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Thread: Newbie DC/DC PSU problem

  1. #1
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    Newbie DC/DC PSU problem

    I am currently undertaking a task to build a power supply for my old P150 to turn it into an mp3 player.

    My motherboard has a built-in video/sound card so that helps save a lot of space. Now, do I need to disable onboard video?

    My power supply unit works fine when not connected to the motherboard, the +12V line gives about 11.70V and the +5V line gives about 5.03V. I dont know how to check the amperage on those lines however.

    I used a maxim max787 for the +5V line and a L7812 regulator for the +12V line.

    As I said, when this is not connected to the motherboard and cpu fan & harddisk, it gives the correct voltages. So I connected it to the cpufan and it turns okay. If I connect the hard disk to it, the fan stops.

    If I connect the lines to the motherboard connector pins (AT style although it also has ATX connectors as well) the fan stops and nothing happens. I checked the voltage at the incoming and its about 4V! Isnt it supposed to be 12-14V? I am confused here. So when I connect the power supply unit to the motherboard everything goes haywire. Is it because I need to use thicker wires? The one I am using is quite thin, aluminum stranded. Its standard electronics wires I believe.

    If you can provide any kind of explanation, please do so.

    I spent quite a lot on this project and I'd love to get to see it working.

  2. #2
    Rob
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    If your not using the on-board video it's probably work disabling it if you can (check the bios). If not don't worry about it, unless you get the no monitor connected beeps, in which case you'll need a terminator.

    The PSU problem might lie with the LM7812, It only supplies 1amp off current, it seems that this might not be enougth based on what your saying. You may need a more powerful chip (there's a 5amp version, but I can't rember it's name) or try using seperate chips for the HD, MB etc, a bit crude but if access to parts is a problem it'll work.
    And you say people actually pay money for M$ Windows?
    www.mp3mini.co.uk (Does what it says on the URL) www.openclassic.co.uk (The new car, with zero rust!) www.rob-web.co.uk (My other site)
    Total re-design underway: on the whole progress is very slow as the car is taking up too much time :)

  3. #3
    Variable Bitrate
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    I think i agree with Rob....the LM7812 doesnt provide enough current. By the way..what are u using to provide the -12V and
    -5v?

    Paladin

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