February 2007

TECHNOLOGY COMPARISON:

AC, DC & BLDC MOTORS

AC or DC? Brushed or Brushless?

DC Motors provide high power in a small package. Oriental Motor manufacturers a wide range of AC and brushless DC (BLDC) products. So why choose one technology over the other? There are several key differences between the different technologies.

Motor Construction

Brushed DC motors depend on a mechanical system to transfer current, while AC and brushless DC motors use an electronic mechanism to control current. The brushed motors have a wound armature attached to the center with a permanent magnet bonded to a steel ring surrounding the rotor. As the brushes come into contact with the commutator the current passes through to the armature coils.

AC induction motors and BLDC motors do not depend upon the mechanical system (brushes) to control current. The AC and BLDC motors pass current through the stator (electromagnet) which is connected to AC power directly or via a solid-state circuit.

In AC induction motors the rotor turns in response to the "induction" of a rotating magnetic field within the stator, as the current passes. Rather than inducing the rotor in a brushless DC motor, permanent magnets are bonded directly to the rotor, as the current passes through the stator, the poles on the rotor rotate in relation to the electromagnetic poles created within the stator, creating motion.

Efficiency

The efficiency of a system is defined as the amount of output received, as a percentage of what was input into the system. Therefore, when we talk about the energy efficiency of brushless DC (BLDC) motors, we are saying that we can obtain a relatively high amount of mechanical power, in return for the electrical power that we use.

Brushed DC Motor Construction

AC Motor Construction

BLDC Motor Construction

All three technologies have power loss in the form of I²R losses. DC motors utilize permanent magnets so none of their energy needs to be used in the creation of an electromagnet as in AC motors. The energy used by AC motors to create the electromagnet decreases the efficiency of the AC motor in comparison to the DC motors.

At the same time, BLDC motors are considered more energy efficient than brushed DC-motors. This means for the same input power, a BLDC motor will convert more electrical power into mechanical power than a brushed motor, mostly due to absence of friction of brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve.

A BLDC motor, for the same mechanical work output, will usually be smaller than a brushed DC motor, and always smaller than an AC induction motor. The BLDC motor is smaller because its body has less heat to dissipate. From that standpoint, BLDC motors use less raw material to build, and are better for the environment.

Brushed DC Motor

BLDC Motor

Service and Maintenance: DC vs. BLDC

Brushed motors are not only larger than their brushless counterparts, they also have a shorter service life. The brushes in the brushed motor are usually made of carbon or graphite compounds which wear during use. These brushes will require maintenance and replacement over time, so the motor will need to be accessible to ensure continued service. As the brushes wear the not create dust but noise caused by the rubbing against the commutator. Brushless Motors have longer service lives and are cleaner and quieter because they do not have parts the rub or wear during use.

Speed Stability

Hall-effect sensors built in the BLDC motor detect the change in polarity from an N pole to an S pole as the rotor is spinning. Based on the time between state changes, the rotor’s speed is determined. This information is then fed to the drive circuit to adjust the speed of the switching sequence.

High Speed Operation

Brushed and Brushless DC systems provide flat torque over a wide speed range while AC motors often lose torque as speed increases. Oriental Motor has several BLDC packages offering speed control ranges as low as 3 rpm to as high as 4,000 rpm.

NEW! BLH SERIES BRUSHLESS DC SPEED CONTROL SYSTEM

BLH Series

The NEW BLH Series Brushless DC Speed Control system combines a compact, powerful brushless DC speed control motor with a 24 VDC, board-level driver. The new system is RoHS compliant and features a
wide range of gearing options including the new Flat, Hollow Shaft gearheads. In addition, the new series offers advanced functionality including a new Acceleration/Deceleration Time Setting Function.

The BLH Series is available in frame sizes from 1.65 in. up to 3.54 in. with output powers between 1/50 HP and 1/8 HP. The compact driver offers a wide range of advanced functions including: instantaneous stop, acceleration/deceleration time setting function and alarm output. The driver also allows speed control via any of the following methods; internal potentiometer, external DC voltage or optional external potentiometer.

NEW! Flat, Hollow Shaft Gearhead

The BLH Series features the new Flat, Hollow Shaft Gearheads. These new gearheads allow for even more space saving by allowing the gearhead to be coupled directly to the application as well as providing right-angle mounting of the motor/gearhead combination.

The Flat, Hollow Shaft Gearheads also provide higher torque in the upper gear ratios. While the parallel gearheads exhibits a saturation of permissible torque at high gear ratios, the flat hollow shaft gearhead enables the motor torque to be fully utilized.

Long Life Gearheads

Both the flat hollow shaft and parallel shaft gearheads for the BLH Series are rated for 10,000 hours* which is twice the life of a conventional gearhead.

*5,000 hours for gearhead equipped with 1/50 HP geared motors.

In addition to the BLH Series, Oriental Motor offers a wide range of brushless DC products to fit the needs of a wide range of applications. For more information click on the product series below or visit the Brushless DC section of our online product catalog.

Product Series	Voltage Input	Output Power Range	Variable Speed Range	Rated Torque
BLH Series	DC	1/50 to 1/8 HP	0.5 ~ 15 to 100 ~ 3000 r/min	0.44 to 600 lb-in
AXH Series	DC	1/50 to 1/8 HP	0.5 ~ 12.5 to 100 ~ 3000 r/min	0.4 to 260 lb-in
BX Series	AC	1/25 to 1/2 HP	0.015 ~ 15 to 3 ~ 3000 r/min	0.9 to 350 lb-in
BLF Series	AC	1/25 to 1/6 HP	0.4 ~ 20 to 80 ~ 4000 r/min	0.89 to 601 lb-in
AXU Series	AC	1/75 to 1/8 HP	0.56 ~ 11 to 100 ~ 2000 r/min	0.4 to 260 lb-in
FBL II Series	AC	1/10 to 1/6 HP	1.5 ~ 15 to 300 ~ 3000 r/min	2.2 to 260 lb-in

MOTION CONTROL QUESTIONS? ASK AN ORIENTAL MOTOR ENGINEER

Oriental Motor's Engineering Team is just a click away. Send your motion control questions to Oriental Motor's engineers and we'll publish their response in an upcoming issue of New Motion.

Q: I have a DC motor in my system and it runs very hot. My end customer wants to reduce the motor heat. What can I do?

A: Consider the option of going to Brushless DC motors. Brushless DC motors are more efficient than brushed motors, therefore they generate less heat. Since the windings are on the stator, heat is dissipated quicker in Brushless DC.

Each issue, our Engineering Team will answer our reader's motion control questions. From how to use a stepping motor to proper motor sizing techniques and specific applications, ask an OM engineer and get your answer directly from the source. Our engineers are dedicated to continuous research and development in motion control technology. E-mail your motion control question to newsletter(Please be sure to include your e-mail address and contact information so our Engineering Team can follow up on your question.)

Visit our "Frequently Asked Question (FAQ)" section online.

Oriental Motor also offers 1-800 Technical Support. Our Technical Support Team is qualified to answer a wide variety of questions. Call toll free 1-800-GO-VEXTA (468-3982) to speak with an Oriental Motor associate or e-mail techsupport