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Old 12-20-2011, 10:31 PM   #1
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Default I need to slow down a 120V muffin fan. Resistor?

If I wanted to slow down a fan (think of a PC power supply fan - but 120V) I could probably put a resistor on it. What size? I'm probably looking to run it 50% speed.

Thanks!

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Old 12-20-2011, 10:51 PM   #2
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If it's a brush motor you can do it. How many amps is it rated for?

If it's an induction motor you can't. you'd have to run it at half voltage and half frequency. I'm gonna guess it's an induction motor, because brushes would result in a short life.
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Old 12-20-2011, 11:07 PM   #3
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It is my father's and I am not looking at it now (he is 600 miles away). I can get the specs on it and post them later. Thanks!
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Old 12-21-2011, 12:46 AM   #4
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Since it's single-phase, wouldn't it be a shaded-pole motor? If so, any off-the-shelf fan speed controller (eg: from the fan section at Home Depot) would work, would it not?
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Old 12-21-2011, 02:40 AM   #5
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Hmm, what kind of fan speed controller? Shaded pole motors' speed is a function of frequency.
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Old 12-21-2011, 12:37 PM   #6
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what is a "muffin fan"?

could you just block off some of the surface area?
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Old 12-21-2011, 01:21 PM   #7
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Quote:
Originally Posted by y8s View Post
what is a "muffin fan"?
It's a catch-all for the sort of fans that you might put in the case of a PC, or which is pictured above in post #1.

The name originally comes from Gerald R. Muffin, a Scottish inventor who first designed fans in this form-factor in the early 1920s for use in

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Hmm, what kind of fan speed controller?
I'll disclaim this by reminding the audience that magnetics are not my strong suite. But from what little I have read on the subject, any triac-based controller ought to work. Clip the AC voltage and the motor will slip.
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Old 12-21-2011, 03:18 PM   #8
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Quote:
Originally Posted by y8s View Post
could you just block off some of the surface area?
Looking to make it more quiet....
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Old 12-21-2011, 04:44 PM   #9
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Quote:
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But from what little I have read on the subject, any triac-based controller ought to work. Clip the AC voltage and the motor will slip.
Triac based controllers work on brush motors. On shaded pole motors they won't let the motor reach half speed. Even if it did, the motor would probably quickly overheat.
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Old 12-21-2011, 04:51 PM   #10
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I take what I wrote partially back. Apparently some cheap shaded pole motors driving fans work OK with triac based fan speed controllers with limited speed reduction (maybe down 60% of orig speed). Watch out and check the motor for overheating. They can also hum BTW. Don't use a light bulb dimmer.

An autotransformer stepping down from 120 VAC to like 80VAC may work better. Dunno where you would get one small and cheap tho.
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Old 12-21-2011, 06:24 PM   #11
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tl;dr

Go buy a fan speed controller
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Old 12-21-2011, 06:35 PM   #12
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Almost seems cheaper and easier to go with a dc fan and a 555 to me.
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Old 12-21-2011, 06:42 PM   #13
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Quote:
Originally Posted by Tw34k View Post
Almost seems cheaper and easier to go with a dc fan and a 555 to me.
Well, yeah. Obviously if the fan in question can be replaced, the easiest course of action is just to find a new fan of the same size with the properties that you want. Even AC muffins can be ordered in all sorts of different speeds: http://search.digikey.com/us/en/cat/...ans-ac/1179729
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Old 12-24-2011, 02:10 PM   #14
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Cool link / website setup
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