# Electronics fan speed regulation: linear or exponential?

Discussion in 'Modding' started by mottl3y, 15 Dec 2006.

1. ### mottl3yWhat's a Dremel?

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Hi folks, long time no post.

I've been looking around at DIY/home-made fan controllers. They all seem to change the speed of the fan vs. temperature in a linear fashion (when exponential seems more appropriate to me).

I assume there is a particular reason for this, I'm just not sure what it is.

Possible problems:
-how on earth do you do exponentials on a PIC?
-the voltage range used to control a fan is too small to necessitate anything other than linear.

m.

2. ### hydro_electric_655Dremelly Dude

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Ya you got the second on eright. You couldn't have really any temp var. and yo uwould end up with super high voltage which you ahve a limited range.

3. ### XiachunyiWhat's a Dremel?

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Think of it this way, how do you perform multiplication using only addition? Just perform successive addition.

How do you perform exponentiation? Just perform successive multiplication or... successive addition in groups.

4. ### fat-tonyWhat's a Dremel?

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If you're ok with powers of 2, you can use the bitshift << operator.

5. ### cpemmaEcky thump

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You're looking at this from the wrong angle. With a temperature-controlled environment, it takes a fan speed/voltage/flow of X to produce equilibrium at temperature T.

PC fan controllers are a compromise, they don't try to hold the temperature steady whatever the heat being produced, they'll let it creep up to a still-safe level by which temperature the cooling device is running at full speed.

So you need control such that the fan will still start at minimum temp and be full speed at maximum temp. Roughly linear in between may give the most pleasing overall noise relationship, though it might be generally quieter under "normal" use to ramp the speed up more gently in the first half of the temperature curve then rapidly at higher temperature - an exponential curve as you say. It's just not easy unless you use a uPC.

6. ### OtakuHawkWhat's a Dremel?

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I find it's just more effective to get 120mm fans that are tolerably quiet at full speed.

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