltage needed to operate the load.

3. Line voltage, or primary voltage, is the voltage from the source.

4. Single-Phase has two lines of AC power.

5. Three-Phase has three lines of AC power.

6. KVA is kilovolt ampere or thousand-volt amperes. (This is how transformers are rated).

Determine the Load Voltage
Load Voltage = ______________________

Determine the Load Current (Amps)
Load Current/Amps = __________________

Determine the Line Voltage
Line Voltage= ________________________

Then use the following calculations:

Single-Phase Transformers:                       Three-Phase Transformers:

Volts x Amps / 1000 = KVA                             Volts x Amps x 1.732 / 1000 = KVA

Should I buy an auto or isolation transformer?

To know which type of transformer is right for you, it’s probably best to get an understanding of the difference between the two. Here is a brief break down of each:

Auto-Transformer – An Auto-Transformer is an electrical transformer that contains only a single winding, a portion of which is common to both the primary and the secondary circuits. An autotransformer uses a common winding and offers no interference or isolation. Pros: inexpensive, easy to hook-up, typically smaller footprint can go Delta to Delta and Wye to Wye, many tap configurations available. Cons: No isolation, cannot go Delta to Wye.

Isolation/Distribution Transformer – An Isolation or Distribution transformer is an electrical transformer that contains two separate windings. Neither of these windings is shared with one another which allows the primary to be isolated from the secondary. The transformation in voltage between primary and secondary windings occurs as a result of the shared magnetic field in the core. Pros: Provides isolation, can go Delta to Delta, Wye to Wye, or Delta to Wye, Con’s: More expensive, larger footprint.

Wye or Delta?

Transformers can be hooked up in a Delta configuration, Wye configuration, Wye to Delta configuration, or Delta to Wye configuration. So which one is right for you? A Delta configuration uses only three-phase conductors, whereas wye-connected systems carry a fourth neutral conductor which is often grounded but sometimes left floating.

An advantage of the Delta connection is higher reliability. If one of the three primary windings fail, the secondary will still produce a full voltage on all three phases. An advantage of the Wye connection is that it can provide multiple voltages without the need for additional transformers. To know what connection is right for you, we recommend that you refer to the nameplate on your equipment.

American Rotary is excited to announce it has partnered with Hammond Power Solutions to bring you a line of high quality, yet cost-effective, Auto-Transformers and Isolation Transformers. In most cases, American Rotary has an array of in-stock transformers ready to be picked up or shipped to you the same day you order. To learn more, visit our Transformers product page.

American Rotary Phase Converter Installation Video

If you’ve recently purchased a phase converter or are considering purchasing one, you may be wondering what is all involved when it comes to setting it up.

In this video, we show you the basic installation techniques of the American Rotary Phase Converter Panel. The idea is to show how easy it is to install, and also to provide a video reference for our customers.

As always, if you have any questions regarding your American Rotary phase converter, or which phase converter might be best for your unique situation, give us a call at 1-888-743-6832 and we will be happy to help.

Phase Converter Installation & Wiring with Jim Bollinger of DoRite Fabrication

Considering updating the electrical in your shop?

In the first video below, Jim Bollinger of DoRite Fabrication walks you through his process of removing and installing a 200 amp panel to power his new American Rotary AI Industrial phase converter.

In this second video, his unit has arrived. Here he takes you inside the box to show you what it looks like and how he rewired his shop to complete the installation.

As always, please consult a professional electrician as needed to ensure your safety.

Phase Converter Installation and Wiring – Part 1

Phase Converter Installation and Wiring – Part 2

Not sure which model phase converter is right for you? Check out our free resource guide below. Inside you’ll learn the difference between products, get an advanced sizing chart, installation guide, and answers to our most frequently asked questions.

We’ve put years upon years of experience into creating what we believe is by far the best selection of phase converters available on the market today. We include a variety of sizes and deployment features, and offer complete on-going support for as long as you have your phase converter.

American Rotary Phase Converter Unboxing, Setup, and Wiring

Thanks to American Rotary customer, Michael Murray, we have a few videos to show you exactly what to expect when you receive an American Rotary phase converter. The unit used in these videos is an AD series model. So keep in mind, some things may vary depending on your specific order for your unique setup, but this should give you a good idea, especially when ordering a similar unit.

Phase Converter Unboxing:

Phase Converter Setup:

Phase Converter Wiring:

Have an American Rotary experience or setup you would like to share? Send us pictures or videos at and we will be glad to share them with our community!

