Stepper Motor Operating Temperature and Humidity

For stepper motor specification, the operating temperature range for stepper motor should be 0～50℃ while humidity should be 20%～90%RH, and storage temperature should be -20～70℃ while humidity should be 15%～95%RH. Now, environmental requirements for stepper motor usage are as follows:
Requirements on Temperature:
The standard of stepper motor insulation material is grade UL B, which indicates that heat resistance of motor insulation system is within 130℃. In consideration of motor temperature difference between inside and outside and safety coefficient, the surface temperature of motor is required below 100℃. In consideration of the normal room temperature within 40℃, temperature rise of motor coil should be controlled within 80K. If the temperature of motor coil is beyond the limit value of insulation system, the elements in it, such as enameled wire of motor coil, insulation slot, PCB board, etc. may be burnt out easily, resulting in motor failure (generally, open circuit occurs, sometimes, short circuit also occur). Parameters for motor rated current is mainly calculated based on the heat that motor can absorb. If the operating temperature of motor is too high, it is necessary to reduce temperature rise by reducing operating current of motor, finally controlling the motor inside heat control within the acceptable range of insulation system. For example, if the environment temperature is 60℃, temperature rise of motor should be controlled within 60K. The insulation materials of most stepper motor manufactures all meet grade B standard and other insulation materials with higher grade are almost impossible to use or have too high cost, so in the usage places where are with high operating temperature, the more realistic selection is to control the temperature rise of motor, which is to achieve the aim by strengthening the heat dissipation conditions or reducing the operating current of motor.
The condition that the temperature of stepper motor is too high will not only affect the safety of insulation system, but also affect the stability of permanent magnet. The permanent magnet will be demagnetized as the temperature rises, reducing the working torque. The condition that the temperature of stepper motor is too low will cause solidification to grease on bearing, resulting in loss of bearing lubrication function, so it is necessary to consider choosing cryogenic bearing when the temperature is below 0℃. The method is available that the user first energizes the motor to make it warms up until the motor reaches the required operating temperature and then rotates before the motor starts to run, but corresponding setting needs to be made on start process of equipment.
Requirements on Humidity:
The stepper motor should meet the humidity requirements, which is mainly to avoid the condensation in motor. Silicon steel plates on rotor outer surface and stator inner surface of stepper motor has no other anti-rust measures except anti-rust oil application during processing. If the humidity is too high, condensation occurs easily on surface, causing rust. Because the clearance between rotor and stator of stepper motor is very small, the rusty spots may make rotor be seized, resulting in motor failure. On the other hand, the condition that humidity is too high can also affect the insulation characteristic of insulation material, which has little effect on small size stepper motor whose normal operating voltage is very low while has noticeable influence on those stepper motor whose drive voltage is high.
Reference Materials: Grade Description for Motor Insulation Materials and Heat Resisting Materials
UL classifies the certification grade of insulation system into Y A E B F H C from low to high according to heat-resistance temperature.
The followings are the maximum allowable operating temperature（℃）for each heat-resistance grade, which can be as the brief description for insulation materials of heat-resistance grades.

1. For grade Y material, the maximum temperature is 90℃, which has such insulation structure that is composed with untreated spun cotton, silk, etc. or their combination, so it is not necessary to do any treatment before using.
2. For grade A material, the maximum temperature is 105℃, which has such insulation structure that is composed with treated or soaked dielectric medium, such as spun cotton, silk or paper, etc. soaked in transformer oil or their combination.
3. For grade E material, the maximum temperature is 120℃, which has such insulation structure that is composed with synthetic organic film, synthetic organic enamel, etc. or their combination.
4. For grade B material, the maximum temperature is 130℃, which has such insulation structure that is composed with mica, glass fiber, asbestos, etc. which are bonded, soaked or applied by proper resin and other inorganic materials, proper organic materials or their combination.
5. For grade F material, the maximum temperature is 155℃, which has such insulation structure that is composed with mica, glass fiber, asbestos, etc. which are bonded, soaked or applied by proper resin and other inorganic materials, proper organic materials or their combination.
6. For grade H material, the maximum temperature is 180℃, which has such insulation structure that is composed with mica, glass fiber, asbestos, etc. which are bonded or soaked by proper resin (e.g., organic silicon resin) and other inorganic materials, proper organic materials or their combination.
7. For grade C material, the maximum temperature is 180℃, which has such insulation structure that is composed with mica and glass fiber which are bonded, soaked or applied by proper resin and untreated mica, ceramics, quartz, etc. or their combination.