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Very specific question on current draw from a dc power supply

  1. Dec 3, 2011 #1
    okay so im just slightly confused about current and about how it is drawn from a power supply, so say we have a device that requires 5 volts and uses a max of 550 milliamps, and now lets say that the power supply used is rated at 5 volts, but 32 amps, does this mean that the power supply pushes out 32 amps regardless? or is current drawn by the device based on what it needs? forgive me if this question sounds obvious to some, but im just a little confused about it, thanks in advance.
  2. jcsd
  3. Dec 3, 2011 #2
    No, the power supply rated 5V and 32A mean it can provide up to 32A of current. If you draw only 0.5A, it is perfectly fine.
  4. Dec 3, 2011 #3
    Okay so theoretically let's just say I wanted to use a 5 volt line from a power supply from a computer, would I be able to just connect the + and ground to a bread board to use with an op amp or 555 chip? I hope I explained the question clearly. And thank you, it was really helpful.
  5. Dec 3, 2011 #4
    Yes, you can safely tap out the +5V and Ground from your computer and use it on the breadboard of 555.
  6. Dec 3, 2011 #5
    You didn't say if this power supply was still in the computer.

    You cannot simple take a power supply out of a computer, connect it to the mains and expect to use any of the voltage outputs - it simply won't turn on.

    It is possible to modify a computer power supply to become a useful and cheap bench unit, but you will need greater electrical experience to accomplish this safely.

    go well
  7. Dec 3, 2011 #6
    That depends on the PSU.

    I can use the 5V supply on mine without any modifications, but as soon as I tried to use the -12V supply it tripped out.
  8. Dec 3, 2011 #7
    Actually you can short the ps_on pin and a common ground pin to turn it on and yes it works I tried millions of times before. And thank you all for your help, but does anyone know why there are so many common ground leads on computer power suPplies? Lol. But thank you all for your helP.
  9. Dec 3, 2011 #8


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    Wall warts are very handy for this sort of thing. Everyone seems o have some of those, skulking about in a drawer somewhere. (Check the label to see what it should be delivering)
  10. Dec 3, 2011 #9


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    very simply...
    For the same reason that there is multiple +5 and +12V etc leads
    it spreads the high current load any one of those single small cables isnt going to carry the 10++ amps so you increase the number of wires to decrease the resistance and therfore decrease the voltage drop.

    and yes, using computer power supplies outside of the computer is VERY easy to do. They make awesome hi current supplies.

  11. Dec 3, 2011 #10
    Oh okay I see, that makes perfect sense actually. Now if I needed to use a 5 volt low potential connection would the common ground be good enough? Cuz I'm used to the traditional low potential and high potential connections.
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