When you buy a PSU, you must buy twice as much as you need!

[Wai_Wai]

When you buy a PSU, you must buy twice as much as you need!!

Did someone hear such kinds of advice:

"You should always get a [power] supply that supports about twice the load (on each given rail), in amperes, because that is how you better assure longevity, cool operation, quiet operation, max electrical efficiency (to save on electric bills), lowest ripple and noise current, and so on."

Twice? And also for each rail?

The statement looks strong. If my system needs 300W (3.3 & 5V: 40W; +12V: 240W), I must AT LEAST get 600W (3.3 & 5V: 80W; +12V: 480W) PSU to be safe. o_O It sounds like it's meant to be the only a minimum requirement.

Regarding the "double requirement" it said:

Twice is the value I have gotten from lots of reading and communication in forums with people that help test and design power supplies.

From the sound of it, the "double requirement" is not some general advice. It has some science or research to support it. Yet I couldn't find one of them.

What do you think?

Edited July 13, 2008 by Wai_Wai

[jaclaz]

Well, since you did not find any article, WHERE did you quote from?

It is a "rule of the thumb" that has it's merits when you look at reliability, efficiency and possible heat peaks of the PSU, of the case, or of the room where the PC is.

Additionally, PSU somehow work like big cars, that can, at medium speed, actually burn less fuel than smaller ones.

You may want to read this article:

http://www.hardwaresecrets.com/article/181

And expecially pages 8 and 9

http://www.hardwaresecrets.com/article/181/8

http://www.hardwaresecrets.com/article/181/9

Very often, besides, it's the initial data that is a bit too high, the use of a calculator to more accurately sum up the amount of power actually needed is strongly advised:

http://extreme.outervision.com/psucalculatorlite.jsp

you may find out that the requirement to be doubled is less than what you expected.

jaclaz

[Wai_Wai]

since you did not find any article, WHERE did you quote from?

Sorry. I mean there is no other (formal/reputable) article on the net which suggests this.

I read it from a page somewhere from an anonymous. It claims "Twice is the value I have gotten from lots of reading and communication in forums with people that help test and design power supplies." So there is some science to back up "double requirement" but I can't find any (except that passage).

It is a "rule of the thumb" that has it's merits when you look at reliability, efficiency and possible heat peaks of the PSU, of the case, or of the room where the PC is.

I understand the merits of not over-stressing a PSU. But this alone doesn't justify we should ALWAYS double the needs of EACH RAIL.

The points mentioned are still too weak to justify the double requirement.

Very often, besides, it's the initial data that is a bit too high, the use of a calculator to more accurately sum up the amount of power actually needed is strongly advised:

http://extreme.outervision.com/psucalculatorlite.jsp

you may find out that the requirement to be doubled is less than what you expected.

I use this to estimate my watt usage. It even calculates 3.3/5/12V rails. It's much better than the above lite calculator:

http://web.aanet.com.au/SnooP/psucalc.php

OK, after doing the calculation, if its recommendation is 300W, do I still need to double the requirement and go buy a 600W PSU?

PS: I know clearly that I shouldn't buy from bad brands. I know total watt is not the only requirement etc. I don't need to use "so much headroom" as a measure to keep me safe.

[CoffeeFiend]

It's just one anonymous guy who says so, don't lose sleep over it.

Going for higher certainly is a good idea -- room for expansion/upgrades, not operating at the max capacity of the PSU (not the most efficient point in the curve, and also not making them heat up as much), as well as working reliably for longer (due to things like electrolytic caps aging).

I have yet to hear anyone knowledgeable (e.g. jonnyguru) say you should double any rating (and I'm not a complete moron either, I've even built simple SMPS'es before -- usually using Maxim's ICs, and also repaired plenty of them)

OK, after doing the calculation, if its recommendation is 300W, do I still need to double the requirement and go buy a 600W PSU?

Nope.

And I can't say I care much for that other calculator myself for various reasons.

[Wai_Wai]

Yes you are right. The advice and the reasons are BS.

Talking about buying much more than needed for future expansion,

When I pick a new PSU, my choice is narrowed down into 2:

A. buy a more powerful PSU (eg 500-700W) to serve me 5-7 years. It should still be able to serve me after 3 years I upgraded most components. The power consumption can be lower or higher but I assume the worse case.

