Optional cooling fans need some common sense
First, buy the general knowledge of the cooling fan:
In the purchase of fans generally have to understand the following necessary information:
★ fan size.
★ determine whether the fan is DC or communication.
★ fan supply voltage value. For example: AC 220V, 110V, 380V. DC 5V, 12V, 24V, 36V, 48V.
★ fan bearing form, ball or oil.
★ fan air volume, speed. For example, how many cubic meters per minute, or how many cubic feet per minute.
★ wind pressure value.
Second, on the bearing:
Oil bearing (Sleeve Bearing)
The traditional DC brushless fan motor design, is the fan rotor (referred to as the rotor) and its axis through the oil bearing, referred to as SLEEVE bearings, pivot fixed in the center of the motor stator, the rotor and the stator to maintain a proper The gap between the shaft and the bearing must also exist between the gap, it will not die deadlock and can not run; and the motor stator structure part (referred to as the stator), after the power input, the rotor and the stator Between the induction magnetic field lines, and the control of the drive circuit to run the fan motor. Therefore, the traditional fan motor structure, only a fan rotor and a motor stator and a drive circuit, and by the hub and the bearing of the hub, with the magnetic field induction and operation.
1. With the advantages of oil bearing
A. Resistance to external impact, damage caused by transport less;
B. Cheap (compared with the ball bearing, the price difference is very large.
2. With the shortcomings of oil bearing
A. The dust in the air will be sucked into the motor core due to the operation of the fan motor, mixed with the lubricating oil stored around the bearing into the sludge, and the operation noise,
B. Bearing diameter easy to wear, shorter service life;
C. Can not be used on portable products;
D. Bearing and shaft gap between the small, the operation of the motor activation effect is poor;
A Motor running shaft and bearing friction generated by the high temperature gas, due to the bearing at both ends of the oil ring, the Chinese Division hindered, can not rule out the formation of nitrification, easy to block the shaft and the bearing gap, hinder the smooth operation of the motor.
Ball bearing
Ball bearing is the use of round metal beads running, belonging to the point of contact, it is easy to activate the operation. Coupled with the ball bearing with the use of the spring, so the spring bracketing BALLBearing outside the metal ring, leaving the weight of the entire fan rotor is located on the ball bearing, and indirectly by the spring brace, it can be used in different directions , The angle of the portable products, but still have to prevent falling, so as not to damage the ball bearing, resulting in noise and life with the damage.
1. The advantages of using ball bearings
A. Metal beads are part of the point of contact, it is easy to activate the operation;
B. Can be used in portable products that are often operated at different placement angles and orientations (but to prevent wrestling or falling);
C. Longer service life (compared to oiled bearings).
2. With the shortcomings of ball bearings
A. Bearing structure is quite fragile, can not withstand the impact of external forces;
B. When the motor rotates, the rolling of the metal beads produces a greater noise;
C. The price is high, can not compete with the oil bearing at the cost price;
D. Ball bearing the source and the number of demand, not easy to control;
A Ball bearings use the flexibility of the spring and make it more difficult to assemble.
Third, the fan works:
DC fan works:
According to the right-hand rule, the conductor through the current, the surrounding will produce a magnetic field, if the conductor placed in another fixed magnetic field, it will produce suction or repulsion, causing the object to move. Inside the fan of the DC fan, attach a magnetized rubber magnet in advance. Around the silicon steel sheet, the axis part of the winding two sets of coils, and the use of Hall sensor components as a synchronous detection device to control a group of circuits, the coil to the axis of the two groups of turns working. The silicon steel sheet produces a different magnetic pole, which produces a repulsive force with the rubber magnet. When the repulsion is greater than the static friction force of the lice fan, the fan leaves naturally. As the Hall sensor module provides a synchronization signal, the fan leaves so that it can continue to operate, as to its direction of operation, according to Fleming right hand rule.
