Fan speed reducer

[Junit151]

I always hear TTL going off about not using motherboard headers and just doing molex and fan speed reducers for his fans.​

How do these reducers work, do they just under-volt the fans? I can't seem to be able to find places to buy them very easily either.
I'd love to be able to get my hands on a couple of these when I get my H80i in because the last thing I'd want in my rig is those noisy stock fans that come with the rad.

 

[Davva2004]

I got mine off eBay for £3, and it just has a resistor in the power wire reducing the voltage from 12v to 7v.

My Corsair AF120 Quiet Edition LED fans now spin at 630rpm instead of 1,500rpm and are utterly silent.

Link to item on eBay is http://www.ebay.co.uk/itm/Zalman-Fa...ther_Computing_Networking&hash=item4d123fe8cb

Or for free, you can modify the Molex connector to give your fans 7v instead of 12v but I run my fans off the motherboard header as my crappy PSU doesn't have a spare Molex.

 

[vorticalbox]

I got mine off eBay for £3, and it just has a resistor in the power wire reducing the voltage from 12v to 7v.

My Corsair AF120 Quiet Edition LED fans now spin at 630rpm instead of 1,500rpm and are utterly silent.

If you have a molex to 3 pin you can rewire them to 7v, changing the ground for 5v forces power the other way slowing it to 7v.

though some PSU's dont like this.

 

[RadeonHDx]

Just have a search on eBay or Amazon and you'll find them pretty easily.

http://www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=fan%20speed%20reducer&sprefix=fan+speed+re%2Caps&rh=i%3Aaps%2Ck%3Afan%20speed%20reducer

 

[Remmy]

I wouldn't recommend wiring a molex to give 7V because you're forcing back current into the PSU through the 5V line, which is supposed to be an output, and it can be harmful to your PSU. If you have fans which run at 5V though, you can instead modify the molex to give 5V by swapping the 12V and 5V leads (yellow and red), and this should be perfectly safe.

Fan speed reducers are simply a 3 pin extender with a resistor on the 12V line. The resistance value depends on the specifications of your fan, and the voltage you want it to run at; there is a calculator for this online if you search 'fan resistor calculator'. You can easily make them yourself but if you do, you need to use power resistors which can handle more power than a standard 1/4W resistor otherwise you could risk setting the resistor on fire.

More easily, you can find premade adapters all over the place, such as these

http://www.ebay.co.uk/sch/i.html?_t...uce&_nkw=fan+speed+reducer&_sacat=0&_from=R40

 

[vorticalbox]

I wouldn't recommend wiring a molex to give 7V because you're forcing back current into the PSU through the 5V line, which is supposed to be an output, and it can be harmful to your PSU. If you have fans which run at 5V though, you can instead modify the molex to give 5V by swapping the 12V and 5V leads (yellow and red), and this should be perfectly safe.

Fan speed reducers are simply a 3 pin extender with a resistor on the 12V line. The resistance value depends on the specifications of your fan, and the voltage you want it to run at; there is a calculator for this online if you search 'fan resistor calculator'. You can easily make them yourself but if you do, you need to use power resistors which can handle more power than a standard 1/4W resistor otherwise you could risk setting the resistor on fire.

More easily, you can find premade adapters all over the place, such as these

http://www.ebay.co.uk/sch/i.html?_t...uce&_nkw=fan+speed+reducer&_sacat=0&_from=R40

i did that in my switch changed the 12 out for the 5 on the fan spliter, i did say the PSU might not like that forcing it to 7v but it can be done.

 

[Remmy]

i did that in my switch changed the 12 out for the 5 on the fan spliter, i did say the PSU might not like that forcing it to 7v but it can be done.

I know, just saying why it's not a good idea, and adding that I wouldn't recommend it The 5V mod is a much better way to go if you have fans which run at 5V

 

[paulstung]

Here you go mate a good selection here

http://www.specialtech.co.uk/spshop/customer/3-Pin-Fan-Speed-Voltage-Drop-Cables-cid-1968.html

 

[Junit151]

Fans + My rig

Thanks guys! I just didn't want those SP120's roaring around at 2700 rpm! I'm waiting on both the cooler and a new case.

