Everything in a PC draws its juice from one metal box sitting in the corner of your case. While you busy yourself with graphics cards and processors and delve into overclocking, it just sits there humming away.
Unless it packs in, or you realise you don't have enough connectors after buying a new component, you probably never give it much thought.
The basis of the PSU is the transformer, first conceived by those brain boxes Joseph Henry and Michael Faraday in 1831. Without the transformer we'd be in real trouble because the mains electricity that comes out of the wall does so at a sizzling 240 volts, which is great for running the vacuum cleaner and electric fire, but useless for transistor radios. It needs taming, transforming, rectifying and smoothing.
There are only two reasons anyone would buy a new PSU. Either your existing one has stopped working and smells funny, or you're finally building your über machine with half an eye on world domination. Either way, you want something efficient, quiet, and capable of running everything with room for expansion.
A soft benefit of investing in a new PSU is the better power efficiency offered by new models. The rise in awareness of power consumption brought on by the eco movement has meant that the overall transforming efficiency of a power supply has become news, with stars and awards for being good. You can pay anything from £13 to well over £200 for a PC power supply.
Over the next few pages we'll tell you what you can expect to get for your money, as well as answer some common questions on the subject. How many watts do you need? Does the quality of the power supply matter much? And what exactly does it do and how?
We've put some of the market-leading power supplies through their paces to see who delivers what they promise, and whether expensive electronics add much to the mix. But first, you'll need to know a little more about your box of power.
There are two main power supply formats: AT and ATX. Since ATX has been around since 1996 we'll skip over AT power supplies, which are strictly for retro systems. The ATX standard has now reached version 2.3.
The main motherboard connection is a 20 or 24-pin block, which carries all the voltages. The extra four pins your PSU may have supply more power for motherboards that need it. Many PSUs have cables with the four additional pins on a separate block so you can use old motherboards – it's a handy feature that you may not know you need at the time of purchase, but certainly worth looking out for.
Processors get their own 12V supply, which used to be via a 4-pin plug (often called a P4 plug), but more commonly now via an 8-pin plug (the EPS12V). Like with the motherboard power cable, you'll often find PSUs that split the 8-pin block into two for compatibility with old processors.
Modern CPUs don't run on 12V, however. Motherboards have on-board voltage regulators to lower the voltage to the right figure (the excess being given off as heat). If it's any good at its job then your graphics card is the biggest draw on power. The PCIe slot can only deliver 75W (that's actually a fair amount for any component in your rig, but not for a graphics card).
This quickly proved inadequate, and so extra 12V cables were drafted in. Initially, these had a 6-pin connector, and added another 75W. Later, 8-pin connectors were introduced, which delivered 150W of extra power. This is not to be confused with the 8-pin EPS12V plug for the motherboard, which is wired differently. If you have to push and shove really hard to get either one in place then you've plugged in the wrong one.
You'll want lots of PCIe power connectors so you can swap and upgrade cards and allow for dual card setups. You might well need four 6-pin connectors or more in the future.
Why run so many 12V lines? The voltage drop rises as the current rises, so it's better to have more low power lines than tax a single one. Plus, with the amount of power some of these graphics cards draw, a single wire would quickly turn into a heating element.
Then you have SATA power cables, which carry all three voltages. You'll want at least three of these, but preferably more. You'll also find old-school 4-pin Molex peripheral connectors for IDE drives, and possibly a floppy disk drive connector and some 'intelligent' fan connectors.
Most decent PSUs use modular connectors, so the power supply has a set of sockets rather than permanently connected wires. This allows you to connect only the cables you need, so you don't get a mess of wires hanging out of the unit, blocking airflow.
Some sources say these modular designs are less efficient, as the extra block connector introduces resistance, and hence waste. Apparently, it's measurable, although we've yet to see any tangible evidence. It's probably true, but completely irrelevant. The extra convenience and flexibility of a modular design outweighs any tiny loss (and it will be really tiny).
Think inside the box
So what's inside a PSU? If you're expecting a big soft-iron-core transformer and not much else then you're in for a shock. Modern PSUs are switched-mode power supplies, which use switching regulators to flip between full on and full off at very high frequencies (50KHz and up). This minimises waste, and means they can be much smaller and lighter than full-on linear supplies.
