fan re-wiring questions

By mod-newbie ยท 12 replies
Jun 2, 2006
  1. hi guys!

    I have read that you can switch the wires on a 4 pin molex fan connector to quiet the fan down. by this I mean instead of the standard yellow and black wires (+12v and ground), you use the yellow and red (+12v and +5v), am I to assume that this makes the fan run on 8.5 volts?

    I have also read that not all power supplies can handle this, as in perhaps some cheap PSUs will overload or something???

    Let me give some background as to why I ask this question. I have an Antec TP2.0 380 power supply, it is a nice PSU and it has two "fan-only" 4 pin molex connectors (with only yellow and black, no red and black). when I connect my fans up to this they run so slow that you cannot hear them at all, if I plug them into a regular 4 pin molex, they run fast and loud. I bought a vantec fan speed controller and hooked my fans up to it. now the issue is that I love the silence of the antec fan only connectors but i want to be able to speed them up as well when the system gets warmer. but the vantec fan speed controller's (variable 7-12v) lowest setting is still quite noisy.

    so my question is... (drumroll please :)), the fan controller has 4 outputs, but only 1 input, if I changed the input to use just the red and yellow (no black) wires, would that lower my fan speeds and still give me the ability to control them? or would this damage my fans or my fan controller?

    thanks alot guys, you are awesome! :D
  2. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 24,177   +19

    I can`t answer your question I`m afraid.

    However, while you are awaiting further replies, perhaps you might want to take a look at this thread HERE. You may find it of interest.

    Regards Howard :)
  3. mailpup

    mailpup TS Special Forces Posts: 7,188   +470

    I don't know the answer to the wiring question either. However, for what it's worth, I can say that when connected to the Antec fan-only connectors, fans are supposed to speed up automatically when the temperature inside the case goes up.
  4. kangaruffian

    kangaruffian TS Rookie Posts: 175

  5. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    I wouldn't play about with the 7V mod tho, its dangerous. I've not read the link yet, but if there's no warning about the dangers of the 7V mod, I'm giving it to you now. Most cheap PSUs can't handle current going the wrong direction, and the 7V mod does that. And PSU's tend to be the most overlooked component in systems, with people getting the cheapest PSU they can find for their top end systems.

    However, saying that, changing the line from the 12V line to 5V is totally fine. You'll get a quieter fan, but bear in mind the fan isn't pushing as much air than before. Going from 5V to 12V may be dangerous, as your fan is not designed for such a high voltage.

    Hope this helps.
  6. kangaruffian

    kangaruffian TS Rookie Posts: 175


    ..good point.! And u can allways buy new silent fans to replace those noise ones.. like Glacialtech SilentBlade 120/80 and or Nexus Silent 80/92/120
    those fans r real quiet
    I allways forget to warn people to mess with they hardware :eek:
  7. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    You always have to warn people when telling them to mess with anything.

    And for those who want to mess around with something, read up on it, at least know the risks, and if there's no risks, make sure that is fully understood what no risks mean. Get 2-3 sources to back up the fact that there's no risks.
  8. mod-newbie

    mod-newbie TS Rookie Topic Starter Posts: 26

    Thanks for all your replies!

    CMH, what is dangerous about it? I have a good quality PSU, not a cheap one. i did not overlook it as an important component. and i do not have any 5v fans, nor was I ever planning to force a 5v fan to run on 12v (where did that come from??)

    I think that maybe I didn't explain it good enough. I don't want to directly wire the fans, what I want to do is reduce the input voltage into the fan controller. so that I can retain the voltage adjustability, but be able to lower them more than I can right now.

    by the way, it is common sense that lowering the voltage to the fan will reduce the CFM of the fan, I am well aware that this happens. my goal is silence, not high CFM

  9. mailpup

    mailpup TS Special Forces Posts: 7,188   +470

    I think your plan is based on a false premise. I should have thought of it before. The fan controller works as a rheostat by restricting the current or amps to the fans, not lowering the voltage. You need a transformer to step down the voltage and a rheostat is not a transformer. As an aside, the power supply is a transformer.
  10. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    the best way to reduce fan speed may be to incorporate a variable resistor into the fan to reduce input voltage. This should be simple enough, and will not have any problems I think. And if you need to reduce it more, adding more variable resistors is an option. These resistors would be in serial with the fan (just mentioning it).

    Good that you know that, there's people out there expecting lower noise, while maintaining a high cfm. I'm also not sure if there are 5V fans, but I'll just add in just in case some company decided to come out with ultra-quiet 5V fans.
  11. mod-newbie

    mod-newbie TS Rookie Topic Starter Posts: 26

    so what you're saying mailpup is that lowering the imput voltage into the rheostat fan controller would not lower the fans speeds any more, wouldn't reducing the voltage and current lower it even more? or would that cause some kind of damage?

    CMH, do they make variable resisters that can handle 4 fans (for the input line) or would I have to put one on each fan output line? also I still don't see how the 7v mod is dangerous :confused:
  12. CMH

    CMH TechSpot Chancellor Posts: 2,039   +9

    The 7V mod is dangerous because it causes electricity to flow the wrong way down the +5V line. Cheap PSU's aren't designed to handle this, and can cause damage to the PSU (which may start fires, etc).

    Variable resistors are cheap I think, but if you want to have just 1 (or 2) variable resistors to control all your fans, you'll have to insert it on the main line. If you know what I mean. In other words, it can be done.
  13. one70three

    one70three TS Rookie

    I think it might be worth mentioning that you cant slap just any variable resistor in there (or maybe im thinking about a "trimpot") or it youll end up with a fried trimpot/variable resister or one that limits the power too much

    Ive fried more than my fair share of variable resistors trying to get 5v out of a 9v battery... not the right way to do that in the first place (didnt know that at the time) but most smaller variable resistors simply cant handle tha amount of voltage... but they do make a horrible smell if you want to drive everyone out of a room :D

    Im assuming you already have a fan controller that adjusts the fan speed, but you can probably stop by radio shack or fry's and ask an employee there for a recomendation on what variable resistor to use (explaining to them what exactly you plan on doing with it is your best bet to get the right one the first try)

    hope that helps, despite this thread being inactive for 10 days lol
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