I have always wondered by most (but not all) fans have a switch that must pass through high first, then medium and low.
I am wondering if anyone knows the reason for this, and I would like to posit a hypothesis.
I wonder if it is because going straight to low could result in a situation where the motor (especially if older, dirty, etc) would not be able to overcome the static friction, causing an overheat. But by passing through the higher settings first, the increased power (torque) ensures that the motor gets moving.
Of course, this is not supported by the presence of push-button fans that can go straight to the low setting.
Does anybody know the reason for this counter intuitive arrangement? Does the hypothesis stand up to scrutiny?
I’m not an expert on motors. But I believe it is less stressful on the motor windings.
When you first apply a voltage to a motor, the impedance is very low. Low impedance = high current = high power dissipation in windings. The impedance increases as the motor RPM increases.
When the fan is set to high speed, and you turn it on, the motor spends less time in the “low impedance” mode. Which means the windings spend less time in “high dissipation mode.” When the fan is set to low speed, and you turn it on, the motor spends more time in the “low impedance” mode. Which means the windings spend more time in “high dissipation mode.”
Most fan dial controllers really do have off, slow,medium ,fast, in my experience.
The fan controller on the wall here can be rotated 360, so you can go from fast to off to slow… ,which means if its off you can go to either slow or fast…
I think the OP is thinking about ceiling fans, which have pull chains that do go “off”, “rocketship”, “normal”, and “slow”. (Nobody I know uses the fast setting because it seems like either your attic or the fan is going to win.) And it does seem kind of weird.
All of the fans I’ve seen here (and that’s a lot as every house seems to have at least eight or ten of them) have push-button controls, ordered 0-1-2-3, which seems to contradict the theory that the ordering on dial-controlled fans is necessarily ‘backwards’ for functional reasons.
I don’t think higher power dissipation would be a problem for a short time it takes it to get up to speed; it takes some time for them to heat up due to heat capacity, similar to how I can hold a 5 watt power resistor dissipating 10 watts for a while (more than a few seconds; these are often rated at 10x rated power for 5-10 seconds because they don’t immediately reach rated temperature) before it gets too hot to hold. Also, the lower speed setting usually adds an extra winding in series, reducing current flow by increasing impedance. Some motors, especially shaded pole motors in smaller fans, are also marked as “impedance protected”, meaning that even an indefinite stall won’t cause it to overheat because current flow stays low enough (not all of the current results in dissipation either due to inductance; 1 amp flowing through a winding with 10 ohms of resistance dissipates 10 watts, even though it draws 120 VA at 120 V).
I have a portable fan with LEDs that display the speed and setting. If I turn on the fan while its set on Low, the Medium light comes on until the blades are up to speed, then it goes down to Low. Since they went to the trouble to program it that way, it would seem they think it is better for the motor.
Well, that’s the problem with all the pull chain fans I’ve ever met - they go off, high, medium, low, so half the time you miss “off” and have to go through it again, only this time maybe it’s just “low” and you watch to see if it’s slowing down any…
I prefer it to A/C.