Hardware Analysis - Power Requirements

Re: Power Requirements

Gerritt — 2008-05-16T19:49:38-05:00

I'd have thought that would have more to do with the overall efficiency rating of the PSU, vs. running it at %50-60 of it's rated output. Though I can see where driving into the higher gain would be more efficient at that particular current draw, by mid-lining the draw to begin with you would still stay on the linear portion of the gain curve, thus lower all around heat production. Or am I, as usuall, missing something here? It's been quite a while since I reverse engineered a PSU, so if there is some new feedback voltage regulation being integrated in the newer PSUs, I've not had the exposure. I did, however, a few years ago, put a inductive current tap on the 120v line on an old 350W PSU that I was replacing, then on the new 500W+ Enermax 641 series, and the Enermax drew less line current under the same loads by about 20%, though this was probably due to better efficiency as well as the 350W PSU being loaded to maximum rating.

Re: Power Requirements

john albrich — 2008-05-16T18:12:23-05:00

I agree, over-powered is better than underpowered from a functional standpoint.

It becomes one of those seemingly endless tradeoffs that must be examined in any computer purchase.

Unfortunately, many PSUs used in the middle region of their capacity are not running at maximum efficiency. When run in that region they tend dissipate much more waste heat, too. So, you end up paying more over time for the energy to run the PSU (as much as 10%-15%), and you may have to further improve cooling for the system (again, a bit more money). Then of course, that waste heat has to be removed from the room(s) in which the computer(s) is installed. It's all incremental, but it does add up...especially if you're running a lot of computers.

Even with just a 20% safety+upgrade margin, there's a measurable loss of efficiency.

I think 20% is a good balance.

Re: Power Requirements

Gerritt — 2008-05-16T15:32:54-05:00

John,
I know that the Newegg calculator is simplistic, but you'll never be stuck with an underpowered unit using it.
Additionally I'm kind of old school insofar as staying in the middle of the linear gain parameters in order to provide for the lowest possible Signal-Noise/Distortion ratios, while providing overhead for instantanious increases in current draw. This is a holdover from my days of rebuilding and modifying audio and radio amplifiers, and though is less applicable in computer PSUs, it hasn't steered me wrong in the past.

Gerritt

Re: Power Requirements

Azza M — 2008-05-16T14:29:56-05:00

Thanks for your response.

I did notice an overhead there with the calculator.

I tested my old machine stats out and it should never have ever worked.

I had a 200W PSU and looking at the new egg Newegg calc I required 418W.

Any how I am happy to use it as a guide. Thanks for your additional sites.

Appreciate the feedback.

Kind Regards
Azza

Re: Power Requirements

john albrich — 2008-05-16T09:48:21-05:00

While the Newegg power calculator is easy to use, in my opinion it can introduce substantial errors and should be used with considerable care. Otherwise, you may spend a lot more money than you really need to spend.

I would recommend using a power estimator that has more granularity. In no particular order, you might look at:
http://extreme.outervision.com/index.jsp (Lite(free) and Pro versions)
http://www.journeysystems.com/?power_supply_calculator
http://web.aanet.com.au/SnooP/psucalc.php

I have used extreme.outer.vision with "ok" results with the "Lite" version (as long as you make sure to set the capacitor aging parameter to 50%, and add my 20% safety+upgrade margin)

The example below shows it recommends a 615Watt PSU when a 440Watt will more than suffice (including the 20% margin). Now, I believe in a good safety and upgrade margin (20%) to compensate for component variations and unplanned incremental system upgrades, and the results reflect that. But, the Newegg calculator I believe tends to really pad the final estimate. One might suspect this is to get the customer to buy the more expensive higher wattage PSUs without a firm need to do so. However, it may simply be because Newegg chose to create a very simplistic power estimating tool.

The Newegg calculator seems to provide results based on very broad generalizations. For example, just one component, the CPU can introduce a tremendous variance. The Athlon 64 90nm CPU category has CPUs with specified power requirements ranging from 51Watts to 89Watts*. (in fact, if one is using the lower voltage settings, the power used by this category CPU can be as low as 45Watts). But, the Newegg calculator provides for only ONE value.

89Watts is 75% more power than 51Watts. (although in this category, most of the CPUs are spec'd as requiring either 67W or 89W). As you can see, that's a big difference yet the Newegg calculator doesn't account for it. Such differences for other components can quickly add up.

A Few "AMD Athlon 64 90nm" Category CPUs
51W Athlon 64 3200+ 90nm (Venice/socket 754)
67W Athlon 64 3000+ 90nm (Winchester/socket 939)
89W Athlon 64 3000+ 90nm (Venice/socket 939)
(values obtained from http://www.techpowerup.com/cpudb/)

In my experience, Newegg's generalizing when distributed over multiple components has resulted in estimates that always seem to exceed by quite a bit the actual PSU rating one requires. (however, as the system power requirements go up, this variance tends to decrease)

Here's an example using the different calculators for ONE specific, relatively simple system. The table shows the PSU Wattage requirement estimated by the listed calculator for the equivalent system configuration. The calculation assumes the PSU is a high-quality PSU.