B. buy a PSU which is just what I want (eg 300-400W). Of course some headroom has been included. Then upgrade PSU again after 3-4 years.

These factors affect my choice:

- price

- usefulness of adapter (it can help my PSU to be more future-resistant)

- degree of aging (how much percentage of power is reduced after 5-7 years)

- average lifespan of PSU

I only upgrade once every 3-4 years. At that time I upgrade I find out I always need throw all components away except "HDD / FDD / DVDRW" and maybe "PSU".

Which choices should I pick?

What do you think?

Edited July 13, 2008 by Wai_Wai

[CoffeeFiend]

A. buy a more powerful PSU (eg 500-700W) to serve me 5-7 years. It should still be able to serve me after 3 years I upgraded most components. The power consumption can be lower or higher but I assume the worse case.

Honestly, I'm not sure one can plan on 5 to7 years on a PSU right now. In the same system? Sure. But eventually connectors change. In the last 5 to 7 years, we've seen drastic changes PSU wise:

-the 4 pin P4 connector

-24 pin motherboard connectors

-SATA power connectors

-PCI-e power connectors

And that's not counting fundamental changes in their design, like the shift from high-amperage 5V bus in old designs to more power on the 12v rails, and more recently multiple rails, and more advanced features in nicer PSUs (things like active PFC weren't exactly common 7 years ago), besides the obvious increase in power ratings.

Just saying. I doubt I'll be reusing my PSUs in a new PC in 7 years.

What to chose exactly is a matter of budget, preferences and priorities. There's many good PSUs on the market nowdays, and plenty of garbage ones too.

Edited July 13, 2008 by crahak

[Wai_Wai]

How serious PSU aging is?

Aging occurs and this will affect the power supply.

1) How serious is aging? How much percentage of power supply will be lost after, say, 5 years of usage? Is there any article which research the aging effect?

2) For whatever reasons, BSOD has been triggered. Doe BSOD hurts any physical component?

3) If it somewhat falls below the maximum watt required by my system, what will happen? Will my other components be physically damaged?

4) When it is old or weak or next to death, is there any sign I can notice before tragedy occurs (eg fire, damaged CPU/RAM/mobo etc.)?

Thanks.

[gamehead200]

[ Topics merged. ]

Please don't create new topics when you've already started a similar one.

[DL.]

How serious PSU aging is?

Aging occurs and this will affect the power supply.

1) How serious is aging? How much percentage of power supply will be lost after, say, 5 years of usage? Is there any article which research the aging effect?

2) For whatever reasons, BSOD has been triggered. Doe BSOD hurts any physical component?

3) If it somewhat falls below the maximum watt required by my system, what will happen? Will my other components be physically damaged?

4) When it is old or weak or next to death, is there any sign I can notice before tragedy occurs (eg fire, damaged CPU/RAM/mobo etc.)?

It's an interesting question you got there about PSU aging, I thought about it myself when checking out the "eXtreme PSU calculator".

2) No, it doesn't. However, it's usually caused by a bad driver or faulty hardware.

3) Your system may become unable to start, for example the hard drive not spinning up or the system won't even POST.

In the worst case the actual PSU itself will be damaged by overload (in rare cases and under too much load there have been PSUs catching fire).

4) Similar to 3). You can also sometimes hear some high-pitched or other unusual noise coming from the PSU. Having multiple components failing in a short period of time is a surefire sign that something i wrong.

Also if the system just shuts down (multiple times) for no apparent reason you could suspect the PSU to have something to do with it. But not everything like that is caused by the PSU, the mainboard may also play a part.

A bad PSU may damage your components; a few of my friends had a number of HDDs dieing on them because they used cheap noname PSUs. After switching the PSUs they haven't had a single problem of that kind.

Edited July 14, 2008 by DL.

[CoffeeFiend]

1) How serious is aging? How much percentage of power supply will be lost after, say, 5 years of usage? Is there any article which research the aging effect?