Product Overview: The AI Industrial Digital Phase Converter

Designed specifically for the outdoor demand of agricultural applications and the hard environment of industrial conditions, the AI Industrial phase converter can save you thousands of dollars per year over utility and diesel generated power sources. Need more power? Need more precise power? Just turn on your American Rotary Smart Series Converter and let our technology do the work…

For more information visit the AI Industrial Converter product page or call 888-743-6832.

Product Overview: The American Rotary MicroSmart Controller

The American Rotary MicroSmart controller is a state-of-the-art microprocessor that delivers the RIGHT power and the RIGHT time in both start-up and run. Available in the AD, ADX, and AI models, the MicroSmart controller monitors voltage every 50 milliseconds in order to provide better voltage control, giving you more precise power, and protection to the phase converter and your machines.

See for yourself how American Rotary utilizes leading-edge technology in our phase converters with our Patented MicroSmart Controller:

Need more power? Need more precise power? Just turn on your American Rotary Smart Series Converter and let our technology do the work.

Top 5 Things To Know When Buying a Phase Converter


Everyday we get hundreds of calls with questions about phase converters. So, we thought we would take a moment and go over the top 5 things you should know before buying a phase converter.

As you can see, there are a few basic things you should know before buying a phase converter.

As a recap:

1. Make sure you have enough single phase power.

Here’s how to calculate how much single phase power you need:

Take the amount of three phase amps of your load x 1.6 = amount of single phase amps. Then, take the amount of single phase amps x 1.2 = required single phase amps with 20% adder. The 20% adder is factored in as a cushion simply because most towns and cities require you have 20% above what your load is.

2. Understand your load.

Is it light, medium, or heavy? To give you an idea, a light load would be something like a drill press or table saw. A medium load would machines similar to CNC machines. A heavy load would be things like HVAC, air compressors, and refrigeration.

3. The size of your load.

Know the horsepower, amps, and kilowatts. Knowing this will help you find the best phase converter for you. As a rule of thumb, you want to go 2:1 (2 times the size of your load) to find the size phase converter you need.

4. Indoor or Outdoor?

Make sure you buy a phase converter that will stay protected in the environment it will be in. For example, if you do welding you will want to make sure your converter stays protected from metal shavings. Likewise, if you are a woodworker, sawdust. If you are a farmer, you want to make sure your equipment is protected in wind, snow, and rain.

5. Who are you buying your phase converter from?

Make sure you are buying from someone who is reputable. We get calls all the time from people who previously bought a phase converter from someone who made one in their garage and it’s not working right and they have no service. By using a quality product to begin with, you will be able to get the exact amount of three phase power you need, protect your equipment, and be able to scale appropriately as needed.

American Rotary Expands Global Distribution of Three Phase Power Converters

American Rotary will offer its industry leading three phase power solutions in partnership with South American distributors

Menomonee Falls, WI, May, 18th, 2015 – American Rotary, the world’s leading manufacturer of three phase rotary phase converters announced it has expanded distribution in Latin America. The company has solidified partnerships with LAERA, Wesco Distribution, Summit Electric, as well as a number of other independent contractors to streamline distribution across South America.


“We are thrilled to join with our Latin American partners to meet the rapidly growing three phase power requirements of the agricultural, industrial, and construction industries.”, Christopher Feavel of American Rotary. “South America is a rapidly expanding market and there is a clear need for reliable, three phase power. Three phase power is the power of choice for many applications. It allows machines to run more efficiently and last longer than machines running on single phase.”

American Rotary has manufactured rotary phase converters in Wisconsin since 1995. Proud of its We Are American Made motto, American Rotary engineers their phase converters to deliver optimum performance. Featuring Variable Impedance Generators (VIT™) and MicroSmart™ Controllers, American Rotary phase converters are designed to be the most powerful and precise rotary phase converter on the market.

Last year, the company expanded its distribution network in Canada in response to growing demand. “With our new partnerships in South America, we can better serve the growing three phase needs of customers throughout the Americas.” David Rehm, CEO of American Rotary. “We are pleased that that our converters are recognized, around the globe, as a powerful and reliable source of three phase power conversion.

