The text is a transcript of a video that explains why most electric fans have a speed selector switch with the order of off, high, medium, low. The video covers the basics of how electric motors work, especially induction motors, and how they need a rotating magnetic field to start spinning. The video also shows different types of motors and fan controls, and how they use various methods to create rotation with only one phase of electricity. The video argues that putting high first ensures that the fan will produce enough starting torque to avoid stalling, which could damage the motor or cause a fire. The video also suggests that this order is more of a tradition than a necessity, as modern fans are designed to prevent overheating or stalling. The video ends with some bloopers and outtakes from the recording.
Here are the key facts extracted from the text:
1. Fans are devices that push air around and have multiple benefits and applications.
2. Most fans run at multiple speeds, usually three, and have a speed selector switch with the order of off-high-medium-low.
3. The reason for this order is to protect the motor inside the fan and reduce the likelihood of a stall condition, which is when the motor cannot start or maintain rotation.
4. Most fans use a type of electric motor called an induction motor, which relies on a rotating magnetic field to produce torque and spin the rotor.
5. Household electricity is usually single-phase, which means it pulses on and off and does not produce a rotating field by itself.
6. To create a rotating field, fans use different methods such as shaded poles, capacitors, or start windings, which provide a temporary kickstart to the rotor.
7. Shaded poles are passive components that create a slight delay in the magnetic flux in some parts of the stator, causing a bit of rotation in the field.
8. Shaded pole motors are cheap and simple, but they produce very low starting torque, which is the force required to start spinning the rotor.
9. To ensure that the fan starts spinning, it is designed to receive the maximum power and torque when it is switched on, which corresponds to the high speed setting.
10. Modern fans have thermal protection or stator designs that prevent them from overheating or burning up if they are stalled for a long time.