Fan Speed and Electricity Consumed

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    Electricity Fan Speed
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Discussion Overview

The discussion revolves around the relationship between ceiling fan speed and electricity consumption, exploring whether higher speeds result in increased power usage. Participants consider various aspects of electric motor operation, torque, and the implications of different speed control methods.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the current drawn by an electric motor is roughly proportional to the torque, which scales with the square of the speed, implying that higher fan speeds draw more power.
  • Another participant argues that at higher settings, the fan moves more air and does so faster, indicating that greater mass undergoing greater acceleration results in increased energy usage.
  • A different viewpoint questions whether the current drawn remains constant while the current reaching the motor varies, raising the possibility that reducing fan speed may not affect power usage.
  • One participant expresses concern that if the current reaching the motor is indeed different, it would imply inefficiency in speed controller design, suggesting that power would be wasted at non-full settings.
  • Another participant discusses the implications of using different speed control methods, noting that AC power typically allows for more efficient speed control with transformers, while resistors may lead to higher power losses at lower settings, yet still result in lower power draw compared to full speed.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the relationship between fan speed and power consumption, with no consensus reached on the effects of speed control methods or the implications of current draw.

Contextual Notes

Participants express uncertainty about the effects of different speed control mechanisms on power consumption and the assumptions underlying their claims regarding current draw and torque.

sanchitgangwa
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Does a ceiling fan consume more electicity at higher speeds or is the same at all speeds?
 
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Current drawn by an electric motor is roughly proportional to the torque. And for a fan, torque is going to scale roughly as a square of the speed. So yes, at higher fan speed, it will draw more power.
 
Another way of looking at it: the fan moves more air at higher settings, and moves it faster. Greater mass undergoing greater acceleration, means more enegry is being used.
 
Somewhere I read that the current drawn is the same but the current which reaches the motor is different. Does this mean there is no effect on power usage if I reduce the fan's speed?
 
Last edited:
sanchitgangwa said:
Somewhere I read that the current drawn is the same but the current which reaches the motor is different. Does this mean there is no effect on power usage if I reduce the fan's speed?
That would be a terrible way to build a speed controller. It would mean that at any setting other than full, power is being completely wasted.

Since a typical household fan will run on AC power, best speed controller will be one using a transformer. In that case, the power loss will be very small at all settings. Another way is using resistors. That would work for both AC and DC, but it would result in higher power losses, especially at low settings. Still, the power drawn at low settings will be lower than at full speed even in this case.
 

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