Page 5 in a 5 page series on selecting the right converter. Page one is here.

Selecting the right converter for you.

We just heard from 4 different manufacturers of 3 types of phase converters.

Out of all the converter manufacturers in business today why did I pick these 4?

Phase Perfect – Because they are completely different from the old style rotary converter, new technology needed to represented.

Smith Electric – Because they give a no nonsense technical explanation on their website. They cover both the good and bad.

Ronk Electrical – They are the only manufacturer that builds and sells both the transformer converter and the rotary converter.

American Rotary – You could think that I am playing favorites here, that maybe I get a kick back from them. I don’t. They got picked because I feel they are progressive in their business approach. When the Phase Perfect technology came out American Rotary didn’t just pack it in and quit. They appear to have taken the competition seriously and have gone back to the drawing board to improve what they are selling.

I did a lot of testing.

Go to my You Tube channel and you can see I built a converter test box and ran a bunch of rotary converters. I have run a 10 hp, 20 hp, 25 hp, 30 hp, 50 hp, 55 hp, and 75 hp rotary converters. The 50 through 75 were combinations of lower motors. In addition to running them I also tested the electric consumption with a utility electric meter.

I also contrasted those with what Ronk Electric sells; the transformer converter.

One obvious conclusion is the starting power of the traditional home made rotary converter is dismal. People looking to get a rotary converter might want to consider that.

American Rotary apparently has come up with away to boost the starting power of the rotary converter. Congratulations to them for actually putting a video up of a 20 hp air compressor.

They don’t measure the amps and volts, and they don’t do it in a fashion that would take away any doubts. You don’t actually see much, they just do a start and that’s it.

The bottom line is you need to know what you want to run and what your shop situation needs.

Doing a little homework in advance of a purchase could save money and time in the long run.

The list below is a basic needs list.
Check through it and there might be something you have not thought of.

How big? Like in how much horsepower?

How many machines all together, and how many run at the same time?

How much current do you have to your shop? This is a big one, many people just can’t come up with enough amps.

Your geographical location? Important to know. I can then determine the odds of finding used equipment and what voltages are needed. If you are out on a wide open area, such as a farm then we have to worry about lightning strikes.

What voltages do your machines run at? Usually 240, 415, 480, 380, or 500.

How many starts per hour? If this machine turns on and off many times an hour that is important to know.

How quiet do you need it? Three phase for a library or hospital is going to have to be quieter then a machine shop.

How much does down time cost? If the machine breaks we need to know how serious that is.

Where is the closest service facility?

Can you get parts for it locally? The availability of parts is crucial. Rotary and transformer converters are the easiest to source parts for.

One big motor load, or one big and one small motor? If you have a 25 hp that runs occasionally but a 3/4 hp that runs all day that makes a difference.

Super hard to start machine. Like my vacuum cleaner. Just a real bear to start. Worse then any air compressor.

How much money do you have, A lot of people will balk at spending 5 grand to run a 500 dollar used air compressor.

Are you going to grow and expand? Need to know if this is all for one year or next year is bigger.

All the above things need to be considered when evaluating what is best for you.
Now the next big thing to consider is how much does this stuff cost? Price is important especially if this is just a hobby. The below prices are taken in October 2016.

Smith Electric know as GWM doesn’t have prices on the website.

The prices for building your own transformer converter and rotary converter are pretty rough estimates.
I can tell you right up front, that if you have a big motor on a simple hard to start machine, it will be a lot cheaper to build the transformer converter. The reason is the size of the idler motor you would have to purchase. To salvage dealers a big running motor must be worth a lot. They know what a motor is and they are real proud of the one you need. We can run a 25 hp motor with a 20 to 25 kva transformer compared to the 75 hp idler motor you would need.

Transformers are different. Nothing sexy about a big lump of iron. Usually the bigger it is, the less it will cost. Who is going to be out buying a used 30 kva 3 phase transformer? Electricians make big money and don’t have time to scrounge around for a used one.

Size of the motor

converter will run





Ronk add a phase















your motor

10 horse 3,500 1,500 3.500 1,400 600 1,500 575
20 horse 5,200 2,900 6,000 2,800 1200 3,000 1,200
30 horse 8,000 4,500 8,000 3,300 1500 4,000 1,600
40 horse 10,000 5,000 12,000 5,000 1500 4,000 1,800



This above table is a approximation of prices. Notice why I recommend the American Rotary company. Look at the price of the homemade converter compared to buying their panel and using your motor. To me that seems like the best deal. How cheap you can make one always depends on how cheap a motor you can find. I little leg work and patience and you got a pretty nice deal for a good price. 

A note on sizing the converter in the above chart. If you have a hard to start load you could easily have to go one size larger. The prices pretty much double when you do that, so be aware of what you are going to run.

