2 simple power supply questions...

[gwolfman]

I have two questions regarding power supplies.

1.) If I want to turn on an ATX power supply without it being connected to the motherboard, which pins do I short out on the 20-pin/24-pin ATX power connector? (either pin number or color) Was it purple and gray?
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2.) This on is with regards to power usage. I know that the wattage of power supplies is determined by the maximum output of that power supply, but what about power usage on a light load?

For example: Say I have a 500 watt and a 1000 watt power supplies both rated at 80% efficiency. 300 watts of power is being drawn from each. Does the 1000 watt use more electricity to provide the 300 watts the computer is using or does it require the exact same amount of power that the 500 watt will be using (ignoring the fact that the 500 watt PSU is at a higher load percentage wise which usually means it will be less efficient at the higher load)?

In other words, will I use/waste more electricity buying a higher wattage PSU than a lower wattage one leaving all else the exact same?
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Any help would be greatly appreciated, thanks!
-GWolfman

 

[foz]

1. Green and any black
2. Check the reviews here, he does an efficiency rundown on all the power supplies he tests. PSUs are the most efficient in the middle of their range.
http://www.jonnyguru.com/reviews.php?catID=1

 

[MrCommunistGen]

In reply to your second question, it entirely depends on how efficient the power supplies are at whatever load you are at. Efficiencies can and do fluctuate based on load. At least theoretically if the efficiencies are the same, then the power being drawn from the wall socket should be the same.

-mcg

 

[DJ_Jumbles]

Your load is what dictates your power usage with either power supply. The amperage that you draw from the wall is based on the efficiency of the PS you have and the total load that you are placing on it (at what voltages). There are a whole other host of factors to take into account, but assuming that your load is the same for either supply and they are both rated for the same efficiency, your power draw should be no different. The difference is in the maximum rated power draw from the components that are connected to the PS. This is, of course, assuming what you said about the higher load percentage on the 500W supply.

 

[gwolfman]

1. Green and any black
2. Check the reviews here, he does an efficiency rundown on all the power supplies he tests. PSUs are the most efficient in the middle of their range.
http://www.jonnyguru.com/reviews.php?catID=1

Thanks, I'll check the link out!

In reply to your second question, it entirely depends on how efficient the power supplies are at whatever load you are at. Efficiencies can and do fluctuate based on load. At least theoretically if the efficiencies are the same, then the power being drawn from the wall socket should be the same.
-mcg

Thanks, well put. Clear and to the point.

Your load is what dictates your power usage with either power supply. The amperage that you draw from the wall is based on the efficiency of the PS you have and the total load that you are placing on it (at what voltages). There are a whole other host of factors to take into account, but assuming that your load is the same for either supply and they are both rated for the same efficiency, your power draw should be no different. The difference is in the maximum rated power draw from the components that are connected to the PS. This is, of course, assuming what you said about the higher load percentage on the 500W supply.

Very descriptive, thanks for the extra details.