As you can see I didn't build from scratch, and all my new bits have outgrown the HP case with just one fan in it. I have to leave the side panel off or risk overheating, and the cable management room is abysmal!

 

[Remmy]

Oh you have Corsair fans, did they not come with fan speed reducers?

On a side note I opened up a Corsair fan speed reducer and found it was a 30Ω resistor, which I calculated should only drop the voltage for the fan to about 10V, which I thought was surprisingly high, I assumed it would drop it to 7V. I've yet to directly measure the voltage the fan gets, but it explains why I still find them loud with the reducer on.

 

[Feronix]

Where are ya located mate?

Bitfenix do some nice braided/sleeved Molex > Multiple 3 Pin adaptors in 12/5/7 volt. Also in different colours of sleeving.
http://specialtech.co.uk/spshop/customer/search.php?substring=bitfenix+molex&in_category=&page=2

 

[Junit151]

I don't have the fans yet, I'll be getting two included with the H80i. As they come included with the AIO I don't know if they come with reducers.

EDIT: The 120's included with the H80i do NOT come with reducers.

Feronix: I was going to do the whole braided cable thing but since I'd try to hide my fan cables anyway I don't want to show them off with fancy cables, I'll just tuck them behind when I get a proper case and use extension cables if needed.

 

[Remmy]

I don't have the fans yet, I'll be getting two included with the H80i. As they come included with the AIO I don't know if they come with reducers.

Oh I see, I thought you had them already

 

[jamesriley94]

I wouldn't use resistors these days myself since if you put more than a couple of fans through them they get very hot.

I don't see a problem at all with 7v wiring these days. PSUs these days are generally high enough quality that they aren't effected at all.

Get one of the Bitfenix ones like Feronix suggested. That way you can always swap the pins over and change them to 5v, 7v or 12v with a thin screwdriver of a pair of tweezers or something.

 

[Davva2004]

There's absolutely no problem with taking a 7v feed from a molex connector, because of the way electricity works. The idea that you're somehow forcing spare volts back down the 5v line to the PSU just simply isn't true.

Voltage works on the difference between two wires. So to get 12 volts, you have 12 volts down one wire and zero volts down the other. The difference between the two is twelve, hence twelve volts.

So if you have one wire with 12v and one wire with 5v, only 7 volts flows between them as that's the difference between the two wires. That's how you can run a fan at 7v, and the PSU doesn't have a single problem with it at all.

 

[Remmy]

There's absolutely no problem with taking a 7v feed from a molex connector, because of the way electricity works. The idea that you're somehow forcing spare volts back down the 5v line to the PSU just simply isn't true.

Voltage works on the difference between two wires. So to get 12 volts, you have 12 volts down one wire and zero volts down the other. The difference between the two is twelve, hence twelve volts.

So if you have one wire with 12v and one wire with 5v, only 7 volts flows between them as that's the difference between the two wires. That's how you can run a fan at 7v, and the PSU doesn't have a single problem with it at all.

The problem isn't the voltage being forced into the PSU because that doesn't even make any sense. It's perfectly fine setting it up the 7V potential over the fan using 12V and 5V, the problem (if any) arises in the current flow. If you make the fan run like this, current must be going into the PSU down the 5V line which is opposite to what it was designed to do.

Edit: PSUs should have protection circuitry on their outputs, and if the current into an output was greater than the current out then the PSU ought to just shut down as a safety precaution. People report this exact thing happening with certain PSUs when they do a 7V molex mod. As long as you have enough load on the 5V line, so a decent amount of current is output, the relatively small input current from the modded molex won't be enough to do anything, but if it isn't then the PSU shuts down.

Just in the interest of safety, either do a 5V mod, or use resistors, you won't cause any problems doing either of those.