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  • Power Talk

    I am going to try my very best here to post intelligent questions and continue personal research as well to help dig myself out of the newb hole lol.

    To start, this is what i'm looking to get: http://store.mp3car.com/Mp3Car_Custo..._p/ccc-122.htm

    1)If you dont feel like explaining it links would be great, but I know when manuals refer to "rails" represented as +12, +5, +3.3 right? I understand a rail is a wire. In persuit to get the right PSU for myself to properly power my system, I have to find out if I will be asking for more power then I can actually draw. I understand that V X A= W. The included PSU(M1-ATX) will supply 24w on the 12v rail, 33w on the 3.3v rail, and 50w on the 5v rail. The site tells me that the processor will require 24v to operate, and I assumed it used the 12v rail, meaning that mp3car would be selling me a system that wont operate. I realized i'm sure that isn't the case, so the cpu must draw power from a different rail.

    How do I know which rail is used for each of the different peripherals? What is the 7v rail used for?

    2)If I have a 90w power supply. Added up, the 12v, 3.3v, and 5v rails total wattages equal 117w. I may be incorrect on this, but I assume you can load up all 3 of the rails as high as they are rated for.

    Am I correct, or does the total wattage for each rail just specify the "Do not exceed" boundry? With the 90w power supply, does this mean that I could max out the 3.3 and the 5 volt rails, equaling 88w, but I would have to only use 3 watts on the 12v to stay within my limits(This is completely theoretical).


    Those are my first few questions, I am reading up in the facts but I want to make sure that i'm on track with understanding some of the specifics. As bad as I just want to get this thing in my car I feel that I can make this a good learning experience for myself about electricity, so I am really trying to grasp every aspect.

    Thanks

  • #2
    1)If you dont feel like explaining it links would be great, but I know when manuals refer to "rails" represented as +12, +5, +3.3 right? I understand a rail is a wire.
    A "rail" is basically just a single output. Its nothing physical, but just a generic industry term. In your case, each output would have its own set of wires.

    The site tells me that the processor will require 24v to operate, and I assumed it used the 12v rail, meaning that mp3car would be selling me a system that wont operate. I realized i'm sure that isn't the case, so the cpu must draw power from a different rail.
    If your processor requires 24V to operate, you then would need a 24V output on your power supply.

    2)If I have a 90w power supply. Added up, the 12v, 3.3v, and 5v rails total wattages equal 117w. I may be incorrect on this, but I assume you can load up all 3 of the rails as high as they are rated for.
    You have to check the manufacturer's specs. They should list a maximum current for each output.

    Am I correct, or does the total wattage for each rail just specify the "Do not exceed" boundry? With the 90w power supply, does this mean that I could max out the 3.3 and the 5 volt rails, equaling 88w, but I would have to only use 3 watts on the 12v to stay within my limits(This is completely theoretical).
    Depends. Some power supplies will have built in thermal protection or overcurrent detection in which case the power supply will shut down if too much current is drawn from a particular output.

    However, you should never run your power supplies close to the limits. You should always derate the outputs by at least 80% (give 20% margin) to increase reliability etc...
    Eastern Voltage Research Corp.
    http://www.easternvoltageresearch.com

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    • #3
      Originally posted by Imdbombboarder View Post
      The site tells me that the processor will require 24v to operate....... What is the 7v rail used for?....

      Sorry, where does it say either of those things?

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      • #4
        Ah my bad, I meant watts. The processor will need *25 watts to operate, but the 12v rail only can supply 24w, leaving it short 1 w. So that's where my descrepency comes from

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