I've often seen figures saying 10% of their capacity per year, assuming it's powered on 24/7. Never actually measured myself. But then again, quality varies a great deal when it comes to electrolytic caps -- another reason not to buy cheap no name PSU's. To offer dirt cheap products, they have to cut corners somewhere, and quality caps are usually one of the first things to go. It's been particularly bad in the last few years, with some manufacturers offering some very poor quality caps that go bad pretty quickly (you might have seen the tell-tale bulge on the tops of caps on a motherboard before...)

Personally, I always go for 30% extra to account for this. I've just gone through WAY too many power supplies before that were just barely sufficient. I'd rather buy one good quality and powerful power supply once for a little more $, than have to replace it every year and dealing with the problems you get when they go bad. Buying twice or more isn't really cheaper than buying a good one in the first place either. And again, going for something that sometimes looks overkill means room for expansion/upgrades and not running near 100% capacity (less heat, better efficiency), even with some capacitor aging.

2) For whatever reasons, BSOD has been triggered. Doe BSOD hurts any physical component?

A BSOD itself doesn't damage your computer. It's Windows' way to make you aware it has detected a serious problem with your system that it can't recover from (bad drivers or faulty hardware). It basically just stops.

3) If it somewhat falls below the maximum watt required by my system, what will happen? Will my other components be physically damaged?

If the PSU is too weak, your system can become unstable, reboot without warning, have various issues (like hard drives "disappearing"), not POST at all, etc.

4) When it is old or weak or next to death, is there any sign I can notice before tragedy occurs (eg fire, damaged CPU/RAM/mobo etc.)?

Most faulty PSUs are found when you try to find out why a system has problems.

Anyways. Pick a good quality model, from a reputable company, with some head room, and you'll be just fine. It doesn't have to be a crazy overpriced model to be good either, look at specials, there's often some good deals on very nice models. I got a fairly decent deal last time, I got a Cooler Master Real Power Pro 750W for $74 CAD. It's made by Enhance, who makes pretty good products (the cheaper CM PSUs come from other not-so-great OEMs). No complaints at all! Like most things, it pays to research what you're buying.

[Wai_Wai]

[ Topics merged. ]

Please don't create new topics when you've already started a similar one.

If it's a rule that all topics about PSU must go to the same thread, then I agree.

Otherwise I don't see it appropriate. Read the title: "When you buy a PSU, you must buy twice as much as you need!"

It's a discussion of the "double requirement" suggested by an anon.

This question is solved, and the answer is BS.

The topic can be closed.

But this topic has nothing to do with the general questions about PSU I'm asking now. It isn't really related. The subject becomes a misnomer too.

If someone is asking those questions for convenience, I would think it's hijacking / off-topic.

Comments given. Thanks for listening. Good day.

Edited July 14, 2008 by Wai_Wai

[Wai_Wai]

4) Similar to 3). You can also sometimes hear some high-pitched or other unusual noise coming from the PSU. Having multiple components failing in a short period of time is a surefire sign that something i wrong.

Also if the system just shuts down (multiple times) for no apparent reason you could suspect the PSU to have something to do with it. But not everything like that is caused by the PSU, the mainboard may also play a part.

What if it restarts suddenly?

I have set to show BSOD. Still it restarts suddenly without BSOD. If it's the case, it's very certain that the problem must lie on my hardware. Am I correct?

A bad PSU may damage your components; a few of my friends had a number of HDDs dieing on them because they used cheap noname PSUs. After switching the PSUs they haven't had a single problem of that kind.

So as long as I'm using a PSU from a decent/good brand, apart from truly bad lucks, my PSU shouldn't kill my other hardware even if it can't supply enough power or suddenly shut down. Am I right?

I've often seen figures saying 10% of their capacity per year, assuming it's powered on 24/7.

The only figures I got is from Extreme Power Supply Calculator:

"Electrolytic capacitor aging. When used heavily or over an extended period of time (1+ years) a power supply will slowly lose some of its initial wattage capacity. We recommend you add 10-20% if you plan to keep your PSU for more than 1 year, or 20-30% for 24/7 usage and 1+ years."

It's scary. I lose 10-20% for 1 year of usage. 20-30% for 1 year of 24/7 usage.

However I wonder it's a general advice. They don't really do some research to come up with those figures.

Personally, I always go for 30% extra to account for this.

So do I. But if the aging is as scary as what the above suggest. My PSU won't survive after 3-4 years of usage.

