What the use of condenser in electric fan?

Answer 1

The Condenser or Capacitor as used with a motor in an electric fan does the job of converting the single phase AC household outlet supply to a pseudo two phase supply.

The two phases of the electrical current flowing through the motor windings create a Rotating magnetic field in the motor , which pulls the rotor along with the rotating magnetic field by attraction. This causes the motor to spin spontaneously. By implication three phase Industrial motors or fans do not need such capacitor since the rotating field is inherently generated by the three phase current and magnetic circuit.

Improvement to above:

It's correct to say that the capacitor is there for starting the motor, as the AC magnetic field is rotating too fast to generate any appreciable starting torque ("push"). Calling it a 'Pseudo Two Phase" supply obscures the fact that this is a *starting* mechanism.

Some motors leave the capacitor permanently in circuit, some (mostly older) designs use a centrifugal switch which cuts the capacitor out of circuit once the motor is spinning fast enough to accelerate without the aid of the capacitor.

Improvement to following:

Be aware that the following explanation, of the capacitor charging, then giving a "kick", is *not* correct.

On an AC circuit, the capacitor is continually charging and discharging, either 120 times (60 Hz mains) or 100 times (50 Hz mains) a second. This is much faster than the motor can come up to speed. The point is that the charging/ discharging allows current to flow in the capacitor, and it's that current in the motor's starting winding that applies the starting torque to get the motor spinning.

The description *would* be true if a charged capacitor's energy was used for starting for Direct Current machines, but these motors are self-starting anyway and need no capacitor.

The analogy with an aircraft engine is strained - it's possible to get one going by *just* pushing it over top dead centre - the fuel-air fires and the motor takes off. This cannot happen with an electric motor - they need to be doing some good numbers of RPM before they accelerate to full speed/power.

The snubbing description is correct, as is the distinction in size of capacitors and purpose.

Condenser is the old term for capacitor. In a motor circuit, there are two uses for capacitors, the first is to provide extra current to get the fan motor to overcome it's own resistance to movement, the way this works is that the capacitor charges until it can supply the requisite current, then discharges, not unlike giving an air plane motor a 'kick' before it can start proper. The other use is snubbing inductive kickback. When a inductive load, such as the coil windings on a motor, are switched off, the properties of an inductor can cause a massive power surge which can damage control circuits. to mediate this problem, small capacitors are put in parallel over the load, so that the sharp 'inductive kick' has a discharge route through the capacitor (since the 'kick' is a sharp voltage spike, it looks like a high frequency signal). If the capacitor is large, it's probably used for the former, if small, the latter.