Americana Rotary expande Distribución Global de los Transformadores de corriente Fase Tres

Americana Rotary ofrecerá su líder en la industria de tres soluciones de energía de fase en colaboración con los distribuidores de América del Sur

Menomonee Falls, WI, Mayo 18, 2015 – American Rotary, el principal fabricante del mundo de convertidores de fase rotativo trifásicos anunció que ha ampliado su distribución en América Latina. La compañía ha consolidado alianzas con Laera, Wesco Distribution, Cumbre eléctrica, así como una serie de otros contratistas independientes para racionalizar la distribución a través de América del Sur.


“Estamos muy contentos de unirnos a nuestros socios latinoamericanos para satisfacer las crecientes necesidades de potencia de tres fases de las industrias agrícolas, industriales y de la construcción.”, Christopher Feavel de América del Rotary. “América del Sur es un mercado en rápida expansión y hay una clara necesidad, la energía trifásica fiable. De potencia trifásico es el poder de elección para muchas aplicaciones. Permite que las máquinas funcionen de manera más eficiente y duran más que las máquinas que se ejecutan en una sola fase “.

Americana Rotary ha fabricado convertidores de fase rotativos en Wisconsin desde 1995. Orgulloso de sus Somos lema Hecho, ingenieros estadounidense rotarios sus convertidores de fase estadounidenses para ofrecer un rendimiento óptimo. Con Generadores variables Impedancia (VIT ™) y controladores MicroSmart™, convertidores de fase Rotary estadounidenses están diseñados para ser la más potente y preciso convertidor de fase rotativo en el mercado.

El año pasado, la compañía amplió su red de distribución en Canadá en respuesta a la creciente demanda. “Con nuestras nuevas alianzas en América del Sur, podemos servir mejor a las crecientes necesidades de la fase tres de los clientes en todas las Américas.” David Rehm, director general de América del Rotary. “Estamos muy contentos de que de que nuestros convertidores son reconocidos, en todo el mundo, como una fuente de conversión de potencia trifásico potente y fiable.

How to Create a Solid American Made Brand

It is increasingly hard to find true American Manufactured products.  So many companies today have a nice American facade, but with products that are imported and re-branded.

American Rotary started in a back bedroom and garage in Illinois, and was born out of the need for a better way to convert single phase power to three phase power.  We needed a phase converter to run a Bridgeport milling machine and a lathe in order to make a large CNC router that could make molds for an airplane we were designing.

Ever since I was a kid, I followed the creations of Burt Rutan (Long-EZ, Spaceship One, Voyager etc.)   Burt not only had a gift for solving flight related problems, but he was also a very passionate opponent of the way the world stifles the creativity and progress of those who wish to challenge it.

In addition to creating an American Made product that brings real value to our customers, there are two driving principles that I attribute largely to Burt Rutan that apply not only to research, but to creating a lasting quality product.

1.  Research should be defined as: “doing something where half of the people say it’s impossible.”, Burt Rutan. This is a great benchmark for creating an outstanding product that performs significantly better than the competition.  Something that re-branded, copies cannot do.

2.  Never Defend!  It is not an engineer’s job to defend what they have done.  The performance of the product wins every time.  I can’t tell you how many times we have made a change to something because one customer had a suggestion.  You can’t do that when you copy what someone else has done and don’t understand the whole system, and you can’t do that when it is made in a factory half way around the world.

Burt Rutan is now retired and is building another innovative aircraft, the way he started, in his garage.  A film company called Antennae films is documenting his latest creation and is funding the film primarily from donations.  This is a rare chance to see behind the scene of one of the our countries greatest visionaries.

Burt Rutan has been an inspiration for true innovation to what we do, and though it is our hope to inspire the same in others, it is only because of those that have come before us.

David Rehm

American Rotary

American Rotary ADX Phase Converter

The American Rotary ADX “Smart Series” Phase Converter demonstrates the starting power of these converters. We compare the time it takes an ADX to start (2.9 seconds) an Ingersol-Rand T30 20HP Air-compressor to the time it takes a typical rotary phase converter (7.9 seconds) to start the same air-compressor. Just over 2 minutes.

Balanced Voltage Claims – Truth or Fiction?

For years, many companies have used (and continue to use) the inexpensive method of “stacking” run capacitors in order to get a phase converter started. Those capacitors are not taken out of the circuit once the phase converter is running, which results in extremely high voltage and current imbalance. This condition causes current overloads that will burn out motors that are smaller than what the phase converter was sized for (ie. running a 2HP mill on a 40HP converter). Furthermore, this condition will ultimately cause the phase converter itself to burn out.

