Power Supply Myths?

Vampyromaniac · Apr 15, 2007, 01:35 PM

I came across this page on PC Power & Cooling's website, and I'm wondering what you guys think of these points, particularly #'s 3, 6, and 8 below:

http://www.pcpower.com/technology/myths/

Quote:

3. DON'T LOSE POWER WITH MODULAR PLUGS
Due to their look, convenience, and cost savings for manufacturers, modular plugs have become a popular power supply feature. Unfortunately, there has been little or no discussion of the impact of this feature on overall performance and reliability. The fact is, modular plugs limit power by adding to electrical resistance. The voltage drop can be as much as would occur in 2 feet of standard wire. Worse yet, modular plugs utilize delicate pins that can easily loosen, corrode, and burn, creating the potential for a major system failure. That's why professional system builders specify uninterrupted wire!

6. SHOULD AN ATX POWER SUPPLY BE COOLED WITH A 120MM FAN?
Most low-noise ATX power supplies today utilize a top-mounted 120mm fan rather than a rear-mounted 80mm fan. The 120’s favorable reputation is based on the fact that under low to medium load conditions, the 120mm fan provides sufficient cooling at low RPM and low RPM fans are generally very quiet.

However, problems occur with this design when the load exceeds 50%-60%. Because the 120mm fan consumes about 1.5” of vertical space inside the PSU, heat sinks, capacitors, and other components are about 30% smaller in height compared to a PSU with a rear-mounted fan. The smaller parts can handle less current, so the maximum power available with the 120mm design is limited. And, because the heat sinks have less surface area, more air flow is needed with this design to keep the thermal situation under control. With 80%-100% load, the 120’s fan speed can double and the noise level can jump by up to 20dB.

In conclusion, for systems that require more than 50% of the power supply’s capacity, a well-engineered PSU with a rear-mounted 80mm fan will provide superior performance and reliability (due to larger components) at a noise level comparable to a PSU equipped with a 120mm fan.

8. ARE MULTIPLE 12-VOLT RAILS BETTER THAN A SINGLE 12-VOLT RAIL?
With all the hype about multiple 12-volt rails (ads claim that two rails is better than one, five is better than four, etc.), you’d think it was a better design. Unfortunately, it’s not!

Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply’s rating. Those losses occur because power literally gets “trapped” on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.

Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete.

PC Power and Cooling is once again leading the industry. All of our power supplies now feature a large, single 12-volt rail. The design is favored by major processor and graphics companies, complies with EPS12V specs (the 240VA limit is not a requirement) and is approved by all major safety agencies such as UL and TUV.

So what do you think?

mkk · Apr 15, 2007, 02:09 PM

3. Edit: Whoops I misread that passage, so I disagree as follows: I've seen tests that prove that the extra interconnecting surface would have to be damaged or dirty to have a real negative effect. Maybe if one uses a large number of adapters in series on a single cable, but these engineered modular interconnects aren't a problem.

6. It's true that when a large amount of airflow is required, a single 120mm fan just not takes up more internal space but also causes turbulence in the air inside the unit. Air can also more easily get trapped in corners, though most manufacturers apply small venting holes at precise points in the PSU casing to lessen that effect. But the bottom end is that this only becomes a problem at times when no powersupply was going to be running "silently". If the 120mm fan doesn't have to rotate very quickly on a regular basis it wins because of the lower noise at low speeds. For PSU's designed for constant heavy loads a push-pull setup of two 80mm fans mounted vertically is the most efficient design. Such PSU's are often longer than the common standard and may be hard to fit in smaller cases.

8. I don't know if the mentioned loss of efficiency is correct when it comes to modern PSU design, but the so called multi-rail setup is with few exceptions really just one rail divided into several lines having separate ampere limitations. PSU's with true separate rails are rare. At time when users with dual graphics cards had problems with some PSU's, those PSU's designed with just one +12V line fared better. Today this isn't much to consider since all manufacturers have gone for the rout of splitting a single +12V rail into multiple +12V lines.

