Static vs Rotary vs Digital Phase Converter: Which Is Right for You?

If your shop, farm, or facility runs on single-phase power but your equipment demands three-phase, you need a phase converter. The question isn't whether you need one — it's which type. Static, rotary, and digital phase converters each solve the same fundamental problem, but the way they generate that third leg of power differs dramatically. That difference affects everything from power quality and equipment longevity to noise levels and long-term operating costs.

This guide breaks down exactly how each type of phase converter works, what it's best suited for, and which one matches your application. No sales pitch — just the technical facts you need to make the right call.

How It Works

A static phase converter uses capacitors and a start relay to momentarily generate a third phase of power. During startup, the capacitors create a phase-shifted voltage that gets a three-phase motor spinning. Once the motor reaches operating speed, the converter drops out of the circuit — the motor continues running on only two of the three phases.

This is the critical limitation: a static converter only provides true three-phase power for a fraction of a second during startup. After that, the motor runs on single-phase power routed through a three-phase connection. The result is roughly two-thirds of the motor's rated horsepower.

Best Use Cases

• Starting simple three-phase motors (fans, pumps, basic compressors)
• Light-duty applications where full power isn't required
• Situations where budget is the primary constraint
• Single-motor installations with predictable, steady loads

Limitations

Price range: $500–$2,500 depending on horsepower rating. The RD series static converters cover most common applications. While the upfront cost is attractive, the power limitations often mean you'll outgrow a static converter quickly — and replacing it with a rotary later costs more than buying the rotary upfront.

How It Works

A rotary phase converter uses an idler motor — essentially a three-phase motor running without a direct mechanical load — combined with a control panel to generate continuous, balanced three-phase power. Single-phase input feeds the idler motor, which mechanically generates the missing third phase through electromagnetic induction. The rotating mass of the idler motor acts as a flywheel, smoothing voltage fluctuations and producing clean, stable output.

Unlike a static converter, a rotary produces true three-phase power continuously — not just during motor startup. The voltage across all three legs is balanced and consistent, which is exactly what three-phase equipment is designed to receive.

Best Use Cases

• Machine shops — lathes, mills, surface grinders, saws
• Woodworking shops — planers, jointers, wide-belt sanders
• Agricultural operations — grain dryers, irrigation pumps, feed mills
• Commercial facilities — HVAC systems, elevators, industrial compressors
• Multiple machines — one rotary converter can power your entire shop
• CNC equipment — balanced power protects controllers and drives

Why Rotary Dominates

The rotary phase converter is the workhorse of the industry for good reason. It handles any load type — resistive, inductive, or capacitive. It runs multiple machines simultaneously without voltage sag. It delivers full-rated horsepower to every connected motor. And when properly sized, it provides utility-grade three-phase power that's indistinguishable from what the power company delivers.

Our NL and PL series rotary phase converters range from $749–$14,780 depending on capacity. The NL series offers excellent value for straightforward applications, while the PL DualZone series adds enhanced voltage regulation for shops running a mix of motor loads and sensitive electronics.

How It Works

A digital phase converter (also called an electronic phase converter) uses power electronics — IGBTs, DSP controllers, and sophisticated firmware — to synthesize the third phase digitally. Instead of relying on a spinning motor, it uses solid-state components to construct a mathematically precise sine wave that matches the utility phases in voltage, frequency, and phase angle.

The GPX series digital converters take this a step further with cloud-based monitoring, allowing you to track power quality, voltage balance, and system status from any device. Built-in diagnostics alert you to issues before they become problems.

Best Use Cases

• CNC machining centers — the cleanest power available for sensitive servo drives
• Medical and laboratory equipment — where power quality is non-negotiable
• Noise-sensitive environments — no idler motor means virtually silent operation
• Precision manufacturing — where voltage balance must be within 1%
• Remote or monitored installations — cloud connectivity enables remote oversight

Considerations

Digital converters deliver the highest power quality available in a phase converter, but that comes at a premium. GPX digital phase converters range from approximately $2,500 to $15,000+ depending on capacity. They're also typically sized to a single machine or a defined load — unlike a rotary, which can flexibly handle varying loads across multiple machines. For shops that need to power a variety of equipment, a rotary is usually more practical and cost-effective.

After decades of helping customers convert single-phase to three-phase power, we can say with confidence: the rotary phase converter is the right choice for the vast majority of installations. Here's why:

Versatility. A properly sized rotary converter doesn't care what you connect to it. Motors, CNC controls, VFDs, welders, lighting — it handles them all. Static converters can't do this. Digital converters can, but at two to three times the cost.

Scalability. Buy one rotary converter sized for your panel, and you can add machines as your shop grows. No rewiring, no additional converters. That flexibility alone saves thousands over the life of the installation.

Proven reliability. Rotary technology has been the backbone of phase conversion for over 40 years. There are rotary converters installed in the 1980s still running today. The technology is simple, robust, and field-serviceable — no circuit boards to fail, no firmware to update.

Value. When you compare cost per horsepower of balanced three-phase output, rotary converters deliver more usable power per dollar than any other option. Our NL series starts at just $749 — less than many static converters that deliver inferior power.