Will a 10 Ω resistor create 2.5 W of dummy load on 5 V line (using an old ATX PSU)?

Question

I am trying to understand something about dummy load resistors.

I have an old ATX PSU. It has a 5 V line; maximum is 34 A, but it says it needs a minimum of 0.5 A. That means it needs a minimum load of 0.5 A to function properly, since its an ATX PSU (let's assume that it does not have a dummy load built in).

So I need to create a dummy load of 0.5 A to have a stable voltage.

In order to achieve this, I need to put a 10 Ω resistor on that line.

Enter Ohm's law:

R = E / I 
  = 5 / 0.5
  = 10 Ω

So a 10 Ω resistor will create a load of 0.5 A on a 5 V line? Is my understanding correct?

And then to calculate how much power it will dissipate:

P = I² * R
  = 0.5² * 10
  = 2.5 W

My goal is to create this 0.5 A load and, of course, not destroy the resistor. So to accomplish this, I need a 10 Ω resistor rated at 2.5 W or above that value, so it can withstand that 2.5 W load as it will get hot.

Is it really that simple?

Answer 1

Yes, your calculations are correct. It's really that simple.

Another way to calculate the power dissipation is by multiplying voltage with current, which results into same 2.5W power.

But it is not that simple to use computer ATX supplies as generic lab power supply. No one can guarantee if your power supply will work in a stable fashion if you simply put a 10 ohm resistor to 5V output.

So it is possible that connecting and disconnecting arbitrary capacitive, resistive and inductive loads to it will make it shut down or be unstable.