Application of thermal protector in fan
As a subdivision application field of motor products, fans have been more and more widely used.
Specific applications include ventilation of buildings, residential or outdoor, air circulation and
purification of dust-free clean workshops, 5g terminal equipment and heat dissipation of wind
power generation, etc. As an electrical equipment that works continuously for a long time or
even 24 hours, the fan has the phenomenon of overload and heating and burning the motor
coil during locked rotor. The installation of overheat protector is a necessary solution. This article
will specifically describe the selection and precautions of installing overheat protector. Due to
different structures, fans are divided into external rotor and internal rotor. Due to different power
supply, fans are divided into DC and ac. the standard focuses on AC external rotor fans.
Part I selection of thermal protector for external rotor fan
Volume requirements: because the coil of the outer rotor fan is very small and the structure is relatively compact,
a miniaturized thermal protector is required in the installation position. EBM papst and Xerox, the world's largest
fan manufacturers, both choose button products with a diameter of about 10mm and a thickness of no more than
5mm. Such products are easier to plug into the interior of the coil or the gap between the coil and the shell.
Moreover, the shell of the button type product is made of metal, and the circular shell is also closely fitted with
the coil, so it can withstand large coil shaping pressure. The electronic products of standard safety are st01 series.
Rated voltage and rated current: normal thermal protector can pass the rated voltage of 250V, and 277v will be
required for UL certification; In terms of current, 5A st01 product can be selected for low power, and 10A S01product
can be selected for high power. The selection standard is that the locked rotor current of the fan is not greater than
the rated current of the protector.
Disconnection temperature: generally, it is 5-10 degrees lower than the maximum withstand temperature of coil
insulation grade. For example, class E insulation grade is the best, and the high temperature is 130 degrees.
Select 120 degrees or 125 degrees thermal protector, and class F insulation grade is 155 degrees.
Select 145 degrees and 150 degrees protectors.
Service life: the locked rotor time of normal fan is 18 days, and the temperature rise and drop cycles are about 2000 times.
The service life of thermal protector is generally 6000~10000 times, which can meet the requirements of locked rotor life;
According to the different use environment, some wind turbines have the opportunity to increase the current for 5000 life
tests, and st01 and S01 series can also meet this demanding requirement;
Manual reset requirements: some fans do not need to be reset automatically if they are overheated and trip protection
during use. You can choose to use the manual reset model of st01+ptc, which has built-in PTC heater. After the protector
contact switch circuit is disconnected, the PTC heater circuit will be immediately connected to let PTC heat up and bake
two pieces, so that it cannot be reset automatically.
Part II precautions for use
For the use of insulating sleeve, since the shell of thermal protector is charged, insulating sleeve must be added in
general use. The head of insulating sleeve cannot be too sharp, otherwise it will cut the enameled wire and cause coil
short circuit. The head of S01 series protector adopts ultrasonic welding technology to seal the sleeve part of the head,
which enhances its anti insulation voltage performance. At the same time, the head adopts a unique process to make its
head very smooth and will not cut the enameled wire. If the actual use has more stringent requirements, the head can
also be made into an epoxy encapsulated form, making its head more smooth and more convenient in the installation
process, which will not cut the enameled wire and meet the insulation and voltage withstand requirements.
Shaping pressure: S01 and S06 series are metal shells, which can withstand 50kg of anti pressure. If you need more anti
pressure, you can customize a thicker shell to solve it.
Some fan products will have a vacuum impregnation process in the manufacturing process, which has higher requirements
for the sealing performance of the protector. S01 series adopts a unique sealing technology.
When the vacuum pressure reaches -0.08mpa, it can achieve a paint entry rate of 1%~0.3%. If it reaches -0.03mpa, there
is basically no probability of impregnation. However, the fluidity of insulating paint in actual use also has a lot to do with it.
Specifically, customers need to provide the model of paint to do corresponding experiments. In the delivery inspection of
electronics, there is a sampling inspection link of dipping paint to prevent this problem to the greatest extent.
For the thickness requirements of the protector, many fan models are different, and the coil winding turns are different.
If the number of winding turns is large, the volume of the coil will be larger, which will overstock the installation space
of the protector. S01 series has ultra-thin version to meet the higher requirements of customers.