Very specific question on current draw from a dc power supply

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Discussion Overview

The discussion revolves around understanding current draw from a DC power supply, specifically in the context of using a computer power supply for various electronic components. Participants explore the implications of power supply ratings, safe usage practices, and the technicalities of connecting devices to power supplies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about whether a power supply rated at 5V and 32A pushes out 32A regardless of the device's needs, or if the device draws only what it requires.
  • Another participant clarifies that the power supply can provide up to 32A, but the device will only draw the current it needs, which in this case is 0.55A.
  • A participant inquires about using a 5V line from a computer power supply for an op-amp or 555 chip, seeking confirmation on the safety of this approach.
  • Responses confirm that it is safe to tap the +5V and Ground from a computer power supply for use on a breadboard.
  • Concerns are raised about the feasibility of using a computer power supply outside of its original context, emphasizing that it typically won't operate without modifications.
  • Some participants note that while some computer power supplies can be used without modifications, others may require specific adjustments to function properly.
  • A participant mentions the ability to activate a power supply by shorting specific pins, suggesting a method to turn it on for use.
  • Discussion includes the utility of wall warts as alternative power supplies and the commonality of having them available for projects.
  • Participants discuss the reason for multiple ground leads in computer power supplies, attributing it to the need to handle high current loads and reduce voltage drop.
  • A later reply questions whether a common ground would suffice for a low potential connection, indicating a preference for traditional high and low potential connections.

Areas of Agreement / Disagreement

Participants generally agree on the basic principles of current draw from power supplies, but there are differing views on the specifics of using computer power supplies outside their original context and the necessary modifications for safe operation.

Contextual Notes

Some assumptions about the operation of computer power supplies and their modifications remain unaddressed, and there are unresolved details regarding the specific requirements for safely using these supplies in different configurations.

matinm90
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okay so I am 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 let's 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 I am just a little confused about it, thanks in advance.
 
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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.
 
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.
 
Yes, you can safely tap out the +5V and Ground from your computer and use it on the breadboard of 555.
 
Okay so theoretically let's just say I wanted to use a 5 volt line from a power supply from a computer,

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
 
Studiot said:
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
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.
 
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.
 
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)
 
And thank you all for your help, but does anyone know why there are so many common ground leads on computer power suPplies?

very simply...
For the same reason that there is multiple +5 and +12V etc leads
it spreads the high current load anyone of those single small cables isn't going to carry the 10++ amps so you increase the number of wires to decrease the resistance and therefore 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.

cheers
Dave
 
  • #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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