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Why does AC wall fan slow down when voltage drops?

From what I remember about AC motors, one cannot lower the voltage to slow it down- it must be the frequency that is lowered. However, I have an AC wall fan which slows down when the voltage in my house drops. Whenever a microwave or similar high-current load is on the voltage drops slightly and I always notice the fan motor slowing or speeding up when the load turns on and off. Why is it doing this? I am assuming that it is not good for the fan but seeing that it has been running this way for years it must not be that detrimental to it...


AC motors as the name implies is run using AC/alternating current.. this is best represented by a sinusoidal graph with time in the horizontal axis and voltage or current in the vertical axis.. motors uses the current to produce power which drives whatever it is that's attached to the motor.. power is directly proportional to either voltage or current.. because of this, low voltage/current produces low power and vice versa.. this is the reason why your fan slows down when voltage drops..

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