"220V Cooling Fan" and DC fan distinction. The former AC power supply, the power supply voltage of alternating positive and negative, unlike the DC fan power supply voltage is fixed, it must rely circuit control, so that two sets of coils in turn work to produce different magnetic fields. "220V Cooling Fan" because of the power frequency is fixed, so the rate of change of magnetic steel sheet produced is determined by the power frequency, the higher the frequency magnetic field to switch the faster, the faster the speed will theoretically, the more the number of poles as DC fan speed more principle as fast. However, the frequency can not be too fast, too fast will cause activation problems. Application on our computer radiator are DC fan. A good general "220V Cooling Fan" mainly on the amount of wind, speed, noise, length of life, what kind of fan bearings.