Here is a page by American rotary on proper sizing. Pretty much all the manufacturer’s have one.

American Rotary’s page on sizing the rotary converter.

Phase Perfect is a bit different in that the 10 hp unit will run a 10 hp motor.

As you can see sizing is a big deal.
As you can see the Ronk Add-A-Phase is more expensive then a Phase Perfect! This leads me to believe they are sold to industries and governments. No small business or hobbyist is going to spring for that.

The conclusion:
Personally it is a trade off between American Rotary and Phase Perfect.

I used to recommend Phase Perfect to anyone who contacted me and was not a candidate for building their own converter. Phase Perfect was my first choice. I didn’t like the rotary converter manufacturers for not admitting they lacked starting power and don’t balance perfectly.

But American Rotary seems to be working on those two issues.

There are still some questions about sizing the converters and what loads can they run.
See this page to view contradictions in sizing requirements.
American Rotary’s page on sizing the rotary converter.
This is the same link as the one a paragraph up. Sizing it right is critical, that is why I am emphasizing it.

Below is a list of things I would be considering if I was advising someone on which type of converter to use.

Some of the video’s on the American Rotary site show large shops with lots of machines. When I watched those I had the gut feeling that if I owned that shop I would prefer to have a solid massive rotary in the back running all that stuff. Why is that? Just personal opinion.

My heater AC system went out on my Volvo. Years ago there was a metal cable that went from the dash lever to the heater thing, now they have a small desk top computer in there running it. How do you fix that? This week I am soured on tech. I think that can happen to anyone. We think tech is so great until one day it doesn’t work.

Look inside the Phase Perfect and you will see something that looks like your motherboard. Stuff like that points back to the old rotary converter. Everyone would have to admit it’s rugged with no complicated parts.

An American Rotary video was on a large farm site that needed 3 phase for a pivot sprinkler. We live in a farm community and the thought of lightning strikes come to mind. If it’s out of warranty and lightning strikes it, you could be out of luck.

So what do I dislike about rotary converters? Lousy starting power, noise, and having to be on first. I show this on my videos with my home built rotary’s. What do I like about rotary converters? Convenience, once running they are pretty much plug and play, rugged and simple. I believe now, after all the testing that I did, that you need to go bigger on the rotary. Don’t skimp, size it larger then you think you need. It is just like this situation; have you ever met someone who’s complaining that he built his shop too large?

A lot of my customers needed the transformer converter because they could not get a rotary to start their machine. When you are limited by how much current you have to your location, you need every advantage you can get. I had people in Ireland and Australia say the same thing; the transformer converter was what allowed them to run a machine,

Take the elevator motor story that Ronk talks about. If someone wanted to run an elevator I can’t image why they would use a rotary over a transformer converter if the price was the same. The transformer converter would be ideal for this, instant on and no noise.

Air compressors are another example. The vacuum I had, perfect example. Why start a 30 to 50 horse motor to run a 10hp vacuum?

The Ronk Add-A-Phase, which is their transformer line, is just too expensive for the average person. And I don’t think they try to market it to hobbyists.

I can see that in smaller shops with a couple of machines, the Phase Perfect is appealing partly because of the lack of noise and the savings on electricity. Some people do complain about a high pitched whine from the Phase Perfect but that depends on how good you hearing is.

That brings up another point, the saving on electricity;
When I did all my tests of rotary’s for the You Tube videos I found that I could idle the 30 hp rotary at 6 amps with the right combination of capacitors. But that is not realistic. That is with every capacitor adjusted to give a low idle amp reading.

Then, when I readjusted the caps with the load motor running at full load, the idle amps of the rotary would be way off when it went back to idle. As high as 29 amps. So how does the rotary converter manufacturer deal with that? Maybe that is why they don’t have amp meters.

Now I want to bring up an important point here about the electricity usage.
As I have said I ran all sorts of tests with rotary converters and the transformer converter. To really delve into this I hooked up a utility electric meter to see just how much we are paying for. The good news for us is that the power company meters don’t measure reactive power. That means you won’t be paying for the reactive portion of your converter. It is surprising how this works. I would recommend you watch those videos to get a clear understanding of what you can get away with.

But! What is the responsibility of a commercial manufacturer that makes and sells thousands of these things every year?
I would say that they have a much greater burden then those of us at little home shops. I would hope that they are concerned about the wasted power and have taken that into consideration when they are designing their converters. The power that is wasted is not free to everyone. Your utility company is actually picking up the tab for that. It is just not practical for them to put the more expensive meters in that would measure it.

In the bigger shop the constant use throughout the day would negate the wasted electricity. The more time the rotary spends running under load the less waste there is.

If you have the time and want to build your own converter look at this page here where I discuss what is the Transformer Converter, one of the two types of converters you can build yourself.