Why are fan controls setup that way?

that would be … INstructions, not UNstructions…

Ok, I’ve been giving this some thought, and I’ve got a WAG: inductance. Most multi-speed fans have multiple windings. The speed is more or less determined by the current through the windings, which in turn is determined by the inductive reactance of the windings. Now, here’s the thing: when you’ve got a current flowing through an inductor, and you stop that current flow suddenly, you get a large voltage induced across it, which is proportional in strength to the inductance and opposite in direction to the original flow of current. The higher the inductance, therefore, the higher the induced EMF. This back EMF will serve to try to spin the motor in the opposite direction, so the idea is to start the motor turning on the winding with the lowest inductance, and therefore the highest speed, so as to minimize internal heating and prolong motor life when you switch speeds.

Balthisar & Algernon:

Yes, you can pass through high and med very quickly. But the fan manufacturers are taking an “all else being equal” approach. They figure that, since they can design the sequence to be anything (high-med-low, low-med-high, etc.), they may as well make it hi-med-low. This is because they assume that many (most?) users will click the switch once, wait, and then select the speed. Or they assume most people want to set the initial speed to high anyway, in order to get the air moving quickly.

The bottom line is this: the fan manufacturers want to give the motor a hefty jolt to overcome the rotational inertia at power up. This is because they often use cheap motors (e.g. dishwashing machine motors) that don’t have much torque at low excitation levels. Or they’re using a high-efficiency motor, which (coincidentally) has the same problem. If they use a motor that has plenty of torque at low speed, it will be more expensive and/or less efficient at higher speeds.

Here’s a short article on the subject:


The linked article certainly confirms your supposition Crafter_Man.

In spite of the way people in the real world can override the engineering preferences by operating the fan controls less than optimally, I guess it still makes sense to design them so that there is at least an opportunity to have a best case scenario.

BYW, I can relate to the fan motor – as a 50+ year old, I don’t have much “torque at low excitation levels” either. :slight_smile:

(bolding mine)

I resemble that remark! :wink:

You do know that they make a pill for that, don’t you? :smiley:

Did you mean to post this to the new fan control thread that was started today, rather than this 9 year old one?

Damn! :smack:
I could have sworn that was exactly what I was doing. My bad. :frowning:

Since this is an old thread that was accidentally revived, I’m going to close it.

General Questions Moderator