MOTORS
Overheating in hand-held tools can be a serious
problem – especially in surgical applications.
Urs Kafader, technical training manager,
maxon addresses the issue.
22 » MARCH 2020 » WWW.MADEIN.IE
There are several factors that cause DC
motors to become hot – something that
should be avoided especially in hand-held
devices. Oversizing the motor can help.
However, there are other options as well.
When a DC motor is operated close to its
nominal torque, it may become very hot. In
continuous operation, the winding can reach temperatures
up to 155 °Celsius, which results in a housing temperature
around 120 °Celsius. No surgeon would want to work with a
tool like that, not even at half the temperature.
What can be done about it? Leaving friction aside, there are
two main sources of loss that cause a motor to heat up:
electrical heat and iron loss.
Electrical heat losses
Electrical heat loss depends on the load torque, which is
proportional to the current. The loss increases with the
square of the current. High currents close to the nominal
current cause temperatures that are unsuitable for contact
with human skin. However, if a motor is running at only half
its nominal current, then temperatures are more moderate
(usually under 50 °Celsius) and suitable for contact with
human skin. For motor selection, this means: Oversize it! The
above considerations are based on continuous operation,
THE
HEAT
IS ON
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