THE Power Supply FAQ

[Tin]

Most newcomers to the DIY PC world, often overlook one of the most important aspects of a stable system. The power supply never garners as much attention as it deserves. Afterall, a poor power supply can render some of your hadware useless, or destroy your machine as a whole. "How do I choose a power supply?", you say?

Most people go by the wattage rating that is advertised somewhere on the power supply itself. Thats all it is everybody, just a rating. Most of the power supplies on the market today are rated at their peak output, which means it puts out that much power when its begging for mercy....ready to take your rig with it. Wattage means absolutely nothing. Heck, a hair dryer puts out 1200W, do you think it could power your computer? Think of a cheap 600W amplifier, but put it up against a quality 400W and it gets killed. Quality is what we're after everybody.

Now that we know what wattage doesn't matter, so what really does matter? The amperage rating is the most important factor when choosing a power supply. Most modern Intel and AMD systems should have the +12V rail putting out 16a or more. If you look at the label on your power supply, you will see a chart showing the +12V, +5V, and +3.3V rails and how many amps each rail puts out. Many of the newer 6800 and X800 video cards run off of the +5V rail, and will need many amps to back it up. 30a on the +5V rail should be the minimum if you want to run the latest hardware, 40a preferably. The +3.3V rail supplies power to components such as your memory. +3.3V rail should be atleast 25a, 35a preferred though. Running your memory at 3.1V will eat up alot of juice, but think how much more you're using up when you add more modules. Most overclockers usually run atleast a 400W power supply. Once you start adding voltage to various components, its taking more juice to get it to run properly.

The more reputable brands out there are Fortron, Sparkle, Enermax, Enlight, Antec, PC Power and Cooling, and Thermaltake. The Fortron and Sparkle units are the most cost effective, in some cases costing half as much as their Antec counterparts. One of the best methods for determining a quality power supply....pick it up and see how heavy it is. The heaviier power supplies are generally built with more heatsinks and capacitors and such. The lightweight power supply is the one that can bring you down. The heavier it is, the better it is.

If anybody would like to add to this thread, feel free and post.

[HAL9000]

This is so true... I get people coming in looking for a power supply... I tell them $50CDN for a decent Sparkle and they get all offended and cry... I can get a case AND 350w power supply for $29.95 at XXXXXXX.... sigh.. ya.. go buy it... the last guy running one of those... well.. it's faster to tell you what was still good in his system when the power supply blew... modem, NIC, and CDRW.

[Designer]

Normally you can judge the quality by the weight, normally good quality power supplies are heavier than cheaper ones (I know that's not the best way to tell but it's normally a good starting point).

Anyway, great guide Tin, that should probably do away with a lot of "what power supply?" questions and help out a lot of new builders

[mikezel]

There is more to a quality PSU than just the number of amps on each of the rails. While that PSU may have enough amps, it is by a relatively unknown brand, which many of us feel cannot be trusted. If that PSU were to fail, it could potentially take out other components in the system. It is much better to go with a reputable brand which will have the necessary amperage ratings, and will be much less likely to fail.

Yes, like Tin Canary said, amperage is important, but he also said that there are many other factors that contribute to a quality PSU.

Hope that helps
Mike

[Hi Ho]

The claimed ratings aren't always accurate. I have seen some very cheap and low quality PSU's that claim high amps and watts, however they are anything but. For that reason it is best to stay with known brands that have good reputations. I see no reason to buy a generic or unknown brand when one can get an Enlight or Sparkle for almost the same price and get top qulality.

[Panama Red]

Originally posted by KoMoDo ... and all the "at leasts" are for the latest hardware.. so i dont see no reason y not to use that PSU ? it seems pretty good! wadda u think ?

Consider this concept. If you were sky diving, who would you have pack your chute? Would you want somebody that "at least" knows how and is unknown to you or would you prefer a fella with a great reputation among other sky divers and the guy they highly recommend? How much is your computer worth to you? With a low quality or unkown psu, you're letting an "at least" pack it's chute!

[icallmedan]

That is a 500w PSU too, something a lot of people won't buy because they don't need it.

What if you need say a 400w PSU, you can jump over to AnandTech and see Allied is not too good for those.;....

http://www.anandtech.com/showdoc.html?i=1841&p=19

You can also see the benchmarks on the next few pages.

[glc]

The one Allied power supply I bought a couple years ago said Deer Group right on the box. I had to get a P4-ready power supply on a Sunday to do an upgrade in an older Enlight case and it was all I could find that wasn't frightfully expensive or total trash. That said, it's still running fine but I won't buy another unless I absolutely have to.

[colecifer]

Just something people might like to know, i read in Maximum PC that you only need the insance 480 watt psu for the nvidia 6800 if its a generic powersupply they were able to run at 350 and 400 watts with a good quality unit.

