Engineering Notes by Oriental Motor

Better Motor Alternatives for Variable Speed Pumps

[fa icon="calendar"] May 6, 2019 8:03:26 PM / by Johann Tang

Johann Tang

What motors do you use for pumps?  For variable speed pump applications that typically use 3-phase AC induction motors with variable frequency drives (VFDs), there is another type of motor that can transfer fluids more consistently and help reduce footprint.

Let's take a look at 2 typical motor challenges in pump applications.

Challenge 1 - transfer fluids more consistently

For many pump applications, such as fluid control, one would imagine that speed consistency is pretty important.  You want to be able to control the rate of fluid transfer to a certain degree so the same result can be expected.

VFDs are able to control the speed of the pump motors by regulating the frequency of the supplied voltage.  While there are several types of control methods available, the open loop scalar volts-per-Hertz (V/f) control method is arguably the most common implemented VFD control method in basic applications (ie: pumps and fans) and has a speed regulation of +/-2~3%.   If the application requires more precise speed control, encoders can be added to close the loop, or vector control can be utilized.  However, encoders are expensive, and vector control requires a more advanced CPU on the VFD.   

It's also important to note that in either open loop scalar (V/f) or vector control, motor response is not guaranteed due to lack of physical feedback.  Load fluctuations, which can be caused by a difference in type of fluid or viscosity,  can slow the motor down and result in inconsistency in transferred volume.

Solution 1 - BMU speed regulation

BMU Series motor and driver

The built-in hall-effect sensor feedback in brushless motors and the speed regulation capabilities of the dedicated driver provide a cost-effective alternative to VFDs.

Learn More About BMU Series

Oriental Motor's BMU Series brushless motor systems have a speed regulation of +/-0.2% max.  As a comparison, the BX II Series brushless motors with encoder feedback have a speed regulation spec of +/-0.05% max (at rated speed); regardless of fluctuations in load, voltage, or temperature. Speed regulation comparison

In some cases, the effective speed range can be extended with brushless motors compared to VFD-driven AC motors.  80~4,000 RPM (50:1 speed ratio) is offered by standard brushless motors while 90~3,600 RPM (40:1 speed ratio) is offered by VFD-driven AC motors.  The constant torque output of brushless motors provides consistent performance throughout the entire speed range, and the limited duty torque boosts motor torque for dynamic acceleration or deceleration.  

3-phase Induction Motor with VFD Brushless Motor with Dedicated Driver
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Challenge 2 - reduce energy consumption

For applications without restraints in mass or energy consumption, using AC motors with VFDs would be fine.  However, since brushless motors are more efficient than AC motors, they can be much more compact and help reduce energy consumption.

Brushless motors significantly reduce power consumption as the use of permanent magnets in the rotor prevents secondary loss from the rotor, which provides a large decrease in power consumption (approx. 27%) when compared to AC motors.   Power consumption comparison - BMU vs AC

Brushless motors are smaller and lighter compared to three-phase induction motors of the same output specifications.  For example, when 200 W (1/4 HP) motors are compared, the overall length of the brushless motor is 83 mm shorter and the mass is 3.2 kg lighter.

Motor size comparison - BMU vs AC

Pump Size Comparison

Pump with AC Motor Pump with Brushless Motor
Pump with AC motor Pump with BL motor
Solution 2 - BMU reducing size, energy consumption
BMU Series motor and driver

With higher efficiency, brushless motors are more compact, consumes less power, and do not need built-in cooling fans to lower its temperature for continuous duty operation.  The lack of a fan also helps prevent dust dispersion or foreign particles from contaminating products such as food, cosmetics or resin.

Learn More About BMU Series

Watch how easy it is to operate a BMU Series motor.

Looking for something different?  Perhaps one of these will work for your application.

Other Speed Control Options
VFD with
Vector Control
Brushless Motor with Advanced Driver Brushless Motor with Encoder Stepper Motor with Speed Control Driver
Fuji Inverter (VFD) BLE2 Series driver and motor BX2 Series brushless motor and driver CVK-SC Series motor & driver

Related Content:

Choosing the Right Motor: AC Gear Motor vs. Brushless DC Motor, Which is Better?

Brushless DC Motor vs. AC Motor vs. Brushed Motor?

Too Valuable To Keep Secret: The Power of Brushless DC Motors (BLDC Motors)

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Topics: AC Motors, Speed Control, VIDEOS, BLDC Motors, Pumps, Application Examples

Johann Tang

Written by Johann Tang

Johann Tang is a Product Specialist at Oriental Motor USA Corp. with 20+ years of experience in sales, technical application support, and training of various types of fractional horsepower electric motors, gear motors, actuators, drivers, and controllers. Feel free to ask him questions on Linkedin.

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