~~DudeBoyz~~ · Apr 15, 2007, 02:27 PM

I'm 100% sold on the idea that a single 12v rail is indeed superior.

swimtech · Apr 15, 2007, 03:25 PM

Yeah, number 8 just makes sense - one 12v output rail can be regulated, overload protected, and impedence matched for low to extreme load handling more efficiently at less cost than three ( or however many...) and with fewer components. Take this water analogy - it's easier to drink from a fat hose than the skinny (albeit adequate for some...) stream from a water fountain. Remember, voltage is the speed of the water flow, amps is the actual quantity of water passing a point in a given amount of time.

Also, about the modular cables (#3), I agree for this reason alone - reliability over time. Sure, there's almost no losses across a new connector - it's tight, with adequate surface contact area - and there is really very little voltage loss over two feet of wire - that shouldn't be the point. The point is that over time, as heating and cooling within the case occur, the connectors themselves expand and contract and in differing ways because of the different shapes (male and female...). Engineering of the connectors over the past years has minimized this problem, but not eliminated it.

Eventually, the connectors loosen and the contact area within the connector decreases - thereby decreasing the current flow and increasing resistance across the connector that decreases voltage. In my work with electronic devices over the years, those using interconnecting modules/cables have much more trouble than those that don't. The interconnecting modules and cables can make a device easier to work on, or manufacture, but I'll take a wire soldered to its source for reliability over a snap on connector any day of the week.

**Grace** · Apr 15, 2007, 03:49 PM

I'm sorry to ruin the mood guys, but all of that is just marketing. Sure PCP&C makes some of the best, if not the best PSUs around, but without marketing they too would fall.

A couple of examples, to support my opinion. I do not endorse multiple 12V power rails for my own reasons, but the above 'rules' state that when drawing a X amount of power out of a Z rated 12V line, you may end up with an Y amount of unused power. That's not true for any quality PSU out there, when any line is overloaded, the remaining lines will support it. True, there is a power loss, but nothing nearly dramatic. Another example could be the mention that modular power supply connectors may cause a large voltage drop on the line. That is true, but it certainly isn't as high as they mention when any connector of average quality or above is used and of course PSU manufacturers have programmed the voltage regulation circuits to compensate for that.

All in all...well, take it easy when reading what each manufacturer says.

~~DudeBoyz~~ · Apr 15, 2007, 04:31 PM

Check this out at Enermaxusa.com:

http://www.enermaxusa.com/catalog/pr...3e06e75eda6fa6

They say they have two rails of 22a each. But total combined is only 32a.

It is on all of their products.

A single 12v rail is by far the best solution, even with a bit of noise generated when compared to multiple rail systems.

Dyre Straits · Apr 15, 2007, 09:48 PM

I'm sold on single 12V rail PSUs, too.

Necrosis · Apr 15, 2007, 10:05 PM

Quote:

Originally Posted by Grace

I'm sorry to ruin the mood guys, but all of that is just marketing. Sure PCP&C makes some of the best, if not the best PSUs around, but without marketing they too would fall.

A couple of examples, to support my opinion. I do not endorse multiple 12V power rails for my own reasons, but the above 'rules' state that when drawing a X amount of power out of a Z rated 12V line, you may end up with an Y amount of unused power. That's not true for any quality PSU out there, when any line is overloaded, the remaining lines will support it. True, there is a power loss, but nothing nearly dramatic. Another example could be the mention that modular power supply connectors may cause a large voltage drop on the line. That is true, but it certainly isn't as high as they mention when any connector of average quality or above is used and of course PSU manufacturers have programmed the voltage regulation circuits to compensate for that.

All in all...well, take it easy when reading what each manufacturer says.

While I agree in some part to what is said I also know PC & Power Cooling supplies are over hyped. I know of three that have died w/ no external reason.

**Grace** · Apr 15, 2007, 11:59 PM

Quote:

Originally Posted by DudeBoyz

Check this out at Enermaxusa.com:

http://www.enermaxusa.com/catalog/pr...3e06e75eda6fa6

They say they have two rails of 22a each. But total combined is only 32a.

It is on all of their products.

A single 12v rail is by far the best solution, even with a bit of noise generated when compared to multiple rail systems.