PSU
Watts CalculatorUsed
615... Newegg
440... my personal estimate
430... extreme.outer.vision ("Lite", 50% capacitor aging)
350... journeysystems
240... aanet

Note: ALL results shown in the table above include an added 20% safety+upgrade margin.
Even so, Newegg's estimate is 40% higher than mine, and 43% higher than extreme's.

*http://www.techpowerup.com/cpudb/

Re: Power Requirements

Azza M — 2008-05-16T04:33:30-05:00

that site is awesome.

Thanks for your help.

Re: Power Requirements

Gerritt — 2008-05-16T03:23:47-05:00

430 may be enough.
I ran a rough calculation with http://educations.newegg.com/tool/psucalc/index.html and came out a 417W PSU, but thats pretty close to the boarder. I'd recommend just a bit more headroom.

Gerritt

Re: Power Requirements

Azza M — 2008-05-15T07:04:34-05:00

The case is an LC17 (HTPC) and doesn't support 120mm fans. (3 x 92mm fans and 2 x 80mm)

http://www.silverstonetek.com/products/p_spec.php?pno=lc17&area=usa

Also I was thinking of using the 600W PSU for a file server machine.....the one mentioned earlier in the thread.

So it was not only to tidy up the machine internals a but also to use the 600W in another system replacing a 200W 6yr old no name PSU.

So - do you think 430W would be enough?

Re: Power Requirements

Gerritt — 2008-05-15T05:44:32-05:00

OUCH, John.
I thought of that, but thats just about as mean as you can get, because if you ever need them in the future, it's major surgery for a new device.

Having said that, if you are a guru with a soldering iron, and have a store of shrink wrap, then go for it...but just cutting them off may lead to a system failure just due to the exposed wires touching each other. OF course if you are very old school, you could always just wrap them off with electrical tape.

Re: Power Requirements

john albrich — 2008-05-15T03:24:41-05:00

In addition to tie-wraps and velcro strapping, as this looks like it will be a pretty much fixed configuration machine, you may even consider the major surgery of cutting-off the extra cables you know you won't require.

Cap-off the cut ends with screw-on connectors or use crimp-on connectors with no wire coming out the other side. Then, you may wish to dip the ends in "Plasti-dip".

Re: Power Requirements

Gerritt — 2008-05-15T01:59:07-05:00

Well,
I'm the wrong one to talk to about going down in Wattage on a PSU, and just trying to tidy up a chassis seems to be a weak reason for doing so. I'd invest in some tiewraps and a bit of velcro instead; a mid-tower chassis has more than enough space to tuck and weave unwanted wire clutter.
Insofar as the noise, 5 fans will cause a bit, especially if they are 80mm or less. I'd look into replacing any high speed 80mm fans with 120mm fans. With the configuration you listed 2 or 3 120mm fans should do the job:
1 intake fan mounted to flow air over and through the HDD mounting cage.
1 exhaust fan mounted as high as possible on the rear of the chassis.
1 suplemental exhaust fan mounted "above" the PCI slots venting out the side of the chassis.
You could also get a fan speed regulator so all of your fans aren't running at full speed all the time. The cost of the regulator and 3 120mm fans is less than the cost of a lower end modular PSU.

Gerritt

Re: Power Requirements

Azza M — 2008-05-14T13:18:17-05:00

Another question re power - I know I am fixated on it. Not too up on power requirements.

I have a HTPC that I built and it has a 600W PSU. Contents below.

E6700, GA-965P-DS3P, 4 x Hard Drives, Gigabyte 8600GT (no fan), 2 x Optical Drives, TV Tuner and 5 case fans - inside a Silverstone LC17.

It is a bit noisy and am going to remove 2 x Hard Drives, and some fans. Also the 600W PSU is not modular and as a result there is unnecessary cabling in there and I wanted to tidy it up a bit and was thinking of a Modular PSU.

Do you think a quality 430W PSU would be enough? Any ideas on a model?

Re: Power Requirements

Azza M — 2008-05-04T09:01:46-05:00

Thanks all - will get another PSU

cheers

Re: Power Requirements

MrBungle — 2008-05-04T05:35:01-05:00

Gerritt is right you need to get a new powersupply. I suggest you get one from a reputable company like Enermax, PC Power & Cooling / OCZ, Antec, Thermaltake, or Coolermaster (there are others). The really cheap powersupplies often have their wattage ratings over exagerated and can provide power with lots of voltage fluctuations which can damage your computer or cause instablility.

Re: Power Requirements

Gerritt — 2008-05-04T04:44:10-05:00

In a lot of packaged systems the PSU is rated to the shipped or shippable configuration.
In your case, you're trying to add a large number of disk.
My recommendation is that you definately invest in a new PSU that supports something in the area of 400-450Watts.

Gerritt