Power Supplies: The shocking truth.

[MediaMan]

"When was the last time you looked at a power supply in the computer case? Have you recently bought a power supply smug in the knowledge that "you've bought the best"? What if that expensive 400 Watt power supply...wasn't? What's on the label isn't necessarily what comes out the cable. Take a closer look with us at power supply specifications and find out if you've really got the power."

Better make sure you are grounded. Check it out here. (http://www.short-media.com/review.php?r=133)

[mmonnin]

Good article. YGPM.

[TheSmJ]

Good stuff. This is the wort of thing I wish CompUSA customers would be aware of....

Those people....

[edcentric]

Nice job MM.
If the foundation isn't solid the building is no good. The same is true with computers.
As much as I hate to say it THG has a good review of PSUs up. Typical Tom's fashion they gloss over a few key points. But at least they actually load test the units. None in this batch smoked, but some droped voltage real bad.

[Gargoyle]

Excellent article MM! Now I've got to go check the new PSU I just bought and find out if it was a good idea or not :D

[Straight_Man]

Good article.

John.

[Unregistered]

Really Good Article, This is Usefull for Students.

M.Madasamy.

[entropy]

Is it just me or is the link dead?

[Gobbles]

link is dead

[Jimborae]

Houston we have a problem ----- dead linkage :)

[MediaMan]

fixed. :)

[tjo]

Good article, but the print friendly version is slightly too wide. Chops off a few characters on the right side. Adjusting margins, etc didn't help; had to cut and paste and then muck with the width parameters in HTML to make it print out OK.

[Unregistered]

A PFC equipped power supply may not affect the overall wattage performance but it allegedly makes the power supply more efficient at managing a stage of converting AC into DC and therefore reduce energy costs.

PFC makes the amps less "peaky," which helps power companies because their wiring has to be capable of carrying the peak amps, and with PFC they can deliver more power without increasing the peak amps. Commercial electric customers are billed according to PF, but, at least in the U.S., residential customers are not, so PFC won't cut their costs. The only benefit PFC gives them is the ability for their UPS to deliver more power (notice they're rated by VA, which is equal to power with a PF of 1). PFC actually reduces efficiency and raises cost of operation a very slight amount.

[edcentric]

MM, I have just gotten around to looking at the Fortron Blue thing.
There is something fishy about the rating.
They list 150W for 3.3 + 5. Sounds low.
and then for 3.3+5+12 they list 440W. It doesn't add up for me.

[floppybootstomp]

Just a small observation. The terms 'positive and negative' are usually used when referring to AC.

When dealing with DC I've always understood 0V (Nought, or zero, volts) to be the 'negative' with either a plus or minus volts being referenced to it.

A split rail PSU would be be a twin rail supply with both a plus and a minus volts referenced to 0V.

Therefore, when considering a minus volts, the 0V (generally referred to as the 'negative') would in fact be the positive.

Therefore, imo, it's always best to refer to DC voltage as plus volts and 0V or minus volts and 0V, not positive and negative.

[MediaMan]

MM, I have just gotten around to looking at the Fortron Blue thing.
There is something fishy about the rating.
They list 150W for 3.3 + 5. Sounds low.
and then for 3.3+5+12 they list 440W. It doesn't add up for me.

Welcome to the wonderful world of specifications. It's a challenge at times to determine what the "real" specs are. Try wrapping your head around stereo specs for a change.


Power Factor...hmmm...hopefully these snippets will help explain.

WHY IS POWER FACTOR IMPORTANT?

KVa is total power available to you and what you pay for. The lower the Power Factor, the more KVa is needed. Low Power Factors tend to make system voltage unstable, increase heat in electrical apparatus and can cause failure of electrical equipment. Many utility companies bill you for your poor Power Factor, increasing your cost of electricity. Utility companies have multiple rate schedules, and depending upon your rate schedule, Power Factor penalties may be a separate line item as a demand charge or may be considered as part your general electrical usage.


And now the marketing doctor's spin


Power factor correction sharply reduces the demand for reactive current which in turn saves fuel, reduces transmission and transformer losses, improves voltage regulation, and increases available capacity throughout the power company's system without additional investment in generation or distribution. Reducing peak current demand can allow the utility to postpone the construction of new generating capacity.


And I always said the PFC is best explained mathematically so ...Expand and bend your mind. (http://www.engr.udayton.edu/udiac/Documents%5CElecSys_PowerFactor.doc)

[EMT]

Neat article. I'm on the middle of page 2 and I disagree with the bottom bit about amps. Suppose the 12V line can put out 20A max (240W). The devices are connected in parallel so they get the same voltage and different currents... then the current delivered by the power supply is the sum of the currents through each of the devices. Note that this means the load is "too much" beyond 20A and beyond 240W (these will always occur at the same time -- you can check for either excessive wattage or amps and one implies the other).