Rotary Phase Converters: 3 HP to 200 HP

What Is a Rotary Phase Converter?

A rotary phase converter uses a specially wound idler motor and a control panel to generate true, balanced three-phase power from a single-phase electrical supply. Unlike static converters or VFDs, a rotary phase converter produces real three-phase voltage across all three legs — the same quality of power you'd get from the utility company.

The idler motor inside the converter acts as a generator: it takes in single-phase power, converts it to mechanical rotation, and outputs balanced three-phase power that can run any industrial equipment. This is why rotary phase converters are the preferred choice for CNC machines, air compressors, HVAC systems, grain dryers, irrigation pumps, and machine shop equipment — they deliver clean, stable power that protects sensitive electronics.

How a Rotary Phase Converter Works

1. Single-phase power enters the converter panel — your standard 240V single-phase supply feeds into the unit
2. The idler motor starts spinning — the control circuitry energizes the motor, which spins up to full speed in seconds
3. Three-phase power is generated — the spinning motor generates the third phase of power, creating balanced voltage across all three legs (L1, L2, L3)
4. Your equipment runs normally — the converter outputs true three-phase power to your equipment, just like utility three-phase service

The entire process takes about 3–5 seconds from power-on to ready. Once the converter is running, you can start and stop your equipment as many times as you want — the converter stays on and delivers continuous three-phase power.

NL Series vs. PL Series — Which Rotary Converter Is Right for You?

Rotary Phase Converter Pricing

All prices include free shipping to most U.S. locations. Ships from 50+ warehouses — typical delivery 1–5 business days.

How to Size a Rotary Phase Converter

The sizing rule is simple: take the HP of your largest motor and double it. That's the converter size you need.

• Standard loads (CNC, pumps, fans): 2x the motor HP
• Hard-starting loads (compressors, hydraulics): 2.5x the motor HP
• Multiple machines running simultaneously: Add all HP together, then double

Dual Zone Phase Converters — For Large Installations

For installations requiring 40 HP or more, our Dual Zone system uses two converters in tandem for maximum performance and redundancy. If one zone needs service, the other keeps running. Dual Zone systems are popular for machine shops, large HVAC installations, and agricultural operations running multiple pieces of heavy equipment.

Advantages of Rotary Phase Converters Over Other Solutions

Rotary Phase Converter FAQ

How loud is a rotary phase converter?

About the same as a washing machine. The idler motor produces a steady hum. Most customers mount theirs on the wall near the electrical panel and barely notice it's running.

Does the converter run all the time?

Most customers leave it running during working hours and turn it off at the end of the day. With the NL series, you flip the breaker. With the PL series, you push the stop button. The converter draws very little power when no equipment is running — about the same as a large ceiling fan.

Can I run a rotary phase converter on a generator?

Yes, but the generator needs to be oversized — at least 3x the converter HP in generator watts. A 20 HP converter needs about a 50kW generator. Call us and we'll help you size it.

What maintenance does a rotary phase converter need?

Almost none. Check the motor bearings every few years. Keep the ventilation clear. That's it. These are industrial motors designed to run for decades.