Can DC motors be used at high temperatures?
07 September 2021
Those familiar with the maxon catalogue and technical specification will have noticed that there are specified maximum ambient and winding temperatures for our motors. The majority of DC motors have a maximum ambient temperature of between 85°C and 100°C, and a maximum winding temperature of between 100°C and 125°C.
Why is this?
First, the difference between the ambient temperature and maximum winding temperature. Input supply is divided into voltage (V) and current (A). The voltage determines the speed, and the current determines the torque. When in use, the current will generate heat in the winding, so when a motor is specified for operation at high ambient temperatures, it cannot be worked as hard as if it were at regular workshop temperatures – otherwise, it will burn out.
What are the problems associated with heat?
Inside the motor is a magnetic circuit generated by the permanent magnet and the electromagnet, the motor winding. Both the permanent magnet and the winding are affected by heat. The neodymium magnets start to demagnetise at around 160°C. Unfortunately, cooling the motor does not reverse the effect; it is a permanent degradation. The winding is encased in an insulating varnish, which provides stability as well as insulation. As the temperature increases above 160°C, the varnish softens and the winding can deform, resulting in rubbing, which wears away the insulation and causes a short circuit and motor failure. Very high-temperature increases can cause the varnish and insulation to melt, again resulting in a short circuit. The results are always the same: the motor is ruined...
Read the full article in DPA's September issue
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