[Panama Red]

Originally Posted by JNasci7906 heres my question...im one of those poor fellas who got the psu with the case....if my power supply goes down the crapper...will it take the rest of my system with it...meaning will it fry my mobo vid card and the like...or will i simply need a new power supply??

That's the sad part about psu failures - they are totally unpredictable as to when and what they take with them. Sometimes it's just a power failure and other times it can take mobo, memory, hard drive, vid card - the works! That's why we don't recommend a gamble with poor quality psu's. Oh yeah, and notice I edited your wording to keep the potty mouth out.

[SeaTech30]

What are some signs of a PSU that can't handle a load? Would computer lock ups under windows qualify? Has anyone ever had that exact same problem where the change of PSU fixed it? If so then you guys will save me the shiping for the RMA of my motherboard so plz let me know thank you.

[Kiwi]

Originally Posted by glc Well, the one Allied unit I *had* to use once is still working - it's a 300w unit in a box with an Intel D865PERLL, 2.6C, and a Matrox G550 video card. That said, I still don't trust them simply because it's made by Deer.

I was building my own PC's when it was difficult for private individuals to get the components retail, and the internet's online merchants didn't exist yet. Back then, the Allied power supplies were considered at least as good, if not better, than what came in the high price branded PC's.

Measured by the simplest method, an Allied 250 watt psu is twice as heavy as a PowMax 400 watt unit. That particular 250 dates back 8-10 years, and was in continuous use for 5 to 7 years, on a 24-7 basis. I also have a 300 watt Allied that is still in use, but for that one, it's "only" for four years, and it wasn't running 24-7 for the past year any more.

Meanwhile, my reason for looking at psu threads today is a need for a 300 watt micro-ATX format unit, and those seem scarce!

[larrymoencurly]

It's possible that Allied was a different company or had better standards 8-10 years ago because those I've seen in the last year were sparse inside and had such small heatsinks and power transformers that they couldn't have been heavier than anything else. I can't be sure that Allied has changed, but I know that Powmax has because I have a 5-year-old 300W Powmax that actually looks decent inside, not at all like today's.

The transformer (yellow thing) in this 500W Allied seems to be on the small side in this photo.

[Cricket]

Originally Posted by JC00 As I understood, the weight is one of the clarified and true determining factors. So generic "light-weight" psus are always a no-no? Are there light-weight branded psus?

The most common "branded" lightweight PSU is the DEER brand and brands made by DEER (L&C and AUSTIN to name a few).

Cricket

[Hi Ho]

As I understood, the weight is one of the clarified and true determining factors. So generic "light-weight" psus are always a no-no? Are there light-weight branded psus?

I'm guessing that you mean a well known brand? There are a lot of "branded" PSU's that are lightweight and low quality. Deer, PowMax, L&C, etc. If a PSU is lightweight it is more than likely something to avoid. I have a cheap "350w" PowMax collecting dust along side a 150w PowerWin AT PSU in my shop. The PowerWin weighs three times as much and is much more substantial inside while the PowMax is barren. I'll take a picture of each tommorow and post them.

[Designer]

Originally Posted by JC00 As I understood, the weight is one of the clarified and true determining factors. So generic "light-weight" psus are always a no-no? Are there light-weight branded psus?

If you open up and look inside a quality PSU and an el-cheapo PSU, you'll notice some big differences (which is why the weight is affected)

A) a high-quality PSU will normally have much larger smoothing capacitors meaning the voltage doesnt tend to 'sag' when a large current load is applied to that voltage rail as the capacitors will smooth this out, smaller caps dont offer the same amount of smoothing.

B) Cheaper PSU's tend to cut back to the bare minimum size of the heatsink(s) required, this leads to overheating and premature component failure as excess heat reduces the operational lifespan.

C) Shielding and filtering are often an area that is cut back on, the purpose of shielding is to reduce EMI (electromagnetic interference) which is generated by switchmode power supplies. Filtering circuitry 'cleans' the incoming power reducing spikes which can affect the output voltages of your PSU.

These are some of the factors that reinforce what I said about quality PSU's being heavier. Just thought I should really expalin why I said that

[Kov-Ice]

Can a PSU be plugged in and switched on directly out of the box before being hooked up to any components? Will its fans kick on? Or can that damage it in any way?

[Panama Red]

You have to jumper a wire in order to do so, but yes it can be powered up without being connected to anything. Here's a little something I "borrowed" from another site.

"Simply Jumper Pin 14 ( which is the green wire) to any of the ground pins which are 3,5,7,13,15,16,17 ( all which have a black wire). I use a paperclip to do so, just stick the paperclip into the connector like you would be pluging it into the motherboard."

[Kov-Ice]

OK, I tried the paperclip trick mentioned above. It got the fans to spin up on both the Enermax PSU I had feared was blown and an old L&C that was still working when I removed it from a system last year.