The justification for continuing to build phase converters this way is that the starting circuit is fail proof. But the consequences of the resulting high voltage and imbalance can be avoided by simply using new designs and updated technology.

With the proven quality and reliability of starting capacitors and contactors, new methods to create starting circuits using these components allow the rotary phase converter to have two stages: starting and running. This gives the best of both worlds – a robust starting circuit, and a balanced running circuit.

To attain the balanced voltage, the phase converter requires a high quality custom idler/generator (not a motor), and a very specific balancing of the capacitance across the windings of the idler. Placing all of the run capacitors across one winding will not produce a balanced voltage!

Outrageous claims of voltage balance of 2% or better. The only phase converter on the market that can produce this type of voltage balance, (actually 1% or better) is the Phase Perfect digital phase converter, which we will cover in another post. Please visit for more information about this product!

The only way a rotary phase converter might achieve such a voltage balance is if the load is constant (which is very rare), and the capacitance is “tuned” across each winding of the idler. Even then it would be very difficult. Switching in and out capacitors with contactors is a difficult thing to do properly. Switching them out once is fine, but not back in. The contactors just can not handle the “in theory” infinite current and the moment of contact.

It is so important to verify voltage claims! In the age of the internet, pretty much anyone can say anything…All in all, look for a (provable) 5% voltage balance, and that it can be achieved in a range of about 50-60% of the full load current of the converter.

There are several other marketing-style claims that are made by various companies. These advertising methods can be quite deceptive. The best defense is a good offense. We will continue to cover key features and benefits of phase converters, what to look for, what to avoid.

As always…please feel free to email if there is a specific topic you would like to see covered on this blog!

Integrated Soft Start – How it came about, why it is so great, and why everyone is talking about it.

We thought we’d take a moment to talk about American Rotary’s integrated soft start. For years, phase converters have had a reputation of drawing a huge inrush current upon start up. This disproportionate power draw has resulted in, among other things, dimming the neighbor’s lights, demand charges from the utility, and large increases on power bills. The engineering team took this age-old problem by the horns and set out to find a solution.

After investigating various forms of “soft starting” a motor (most of which are inefficient and/or delicate, not to mention very expensive), the lead engineer and co-founder, David Rehm, took it to a new level all together. His original idea was to make the soft start feature solid state (so that no failure of moving parts would ever occur), and to keep the cost down enough that everyone could afford this feature. The team set up meetings with the engineering department at Baldor Electric. After a year of design and development, we were ready to begin the testing phase of the new generator. What resulted surprised us all!

The new generator design achieved an 83% reduction in inrush (starting) current – and was granted a soft start rating. What’s more, is that American Rotary’s soft start phase converters deliver all the power required for hard starting, heavy duty applications, along with balanced pure sine wave output and power factor correction (I’ll address these features in another entry) for CNC and other voltage sensitive applications. This motor-integrated solid state soft start design is proprietary and exclusive to the Baldor/GENTEC American Rotary phase converter generator. It is affordable, reliable, made in the USA, and no one else has it.

Our marketing department launched the new Baldor/GENTEC phase converter with gusto! And the product is everything we hoped it would be. Then, as days and weeks went by, we started seeing the phrase “soft start phase converter” popping up in all sorts of places… Unfortunately, many phase converter manufacturers now claim that they too have soft start when indeed they do not. Many phase converter manufacturers use a regular stock motor by rewiring it for low voltage and cutting off the exposed rotating shaft (consequently, most of these companies are uninsured since the remnant of the shaft is a huge safety hazard). A regular stock motor is going to take the values of capacitance (in microfarads) shown here:

3HP: 240-360
5HP: 300-600
7.5HP: 600-900
10HP: 800-1200
15HP: 900-1800
20HP: 1600-2400
30HP: 2400-3000
40HP: 3200-4000
50HP: 4000-5000

Therefore, one way to verify a claim of “Soft Start” is to check the starting capacitance of the phase converter (How many microfarads are used in the starting circuit – or – how many capacitors and at what values are used?). If the microfarads fall within the values above, it is simply a stock motor and is not using integrated soft start.

American Rotary’s Soft-Start phase converter generator uses anywhere from 1/3 to 1/6 of the capacitance needed to start a stock motor. This also reduces inrush current by the same amount, which virtually eliminates demand charges from the utility and dimming the neighbor’s lights.