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Old 7th July 2004, 06:20 PM   #1
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Default How do you slow a fan

Hi All,

Please help me out. I have 10 PE fans rated at 12 VDC and .8 Amp.

I have a PE DC power supply rated at 13.8 VDC and 5 Amps.

I wanted to use 4-8 of the fans to help cool down three amps and my receiver.

The problem is when I connect one or two fans they spin VERY fast and make far, far too much noise.

What can I do to slow them down so that they are quiet enough to use.

Also should they be wired in series or parallel.

Thanks for the help.
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Old 7th July 2004, 06:24 PM   #2
RobM is offline RobM  United States
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Lower the voltage to them. You can use something like an LM317 and a pot to make a variable power supply.
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Old 7th July 2004, 06:28 PM   #3
cowanrg is offline cowanrg  United States
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a simpler (but not better) way of doing it would be by using a rheostat. depending on your application, you might need a higher value one, which can be tough to find, and not the cheapest thing out there. but, its very simple and effective.
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Old 7th July 2004, 06:40 PM   #4
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Whats wrong with series parallel to give low voltage on them. Use 6 fans, three in series then paralleled with another three. I have rewired the fans in my computer to use 5v this keep them nice and quiet.

The fans you have could be loud noise fast spin types in which case wire 4 in series parallel. I needed to use 3.3v on one like this.
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Old 7th July 2004, 07:05 PM   #5
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I use 7809 1amp. regulator on my PC. (7810 available )
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Old 7th July 2004, 07:31 PM   #6
K-amps is offline K-amps  United States
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Use 5 sets of 2 fans in series and then paralell the 5 sets, that will do 6v into each fan. Or have 2 sets of 3 fans in series and the last 4 in series and paralell the 3 sets...... lower voltage 4v into the 3 fan sets and 2.4v into the 4 fan set....

If you want more control (i.e. more components and complexity) then you can go to a regulator type circuit.

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Old 8th July 2004, 08:56 AM   #7
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there's always a lowest voltage u can go before the fan stops working...I'm assuming u're using brushless fans here...wad u can do to provide more control is to use a PWM circuit...I use it on my PC to provide speed control...however I have to hack the fan speed monitor coz the MB will switch off if the fan speed drops too low...duhz...
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Old 8th July 2004, 09:20 AM   #8
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Pots work too...especially a pot parralleled with like a 50 Ohm 5 watt sand resistor.
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Old 8th July 2004, 11:23 AM   #9
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do note that the pot has to be suitably rated...if you're using it he reostat way...due to it having to dissapate some heat...but as a potential divider it might do ok...start-up seems to be a problem on low voltages though...
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