Slowing down a fan! - Fiberglass RV


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Old 01-01-2011, 01:24 PM   #1
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Slowing down a fan!

Have any of the members purchased a Vortex fan or any thing similar that doesn't have a speed control on it ever wondered if a speed control could be added. Well I haven't tried this but just found it on line and looks inexpensive. I am getting one. I think it will work. 12 volt and all.

Manual 12V DC Variable Speed controller with Molex connector
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Old 01-01-2011, 01:59 PM   #2
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Russell, I think it should work fine. I guess it's worth the price to find out. Let us know.
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Old 01-01-2011, 02:17 PM   #3
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Hi Russ. Two ways to do it. 1) Voltage reduction-A resistive network (i.e. voltage divider) where one resistor is variable, the other includes the fan. Reducing the voltage to the fan will slow it down atleast to a point. Inefficient and could damage the fan motor. 2) Pulse width modulation- Here an electronic circuit outputs the full voltage or none . On off on off etc. The duration (period ) of on+off is always the same. If on is longer than off (wide pulse) the fan goes fast. If on is shorter than off, the fan goes slow. Always on, max speed. Most efficient way to do it. I did this to my fan.

I can't tell by the description but I bet it's PWM. Probably enough current to control a muffin fan, like the ones used on a desktop computer ( less than an amp). When it comes connect it to a digital voltmeter. The meter reading will be erratic if it is pulse width modulation and steady if it's a resistor network. Good luck, Raz
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Old 01-01-2011, 02:22 PM   #4
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Russell, I think it should work fine. I guess it's worth the price to find out. Let us know.

Comes out to $14.50 shipped. Gonna give it a try! Let you know.
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Old 03-20-2011, 11:58 AM   #5
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Originally Posted by Russell A View Post
Have any of the members purchased a Vortex fan or any thing similar that doesn't have a speed control on it ever wondered if a speed control could be added. Well I haven't tried this but just found it on line and looks inexpensive. I am getting one. I think it will work. 12 volt and all.

Manual 12V DC Variable Speed controller with Molex connector
Hi Russell, I was wondering how the speed controller worked out for you? I'm trying to do the same thing with a muffin fan but haven't found a solution. I tried a variable resistor rheostat (3 watts, 25k ohm) with a 12 volt 0.25A muffin fan but the resistor heated up too much. What I would really like to do is connect 2 of these muffin fans.

Does anybody have any suggestions? Please keep in mind that I'm electronically challenged.

Thanks, Karen
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Old 03-21-2011, 11:05 AM   #6
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I'd be a little concerned. Multi-speed fans, like my Fantastic Fan, use resistors to reduce the line voltage going to the fan motor. Putting a resistor in the line does two things: reduces the line voltage (the flow of electricity) and generates heat. To dissipate the heat Fantastic puts their resistors in a little alcove that the fan blows air through to cool them down and prevent fires.



In this pic you see the original Fantastic Fan resistors, which are the coils of wire, and an extra resistor I added for a 4th fan speed, the rectangular block-like-thing, all sitting next to an opening in the fan casing so they get a constant airflow.

Just something to think about.
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Old 03-21-2011, 12:08 PM   #7
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I think a house dimmer switch should work.
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Old 03-21-2011, 12:11 PM   #8
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I have called Fantastic Fan in the past and asked about slowing down the speed and they sent me a free kit which I installed to slow the speed down. They also sent me a reverse switch, again free, to reverse my fan. Great company to deal with.
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Old 03-21-2011, 06:06 PM   #9
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I think a house dimmer switch should work.
Attachment 34086
Those won't work on DC. They're TRIAC or SCR operated. They work on AC circuits by turning the load on at different phase points on the leading or trailing edge of the sinusoidal input waveform. Since the DC power has no phase change, you'd get no modulation.

Regards,

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Old 03-21-2011, 08:06 PM   #10
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I'd go with what Jim suggests, call Fantastic first.
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Old 03-22-2011, 01:32 PM   #11
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Thanks everyone for the suggestions. Is the fantastic fan kit a whole new switch or add-on part to the existing one? My muffin fan has no switch and is only about 4 inches square. I beleive they are used to cool computers and other electronics.
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Old 03-22-2011, 01:53 PM   #12
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Thanks everyone for the suggestions. Is the fantastic fan kit a whole new switch or add-on part to the existing one? My muffin fan has no switch and is only about 4 inches square. I beleive they are used to cool computers and other electronics.
If you have a 12v muffin fan you could certainly use one of the regulator circuits linked in the early posts. You might even be able to buy a fan controller at a computer store that's dedicated to pc builders Those small fans draw well under an ampere. The larger ones like the 14inch fantastic fans approach 5 amps at top output.

To answer your question the sophisticated controllers are pulse width modulated and more efficient, offering more steps or even continuously variable speed. If it's just a 3-speed fan it probably (almost certainly) has a resistor network and just burns off the energy as heat.

Regards,

Matt
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Old 03-22-2011, 02:16 PM   #13
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Perhaps implied in all this is matching the resistor rating to the expected current. Many of the hobby shop resistors are 1/4 watt (or less). For example, I believe 1 amp at 12 VDC is 12 watts. Heavier duty resistors are sometimes called "power" resistors.
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Old 03-22-2011, 02:32 PM   #14
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I don't see a curent rating on the speed controller listed above, but if you need one that can carry up to 8 amps, check This ebay unit. I use it to control a string of lights.
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