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I want to power four devices with different working amperages.

  • 1st device: 0.015A, 12V
  • 2nd device: 1A, 12V
  • 3rd device: 1A, 12V
  • 4th device: 3.5A, 12V

Power supply: DC 12V 6A Power adapter

I'd connect all four of them to power source in parallel, to make the voltage stay the same in each branch (correct me if I'm wrong)

Would a power supply with an output of 6A be enough to properly power them all? Because 1A+1A+3.5A+0.015A=5.515A≈6A= Output of the power supply (Is that correct?)

So how can I provide different amperages to devices with single power supply? Here is a simple scheme if it helps: enter image description here

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    \$\begingroup\$ I don't get what you really want. You connect them in parallel, established that the amperage of the psu is enough, what else do you need? \$\endgroup\$ – PlasmaHH Mar 23 '18 at 16:18
  • \$\begingroup\$ As long as some of them or the biggest does not have a start surge > current limit then it wont shut down. But generally you have to derate max current to run cool or allow for start surges \$\endgroup\$ – Sunnyskyguy EE75 Mar 23 '18 at 16:18
  • \$\begingroup\$ You are correct, the voltage is regulated to 12v and the current draw by all devices combined is less than the supply can provide. The only thin you need to consider is whether the devices draw more power on startup ...this could be because of a motor within a device or even just large filter capacitors in a device. \$\endgroup\$ – Jack Creasey Mar 23 '18 at 16:18
  • \$\begingroup\$ PlasmaHH What I don't get is how these four devices will draw the current out of the power supply. Will they just draw the amount of current that they need or will the power supply itself just spread the current across all four branches however "it wants". I know that I=V/R, but what I don't know is what will the resistance of each branch be. Excuse my newbieness, but I don't think it would be good to use R=V/I formula on this one. I hope you now understand what I want. \$\endgroup\$ – Spoods Mar 23 '18 at 16:32
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You are correct. As long as the sum of the currents does not exceed the output capability of the 12V supply, it will work fine. It is also good to add a little margin, as you did by selecting 6A.

Note that if you are using actual wires to connect up the various devices, there will be a different voltage drop from the source supply to each device, but with a decent wire size and your current levels, this will be negligible. There is a voltage drop calculator here.

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V=IR

Different current draw at the same working voltage means they have different resistance. Wiring them in parallel gives them all the same voltage. They will draw current as needed.

That being said, it's good practice to leave some buffer for a supply's current capacity. So if you need 5.5A, you may want to use a supply labeled for 7A. This is called "de-rating". Not derating (may) result in a supply than can get very hot or even fail (and the voltage will drop).

Reasons for needing to derate stem from inaccurate capacity ratings, unforeseen current spikes, and device aging. You may be able to get away with a 6A supply, but be sure your measurements are accurate for current draw and supply voltage. If the voltage drops is large after connecting the load, you may want a larger capacity supply.

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