Fan as a long time or even 24 hours of uninterrupted work of electrical equipment, there is a phenomenon of overload work and blocked rotation heat burn motor coil, adding overheating protector is a necessary solution. This paper will specifically describe the selection of superheat protector and matters needing attention.
The first part is the selection of thermal protector for external rotor fan.

Volume requirements:
Because the coil of the external rotor fan is very small and the structure is relatively compact, a miniaturized thermal protector is needed in the installation position. Ebm-papst and Xerox, the world's largest fan manufacturer, both choose button products with a diameter of about 10mm and a thickness of no more than 5mm. Such products are easy to be stuffed into the inside of the coil or the gap between the coil and the shell. In addition, the button-type product shell is made of metal material, and the circular shell also fits the coil closely, so it can withstand large coil shaping pressure. HKW Electronics' products are HKW9700 series.

Rated voltage and current:
Normal thermal protectors can pass the rated voltage of 250V, UL certification will require 277V voltage; In terms of current, HKW9700 products of 5A are selected for small power, and 17AM products of 10A are selected for large power. The selection standard is that the fan blocking current is not greater than the rated current of the protector.
Disconnect temperature:
Generally, the maximum temperature of the coil insulation level is 5-10 degrees lower than that of the coil insulation level, such as the E insulation level is the best, the high temperature is 130 degrees, the choice of 120 degrees or 125 degrees thermal protector, the highest temperature of the F insulation level is 155 degrees, the choice of 145 degrees and 150 degrees protector. Life: The normal fan for blocking time is 18 days, heating and cooling cycle is about 2000 times, the life of the thermal protector is generally 6000~10000 times, can meet the requirements of blocking life; According to the different operating environment, some wind will increase the current to do 5000 times of life test, HKW9700 and 17AM series can also meet this harsh requirements;

Manual reset request:
some fans jump off during use if overheating protection, do not need to automatic reset back to work, can choose to use 17am+PTC manual reset type, the type of built-in PTC heating tablets, after the protector contact switch circuit disconnect, immediately on PTC heating circuit, let the PTC heating oven double feature, make its cannot be automatically reset.

The second part is the matters needing attention
The use of insulation sleeve, thermal protector because the shell is charged, the insulation sleeve must be added in general use, the head of the insulation sleeve can not be too sharp, otherwise it will cut the enameled wire, resulting in short circuit of the coil. The head of HKW9700 series protector adopts ultrasonic welding technology to seal part of the head sleeve, which enhances its anti-insulation voltage performance. At the same time, the head adopts unique technology to make its head very smooth and will not cut the enamaled wire. If the actual use has more demanding requirements, the head can also be made into epoxy encapsulation form, make its head more smooth, more convenient in the installation process, will not cut the enameled wire also meet the insulation voltage requirements.