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Synchronous AC Motors

By January 9, 2019December 26th, 2021Briefs

What is it?

Synchronous AC motors are motors that rotate at a speed that is perfectly “in sync” with the frequency of the electric current supplying it. This is different than the much more common induction AC motors, which rotate at a speed out of sync with the current (known as “slip”).

How does it work?

A unique internal structure and special electronic control circuits allow these motors to operate at a speed perfectly matching the incoming current’s frequency. They are more efficient than other motor types, including electronically commutating motors (ECMs). ECMs must convert incoming AC current to DC using a rectifier, but synchronous AC motors do not require this which leads to efficiency gains.

What are the most appropriate applications?

The best applications are in commercial refrigeration, such as evaporator fans for coolers and freezers in grocery stores. They tend to have long run hours and the energy benefits are multiplied by also saving energy on the refrigeration system.

What are the savings?

As an example, switching from a permanent-split capacitor (PSC) evaporator fan motor, which is common, to a synchronous (like the Q-SyncTM) motor can result in an efficiency gain of 44% or 218 kWh per year for a typical 12-watt output evaporator fan. The efficiency gain over ECMs is 27%[1], or 44 kWh per year. Those savings are about 339 kWh and 68 kWh when refrigeration interactions are included.

What are the non-energy benefits?

Synchronous motors tend to have longer lifetimes than other motors due to fewer moving parts when operating at constant speed. Further, they have much higher power factors than other motors.

What is the cost?

Costs depend on size, but small motors for commercial refrigeration typically cost about the same as ECMs. Costs are $140 for 38-50 watt motors, $120 for 12-watt motors[2].

What is the status/availability of the technology?

This technology is available through select vendors, with QM Power being the sole provider of Q-Sync motors. Q-Sync motors are only available for 12 or 38-50 watt motors.

What kinds of incentives/programs are available?

Right now, this technology would be evaluated under the Custom Rebate program. Incentives will vary depending on project and customer specifics.

[1] Savings numbers and values used in custom analysis come from:


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