A PSU supplies different voltages, and has separate circuitry to deliver each – these are the rails. An ATX power supply has a 12V, 5.5V and 3.3V rail, plus an additional rail to supply stand-by power. However, this wasn't enough, so ATX 2.0 added a second 12V rail to help power those graphics cards.
The first rail, 12V1, is used to power the processor, and the second rail, 12V2, powers everything else. It's this second 12V rail that's going to take much of the strain of your system.
Some power supplies boast more 12V rails, which is great, but there's no advantage other than the higher overall output. In fact, virtually all supplies split one 12V single rail into two, each with separate current-limit circuitry. This avoids potentially dangerous levels of electricity (240AV is the specified maximum, which is 20A per rail). However, you can't draw as much overall power through both lines because they share the transformer.
Fully independent 12V rails are expensive, although they give a cleaner signal. The 5V current is usually taken off the same transformer, and the 3.3V current is created by voltage regulators. In the past most power was required at the lower voltages, so the 5V rail took most of the load. Times have changed though, and now it's the 12V supply that's doing most of the work, with the additional 3.3V rail for the newer, low-voltage components.
The different power distribution between rails is one reason older power supplies don't always work on newer motherboards, despite being able to deliver the watts on paper. What your PC would really like is a lovely, flat DC signal, sending 12V right across the line. However, the PSU has a job to do here because the mains is a rather dirty 50Hz AC current. You can't just chuck a transformer and a diode at it and expect a smooth, constant voltage.
This is where the smoothing capacitors come into play. These little beauties can be the difference between a quality PSU and a poor one.
Waste not, want not
Power supplies get hot, and this heat is, of course, wasted energy. The ATX 2.3 specification requires an efficiency of 70 per cent, and recommends one of 80 per cent. That's still a fair amount of loss – your 400W PSU is drawing 500W at the wall.
There are higher efficiencies available, and there's a whole green movement to promote them. However, try not to get too carried away with it and spend a fortune on a 95 per cent efficient supply. Electricity is still relatively cheap, and you probably won't see any large return for your outlay. We recommend models on the '80 Plus' list or any model that's Energy Star 4.0-rated.
Another factor you should consider is the loading. Like most machinery, a power supply has sweet spots where it's most efficient. You need to avoid the extremes. You wouldn't drive from London to Manchester at an average speed of 30mph. Nor would you make the same trip at 150mph (even if you could get away with it). Sure, it's possible to drive at such speeds, but you'll burn through fuel much quicker than if you cruised at the optimum speed.
It's the same with PSUs: you should aim for a load of between 50 and 80 per cent – anything more or less will introduce waste.
Temperature plays a part too. The colder it is, the more output you get. In an ideal world, PSU power ratings should be accompanied by a temperature. If this temperature is below typical operating values (30-50 degrees), you know you've lost a few more watts.
What else might you consider? Well, there's the noise from the fan, and of course, its looks. In terms of sound, you don't want a constant reminder that your machine is on. As for looks, rugged and handsome, preferably with lights, always goes down well (although you'll lose your green cred with these).
Is more power better? Not necessarily. Some spare capacity can always come in handy in the future, but going wildly off spec adds nothing. There are an awful lot of high-power PSUs out there running well below capacity. It's tempting to show off with a high headline power capacity, but it won't increase your PC's speed one jot. Go for a high-quality and efficient supply, rather than the big number.
Now, the most important question: am I going to run two really powerful graphic cards at some point? This is the one component that really draws the watts, and you'll need to be prepared for it, or spend the same money all over again on a slightly bigger PSU.
Silverstone Strider - £43 (ST50F-ES 500W)
Modular PSUs may be the cat's whiskers, but such versatility comes at a notable premium at this end of the market. It's a luxury that SilverStone feels you can ill afford – providing fixed cables on this unit.
It isn't an awful decision though, as it means that the Strider strolls in with a surprisingly low price tag. In fact, in terms of pure cost per Watt, the Strider is way ahead of every other PSU here.
Antec TruePower - £73 (TP-550 550W)
Antec has been shifting power supplies for years, but it isn't a company that rests on its laurels. It's recently redesigned its popular TruePower range to improve efficiency.
The unit we looked at is the model with the lowest power rating in the family, rolling in at 550W. If you're looking for something with a bit more more grunt, then you may prefer the 650W or 750W version.
