How do you adjust the speed of a DC fan, and what’s the difference between it and an AC fan?
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News Center
Release time:
2021-02-02
Typical DC motors can achieve speed regulation by adjusting either the excitation magnetic field or the armature voltage—these two methods are also the most effective ones. The armature is a critical component that plays a pivotal role in the motor's conversion between mechanical energy and electrical energy. In generators, the armature is the part that generates electromotive force—for example, the rotor in a DC generator or the stator in an AC generator. In electric motors, the armature is the component that produces electromagnetic force—for example, the rotor in a DC motor.
What’s the difference between DC fans and AC fans?
1. Working principle:
The operating principle of a DC cooling fan is as follows: It converts electrical energy into mechanical energy through direct current voltage and electromagnetic induction, thereby driving the fan blades to rotate. The rotation of the fan blades is continuously driven by the alternating switching of coils and ICs, which in turn induce the magnetic ring to rotate.
The operating principle of an AC fan is that it’s driven by an AC power source, where the voltage alternates between positive and negative. The fan generates a magnetic field entirely without relying on circuit control. The power supply frequency is fixed, and the rate at which the magnetic poles change in the silicon steel laminations is determined by this frequency. The higher the frequency, the faster the magnetic field switches, and theoretically, the faster the rotor speed will be. However, the frequency cannot be too high—otherwise, it will become difficult to start the fan.
2. Structural Composition:
The rotor of a DC cooling fan includes the fan blades, which are the source of airflow; the fan shaft, used to support and balance the rotation of the blades; the rotor magnetic ring, featuring permanent magnets that play a crucial role in driving the switching of magnetic poles and adjusting the rotational speed; and the outer frame of the magnetic ring, which secures the magnetic ring in place. Additionally, the rotor assembly incorporates supporting springs, which help stabilize the entire rotating assembly. The motor section generates the rotational direction and determines the magnitude of the rotational speed—key factors for precise control. This design boasts excellent speed regulation performance and simple control.
The internal structure of a single-phase AC fan consists of two coil windings: one is the start winding, and the other is the run winding. These two windings are connected in series, forming three connection points. The common terminal is the point where the two windings are connected in series; the end of the start winding is the start terminal, and the end of the run winding is the run terminal. In addition, a start capacitor is required—typically with a capacitance ranging from 12 μF—and a rated voltage of usually 250 V. The capacitor has two terminals: one connects to the end of the start winding, and the other connects to the end of the run winding, forming a delta configuration. The power supply (which does not require distinction between live and neutral wires) is connected as follows: one wire is connected to the end of the run winding (which is also connected to one terminal of the capacitor), and the other wire is connected to the common terminal. The ground wire is connected to the motor housing.
3. Material characteristics:
Material of the DC cooling fan: It is made of alloy material and can operate continuously for over 50,000 hours. The internal DC structure includes a transformer and a main control board (which comprises a frequency conversion circuit, rectification and filtering circuit, amplification circuit, etc.), and is unaffected by voltage fluctuations, thus ensuring a longer service life.
The internal structure of AC fans is primarily based on transformers. Most AC fans use domestically produced discharge needles, typically made of tungsten or stainless steel. If the voltage fluctuates excessively, it can shorten the transformer's service life.
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