Page 11 - Industrial Technology EXTRA 19th July 2021

coil is fixed in the stator and the permanent magnet
is rotating with the shaft. The moving
magnetic field around the stator
results in iron losses, where an
electrical current is induced within
the iron laminations of the stator.
This current generates heat,
adding to the heat
already generated in
the coil. Iron losses
are proportional to motor speed; they coil temperature
aren’t significant at lower speed but doesn’t exceed its maximum
become greater at high speed and at this admissible temperature. This means that
stage, torque must be reduced. the duration of the operation must be limited.
Whether brush or brushless technology is Slotless brushless motors are particularly well-
required, the thermal challenge is the same: keep suited for short peak torque as the design makes it
the coil temperature below its maximum, possible to typically reach 10 times the motor’s
admissible temperature. Creating a contact of high maximum continuous torque with 10 times higher
thermal conductivity with the motor can improve current. At the same time, slotless coil designs can
heat dissipation. This can be achieved by increasing accumulate a great quantity of thermal energy
the surface exchanging heat with the ambient air, thanks to their higher thermal capacity, making it
for example. In most cases, a motor installed on a possible to provide high torque during a short
metallic base, mounted from its front face onto a duration without relying on heat dissipation.
metal stand that will help drain heat out of the Another way to manage heat to improve motor
motor, provides better cooling than having the performance is to design stators with an integrated
motor surrounded by air only. air path so that the air flow can carry heat away
Motor designers and manufacturers like from the motor. This focuses on the heat convection
Portescap engage with customers early in their inside the motor, rather than designs that rely
development process to assess the dissipation mainly on heat conduction. It might also be possible
capability of a motor or motor/gearbox assembly. to integrate a fan on the motor shaft, driving airflow
Taking the specific application setting into account, through the motor body as it is operating.
the design and configuration can then be optimised The lifetime and performance of a miniature
for best motor performance. motor is closely linked to successful heat
Some applications require high torque for a management. The solution depends on the
short duration. Industrial power tools, such as challenges of each individual application setting and
screwdrivers, require speed during the run-down the success factors required, be that achieving a
phase and then peak torque during the tightening given torque to realising maximum efficiency. To
phase, which typically lasts up to a second. For a design a system most capable of achieving your
peak torque requirement, a motor can be supplied specific mini motor application goals, the input of
with a current that exceeds the motor’s maximum an experienced design team is valuable for success.
rated continuous current as long as the www.portescap.com

July 2021 • INDUSTRIAL TECHNOLOGY EXTRA • p11