Xigmatek NRP - £61 (NRP-PC602 600W)
Xigmatek nails its green credentials to its PSU straight from the off, shipping this 600W power supply in a recycled box that's emblazoned with a suggestion to 'build a forest in your PC.'
We don't think they're being literal with that one, but it's a novel approach that underlines the fact that the 80 Plus Bronze certificate benefits the environment as well as your bank balance.
OCZ StealthXStream 2 - £51 (OCZ600SXS2 600W)
Efficiency is the name of the PSU game at the moment, and OCZ is right to be proud of its StealthXStream 2, managing the highest standby efficiency of any of the power supplies on test.
When you consider how long your machine is left in standby mode, you'll quickly see how important that is. Unless you're the type to turn off the machine at the plug (in which case we salute you), each percentage difference here equates to real-world savings.
Spire BlackMoon - £65 (SP-ATX-650WTB-PFC 650W)
Like the Antec TruePower, here's a power supply that brandishes the Nvidia SLI badge – putting this squarely in the gamer bracket of PSUs. It's similarly priced to Antec's offering too, but boasts an extra 100W of power for you to play around with.
Unfortunately, if you go by the numbers alone you're going to be in for a nasty ride, because in the tests that matter, this is an inferior unit in every respect.
Fractal Design Tesla - £90 (FD-PSU-TESLA-650 650W)
The 650W bracket is surprisingly crowded. Manufacturers see this position on the scale as either the top end of entry-level power supplies, or the bottom end for the more demanding buyer.
Fractal Design has positioned its Tesla 650W in the former group, as this is as high as the family goes in the performance stakes. Unfortunately, as with the Spire offering, the Tesla fails to impress both from a performance perspective and also in terms of value for money.
Scythe Stronger - £95 (SPSN-070P 700W)
This oddly named PSU is available in three different wattages, topping out at this, the 700W model (it's also available in 500W and 600W if your needs aren't so demanding).
Thanks in no small part to the Scythe Slip Stream 140mm fan attached to the unit, the Stronger is a whisper-quiet device. Somewhat surprisingly, this wasn't the quietest PSU in our test rig, although the difference was marginal at best.
Nesteq ASM XZero - £130 (ASM XZERO 700W)
You'll be delighted by the concept of the NesteQ if you're the type to leave your PC on all night rendering images or movies. In theory, you can run this heat-piped PSU in a well-ventilated chassis with the PSU fan completely off, so the noise shouldn't keep you up all night.
Unfortunately, under load we found that the fan did kick in from time to time, rendering such dreams as just that. It's a surprisingly loud fan in operation too. At full spin it was almost the loudest fan here, which was not quite what we expected.
CoolerMaster Silent Pro Gold - £128 (RS-800-80GA-D3 800W)
What do you need from a PSU? Great efficiency? Silent operation? Room for expansion as your rig grows? A great-looking PSU to show off your rig building skills? Good value for money?
Whatever you're looking for, the Silent Pro Gold 800W is the PSU for you, and represents the pinnacle of modern PSU design. We happily admit that it has impressed us that much.
XFX Black Edition - £120 (XFX 850 850W)
XFX has made a name for itself over the years for producing graphics cards that are either tweaked a little bit more than the competition's cards, or by simply looking the mutt's nuts.
Can it do the same with its power supply range? Possibly, although a little more work is needed before this can take on the likes of the Cooler Master.
Silverstone Strider Plus - £153 (SST-ST1000-P 1000W)
There was a time when 1,000W PSUs were the stuff of dreams. They were stupidly expensive, and surely no one really needed that much power anyway? Those days are clearly behind us, and all the major PSU manufacturers have whole families of PSUs at this capacity and above.
This 1,000W unit represents the top-end of SilverStone's Strider Plus range, but doesn't cost that much more than far less powerful units. Does it have what it takes to tempt the serious system builder?
Nexus RX-1.1K Gold - £188 (RX-1.1K GOLD 1100W)
The higher the wattage your power supply offers, the greater efficiency you'll need so as not to waste a lot of that power as heat. And with more raw power being drawn, even good efficiency will equate to hundreds of watts of waste, which in turn means that these bigger PSUs need ever better cooling solutions.
At this end of the PSU gamut, everything suddenly costs a lot more, so it certainly pays to spend wisely. Can the impressive looking RX-1.1K GOLD deliver at this most exacting end of the market?
