What do I need to slow a case fan voltage down resistor or capacitor?

[AnMig]

Okay I have 4 80 mm case fans that came from various cases mostly pulled from powersupply units and replaced with panaflo's.

I have mess around computer with a 750 duron overcloked to 900.

I want to slow down at least 3 of these fans by undervolting them. Those thermosistor molex at radio shack are $4-5 each and I might as well buy panaflos of I where going to do this.

I want to decrease the voltage to around 8-9 volts from 12 volts so hopefully the noise from these beasts can somewhat be diminished.

Can I use a capacitor or resistor to bring the voltage down? how many ohms do I need to get 8-9 volts?

anybody tried this?

thanks

I remeber somebody posting about this but I cant seem to find the post

 

[Jeff7]

I believe there is a way to connect the fan using the 12V+ and 5V+ wires to give the fans 7V. I have never done this personally, and I don't know if it can damage the power supply over time.
Found a good link. Search on Google for "7 volt mod" for other links.

 

[AnMig]

Thanks for link.
Although it appears toe labor intensive and elaborate.

I was hoping to just cut the red wire and put a resisitor or capacitor between them to decrease the voltage.

I bought 10K-Ohm resistor at radio shack but it does not appear to transmit any voltage (fan did not spin at all.

anybody have any ideas on what to use to decrease the voltage?

thanks

 

[Jhhnn]

The guys at O/C hideout seem to be able to find the hard way to do anything. I think they may have management potential. 7 volting a fan is a lot easier than that.

At the pass thru connectors, push back the locking tabs on the pins for the red 5v wire, remove & set it aside. Do the same for the black wire Y that's the fan ground. Reset the lock tabs, put the black wires where the red came from, put the red wire into the only open holes. You'll have the fan running at 7v, and standard voltages on the open end of the pass-thru. This last part is very important.

Modding a fan plug w/o a pass-thru is even easier...... just move the black fan ground over to mate with the red on the other molex... nothin' to it.

This harms nothing, it augments the power output on the 5v line.

 

[CaptnKirk]

Voltage reduction is accomplished by using RESISTORS.

Ohms Law

 

[OulOat]

Lol, capacitors. You really have no idea how electronics works eh? That's okay. You want to use resistors, although not the 10K variety. That is WAY overkill. When you want to find out what resistance you should use, just use OHM's law. I'll use Vin to represent Voltage in (from the PSU) and Vout to represent Voltage out (to the fan). I is current and R is resistance. The law is:

(Vin - Vout) = I*R.

Well, since you know the voltage coming from the PSU (12 V), and how many Volts you want the fan to recieve (lets say 9), then left hand side of the equation is 3 V. Basically you want your resistor to dissipate 3 V. Now, what you need to find out is what current your fans need. The sticker on the fan's spindle should tell you how many Amps the fan requires (mine are .20 A, it may vary). Then all you need to find out is what R is. In this case, R=15 Ohms.

The reason why your 10K resistor doesn't work is that it's dissipating too MUCH voltage. Thus, not enough voltage is getting to your fan = fan won't turn on. You can also see it this way. Solve Ohms law for I. If you use Vout = 9V, you get I = .3 mA (1/1000 A), which is not anywhere near the required .20 A to work the fan.

Or you can do the 7V mod, I think it's much cleaner and don't cost me anything. It's not that hard once you understand the principle behind it, I did it just after looking at my lines.

 

[vailr]

If you use the power supply's minus -5 volt and the plus +3.3 volt lines, you get 8.3 volts. No resistor required.

 

[Jhhnn]

Uhh, the -5v and -12v lines from the psu really shouldn't be used for anything other than mobo electronics- check the available amperages, the likelihood of something going poof! is quite large.....

 

[Goi]

I'm running a 120mm Sunon fan at 7V now by connecting the + to 12V and GND to 5V, works like a charm.

 

[FenrisUlf]

I agree on doing the 7 volt mod - much easier. If you really want to do a resistor, a 100 ohm variable is probably a safe bet for most fans, just make sure it's rated for at least a watt (dropping 5 v at 200mA = 1 watt). Otherwise, you're probably safe with a 47 ohm resistor. You could get several 22 ohm resistors and put them in series - just keep adding resistors until the fan slows to your liking.

 

[jaybee]

I wired up my chassis fans with a switch (quiet mode) to increase resistance. Position A is fan-psu, position B is fan-resistor-psu. What resistance to use? The specs are usually listed on the fans but sometimes not. Check for a current spec, like .25A. V=IR means the circuit resistance (R) is 12/.25 = 48ohms. One or two 10ohm resistors should be a good match for the circuit.

jaybee

PS Get 1/2W or better resistors. P=I²R = ~.2²*10 = ~.4W