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DC Brush Motor Engineering

Selecting a DC Brush Motor

MinebeaMitsumi’s DC Brush motors are cost competitive, easy to use, high precision motors, with a broad range of applications ranging from automotive, office automation, industrial equipment, home electronic appliances, consumer and audio visual equipment. Our unique development and supply system enable you to select from a wide range of sizes and outputs that vary from compact, to thin, to high torque motors, with a combination of characteristics to suit your particular application requirements.

When selecting the appropriate motor to meet your size, usage, applications and standard load/rpm requirements, we recommend that you select the optimum motor characteristics for the application, usage conditions, structure of the actual motor installed and temperature range, among others.

Motor output is basically proportional to the voltage used and the size of the motor, therefore, selecting the largest size allowable is best for power consumption and the life of the equipment. Even when using the same size motor, the output and current consumption, starting torque and cogging torque will vary depending on the type of magnet used and the winding specifications. We recommend you review the relevant characteristics for each type of motor.

After reviewing the information enclosed, order a sample and test it in the actual application. Product samples and engineering consultations are available to you. Contact us directly to connect with an engineer and discuss your current requirements.

DC Brush Motor Construction

dc brush assembly diagram

How to Read DC Brush Motor Performance Curves

S-T: Speed-Torque characteristics illustrate the relationship between speed and torque

I-T: Current-Torque characteristics illustrate the relationship between current and torque

Numerical values such as Ts (Starting Torque), Is (starting current), No (no load speed) and Io (no load current) are necessary to find out S-T (Speed-Torque) characteristics and I-T (Current-Torque) characteristics in evaluating motor performances.

No: No Load Speed

Io: No Load Current

Ts: Starting Torque

Is: Starting Current

dc brush motor performance curve

Factors Affecting DC Brush Motor Performance

Factors Conditions Changes in Characteristics Motor Performance
Voltage (V)
(to increase)
Other conditions
being equal
If all conditions remain equal and only
the voltage is increased or decreased
the resulting change to “no load speed”,
“starting torque” and “starting current”
is in direct proportion to the change in
“voltage.”
voltage affect DC motor speed
Magnetic Flux (Φ)
(to increase)
Other conditions
being equal
If only the “magnetic flux” is changed
and all other conditions remain the same,
the change in “torque” is in direct
proportion to the change in “magnetic
flux” and the change in the “no load
speed” is inversely proportional to the
change in “magnetic flux”, while there
will be no change in the “starting current”
and “torque constant” in direct proportion
to the change in “magnetic flux”.
magnetic flux distribution
Wire Diameter (d)
(to decrease)
Other conditions
being equal
If only the “wire diameter” changes with
all other conditions being equal, the
change in motor performance such as
“starting torque” and “starting current” is
in direct proportion to the change in the
square of the change in “wire diameter,”
while there will be no change in “no load
speed” and “torque constant.”
wire diameter dc motor
Number of Turns per Slot (Z)
(to decrease)
Other conditions
being equal
If only the “number of turns per slot”
increases with all other conditions being
equal, the change in motor performance
such as “no load speed” and starting
current” decreases in direct proportion,
while there will be no change in “starting
torque” and “torque constant.”
turns per slot dc motor

The torque constant (Kt: Nm/A) of a motor is a parameter for sizing and controlling motors showing a linear speed / torque relationship. (Both DC brush type and brushless motors exhibit this linear performance curve relationship.)