That's not because of the two 12V lines, but because of the total output the 12V circuit can hold, and it's more than enough. For example, 32A out of the 12V line for the PSU you linked us to is already as high as ~390W, out of a 485W total output.

Most multiple 12V line 700W+ PSUs have four 12V lines of 20A maximum output each. So, if the 12V circuit could deliver all 80A, that would make them able to output 960W from the 12V line alone.

No matter how many lines you have, they can individually have a certain output which you NEVER can simply add them together, the total output of the 12V circuit is always lower.

~~DudeBoyz~~ · Apr 16, 2007, 12:06 AM

Meh.

With a PSU rated at 22a per rail, it should add up to 44a total. It's like that 17" CRT thing - it's really a 16" vert measurement, not actually 17".

I'm all about a single 12v rail. No muss, no fuss.

I do think it sucks that on their Silencer 470:

http://www.pcpower.com/products/view...hp?show=S47ATX

Only has 26a on the 12v rail.

I never heard of these guys - is their stuff any good compared to Antec or Enermax? Why do they have FIVE different 510 class products in the same category?

http://www.pcpower.com/products/powe...h-performance/

I'm not so sure on their claim about 2 fans not being good. I thought the two fans both worked together to help pull air out of the case for exhaust? Not all 2 fan setups are spot cooling ones, are they?

**Grace** · Apr 16, 2007, 02:30 AM

Quote:

Originally Posted by DudeBoyz

I never heard of these guys - is their stuff any good compared to Antec or Enermax?

Actually, PCP&C PSUs are considered to be the best of the type.

26A from a 12V line are pretty good for a 470W PSU; they are 320W worth of power, more than a system with 2-3 HDDs, a dual core processor and a high end GPU card can ever use. Anyway, even if it had a 40A 12V line, it could never output that kind of power when the total capacity of the unit is 'only' 470W. Let's be a little bit more reasonable.

~~DudeBoyz~~ · Apr 16, 2007, 02:44 AM

Man, I dunno. I'm running tons of crap from my Enermax with 33 amps on a single 12v rail. Seems like some of the numbers just don't add up when I look at some of these multi-rail PSU's. Maybe Enermax just makes better PSU's than others. I don't know enough about the numbers and the fudge factors to be sure. I do know that when stuff works, everybody is happy, and folks seem to be having a lot of issues with Multi-Rail systems not carrying their weight, as it were.

What do you think about this statement they make:

Quote:

Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply’s rating. Those losses occur because power literally gets “trapped” on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.

Is that actually correct?

RoyBatty · Apr 16, 2007, 07:22 AM

Quote:

Originally Posted by DudeBoyz

Is that actually correct?

Dude, have you actually read what Grace said in post #5?

~~DudeBoyz~~ · Apr 16, 2007, 07:33 AM

Quote:

Originally Posted by RoyBatty

Dude, have you actually read what Grace said in post #5?

Brain fade - sorry about that.

Odd that an actual corporation would make those claims and have them be false.

All these crazy numbers is freakin' my simple mind out. Doh!

Lowfat · Apr 16, 2007, 08:00 AM

Meh, 120mm PSUs are quieter, no matter what they say, definately over a loud screaming Delta fan that Pc P&C uses.

The .001 Ohm of resisitance a little alluminum connection is going to make in a modular PSU is absolutely nothing. Very bogus claim.

True single rail PSUs are better, but really doesn't make the biggest deal imo.

Zelig · Apr 16, 2007, 08:08 AM

Most of the problems I've seen from multi-rail designs occur when manufacturers don't think out the layout of the rails properly, and what they're going to assign to the different rails.

Power supplies with an equivalent total amperage will generally perform equally, other factors equal. Single rail designs are going to be easier to hook up though.

FWIW, there are a few multi-rail PSUs where the total +12v A available is a simple sum of each rail. The Silverstone Zeus 850 watt has 18A on each of the 4 +12V rails, and 72A total.

Quote:

Originally Posted by Lowfat

Meh, 120mm PSUs are quieter, no matter what they say, definately over a loud screaming Delta fan that Pc P&C uses.

