Sizing Help for Single Motor, Multiple Motor, Resistive, and Computer Loads
HP x 2.8 = approx. current (amps)
kW x 1.34 = HP
three-phase kVA = volts x amps x 1.73
kW x 3.75 = approx. current (amps)
Single Motor Loads (ex. Milling machine, blower, bandsaw, lathe, pump)
There are no restriction on how small of a motor can be run with any given size converter.
Easy Start (no flywheel, clutch, little resistance/inertia, 1-2 times full load current on start-up)
Formula: Round up equipment HP one size
Medium Start (machine inertia, medium resistance, 3-4 times full load current on start-up)
Formula: Round up equipment HP one size
Hard Start (flywheel, no clutch, Start against load, 5-6 times or locked rotor current on start-up)
Formula: Minimum 2.0 times equipment HP.
Hard Start/Run (elevators, hydraulic pumps under continuous load etc.)
Formula: use 3.0 times equipment HP
Frequent start (reversing, heavy running loads)
Formula: add one size or 25% to correctly determined phase converter size.
Multiple Motor Loads (ex. Two milling machines, dust collector &
Formula: Use the Single Motor Loads formulas to determine the largest converter needed for
each piece of equipment. Your converter cannot be smaller than this. For multiple motor
starting, size each piece and add the converter sizes together. (this can usually be avoided)
Next, the other equipment (totaling no more than 2 times the rated HP of the converter) may
be started and run assuming the loads are not heavy.
Note: Combined motor loads and resistive loads must be sized by subtracting the resistive
current from the converters full load current rating. Combinations exceeding the converters
hp rating should be wired using the multiple motor load wiring diagram.
Resistive Loads (ex. Heater, transformer, welder, power supply
Formula: Divide the current rating of the equipment (Use the equipment's 230 Volt amperage)
by 0.6 and round that number up to the nearest converters full load current. This maintains a
5% voltage balance.
Note: If only KW are know, estimate the current by multiplying the kW by 3.75.
kW x 3.75 ~ current (amps)
CNC / Computer Controlled Equipment (ex. CNC Machining/Turning Centers, PLC's, EDM)
These applications need to operate with balanced voltage between each of the three legs.
All American Rotary Rotary Phase Converters are CNC balanced.
Formula: 2.0 times the rated equipment horsepower (spindle horsepower) unless extra large axis
motors are used. Increase size for non-standard equipment, i.e. forth axis, bar feeder etc.
Formula: Multiply the machine kW by 2.7, then round up to the nearest HP converter
Note: Do not combine other loads with these converters unless they are small compared
to the loads rating.
9. What is a Soft Start and does my American Rotary brand rotary phase converter have it?
10. How does the rotary phase converter start?
11. Does the rotary phase converter need a lot of electricity to start?
12. Can I start my rotary phase converter and my equipment at the same time?
13. How big of a circuit breaker do I need to start my rotary phase converter?
14. How much in-rush current does my rotary phase converter see?
15. Is wire size critical for starting my rotary phase converter?
16. Does the rotary phase converter use a lot of electricity to run?
17. How noisy is a rotary phase converter?
18. Can I run the rotary phase converter all the time?
Mounting & Installation Questions
19. Can I fasten the control panel to the generator?
20. What is the best way to mount the generator and control panel?
21. Can my rotary phase converter be mounted outdoors?
22. What temperatures can the rotary phase converter be run in?
23. Does altitude affect the performance of a rotary phase converter?
24. Can I mount my rotary phase converter sideways or upside down?
25. What size wire should I run to my rotary phase converter?
26. What size circuit breaker should I use?
27. What do I need to ground?
28. What size should my ground wire be?
Question 1: What is a rotary phase converter?
Answer: In brief, a rotary phase converter is an electrical machine that efficiently produces 3-phase power from a single phase power source. A rotary phase converter generates one line from a generator motor and combines that with your 2 single phase lines to produce true 3-phase power.
Question 2: How does a rotary phase converter work?
Answer: A 3-phase generator (a three-phase motor will work to some extent) is started across a single phase line by creating a temporary third phase. Once the generator is up to speed, a special circuit switches from the starting circuit to the running circuit. The first two windings in the generator keep the rotor spinning as current and a voltage is induced in the third winding. This voltage is conditioned in the control panel and output to your equipment.
Question 3: What does CNC mean?
Answer: CNC stands for Computer Numerical Control. CNC equipment has a computer that can be programmed to run the operation of the machine. Computer operated machines are very voltage sensitive. All American Rotary All Purpose/CNC phase converters are voltage balanced to within +/-5% to safely operate CNC equipment. CNC equipment are becoming very popular as used machines can be purchased for pennies on the dollar as large companies upgrade to new CNC equipment.
Question 4: How long will my rotary phase converter last?
Answer: Our rotary phase converters have been designed and tested to last as long as possible. Current testing at approximately 15,000 hours under normal operating conditions, showed no reduction in performance. For normal use 4 hours per day, this is about 25 years. If a failure does occur, components have been designed to be easily replaced.
Question 5: What is the difference between the GENTEC generator and a
regular three-phase motor?
Answer: Soft Start
Question 6: What single phase voltage can the rotary converter run on?
Question 7: Why 3-phase?
Question 8: What is the difference between single phase and 3-phase?
Question 9: What is a Soft Start and does my American Rotary brand rotary phase converter have it?
Question 10: How does the rotary phase converter start?