Reduce fan speed iN PSU

[blinky88]

Hi all.

My cheap gentic heatsink has a noisy fan running full bore at all times, I would like to reduce the speed to around 80% of its current speed. I think an inline resister on the 12v line would do the job ..but.. unsure of what size the resister should be. Seeking help from a member who know about resisters and how to achieve the result I am seeking.

Would really appreciate advise from someone who can recommend what I need to do.

Cheers from downunder.

[redwudz]

It would be easier to just get a better fan or use a solid state fan speed controller, especially if you have to open up the PSU anyway. You can use a resistor, but you need to know what wattage and what resistance to use, and how much amperage the fan draws. Most case fans are about a half amp or .5A@12VDC. That gives you six watts, a ten watt wirewound would be the better choice. 80% of 12V is about 9.6VDC, so you would have to drop about 2.4VDC through the resistor. That seems to show a 5 Ohm resistor. Of course that will give you no idea what the resulting fan speed will be.

And the price of the resistor may be about the same as a quieter replacement fan.

But it's been a long while since I've done those calculations for voltage drop. Someone more familiar with the math might get a better answer. And be aware that some fans won't start if the supply voltage is too low. Though that usually happens below about 5VDC.

If you are indeed planning to open up a power supply, (Unplugged of course) watch out putting any metal objects in there. The lethal voltages may be gone, but there is often enough low voltage current stored in the PS capacitors to melt the blade off a screwdriver and give you a nasty burn.

[blinky88]

G'day Redwudz,

I was also thinking of a replacement fan ..but.. no matter what fan I replace it with, it will be still running full bore because the PSU doesn't have thermal control, only 2 wires red/black. I will eventually replace the PSU.

I intend to buy either a Corsair or Antec when I come across a good 2nd hand one on eBay. In the meantime, I thought a resistor might do the job.

I have 2 PC's, one solely for internet use, the other for work. Needless to say, the PC I use on the net isn't near the quality of the one I use for my work, which is silent (Corsair PSU and quality fans).

Thanks for taking time out to help. You have come to my rescue a number of times, be assured, your comments are always appreciated.

Cheers from downunder.

[redwudz]

Not sure what you may have available locally, but most PS fans are 80mm and there are ones out there that have their own internal thermal speed control and just use a two wire hookup. Or just find a fan that's rated at a lower db sound level. I use Enermax fans and some of their 80mm fans are virtually silent. Most fans rated below 20 db are very quiet. So are most fans that run below ~1000 RPM.

A couple of problems replacing PS fans. A lot use soldered-in wire connections, but you can cut those leads off long and splice the new fan wires in directly. I use solder and heat 'shrink' tubing for that. You don't have to necessarily solder the connection, just twist the wires together tightly and insulate them. Electrical tape can come unraveled, so shrink tubing is the better choice there. It's available at many hardware stores. Just use a match or a butane lighter to do the shrinking.

Another problem is if you presently have a high speed fan in there and and the PS runs warm, it may need a lot of air running through it or it could overheat. If it runs fairly cool, not a problem. Older PS fans are usually louder and the PS's aren't as efficient as the newer ones. I like the PS's that use 120mm fans, usually on the bottom of the PS. I have a couple of Themaltake PS's that use 140mm fans and they are very quiet and run fairly cool.

A 450 - 500W PS is usually more than sufficient for most PCs. If you have a high powered or SLI video card(s), then a larger PS may be called for. I run two video servers with about nine hard drives each, along with a DVD burner and six or so fans and a 500W PS runs them with no problems.

[greymalkin]

yeah in my experience the minimum amount of cooling is usually used in electronics...cut the airflow and you'll ps will probably die before too long.

[INFRATOM]

rule out using a resistor, if you add a resistor to reduce voltage , the amp that is wasted turns into heat so you have to buy a resistor with high watt to stand the heat. So you would have a heat radiator. one other option is to disconnect the fan and add a quite fan from outside the psu, better if it pushes air from below.

[blinky88]

G'day all,

Problem solved .... I went to a computer scrap yard to pick up a couple of I/O shields for a buck each. Whilst there, I asked the guy if he had any power supplies, he answered yes. I then asked him if he had an Antec, he replied one only, you wouldn't believe it was brand new, Antec 350w Basiq and $20 (US$15) was his asking price = problem solved, installed the P/S, case is now silent. I use this PC solely on the net, 1x10g HDD, 1xCD writer, half a gig of RAM and a 64MB graphics card. All is quite downder and running cool all round. Redwudz I've been fiddling with computer gear for years now, all wire solder jobs I have always used shrink tubing, it's the only way to go.

My thanks to all for taking time out to respond, appreciated.

Cheers from downunder.

[redwudz]

That sounds like the best solution. (And a good deal. )