The major worry about PSU aging is I can't detect it until it causes damages on my hardware.

But after hearing what both of you say, I am relieved. It happens the PSU will signal us by keep shutting down / rebooting. STILL it won't kill my hardware, perhaps unless I keep ignoring its signals.

Of course I never buy bad/ no-name brands. I only use decent-to-good brands (or rather OEMs).

PS: Actually my monitor is acting weird. Eccentric behaviour:

1) Restart. Suddenly off then on again.

2) Soft Off. I need to press the button to turn it on.

3) Hard Off. I need to unplug and plug the cable connector to revive it.

It only happens a few times in this 1-2 months. I don't think my computer causes it.

I suspect the cable. But how can I verify my "theory"?

[jaclaz]

@Wai Wai

Just to clear things up.

You asked a question, I gave you my best answer, citing what I consider a reputable source, Hardware Secrets.

Then, once you have read the article where the reasons behind the "rule of thumb" are explained, you are free to simply ignore it or comment it's contents, to trust what is written in it or confute it, but I find ignoring it or classifying it as BS only because it does not contain what you want to hear, to be simply unpolite to me and to the time I spent trying to help you better understand the problem.

You weren't able to find a single article about the question, I gave you one.

Go and buy your 300W PSU, you'll be happy with it, rest assured.

jaclaz

[CoffeeFiend]

citing what I consider a reputable source, Hardware Secrets.

That's one of the few good places for sure (along with jonnyguru.com and a few others)

but I find ignoring it or classifying it as BS only because it does not contain what you want to hear, to be simply unpolite to me and to the time I spent trying to help you better understand the problem.

I think you misunderstood what he was calling BS. From my understanding, he was saying the "double the rating" nonsense is BS, not the stuff you said or linked to.

Also, the calculator you linked to is my favorite as well, it's not perfect, but I have yet to see a better one out there. I personally wouldn't use the one in post #3. Even side-stepping countless things that bug me (like only having a handful of CPUs on the list, and having to calculate your OC'ed wattage by hand, having to enter DDR2 speed for no real reason, being forced to pick a specific hard drive in a list where yours aren't, the limited max amount of hard drives, them expecting to lookup your fan's models even though it hardly makes any difference, the lack of many options, etc), the results are WAY off. Just try my current main box:

E2160 @ 3400/1.25v, 4x DDR2 800, GeForce 8500GT, 12x Seagate 7200.11 (SATA), 1 DVD writer, check TV Tuner - Satellite & PCI SATA RAID Card, 1 extra PCI-e x1, 4 USB devices, 6x 120mm & 1x 80mm fans, 90% load, 30% cap aging. Do the same on the other -- no E2160 on the list, so perhaps try with a E6300 (same 65W TDP, only 0.06GHz diff), OC'ed to 3400 too, and Arctic cooling fans. The results? Outervision says 756w, whereas aanet's calc says a 367w PSU will suffice, when I'm 100% positive it won't (a good quality 450w isn't quite enough -- I've actually tried!), and only 23.4 amps combined draw on the 12v bus, whereas each hard drives takes about 2 amps when they spin up, so the hard drives by themselves will use that much power, leaving none to the computer... It probably wouldn't even POST, or the PSU would die a very quick death. I'm very much un-impressed by that calculator.

Edited July 14, 2008 by crahak

[jaclaz]

That's one of the few good places for sure (along with jonnyguru.com and a few others)

I think you misunderstood what he was calling BS. From my understanding, he was saying the "double the rating" nonsense is BS, not the stuff you said or linked to.

Sure, I may have misunderstood that, but I must have misunderstood the whole thread as well.

How I would thought this thread would go (condensed):

I haven't found anything from a reputable source explaining why it is advised to double PSU power..... bla bla.

Here are the reasons, in an article from a known source.

The article, among other things, suggests the use of a (given link) calculator.

Thanks, I'll study the thing.

....

How the thread has gone (condensed):

I haven't found anything from a reputable source explaining why ..... bla bla.

Here are the reasons, in an article from a known source.

The article, among other things, suggests the use of a (given link) calculator.

I use a better calculator than that.

The idea of doubling the PSU power is BS.

No problems though, just wanted to clear my view on the matter.

jaclaz