Efficient Power Supplies: Part 1

Good morning!  This is an intro article…feel free to skip if you already know what efficiency means for power supplies.  Part 2 goes into detail of the 80 Plus standard and is likely a more enthralling read for you spec heads!

Let’s talk about the most important piece of hardware that a desktop computer can have…the power supply!  This little guy is responsible for electrifying all the goodies inside your computer.  Furthermore, a good power supply protects your computer from dirty power (voltage spikes, EMI ripple, power fluctuations, etc).  If you have ever read an article on custom desktop building, you probably know how crucial a good power supply is, as well as the consequences of using a cheap PSU.  Suffice it to say that, for the sake of your computer’s health, this is one area where you don’t want to skimp on cost.

There is one trait of quality power supplies that is often overlooked, and that is energy efficiency.  In a perfect world, a PSU would convert every watt of 120 V AC input power into usable DC power.  In reality a portion of the power is lost as heat.  The more efficient a power supply, the less energy it wastes as heat.  In other words, your computer simply draws fewer watts from the wall.

Having an efficient power supply is crucial for F@H contributors and non-folders alike, because it will make your computer less power hungry no matter what it is doing.  From gaming and graphics design to office work and Folding@Home, an efficient PSU will put a smile on your P3’s cute little face.  (If you don’t get the reference, please also read the previous post about Watt meters)

Before I go on, I should note that the target audience of this article is those who have built or are building their own custom desktop.  People with laptops or with name-brand consumer desktops are sometimes out of luck because the power supplies are often proprietary and can’t be upgraded.  However, it doesn’t hurt to find out from the manufacturer of your computer what the efficiency of your power supply is.  Some brands, such as Dell, HP, and Apple (among others) do have energy efficient power supplies of varying levels in their machines.

Cheap No-Name Brand Power Supply Unit

If your power supply looks as lame as the one in the above pic, then it probably has an efficiency rating of 60 to 70 percent.  This means that if your computer parts need roughly 200 watts of power to run, your PSU might draw 250 watts or more from the wall in order to supply the 200 watts of DC power.  That extra 50+ watts is wasted as heat.

PC Power & Cooling SILENCER PSU

Seasonic SS-380GB PSU Installed

But, if your power supply looks like the one in Pic # 2 or #3, it might be closer to 80 or 90 percent efficient.  For that same 200 watt load, it is only drawing perhaps 220 watts from the wall.  The thirty watt difference might not seem like much, but for a Folding rig running 24/7 the wasted wattage of the el-cheapo unit adds up.  Let’s assume we are running a machine with the craptastic PSU.  To calculate the total extra energy wasted relative to the better PSU (remember, watts is a power quantity, which means energy/time), we need to multiply the wasted wattage by the amount of time the computer was in service to get an energy quantity in watt-hours.  So, 30 watts * 24 hours/day * 365 days/year = 262800 watt-hours.  Converting to kilowatt hours (dividing by 1000) gives 262.8 kWh.  Assuming an average electricity cost of ten cents per kWh, we get an annual cost of 262.8 * 0.10 $/kWh = $26.28.  Assuming the folding computer is running with that same power supply for 5 years (mine has been going for longer), that is over $125 wasted dollars, not to mention a slap in the face for poor planet Earth!  A good energy efficient PSU could have been bought for $40 in the first place to negate this wasted energy cost and lessen the environmental impact.

So how can you spot an efficient power supply unit?  Well, for that you can go by the independent test & certification program known as 80+.  I will cover this in detail in the next article, so that people who want to jump right into the specs and skip this intro can do so.