AC fan works:
AC fan and DC fan difference. The former power supply for the exchange, the power supply voltage will be positive and negative, unlike the DC fan power supply voltage must be dependent on the circuit control, so that the two groups of turns to work to produce different magnetic field. AC fan due to power frequency fixed, so the silicon steel chip to produce the magnetic pole change speed, determined by the power frequency, the higher the frequency the faster the magnetic field switching speed, theoretically the speed will be faster, like the number of DC fan pole more speed faster principle same. However, the frequency can not be too fast, too fast will cause activation difficulties.
Fourth, on the noise:
The noise of the fan is measured in background noise less than 15 dBA without reverberation. The fan to be tested runs in free air and dispose of a noise meter from the air inlet.
The noise level of the fan is usually plotted at the octave of the sound pressure level (SPL). The effect of the change in decibels (dBA), as shown in the following signs:
A> 3 dBA almost no feeling
B> 5 dBA feel out
C> 10 dBA feel twice as loud
Noise level:
A> 0 ~ 20 dBA very weak
B> 20 ~ 40 dBA weak
C> 40 ~ 60 dBA moderate
D> 60 ~ 80 dBA loudly
E> 80 ~ 100 dBA very loud
F> 100 ~ 140 dBA deafening
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5, on the air volume:
Air volume unit (click: air volume pressure automatic conversion table)
CFS: Cubic Feet Per Second, cubic feet per second (ft3 / s)
CFM: Cubic Feet Per Minute, cubic feet per minute (ft3 / min)
CMS: Cubic Meter Per Second, m ^ 3 / s (m3 / s)
CMM: Cubic Meter Per Minute, m3 / min (m3 / min)
CMH: Cubic Meter Peter Hour, m3 / h (m3 / h)
L / s: Liter Per Second, L / s (L / s)
L / min: Liter Per Second, liter / min (L / min)
Six, on the static pressure:
Static pressure unit
N: Newton, 1n = 0.101097Kgf
Pa: Pascal, Pa = N / m ^ 2
mmAq: Aq = Aqua (water column) abbreviation, mmAq also known as mmH2O; 1mmAq = 1Kg / m ^ 2
Atmospheric pressure; atmospheric pressure equal to 760mmHg at 0 ℃ dry state pressure.
Because the weight of mercury is 13.5947 times the water, so an atmospheric pressure equal to 10332mmH2O pressure
bar: 1 bar = 0.00001 Pa = 10-5 Pa
Air volume
Air volume, Air quantity (Air volume, Air quantity), usually Q (m * 3 / min) for the amount of gas in the inhalation of air called air volume, fan, also known as air volume. (Capacity) gas according to its pressure, temperature and change the volume, so mention the amount of air discharge, be sure to note the pressure and temperature of the place, so called the amount of air intake.
* Standard status Air:
Temperature 20 ° C, atmospheric pressure 760mmHg, humidity 65% ??of the humid air as the standard air, then the unit volume of air weight (also known as the specific weight) is L2Kg / m * 3
* Benchmark state air:
Temperature 0 ° C, atmospheric pressure 760mmHg, humidity 0% of the humid air as the standard air, then the unit volume of air weight (also known as the specific weight) is 1.293Kg / m * 3. Expressed in Nm * 3 / min
Seven, IP rating:
The IP rating is a set of physical criteria defined in IEC 60529 (BVSEN 60529: 1991). IP levels are expressed as two digits (eg IP55). The first number defines the protection level of the contact and the particles, and the second number defines the protection level for the water.
* Insulation class reference:
Insulation material system is estimated by the National National Manufacturers Association (National Electronics Manufacturers Association) The maximum allowable operating temperature is as follows:
? T (oF) = [T (oC)] (9/5) + 32
The permissible temperature rise is based on the reference ambient temperature of 40 ° C. The operating temperature is the reference ambient temperature + the allowable temperature rise + coil allowance "hot spot".
The following example temperature tolerance rating F: 40oC + 105oC + 10oC = 155oC.
General motor operating temperature should not be used on top of the maximum, every rise of 10oC may cause the motor life to be reduced by half.
Temperature Tolerance Level B is commonly used for 60 Hz and US motors. Temperature Tolerance Level F is commonly used for international and 50 Hz motors.