resister for fan

[Gus K]

Anyone know what size/type resister I'd need to drop the voltage from 12v to 6v for a Thermaltake 80 fan?

Thanks

 

[Zedric]

Normally a resistor would be a bad choice for this. I suggest you use one of two other ways:
1. Get a voltage regulator for 6V. I know there are 5V and changable regulators so I guess you can find 6V somehow.
2. Connect the fan between 5V and 12V giving it 7V. Close enough?

 

[XP Abuser]

wire up an adjustable resister to it or get a step down transformer... id go with the former

 

[LeeJend]

Gus

Ignore both of the previous answers.

A decent voltage regulator with heatsinking will cost as much as a new fan with a built in speed adjuster. Any reasonably sized variable resistor will burn up under the current (0.5-0.7 Adc) a fan draws.

The resistor idea works fine. I've been using it on a noisy fan for the past 6 months. I put 2, 10 ohm 10 watt resistots in parallel and it drops the 12 Vdc down to ~9.5 Vdc which turns the 6800 rpm shrieker into a nice quiet 5200 rpm fan and it still does a good job cooling. Radio shlock has 2 pack power resistors for $1-2. You could get 5 ohm and use a single one but I used the 2 in parallel to spread the heat.

NOTE: A 10 watt rating on a resistor means that it can handle 10 watts when attached to an infinite heatsink with a 72 deg F temperature. I taped my fan slowing resistor to a metal channel running across the PC to help keep it cool.

Or just go buy one of the new fan control modules for $20 bucks or a volcano 9 with its own speed control for $20.

 

[Gus K]

or a volcano 9 with its own speed control for $20.

Makes sense, thanks to all.

 

[Taurus]

Originally posted by Zedric
2. Connect the fan between 5V and 12V giving it 7V. Close enough?

i know i'm late. but this is my favorite method.

 

[Maveric169]

RatShack should have 12V variable resistors, I have used them before.

 

[Zedric]

Originally posted by LeeJend
A decent voltage regulator with heatsinking will cost as much as a new fan with a built in speed adjuster.

Really? That's got to be some really cheap fans!
A very decent voltage regulator (witout heatsink, none needed) costs about 50 cents here.

 

[XP Abuser]

lol

im just trying to think how does that 12v and 5v make 7v **** work

 

[Taurus]

Originally posted by XP Abuser
lol

im just trying to think how does that 12v and 5v make 7v **** work

the positive lead for the fan goes to the 12v... and the negative lead goes to the 5v... 12 - 5 = 7 volts.

 

[XP Abuser]

ahhh i see

 

[Zedric]

Yep, I thinks it must be the most common "mod" ever.

 

[XP Abuser]

rub it in then zedric

 

[Zedric]

Originally posted by XP Abuser
rub it in then zedric

No offence intened!

 

[XP Abuser]

lol

 

[LeeJend]

Doesn't dropping the voltage to 7 Vdc make the fan turn too slow to get enough airflow? My 6800 @ 12Vdc is at 5200 @ 9.5 Vdc.

Anybody got any speed numbers for the 5-12Vdc conenction?

 

[Taurus]

Originally posted by LeeJend
Doesn't dropping the voltage to 7 Vdc make the fan turn too slow to get enough airflow? My 6800 @ 12Vdc is at 5200 @ 9.5 Vdc.

Anybody got any speed numbers for the 5-12Vdc conenction?

sure, it still moves air. you can feel it. a fan at 7v runs roughly 60% the speed of 12v. if you want something between 12v and 7v, then i think you're only choice is a regulator or resistor (not sure what the difference is).

 

[Zedric]

A regulator is guaranteed to give you a certain voltage, regardless of load (ut to a limit of course), but a resistor gives different voltage on different loads.

Thus a regulator is better. You can add more fans to it if you wish.

 

[Taurus]

thanks, zedric... i'll be looking around for a couple to play around with.

since they aren't resisting current, they don't create heat, do they? i mean, they aren't drawing more current from the mobo/psu than the fan needs, correct?

 

[XP Abuser]

no zedric is right resisters limit electricity by changing the energy from the electricity into heat. thus reducing the voltage but they do not have a constant voltage...



but its not a case of wiring it up you have to build a circuit with a few resisters and capacitors to actually tell the VR what voltage to regulate