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Choosing power supply, how to get the voltage and current ratings?

I have a pc power supply which I modded to use as one for my projects. It's really cool, and I love it.

I just have a question though. Say I am using the 5V port with a device like a regular old dc motor. Can I connect the motor directly to the power supply without regulating it in some way?

What I am trying to say is that the power supply is capable of delivering high current, so are there devices which will actually try to take as much power as possible just because it is available? If so, do I have to control this in any way?


A common misunderstanding. No, a 10 A supply will only deliver 10 A if the load asks for that. If you connect a 1 kΩ resistor between the 5 V output and ground, then, due to Ohm's Law there will be a current of 5 V/ 1000 Ω = 5 mA. The resistor doesn't care about the 10 A, it only cares about Ohm's Law. Even a 5 kW supply, able to deliver 1000 A at 5 V won't hurt the 1/4 W resistor.

Depending on the motor's power you can connect it directly because the 5 V is regulated. You may want to decouple the motor though, by placing an electrolytic capacitor in parallel with it. The value depends on the motor's current.

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  • \$\begingroup\$ Since this question is so common we made a standard reference post for it. I would enjoy if you added to a post or made your own there. \$\endgroup\$ – Kortuk Jul 25 '12 at 17:21
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    \$\begingroup\$ @Kortuk - Dammit, I have an answer there, I just forgot. Sorry. (This calls for a question on meta. All to meta!) \$\endgroup\$ – stevenvh Jul 25 '12 at 17:24
  • \$\begingroup\$ Thanks a lot! And I am sorry about the duplicate question, I didn't notice something similar. I will be more careful next time. \$\endgroup\$ – capcom Jul 25 '12 at 17:25
  • \$\begingroup\$ @capcom we appreciate you will try to do better, since that one was worded a certain way you might miss it, nothing to worry about. \$\endgroup\$ – Kortuk Jul 25 '12 at 17:25
  • \$\begingroup\$ @stevenvh sounds like you right answers so fast no one has a chance to warn you it is duplicate, we all have our flaws :) \$\endgroup\$ – Kortuk Jul 25 '12 at 17:26

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