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Unique3phase LLC

Runs three phase motors

Great starting power

No wasted electricity

What is the Transformer Converter?

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If you’re here because you’re researching ways to run three phase motors on single phase power, I would like to help.


     For the last ten years I have sold a DVD set with an e-book on how to build three phase converters.

     I named my business Unique3phase because a lot of my ideas were original, unique, and not published anywhere else.

      I am an advocate of using the transformer converter for a lot of your motor running needs. This is in contrast to what the most popular converter is, the rotary converter.

How I got started in this:

     My story starts when I bought a used 10 hp Invincible Vacuum Cleaner (now Gardner Denver Corp.) in the early 90’s. This vacuum was a fantastic deal and I just needed to run it a few hours a week.

Gardner Denver vacuum cleaner

     Ten horse power 3450 rpm motor drives a turbine at almost 6k rpm’s. This is an extremely hard to start load. It averages about 4 full seconds to get up to speed. The faster it turns the more air is sucked in and the larger the load on the motor. It’s the BEST vacuum I ever owned! You could vacuum up bondo dust or sheet rock dust all day and never have it clog up.

     To make a long story short, a sales person brought a 25 hp rotary converter out to the shop and almost burned out my vac motor. He couldn’t get it to run and claimed I needed a bigger rotary. He started talking about a 30 horse and maybe even upgrading to a 40 horse.  It seemed so foolish to be trying to use a 40 hp motor just to run a 10 hp one. I would have had the additional expense of the oversized converter plus the need to upgrade the shop wiring to run it. What kind of efficiency is that?       Note! check out my new videos on youtube. I test the 20,30,& 55 hp rotaries

     He told me that the vacuum was much harder to start than he had figured. I knew there had to be a better way.

With some research this is what I found!


     I came across a converter circuit that was used in the 1940’s. It used a transformer instead of an idler motor.  I’ve called it the transformer converter.

     You may be wondering why you haven’t heard of it? I wondered that myself especially after I built one and found that it started the vacuum up like a dream with a fast, quick start, great amps and volts balance, and no noisy wasteful idler motor.

     Instead of a monster 40 hp motor filling the shop with noise and heat, I had a small, silent, three phase transformer which I modified for the converter.  I got so excited that I bought some more three phase things and ran them all off the transformer.

Modify a commercial transformer

    I thought everyone should have a transformer converter.

     But out of all the converter manufacturers there was only one making them.  As time went by, I realized that the transformer converter was not pushed by manufacturers for one reason; there are some operational differences in how the rotary converter and the transformer converter would be hooked up and used by the purchaser.

     The rotary converter is a lot easier to sell to the average non-technical person who needs three phase. It offered manufacturers a machine that was more ‘plug and play’, with less knowledge required from the end user.

     The ad copy could read “Have three phase at home - just connect to your power panel and run all your machines.” There would be no adjustments that the customer would have to make. There would be no need for the customer to have amp and volt meters, or even know about amps and volts; just turn it on and run your motors.

From American Rotary website

     This is from American Rotary’s website. The intent of the message is; hook it up and never worry about it again. It’s just going to power any combination of 3-phase equipment you throw at it.

Rotary Converter Basic Transformer converter

     Of course the bigger the converter they sell you, the more they can guarantee that it will start your motors, with the additional benefit of boosting their bottom line. With the rotary converter, you use capacitors to shift the phase of the incoming power to get the idler motor running. Once that is running, you can now ‘steal’ three phase power off of that motor.

That’s why it has to be oversized, not so much to run the other motors, but to get them started.  Remember starting a motor takes 6 times the power than just running it under load.


     Just because these rotary converters need no user adjustments and come prepackaged to work out of the box, doesn’t mean it’s the best for every machine. To me it is a compromise based on how easy it is for them to sell and how easy it is for the customer to install. As in my story of the vacuum cleaner, they wanted me to purchase an expensive oversized unit.

So what are these differences?

The transformer uses the machine’s motor as part of the converter. There is no extra idler motor. Each motor that is run from the main transformer needs to have run capacitors, start capacitors, and a start relay or switch.

     Because the transformer converter uses the machine’s motor as part of the conversion process, it only runs simple motors. By simple motors, I mean something like an air compressor, vacuum pump, dust collector, fans, grinders, etc. For a welder or machines like lathes and mills with more than one motor, or a machine with reversing and speed controls, the rotary converter works because it has a motor before the other motors. A motor with no load attached smooth’s out the power.

Static converter

     Take a look at the diagram on the left. That is a static converter. Slightly missed-named because then anything without moving parts should be called ‘static’. But that is how it got it’s name. It was missing the idler motor. How does it work? It uses capacitors to shift the phase of the third leg. It has no starting power and the motor can not be fully loaded or it will burn out. Besides that, it works.

     Here is a simplified drawing of a rotary converter. We are leaving out some of the extra capacitors that are used to help balance the converter under lighter loads. Notice that this is just a static converter with a moving part, the idler motor. Remember how we just bashed the static converter for lack of starting power? Well now we are expecting the same static converter to start a 30 hp motor.

If the static converter has no starting power, and we want to run a 10 hp motor why are we now expecting the static converter to start a 30 Hp to run the 10 Hp?

So let’s see a transformer converter

     Here is a transformer converter. You could call it a static converter because there are no moving parts. But humor aside, look at what we are doing. We replaced the extra large oversized idler with a transformer. What size transformer? Around the size of the motor you want to run, 10 for 10, 20 for 20. Hit the switch and if the machine is not bolted down, the torque of the motor could tip it over. (No exaggeration. It happened to one of my customers.)

     So here we have changed one component and we have fantastic starting power! Starting power is very important in various situations. Lack of it might just kill the project for some people. Overseas, they sometimes don’t have enough power to try and run a huge rotary. They need to get their motor running on the power they have which is just barely enough. The transformer will supply the starting power. It is a form of soft starting. It is quiet, and doesn’t waste energy.

So what are the drawbacks and why doesn’t everyone use one?

Here is the perceived drawback:

     The advantage is the drawback. The advantage of not needing a wasteful idler motor and using the machine’s motor as part of the converter means you can not just willy nilly connect the transformer converter up to any old machine. This is a real killer for the manufactures selling 3 phase conversion equipment. What are they going to tell you? “You have five machines you want to run? Okay you need to buy five converters!” That would not make great ad copy.  They want to say “…any combination of 3-phase equipment.” They want to imply that no user intervention is needed; just simple, easy hook up.

Learn more about how the perceived idea is not really true and how you can run multiple motors and complicated machines from the transformer converter.

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New videos  On youtube Sept 2016