However, PC P&C have some of the loudest PSUs in the market. Comparable Etasis or Silverstone power supplies match them for quality, and have much quieter 80 mm fans.

Lowfat · Apr 16, 2007, 08:55 AM

Ya I don't think I've owned any other PSUs that had a single 80mm fan besides a PC P&C one, but good to know.

Matth · Apr 16, 2007, 11:10 AM

1. Efficiency - 80-plus is good, nothing more to say... Cheap PSU s generally don't mention efficiency.

2. Wattage - damn lies and statistics, frequently a cheap "500W" would be only equivalent to a 400, 350 or even 300W drom a more reputable maker.

3. Modular cables - not a fan of them myself... if I needed to fit one back, you can bet it would have vanished into the junk. Since there is always one connector in line at the end, one at the start cannot be that evil though.

-

5. SLI - seems to mean little other than having dual PCI-E plugs.

6. Not convinced either way, a 120mm blowing IN may give BETTER circulation and cooling than the lazy intake making up for an 80mm extract fan. also, from CPU heatsinks, it seems that the fan blowing into the heatsink is better. Also, it seems there are fewer "really bad" 120mm units.

7. Dual fan - more a fashion than anything, and many BAD units are dual fan. Unless the flow is so constrained that it needs the push-pull of two fans in series, the only real advantage is that the second fan is normally positioned such that it will serve as a CPU exhaust fan, though a seperate rear exhaust fan would be far superior.

8. I'd disgaree with the "lost power" issue, as the multiple 12V rails are rarely capable of 100% concurrent load - more to the point, many dual rails are only seperately limited, from a common feed, so any claimed advantages of dual rails are mythical in that case. The main point seems to be that a high current, single 12v is considered "hazardous", as it can deliver a lot of wattage into a short or partial short.

~~hackerx~~ · Apr 16, 2007, 11:53 AM

isn't efficiency=total output/total input * 100?So in a 500W PSU output can always be upto to max but as efficiency decreases the amt of watts drawn by the PSU to generate
the 500W increases.Is that right or is my concept wrong?
and another question

if i were to buy an antec power supply of 500/550 watts
would u suggest me to buy a 500W PSU with no modular connectors,an 80mm fan and dual 12v rails of 17A each or buy the 550W PSU,with no modular cables,a 120mm fan and 3 12v rails of 18A each?
1.Antec EarthWatts 500W
2.Antec True Power Trio 550W

Its a real question,i'm in need of a new PSU

Zelig · Apr 16, 2007, 12:26 PM

Quote:

Originally Posted by Matth

6. Not convinced either way, a 120mm blowing IN may give BETTER circulation and cooling than the lazy intake making up for an 80mm extract fan. also, from CPU heatsinks, it seems that the fan blowing into the heatsink is better. Also, it seems there are fewer "really bad" 120mm units.

Might be worth noting that there are several variations here. Some PSUs have single 80mm horizontal intake fans. Regardless of the effect on cooling, the placement of fans on the inside tends to produce less noise.

**Grace** · Apr 16, 2007, 05:15 PM

Quote:

Originally Posted by hackerx

isn't efficiency=total output/total input * 100?So in a 500W PSU output can always be upto to max but as efficiency decreases the amt of watts drawn by the PSU to generate
the 500W increases.Is that right or is my concept wrong?
and another question

if i were to buy an antec power supply of 500/550 watts
would u suggest me to buy a 500W PSU with no modular connectors,an 80mm fan and dual 12v rails of 17A each or buy the 550W PSU,with no modular cables,a 120mm fan and 3 12v rails of 18A each?
1.Antec EarthWatts 500W
2.Antec True Power Trio 550W

Its a real question,i'm in need of a new PSU

That concept is correct. However, if (example) a 500W PSU can actually output 500W or if it can only draw 500W and deliver a 500W*efficiency % inside the system, depends on the manufacturer of the PSU. Most generic PSUs state their maximum power DRAW, not output. So a generic 500W PSU with 75% typical efficiency can output only 375W max. Tricky, isn't it?

The Power Trio 550W PSU is superior by every aspect, I see no reason why not to get that one.