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How to Choose a VFD for a Motor

There are a lot of factors to consider when selecting a VFD. Below are some factors to consider, helping you select the best option for your application. With so many options available, it can be overwhelming to choose the right one, and making the wrong choice can lead to more problems than solutions. Contact our team for additional assistance selecting your VFD.

To help you make an informed decision, here are 8 important considerations to keep in mind when selecting a VFD for your application:

1. The motor: Is your motor inverter duty rated. You’ll find this on the nameplate of your motor or in the data pack. Ensure the motor you’ll be using has the correct turndown for the speed range you want to use. Otherwise, the motor insulation will quickly wear down and ultimately, lead to motor failure.
2. Current Requirement: Firstly, take into account the Full-Load-Current. The drive’s rated current output must exceed the current required by the motor. If your load is sized by horsepower, VFD manufacturers do the math for you and provide HP ratings on their drives as well.
3. Speed range and regulation: The minimum/maximum speeds and speed tolerance required for your application will determine whether a vector motor with an encoder is required.
4. Regeneration: If your load is regenerative, i.e. it spends time accelerating/moving on its own, it will send this regenerated energy back to your drive and the drive must be capable of dissipating that power. Alternatively, you may need to size a braking resistor to prevent overloading the drive.
5. Environment: It's crucial to consider the operating conditions, such as ambient temperature, presence of gas, moisture, and dust, as well as cooling air supply. These factors will guide you in choosing the appropriate drive, enclosures, and protective features.
6. NEMA4X enclosures offer the highest degree of protection for your drive – equivalent to IP66. This means that the enclosure is dust tight and protects against high pressure water jets. These are often used in washdown applications.
7. Heating: The temperature of the motor or controller is affected by ventilation and losses. Operating self-ventilated motors at reduced speeds may lead to higher temperature rises, requiring derating or forced ventilation.
8. Additional Protection: Electric motors equipped with variable frequency drives face the potential danger of bearing damage caused by an accumulation of current in the rotor that discharges through the shaft. This discharge not only harms the lubrication and bearing surfaces but also generates detrimental vibrations that ultimately lead to bearing failure. Consequently, the motor's overall lifespan is significantly reduced, resulting in a profound impact on productivity and substantial costs for equipment repair and downtime. Introduce a solution to divert the current in the shaft away from the bearings, achieving this with the aid of a grounding brush or ring. We highly recommend utilizing AEGIS grounding rings when connecting a variable frequency drive with a motor.
9. Expected Delivery Time: Once you’ve determined the right variable speed drive for your application, it’s time to source it. In the unfortunate event that your preferred brand is backordered, it’s often feasible to cross-reference an alternative with the same exact specifications. Sourcing an alternative to your preferred brand may result in a faster delivery date, allowing you to maintain your project schedule. However, keep in mind that every VFD brand leverages different operating systems and there may be a small learning curve when working with a new brand.

By considering these factors, you can confidently select the right variable frequency drive for your specific application, ensuring optimal performance and efficiency.

Gage walks us through how to source a VFD in the video below.

What is a Variable Frequency Drive?

To put it simply, VFDs (also called AC drives) are speed controllers for AC motors. Installing one for your motor can lead to significant savings on your power bills, enhanced performance, and safeguarding your valuable motor and equipment.

AC motors, particularly the induction-type ones, are the trusted workhorses in various industrial applications. They are cost-effective, reliable, and built to last, operating critical machinery under diverse conditions. However, achieving precise speed control has always been a challenge. Unlike DC motors, AC motor speed cannot be controlled by adjusting the voltage. Instead, the frequency needs to be changed, which is a more complex process. This why they are often referred to as adjustable frequency drives.

By default, AC motors operate at speeds determined by the line frequency (usually 60Hz), and controlling the speed requires a method of altering that frequency. However, since the motor's torque is influenced by the ratio between the frequency and the voltage, an effective speed controller needs to adjust them simultaneously. Learn more about how VFDs work in this article.

Where to Buy VFDs in Canada

Shop AC drives online through our Canadian website today. With over 700 SKUs and convenient filtering options, you can easily find the VFD you're searching for. Our VFDs are distributed from Edmonton, Alberta; Toronto, Ontario; Montreal, Quebec; and Langley, British Columbia. Most VFDs will be delivered within 1-5 business days when shipping within Canada.

Contact our team for support through phone (800-890-7593) or email (customerservice@emotorsdirect.ca).