How do you slow down 120m fans with 4 pin connectors?

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hero
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How do you slow down 120m fans with 4 pin connectors?

Post by hero » Sat May 08, 2004 3:49 pm

I like using fanmates since I have a few and they take you all the way down to 5V instead of the 7V most rheobuses do. So I'd like to use these with my 120m fans (Antec,Nexus) but I'm wondering if there will be a problem using a 4 pin to 3 pin adapter or if there's another way to slow them down to 5V.

bomba
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Post by bomba » Sat May 08, 2004 4:52 pm

Luddite w/ old-skool P4 desktop rigs, incl. custom home server w/ 8 fanless/trayless hot-swap SATA bays in a mid-tower case w/ single 120mm fan.

al bundy
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Re: How do you slow down 120m fans with 4 pin connectors?

Post by al bundy » Sun May 09, 2004 1:45 am

hero wrote:I like using fanmates since I have a few and they take you all the way down to 5V instead of the 7V most rheobuses do. So I'd like to use these with my 120m fans (Antec,Nexus) but I'm wondering if there will be a problem using a 4 pin to 3 pin adapter or if there's another way to slow them down to 5V.
I use fanmates with 4-to-3 pin adapters all the time with 4-pin fans of all sizes. You should have no problems at all.

I personally prefer to use a 5V fixed mod however, since it is so easy.

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Ralf Hutter
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Post by Ralf Hutter » Sun May 09, 2004 4:50 am

Usually I just hardwire them as shown in bomba's link, but if you want to run them through a Fanmate, just get yourself some of these 4-pin to 3-pin adapters. These work great.
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hero
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Post by hero » Sun May 09, 2004 6:33 am

Can somebody explain this part?
Caution! There are people, who will say "You can't feed current back into your power-supply" and they are right!

If you plug something between the 12V and 5V lead, you have to be absolutely sure, that no current is fed back into the PSU. Which means, that you need to have other loads on that 5V lead, which suck out more current than you feed to that lead from the 12V lead.

For example: Your fan uses 100mA at 7V. You take 100mA from the 12V lead and feed them into the 5V lead. If you have a different fan (or whatsoever), that sucks out 200mA from the 5V lead and feeds them to ground, you're fine. 100mA are sucked out of the 5V lead, 100mA come from the 12V lead and 200mA go to ground.
I've read it about six times and I still can't visualize what he's trying to say.

cpemma
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Post by cpemma » Sun May 09, 2004 2:18 pm

hero wrote:Can somebody explain this part?
...If you plug something between the 12V and 5V lead, you have to be absolutely sure, that no current is fed back into the PSU. Which means, that you need to have other loads on that 5V lead, which suck out more current than you feed to that lead from the 12V lead.
I've read it about six times and I still can't visualize what he's trying to say.
There's a rectifier diode on the 12V and 5V psu outputs, if the negative lead of the fan is connected to +5V the current can't flow against the rectifier unless there's more current coming out than there is trying to get in. The current coming out keeps the "one-way valve" rectifier open.

Quite a few people have tried running 7-volted fans with no other load on the ATX psu (for testing purposes or whatever) - the psu will trip out, as the ATX circuitry has safeguards against load imbalance.

With "normal" system loads on the 5V line there's no problem in 7-volting.

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