Static Versus Rotary Phase Convertors

      A big rotary phase converter will give you room to grow as you add more equipment. February 13, 2009

For a 3 phase table saw at 5hp to run on single phase do I need a rotary or static phase converter?

Forum Responses
(Cabinetmaking Forum)
From contributor G:
With a rotary you will still have a "5 hp" machine, or very nearly so. With a static converter you will lose 1/3 of the hp so you will have a "3.3 hp" machine, or very nearly so. Presuming that we are talking about a 10 or 12 inch cabinet saw the 3.3 will be just fine unless you make a habit of sawing really heavy planks.

With the rotary you have a running cost of the dummy motor, and with the static you have some losses there also. I don't actually know which will eat up more electric at the meter. My guess is the rotary. Perhaps someone else knows for sure. I have never found a chart giving either idle or running draw through a rotary. I do know that if the company has designed the dummy motor for specific use as an idler it will produce a greater efficiency, due to better core saturation.

The rotary has an advantage of allowing you to add other 3 phase machines, so long as the maximum motor size being started at any time is not greater than 5 hp (Presuming that you buy a 5hp rotary converter) and that the total load is under 10 hp. The static can only be shared with another machine if it is in the same range as the original motor AND only one machine is run at a time. (Statics are fitted to the motor size, and you need one that is neither too small, nor too big, for the motor it is running.)

From contributor J:
Good info so far except that you can definitely run more than one motor on a static converter. In fact, performance improves if you do so because the largest motor starts to act like a rotary converter. I did this for years when I started and only had 1 PH power available.

From contributor P:
Get a good-sized rotary -15 hp at least, to start the inevitable widebelt addition that you haven't even dared to dream about yet. American Rotary been very good to me - five years and counting and great tech support. I'd buy another in a heartbeat!

From contributor W:
Phase-A-Matic is also a very good company with great support and they have re-conditioned units.

From contributor K:
I agree with what contributor P said. I've used both a static and a small rotary but when I added an Altendorf I shopped and ended up with American Rotary. The largest motor in my shop was a 10hp so they recommended a 20 hp. Seemed like overkill at the time but I'm glad I did it. Having a proper power plant removes the question of "how am I going to run this thing” when you’re looking at a great deal at an auction.

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