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Old 02-02-14, 03:52 PM
Junit151 Junit151 is offline
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Question Fan speed reducer

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.

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Old 02-02-14, 04:03 PM
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Davva2004 Davva2004 is offline
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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-Fan...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.
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Old 02-02-14, 04:06 PM
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Quote:
Originally Posted by Davva2004 View Post
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.
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Old 02-02-14, 04:07 PM
RadeonHDx RadeonHDx is offline
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Just have a search on eBay or Amazon and you'll find them pretty easily.

http://www.amazon.co.uk/s/ref=nb_sb_...peed%20reducer
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Old 02-02-14, 04:22 PM
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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?_tr...at=0&_from=R40
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Old 02-02-14, 04:24 PM
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Quote:
Originally Posted by Remmy View Post
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?_tr...at=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.
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Old 02-02-14, 04:26 PM
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Originally Posted by vorticalbox View Post
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
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Old 02-02-14, 04:32 PM
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Here you go mate a good selection here

http://www.specialtech.co.uk/spshop/...-cid-1968.html
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Old 02-02-14, 05:22 PM
Junit151 Junit151 is offline
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Lightbulb 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!
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Old 02-02-14, 05:35 PM
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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.
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