Corsair AX1200 - £232 (CMPSU-1200AX 1200W)
Rolling in as the most expensive power supply in the test, Corsair's AX1200 needs to be something special to warrant such an outlay.
The good news is that it manages this feat admirably, thanks to its focus on performance where it counts. At 1,200W this may not be the PSU for everyone, but if you're building the ultimate gaming rig, you'll find this capable unit is well worth the price.
Thermaltake ToughPower - £194 (WO171 1500W)
For many, Thermaltake's power supply represents the pinnacle of modern PSU design, not because of what's happening under the hood, but purely because it offers a cool 1,500W of power.
That's a lot of power by anyone's standards, but is this a power supply you should seriously consider building your rig around? Possibly, but there are a couple of provisos.
Power supplies can be judged on numerous criteria – from efficiency under load through standby power draw to the amount of noise produced while it's strutting its stuff. Below we present the most important figures that should influence your purchasing decision.
Operating efficiency is the most important result here, as this defines just how good the inner workings of your PSU is at doing its job – better efficiency not only saves you money, but it will reduce the amount of heat in your system, which in turn will reduce the workload on your fan. This in turn will reduce the noise produced.
Standby efficiency is also important, as most of us leave the machine connected at the wall ready to be turned on at the push of a button. It's surprising how much of a difference there is in the power draw between the worst and best performers here.
We've also measured the noise produced by the PSUs under load, as well as the temperature inside the case.
The world of power supplies has changed. It's a dog-eat-dog world out there, and any weakness is jumped upon. These aren't the nameless blocks that we used to get free with our cases any more, that's for sure.
They are precision components in their own right, and they cost a serious premium for the privilege. In order to justify price tags that match an ever rising output wattage, a number of metrics have come in to play to help separate the must-haves from the must-ignores.
Operating efficiency, standby power, fan noise, operating temperature and signal clarity are all now essential elements to inform your purchasing decision. The most important of these figures is the operating efficiency, as this is a measure of how good the PSU is at doing the job it was designed for – turning AC mains power into a smooth DC signal for your precious components.
The big figure that all modern PSUs need to hit here is 80 per cent efficiency, thanks to the introduction of the 80PLUS initiative. With the best PSUs offering considerably better efficiency at a range of loads, this isn't too unreasonable a thing to ask, which is why it's surprising that there are still power supplies that fall short of the mark.
By this criteria alone we can wave goodbye to the Spire BlackMoon, SilverStone Strider, Fractal Design Tesla and NesteQ Xzero, as they simply don't cut it by modern efficiency standards.
The next factor that differentiates the better PSUs from the rest is the standby efficiency – the amount of power that the PSU draws when your machine is essentially waiting for you to press the power button or to wake the machine up by some other event. Most of us leave our rigs in such states, so better standby performance makes a difference.
Here the Scythe Stronger, Xigmatek, SilverStone Strider Plus and Thermaltake Toughpower 1500W all bow out due to their unimpressive standby efficiencies.
Of the PSUs that are left, you're generally looking at a good bunch, all in a range of wattages and abilities. The Antec TruePower 550W, for instance, is a tempting offering if you have low enough power requirements, although the modular design does mean that it costs a little more per watt than its direct competition.
At this level we'd give the nod to the OCZ StealthXStream 2 600W, which, while not modular, does offer great value, and it isn't as loud in operation as the TruePower. Meanwhile the XFX Black Edition and Nexus RX-1.1K both suffer from high voltage noise, which pushes those out of the competition for the top spot as well.
This leaves two power supplies that just so happen to stand out from the crowd on their own anyway – the Corsair AX1200 and the CoolerMaster Silent Pro Gold 800W. Both are incredible power supplies, offering top-of-theclass efficiency, build quality and signal output.
The CoolerMaster ultimately gets the nod, though, for being very quiet in operation and offering better value for money. In fact, looking at the CoolerMaster Silent Pro Gold 800W, it's hard to see what more you would want from a power supply, other than more of the same.
It's an amazing PSU, and anyone looking for a replacement unit for an existing system or anyone building from scratch should look no further. Highly recommended.
0 comments:
Post a Comment
Click to see the code!
To insert emoticon you must added at least one space before the code.