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Can I connect two 12v rails on a PC power supply?

  1. Apr 26, 2007 #1
    I just bought a 320w TEC to cool my processor. But the problem is, I can't afford a power supply that can provide enough amps through a single 12v rail. If I buy a power supply that has dual 12v rails, can I wire them together in order to provide enough amps to the TEC? I won't have anything else hooked to this power supply, only the TEC. Thanks in advance for the help!!!
  2. jcsd
  3. Apr 26, 2007 #2
    Yes, as long as they share the same ground, which they should.
  4. Apr 26, 2007 #3
    THANK YOU SO MUCH!! I've been trying to get an answer to that for 2 days on various PC forums... That made my day! Decent power supplies with a single 12v rail are hard to come by nowadays. And I wasn't willing to pay over $200 for a PSU with strong enough rails. Thanks again for your help!!!
  5. Apr 27, 2007 #4


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    Staff: Mentor

    I have to disagree with waht on this one. You might be able to parallel the two power supplies to increase the overall output current, but in general that may not work.

    There are two potential issues -- stability and output voltage. Stability can be a problem because you will have two separate switching power supply loops that are both trying to stabilize the output voltage, and they can talk to each other and cause oscillations or even worse, overvoltages.

    The second problem is that each of the two power supplies can only pull the output rail up, and will only pull up (supply output current) if they see that the rail is at or below the output voltage that they are trying to get to. So if one supply's output voltage stand-alone is 12.1V, and the other is 11.9V, then the 2nd power supply will not supply much current into the output as long as the 12.1V power supply is connected to its output.

    Paralleling power supplies in the general case is a pretty difficult problem, and requires some extra circuit features to make it work reliably.
  6. Apr 27, 2007 #5
    I agree with Berkman, but I'm actually confused more about the original question, the rail thing.

    I'm aware a PC power supply taps the voltage from the transorfmer. More power means you need a more powerful transformer. In regular power supplies, a 12V is tapped from one winding providing the necessary current.

    Is this what you call a single rail? This way all 12V outputs (usually the yellow cable) can be hooked up to anything.

    Now the dual power supplies, for high performence PCs have two independent 12V taps from main transformer, making it more stable because it's easier to stabilize two lesser power outputs.

    I think this is what you refer to is dual rail?

    But even in this, the two indepentent 12 V output have to be phased locked anyway since this is a switching power supply, so you could use either rail whenever you want provided the power supply can supply enough amps.

    But if you want to hook up two different PC power supplies together, single rail then you might ran into problems berkman explained. But if the other power supply is powering a fan that would no problem.

    Hope that helps.
  7. Apr 28, 2007 #6
    I'll be connecting two 12v rails off of one power supply with dual 12v rails. It has overvoltage protection, and they do in fact share a ground, so I'm confident that it'll work. Thanks for your help!!
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