Atx power supply

Discussion in 'General Electronics Chat' started by Ohms Law, Jan 4, 2008.

  1. Ohms Law

    Thread Starter Active Member

    Oct 14, 2007
    32
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    Anyone have the schematics on using a pc atx power supply ,for a bench power supply and any idea on the usual amp load rating they put out, i'm lookin for a cheap way to power my mobile ham radio thanks guys.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    http://www.instructables.com/id/ATX-->-Lab-Bench-Power-Supply-Conversion/

    Or, just Google for "ATX bench" or "ATX lab"
    I converted an ATX supply out of an old Compaq computer, the supply is rated 250W.
    +5V @25A, +3.3V @14A (max 146w for both)
    +12V @8A
    -5V @0.5A, -12V@0.8A, max 0.8A for both.
    "Your Mileage May Vary" - check your salvaged ATX power supply for details; there should be a label on it.

    One thing nobody seems to mention in those conversions is the ratings of the banana jacks. They're usually around 10A. I doubled up on my 3.3V and 5.5V jacks, and I have a separate ground jack for each voltage. I wound up using 14 banana jacks:
    4 for +3.3/grounds
    4 for +5V/grounds
    2 each for +12V, -12V, -5V
    I have pilot LED's for power, +3.3V and +5V. I didn't bother putting pilots on the others.

    Note that if you don't have a built-in load on the supply, your output voltages won't be correct. I have a 10 Ohm 10W power resistor across my +5V rail mounted to a heatsink; that corrected my +12V supply which was initially reading 1 volt low.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I just did this. I used this site as a reference, although there are several to be found by Googling. Below is a picture of how mine turned out. I added the binding posts, the switch, the labels on top, and the LED. The hardest part was cutting oval holes for the binding posts so they won't rotate.
     
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    We've had problems with switchers producing excessive RF noise. If you have an issue with it cold water ground the case or make sure it is grounded by the AC plug. Use a snap on ferrite core on the DC outputs.
     
  5. h.d

    Active Member

    Oct 22, 2007
    150
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    nice experiment and good implementation
     
  6. Gadget

    Distinguished Member

    Jan 10, 2006
    613
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    If you need more than 8 or 9 amps (I'm guessing you do for a mobile Ham rig), then you may have to rewind the transformer and modify the voltage sense circuits. Silicon Chip issue October 2003 has all the details, involving paint stripper for getting the cores apart, rewinding the primary (40 turns) and the secondary (10 turns bifilar with centre tap) and providing the correct signals and voltages to the TL494 PWM controller. They rate this at 13.5 volts @ 17 amps.
    BEWARE however, some nasty voltages doth exist on thee primary side of this PSU.... lethal ones at that.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    I missed this first time around. I did a search for that article online - the first part is available for free here:
    http://www.siliconchip.com.au/cms/A_30705/article.html
    however, it also states:
    "It must not be an ATX type since they work quite differently to the types under discussion in this article."
    so, it doesn't appear to be of much use, unless the OP has a pre-ATX PSU sitting around.
     
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