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Quick and Dirty Multi-Voltage DC Power Supply

Discussion in 'Home Brew' started by ButtFuzz, Apr 24, 2015.

  1. ButtFuzz

    ButtFuzz
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    Anti-BS Advocate ● N4REV ● Reverend Doctor

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    How to easily re-purpose a PC power supply one may find on the curb.

    So you find an older XPS / Precision Workstation / Server on the curb. Grab it! Chances are the Power Supply still works. Here's the one I found. A BIG FAT one that attaches to the BOTTOM of a Dell Machine. 650 Watter. Pull it off, and salvage the wires inside the machine connected to "P3".
    [​IMG]
    Almost any power supply will do... This one is rather nice. Remove Power! DUH. Remove Lid of PS. Cut wire ties (NOT the wires) that hold that snakehead mess of wires together so they are free.

    YELLOW CIRCLE: On connector "P1" find the GREEN wire... pull ONE of the nearest BLACK wires and the green wire out of the connector, strip and solder/twist together. Cover with shrink tube for safety.

    RED Circle: Bend the aluminum deflection fin into a small bend so you can fit all the wires EXCEPT THOSE going to P3 into the emply channel. Plug AC power cord into back of unit and into wall. Fans should spin. DANGER: Those larger capacitors can hold quite a wallop.
    [​IMG]
    More info: You could pop a hole in the chassis, and put a switch on the green-black wire for an on-off switch. I am not concerned with such niceties, but you may be!

    Hook up digital VOM to P3, Yellow wire to "+", any black wire to "-". Measure DC Voltage. Should be around 12V. In most other power supplies we would be done except for replacing the lid. This little beauty, however, has a voltage adjustment potentiometer. How convenient. Computer Power Supplies 12V spec is about +/- 5%, so there may be some headroom left. Turn the potentiometer in the YELLOW Pentagon, indicated by the BLACK arrow CCW until your Digital VOM indicates 12.75 volts. DO NOT booger with the blue pots, as indicated with the universal "NO TOUCHEE" symbol in RED. Remove A/C power. Apply a little liquid electrical tape (or plasti-dip) on the voltage potentiometer to lock it down. Replace lid, careful not to pinch wires attached to P3. (Wires that will exit the chassis circled in grey) Use the salvaged wires on the other end of connector P3 that used to be in the machine to make a DC quick-disconnect to the main unit.
    [​IMG]
    More info: One could replace the potentiometer with one of greater resistance. Pop a hole through the chassis and mount it up. Your mileage may vary on this, and you may very well find the "I'm shuttin' right on down" safety limits of this unit. Or you may cause components to overheat and make man's red fire. I chose 12.75 volts because it is easily obtainable, stable, and a nice compromise between 12V and 13.8V.
    Even more info: Regarding the potentiometer: If it is of common design, the MORE resistance one injects, the HIGHER the voltage. I know... makes no sense... until you realize this resistance is likely being injected between +5V and ground @ pin 1 of a LM317 Voltage Regulator. So you offer more resistance, the voltage drops a bit, at pin one, and The 317 pumps it up to get it back to a reference level. Or something like that.



    Here's the finished product in use, with just over 50 Amps (!) available on the 12 V tap. Cost: About an hour of your time, and disposal of the old computer / parts you didn't use.
    [​IMG]

    At connector P3:
    Black wires: Ground
    Yellow Wire: +12 VDC
    Blue Wires: +12 VDC
    Red Wires: +5V VDC at some ungodly amperage capacity.
    Orange Wires: +3.3 VDC.

    Enjoy!
     
    wavrider and Moleculo like this.

  2. Robb

    Robb
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    Yup

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    Nice job, Butt Fuzz.
    Glad to see ya back here, too . . .
     
  3. Moleculo

    Moleculo
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    Nice!!
     
  4. K6BIG

    K6BIG
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    I have one of these workstations at work...
    the power supply BLEW UP about 2 yrs ago...
    I mean detonated !!

    these power supplies are not cheap... I think we paid
    150 to our door. so if you find one of these working... ship to me
    and I will give you an ASTRON !!! LOL


    K6BIG
     
  5. KG6YGC

    KG6YGC
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    Nice write up!

    Instead of hacking the wires together I use one of the following. They're great.

    http://dangerousprototypes.com/docs/ATX_Breakout_Board
     
    BBB and ButtFuzz like this.
  6. ButtFuzz

    ButtFuzz
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    Now that's a great idea. Going to order a couple from Honk Kong and WAIT! Sweet!
     
    KG6YGC likes this.
  7. ButtFuzz

    ButtFuzz
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    Just put a 'remote' on-off switch on the thing that 'shorts' the black and green wire... and added a nice set of HD speaker lugs for the 12V output. Got the speaker cups/lugs on closeout at Parts Express for $1.25. The power switch is a on-off switch for a set of driving lamps that I pulled out of my parts bin.

    [​IMG]


    All set until the next idea.
     
  8. ButtFuzz

    ButtFuzz
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    Here's a little bench supply I made this evening.
    Introducing: "The Medusa-Matic"

    [​IMG]
     

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