Another Power Supply question.

[Byte 2.0]

Ok, I am trying to settle and argument at work. I don't care if I am right or wrong, but I want to know for sure.

If you have 2 computers, both with 450 power supply's. Lets say one has several extra componets, while the other is very light on features.

Call them PC Lite and PC Heavy.

would PC Heavy use more AC power then PC Lite, or would the Power Supplies Cause an equal Draw on AC power?

I made a statement to that in this example, if PC Lite only needed 250 Watts to run, the Power supply would supply only that much power, in short using less AC power.

Whereas PC Heavy, if it needed 400 Watts to run, the Power supply would produce 400 Watts and would draw more AC power then PC Lite.

I had a person arguing, that both would use the same amount of AC power, that the 450 Power supply's made consist 450 Power, so that much would always be available instantly for the PC should it need it.

I thought that was totally wrong, in that 450 would normally be a Max power rating, to me meaning the power supply would supply on a demand level up to the max it could.

Anyone want to jump into this one?

[Panama Red]

I think yours is the right answer. Electrical devices, whether AC or DC are rated in watts or amps. Those are LOAD ratings. The load is only applied when those devices or doing work. This shows itself quite clearly when you load a cpu or vid card using Prime95 or 3DMark programs. The load is evidenced by the increase in heat and the corresponding increase in heat coming from the power supply. If he wants to validate or disprove this theory, open up a power cord feeding the power supply so you can access a single wire. Attach an amp clamp and try a no load and loaded test.

[Larry E.]

You are right the power supply will deliver whatever power is needed up to it's max then things happen that bring people to post on this forum.

[Byte 2.0]

Larry E. I just notced you are in Aberdeen. I talk to people in Aberdeen almost daily from work. I also talk to people in the North Sea on the platiforms.

[pam123]

I'll take a shot at it.
I remember this quote : " It's okay to buy a power supply that is larger than necessary because the power supply will step down to your power requirements. "
So okay power supplies do self-regulate.
Antec's True power has a spec page : http://www.antec-inc.com/specs/true430_spe.html
What catches my eye in the box on input, how much current the psu draws.
This is where someone who knows more than I will have to take over.
I think I'm looking at the average draw for the power supply which means it changes.

[Larry E.]

Yup, been in Aberdeen all my life. Great little town about 20 miles from the coast.

[Techdec42]

The temperature also depends on which room the PCs are in and the temp in the rooms, referring to the second law of Thermodynamics

[Byte 2.0]

Both are in the same room about 2 to 3 feet apart, both on the floor.

[David M]

Watts are the units for power. Amps are the units for current. You can't measure power directly. You have to measure the amps and then multiply by the potential (units being volts) to measure the power being drawn.

To answer your question though, a power supply will put out what is being demanded of it up to the point where its incapable of producing more power.

A power regulator senses the voltage and if the voltage drops it will strengthen the magnetic field which in turn increases the amperage until the voltage comes back up to spec. This all happens very fast.

Efficiency and power factor is affected by a whole slew of variables including temperature.

Therefore, if 150 watts is being drawn from a 300 watt and a 400 watt PSU then both will be drawing the same amount of watts from the wall outlet provided all those variables are the same. I doubt any PSU is exactly the same, even those coming off the same assembly line.

[allburnintegrated]

The first law of physics: Energy cannot be created or destroyed. So if the PSU was drawing more power than was needed by the components, it would have to be released somehow, it can't just do nothing in the PSU. And the current drawn from any power supply (not just computers) increases as components need more (resistance decreases). The current drawn isn't decided by the power supply.