Question slowing down a fan with a resistor

[loadyo]

I have just finished rearranging a server and put 5 of the hdd into a how swappable enclosure that fits into 3 of the 5.25 bay, it has a fan on the back to draw air over the drives, however, one of the fins has broken and it is off balance and rattling like crazy and i imagine will cause a lot of uneeded vibration, i have just raped an old fan from a computer CPU and plugged it in, its not rattling but it is running so fast the noise of the air rip is unacceptable, i read the i could add in a resistor to it to slow it down, i just tried two random resistors on the red wire but the fan does not spin, the fan is 12v 0.25a and has four wires red, black, blue and yellow, not sure where i should be adding the resistor or whether i have done something wrong, i dont understand the values and the fan is not for cooling a cpu, it just needs to draw a bit of air over the drives, can someone advise me how to do it ? i have lots of different resistors available.

 

[jsmithepa]

Going through a lot a trouble to not replace the fan...

I would simply run it on 7v. All u have to do is switch the ground pin to +5, so PC (+5) ---> FAN (-), PC (+12) ---> FAN (+), no resistor needed.

 

[loadyo]

Going through a lot a trouble to not replace the fan...

I would simply run it on 7v. All u have to do is switch the ground pin to +5, so PC (+5) ---> FAN (-), PC (+12) ---> FAN (+), no resistor needed.

Agreed, I was hoping to control it via bios and header but my board doesn't allow it. So doing what you say, could I just splice straight into one of molex plugs that power the HDD chassis ?

 

[TJ Hooker]

I am quite confident your motherboard is capable of fan control, but maybe not with linux unfortunately.

 

[loadyo]

I am quite confident your motherboard is capable of fan control, but maybe not with linux unfortunately.

It's known not to have this capability, that was 8 years ago as per that forum, whether it was added in the latest bios update I don't know and can find out unless I flash the bios, I might do that anyway. Maybe there is a docker container that I can install on my server that can do it..worth a look.

 

[Karadjgne]

And there's no motherboard software suite? It's basic, but both my Z77's have rudimentary fan control. You running lga775/1366 mobo?

 

[loadyo]

And there's no motherboard software suite? It's basic, but both my Z77's have rudimentary fan control. You running lga775/1366 mobo?

There may well be but it will be windows and this is being used as an unraid server which is essentially linux

 

[Karadjgne]

Have you looked into coreboot or Libreboot, those are bios alternatives for Linux systems and can be written with different echos for fan control, think it's under apci_thermal

 

[loadyo]

Not that runs on Linux in an unraid server environment

 

[Azzyasi]

Run it on 7v (red and yellow) and see if that speed and noise is ok. If not you can try even the 5v (red and black) but it may not spin.. some spin at 5v
If you would like a bit of control, a 1W potentiometer of lower values of resistance (0-100 or 0-20 ohm) will add speed control to your fan as you desire and can mod and integrate the knob on the case somewhere.

 

[Paperdoc]

Here's a resistor colour code guide

https://www.digikey.com/en/resource...version-calculator-resistor-color-code-4-band

Yes, 36 Ohms would have colours orange, blue and black (3,6, no added zeros). Tolerance band on the other end could be either gold or silver, does not really matter for this application.

As I said, however, you might want to go with a lower resistance value for somewhat higher speed. For example a 20 Ohm unit would have colours red, black, black.

Regarding power rating, there is no code on the resistor body for that normally. You need to ask the shop where you buy for their advice. They usually can tell just by looking at the physical size of the unit. The photo you posted on DropBox seems to show small-wattage units of ½ Watt, maybe less. IF you have to use something like those, here's another "dodge" you could do. If you connect TWO identical resistors in PARALLEL to create effectively a single resistor, then each will be carrying only half the current and hence half the wattage so you can use smaller ½ W resistors, but the value of the combined parallel pair is half the value of the individuals. So each such resistor must be TWICE the value you want from the pair. Thus two resistors of 40 ohms each in parallel makes a 20 Ohm unit; two of 60 Ohms each makes a 30 Ohm unit.

 

[Karadjgne]

Or get creative and use 4x 20ohm. 2x pairs in-line or ——=—=——. That'll give each resistor ¼w, each pair being equal to 10ohm. There's also a redundancy factor to that, if any one resistor fails, you'll have a 10ohm pair + 1x 20ohm for a total of 30ohm and a really slow fan.

 

[loadyo]

Or get creative and use 4x 20ohm. 2x pairs in-line or ——=—=——. That'll give each resistor ¼w, each pair being equal to 10ohm. There's also a redundancy factor to that, if any one resistor fails, you'll have a 10ohm pair + 1x 20ohm for a total of 30ohm and a really slow fan.

Went for adaptation of a spare small form factor connector that wasn't doing anything, soldered some jump wires to ends and of fan, now got it running at 7v with enough airflow a no noise. Thanks for all the input, it's enfused me to learn more. !

 

[Karadjgne]

Electronics is a very wide world of info. Good luck 👍

 

[ElectrO_90]

Buy a 24v fan and plug it in and run it at 12v - sorted
Or variable resistor, then have the speed to what you want

 

[Crosslhs82x2]

Heres a thought noctua has Great industrial grade fans.
Higher cfm fans at lower speed for still plenty of air flow but easier on the ears.

https://m.newegg.com/product/9SIA4RE5WA9416

https://noctua.at/en/products/fan

 

[loadyo]

Heres a thought noctua has Great industrial grade fans.
Higher cfm fans at lower speed for still plenty of air flow but easier on the ears.

https://m.newegg.com/product/9SIA4RE5WA9416

https://noctua.at/en/products/fan

Which I use as a matter of course, alas, not in this instance as the fan is seated in a molded screw on shrouding and it's not possible to adapt.

 

[Paperdoc]

Glad to hear you have a solution that suite you.