I did find elsewhere that while it would get it to spin, doing it for too long or too many times could cause damage.

Without any testing equipment or a spare mobo to tell otherwise, does the fact that the fans spin up mean the PSU is in working order?

[Designer]

What your gonna need to do is get a voltge tester and check ll your voltages are correct/present. Although this doesnt prove that thye voltages stay correct when under load (testing that is slightly more difficult) but at least you can see whether it's worth investigating the fault further than just assuming the PSU is dead

[flanzig1]

Just did a quick visual comparision between a four year old 200w Sparkle and a new MGE("Manufacturer of Good Electronics" is their slogan) 400w PSU. The sparkle has big, extruded heatsinks will the MGE heatsinks are flat metal plates. Even the components like wire size,choke size, transformer size looks heftier in the old Sparkle than the MGE.

[Designer]

Saw this on Xoxide and thought this would be ideal for people wishing to test out power supplies without the hastle of bridging connections and hooking up a voltmeter

http://www.xoxide.com/atx-power-supply-tester.html

It's a complete PSU tester (only indicates the correct voltages are present) and that the power good signal is present, not bad for $9.99 i thought

[WhatsThisBoxFor?]

Saw this review, and thought some might be interested: http://www.trustedreviews.com/articl...d=64&page=2279

Shows how important it is to get a good power supply - two of the tested ones blew up, and they brand name ones, not generic or Deer ones.

I make up units for charitale groups out of other peoples discards. I found a mb with an amd 750 chip that was thrown out.At first the mb just sat on the bench and twinkled. Tried a different ps and video board and got beebs, different video and ps (400 watt) and voila, then got a 500 watt ,hooked it up and was at square one again. Just for kicks I tried a 200 watt from a gateway and it worked, another gateway of the same type got me to square one again.Is there a timing difference in power supplies? If so how can it be tested?

[Hi Ho]

There is not "timing difference". They are all the same as long as they are the correct form factor (Mini-ATX, ATX, etc.). Many of the big name manufacturers use proprietory power supplies that will not work with anything else and a standard ATX PSU will not work in their machine. If could be that either the power supplies you were trying were low quality or defective or the motherboard was.

[larrymoencurly]

Originally Posted by jerryhall I found a mb with an amd 750 chip that was thrown out. At first the mb just sat on the bench and twinkled. Tried a different ps and video board and got beebs, different video and ps (400 watt) and voila, then got a 500 watt ,hooked it up and was at square one again. Just for kicks I tried a 200 watt from a gateway and it worked, another gateway of the same type got me to square one again.

The only possible timing differences are with the Power_Good signal on the grey wires, but I haven't heard of problems related to this except with very, very old PSUs where crude circuitry was used for the timing.

I think that one of your 200W Gateways and the 400W were OK, while the other Gateway may have been defective and the 500W was just wimpy.
Gateway and the majors tend to use the best PSUs that can put out more power than most with the same watt ratings, but some so-called 500W PSUs are actually built more like 200-300W PSUs, only with the overload protection calibrated for a higher power level (maybe too high for the PSU to stand).

If a PSU works OK only at lower power levels, then maybe its electrolytic capacitors have gone bad. OTOH complete failure may mean a blown diode or transistor.

[Hi Ho]

Gateway and the majors tend to use the best PSUs that can put out more power than most with the same watt ratings

Actually, many big name manufacturers install the bare minimum required to run the system as is. Anything more in many name brand systems can overload them. Worse, a lot of the time they use proprietory power supplies so the only chance of upgrading is to buy a PSU from them at an inflated price.

[Andrew Downie]

I don't know whether or not i have posted this link up here, but this is a good site to go where you can add the specs of your machine in, along with some other devices, and it will give you a reading of what wattage your PSU should be to cope with your machine.

http://www.jscustompcs.com/power_supply/

Hope this helpes some people!!!


Thanks,

AD

[Hi Ho]

Those calculators can be useful but they tend to over estimate power needs.

[larrymoencurly]

Originally Posted by Hi Ho Actually, many big name manufacturers install the bare minimum required to run the system as is.

What I mean is that a big name computer manufacturer's 275W PSU can probably put out more power than the typical 300-350W PSU.

Anything more in many name brand systems can overload them. Worse, a lot of the time they use proprietory power supplies so the only chance of upgrading is to buy a PSU from them at an inflated price.

Dell proprietary PSUs have the same plug as standard ATX ones do, and plugging one of those Dells into a regular mobo will match several +5V wires with grounds. But most other major brand PSUs and some Dells with the same plug are compatible with regular mobos.

I've had no problems using Acer (Delta) and IBM (Lite-On) PSUs with regular ATX mobos, and these things are unusually heavy for their 300W ratings, and the Delta has a larger than normal transformer despite it running at a higher frequency than normal (higher freq. usually means a smaller transformer can be used for the same power).