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Phase Converters 101


Phase Converters...

Phase Converters convert single phase power to industrial 3-phase power. Different types of phase converters exist, and they each have a certain method to achieve the conversion. Because American Rotary offers every type of phase converter available...Rotary, Digital, CNC, and can always be sure that we will recommend the method that is preferred for your specific application!

Rotary Phase Converters are a cost-effective and efficient means to start and run 3-phase motors on single phase power at 100% of their rated horsepower. Rotary phase converters can be used with heavy loads, resistive loads, multiple motor loads, multiple speed loads, and CNC equipment.

Phase Converter 101

General Information about phase converters:

There are three major categories of phase converters:

  • Static Phase Converters these straightforward units will start a 3 phase load but run it only under single phase power. The load is limited to about 2/3 of its rated capacity.
  • Rotary Phase Converters these much more sophisticated units create true three phase power supply, often more precise than utility-supplied three phase power. There are two types of Rotary Phase Converters:
    • Basic providing excellent three phase power with voltage on all three lines being +/- 10% of one another.
    • CNC a more precise system that keeps tolerance +/- 5% or less, which is appropriate for more sensitive loads including CNC machinery.
  • Digital Solid State Phase Converters often sold under the brand name Phase Perfect, these units use a digital signal processor to produce virtually perfect three phase power for extremely sensitive applications.

What are static phase converters?

Static phase converters can start 3-phase motors, but cannot be used as CNC phase converters. Once an electric motor has been started, the static phase converter will disengage and allow the electric motor to run only on single-phase power. The resulting power is unbalanced and the equipment is only able to operate up to around two-thirds its rated horsepower before forcing too much current through the winding of the motor. This unbalanced output and the resulting "single-phasing" of a 3-phase motor is hard on 3-phase equipment and may shorten the life of the motor itself. All three phase applications that require smoothly balanced 3-phase output, or will be operated at or near 100%, will require rotary phase converters, CNC phase converters, or digital CNC phase converters to operate effectively. While static phase converters work fine in some applications, they tend to be hard on 3-phase equipment and their use is limited.

What are CNC phase converters?

CNC phase converters are phase converters that meet the requirements of 3-phase CNC applications by maintaining at least a +/-5% voltage balance. American Rotary offers Phase Perfect® digital phase converters as well as GENTEC's complete line of CNC balanced rotary phase converters. Designed with a custom-balanced soft-start three-phase generator, pure sine wave output, and power factor correction produces extremely smooth and balanced 3-phase output. GENTEC American Rotary CNC phase converters are recommended for all types and brands of CNC equipment and applications.

What are digital phase converters?

Digital solid-state phase converters, or simply, digital phase converters are the latest advancement in CNC phase converter technology. Phase Perfect® has led the industry in this state-of-the-art technology using a digital signal processor, or DSP, to monitor the phase conversion process and then adjusting the input and output continually of the CNC converter to maintain a perfectly balanced power condition under all load conditions.

Who can use a Rotary Phase Converter?

Rotary phase converters are most commonly used in commercial, industrial, home or hobby settings to power three phase equipment when utility 3-phase power is either too costly or not available. Rotary phase converters convert single-phase power into balanced three-phase power. Rotary phase converters are a very cost-effective way to power three-phase CNC equipment, and they come with simple and easy to use installation manuals. Rotary phase converters are rated using the maximum horsepower that they can handle. Due to the consistent voltage balance, the electric motor will operate at or near its full horsepower capacity. The output is custom balanced to meet the requirements of CNC equipment as well as other loads.

Should I use a CNC phase converter even if my equipment is not CNC?

The voltage balance obtained with CNC phase converters is optimal for any application. The more balanced the output of the rotary phase converter is, the better a piece of equipment will operate and the longer it will last. Unbalanced voltages seen with non-CNC phase converters can be hard on the equipment they are running as well as cause other undesirable conditions - such as excess noise and poor performance.

Is a rotary CNC phase converter right for my application?

By balancing the output, rotary CNC phase converters can be used on any type of equipment especially voltage sensitive equipment such as CNC machining centers, milling machines, lathes, PLC's, EDM's, and any other type of equipment that relies on balanced power input. You will want to verify that the rotary CNC phase converter is rated for the specific kilowatts (kW) that your equipment or machine requires. Our technical support team is available at 1-800-458-3687 to answer any questions you might have and to help you properly size the right CNC phase converter for your specific application.

Determine the load type of the application, and then consult the chart below. 
Please call us toll free at 1-800-458-3687 for sizing assistance and/or a professional recommendation.

  • Easy - no flywheel, clutch, little resistance/inertia, 1-2 times full load current upon start-up
  • Medium- machine inertia, medium resistance, 3-4 times full load current upon start-up
  • Hard - flywheel, no clutch, starts against load, 5-6 times, or locked rotor current upon start-up
  • Very Hard- elevator, hydraulic pump, equipment under continuous load etc
  • Frequent Start- instant reversing, heavy running loads
  • CNC - turning centers, PLC's, EDM, CNC machining
  • Resistive - heaters, transformers, welders, power supplies etc.
Rotary Phase Converter Largest HP Motor Load Maximum CNC Load Max Total Load Combined Equip Operating Cost
HP kW Easy Med Hard Amps kW HP* Amps kW ($ per/hr)
3 2.2 2 2 1.5 0-5 0-1.5  1.5  9  2.7  $.01
5 3.7 3 3 2 0-8 0-2.4  2.5  15  4.5  $.015
7.5 5.6 5 5 3 0-11 0-3.3  3.75  22  6.6  $.02
10 7.4 7.5 6 5 0-15 0-4.5  5  28  8.4  $.03
15 11.2 10 10 7.5 0-20 0-6  7.5  42  12.6  $.045
20 14.9 15 12 10 0-25 0-7.5  10  54  16.2  $.06
25 18.6 20 15 10 0-30 0-9  12.5  68  20.4  $.07
30 22.4 25 20 15 0-42 0-12.6  15  80  24.0  $.09
40 29.8 30 25 20 0-55 0-16.5  20  104  31.2  $.12
50 37.3 40 35 25 0-70 0-21  25  126  37.8  $.15
60 44.7 50 40 30 0-80 0-24  30  150  45.0  $.18
80 58.7 60 50 40 0-110 0-33  40  208  62.4  $.24
100 73.3 80 70 50 0-140 0-42  50  252  75.6  $.30
120 88.0 100 80 60 0-160 0-48  60  300  90.0  $.36
* total spindle horsepower: total kW of the machine must be less than max CNC load kW.
† combined loads do not include CNC or voltage sensitive loads.
‡ cost based on national average of $.10/kWhr.
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