It seems like fans are always off-high-medium-low. Is there a reason for this?
In: Engineering
One of my electrical engineering professors explained this to us.
The main reason is safety. A multi-speed fan is an electric motor with several windings. By using different windings, you get different torque and speed.
An electric motor winding is essentially an inductor, and inductors react in specific ways to changes in current and voltage. When you first apply a voltage to an inductor there’s a current surge, almost like it was a short circuit.
The high speed windings have the lowest such start-up current surge. They are put first so that the surge and associated heating of the wires is minimized.
I believe (but am not certain) that doing it this way is also a UL requirement.
I’ll take a stab at it.
0 no power
3 = highest speed which means the least resistance to the motor.
Each step down (3 -> 2, 2-> 1), you apply more resistance. Which decreases the power to the motor.
Basically, they could go up in speed but it would increase the complexity of the circuits driving the motor.
because you use the cheapest motor you can for the fan and at max power, it barely has enough torque to get the fans going from stop. once the fans are spinning, then you can reduce power/voltage and lower the fan speed.
Protects the motor.
When I was a fairly young & newish car owner, I burned out a fan motor in the cabin air circulation because I’d consistently turn it on low (from off).
The mechanic who replaced it was kind enough to explain to me that he saw lots of this exact thing, for that exact reason, and recommended starting a fan by turning it to high first, then reducing to the desired speed.
Have followed his advice ever since and never burned out another fan motor, whether in a car or home fan.
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