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Thread: testing for current and AT / ATX

  1. #1
    Newbie
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    Dec 2001
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    Post testing for current and AT / ATX

    Hi, I'm planning to build a Sproggy power supply, 2.5 or 2.6. How can I determine if my computer's motherboard is an AT or ATX? The computer is an AST Bravo 486DX2/66 and the motherboard has Socket 3 written on it for the processor socket, if that helps. Also, I've read some posts that say the Sproggy power supply will not supply enough current. How can I test (without cutting the wires of my power supply) the current running through the pins?

    - Chris

  2. #2
    Raw Wave Rob Withey's Avatar
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    Apr 2000
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    Bedfordshire, UK
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    Post

    If it's a 486, it's probably an AT. AT mobos have a single row of pins in their power connectors, usually with two connectors from the power supply place end to end. ATX have a single power connector from the power supply, but with a double row of pins.

    To measure the current on supply lines, connect an ammeter in series with the power line to measure on.


    Rob

    [ 12-15-2001: Message edited by: Rob Withey ]
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  3. #3
    Newbie
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    Dec 2001
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    Rob, thank you for the info. That means I have an AT like your thought. So does this mean that I do not need to build 2.6 with the Power Good feature, that I can go with the 2.5 model?

    I know I need to connect the ammeter in series with the pins but I'm more concerned with which pins (of the 12 going to the motherboard) and how should I do it so that I do not have to cut the wires in my existing power supply only to tape them again. I suppose I'm looking for tips. Does it matter if I only connect 1 of the 12 pins to the mobo at a time, testing each one separatly?

    Do you think that the 2.5 Sproggy will power my 486?

    - Chris

  4. #4
    FLAC
    Join Date
    Apr 2001
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    Portland OR
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    One of the best ways to measure the current on an atx computer is to build an atx current tester. You get an ATX extension cable (www.pricewatch.com) and put a .01 ohm 1% 3 watt resistor (www.digikey.com) in series with all the main power lines, 3.3, 5, 12, or whatever else you are interested in. Then take a multimeter and measure the voltage across that resistor. For example: If you are drawing 1 amp on any of the lines you will read 10 millivolts if you are drawing 10 amps you will read 100 millivolts. If you know you aren't going to go above say 2 amps, you could use a .05 ohm resistor to get more dynamic range. If you know you are going to draw 20 amps or so you could go with .005 ohms or something. You get the idea. That way you don't have to break the circuit. You can run some kind of time refresh rate on a video game and see how much that makes the 3.3 volt line go up in current etc. Remember V=I*R I=V/R R=V/I.

    -Jeff

    [ 12-15-2001: Message edited by: Jeff Mucha ]
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

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