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Old 01-27-2010, 04:31 AM   #1 (permalink)
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Default Voltage controller influence on PSU?

I was thinking to do a controller for fans by installing a switch to make fans run on varible speed as follows:

12v regular (+12 and ground)
5v redused (+5 and groung)

But i thought maby its better to raise the lower speed a bit , stil no noise but more air:
7v moderate (+12 and +5)

Will it do any negative effect on a power supply in a such configuration especially in 7 volt application???
(I have 5 fans in Element S case, who together draw about 1.5-2 Amps at stock)

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Old 02-01-2010, 11:12 AM   #2 (permalink)
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Default Re: Voltage controller influence on PSU?

It shouldn't have any negative effect on your PSU, assuming you wired it up correctly. I would just connect a potentiometer to the 12v lead of the fan.

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Old 02-01-2010, 03:39 PM   #3 (permalink)
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Default Re: Voltage controller influence on PSU?

You could use one of these for converting the 12v to 7v. And no, it won't affect your power supply.
7 Volt Fan Speed Resistor
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Old 02-03-2010, 07:33 AM   #4 (permalink)
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Default Re: Voltage controller influence on PSU?

Just add a resistor of appropriate resistance
V = IR
fans typically run at 0.2A, and therefore have a resistance of 12/0.2 = 60

to run it at 7V, find the current required, which is 7/60 (V / R)

Then calculate the value of the resistor needed for a (12 - 7 = 5) volt drop
5 = (7/60)*R
5 / (7/60) = 42.85 ohms
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