Determining The Power Requirements Of A PC System

  King Diamond 19:43 19 Mar 03

How would you do the above?

I asked a similar question earlier on, but I did not explaing myself very well. But thanks to the chap who replied so quickly.


  eccomputers 19:53 19 Mar 03

The strange thing is, the power supply should handle power adequately to all the connectors it has for plugging into hard drives etc.
However, I think the main problem these days is from the motherboard connection. There are more and more cooling fans than ever being run from the motherboard. Mine for example has a cpu cooling fan, case fan, 2 graphics card fans.
These and the power a graphics card like my nvidia geforce4 ti4600 can pull can drag a power supply too much. I have seen systems struggle with less than a 300watt power supply but never with 300 and above. I have a 350watt which has never given problems.
Some cheaper power supplies should also be avoided. If you monitor the voltages for these, they fluctuate all over the place. The more stable the psu, the better the system will behave.

  woodchip 20:03 19 Mar 03

As eccomputers say's 350 Watts should handel all you need if it's a good-en

  powerless 20:07 19 Mar 03


A7V333 mobo, AMD2400+, 512DDR, Ti4600, 120GB and 3GB HDD, CD-RW, DVD, Audigy card, 18.1TFT...

All powered by a 250Watt, no problems what-so-ever.

  King Diamond 20:10 19 Mar 03

Thanks for the answers guys, appreciated, but I'm looking for more specific answers to the question rather than a generalisation.

I use a 400w with my machine with great results.

The question is actually a college question I have on my HNC computer/network support, so I'm just looking for something to get me started on it. The subject I have typrd in is the same as the question.


  woodchip 20:16 19 Mar 03

Then it mean's research. Do you know how to do that, just a add up of the Watts that items draw from the PSU plus 10%

  Gongoozler 21:38 19 Mar 03

Hi King Diamond. It's best to keep just one thread running on a subject. You can always post a refresh to bring it back to the top of the list.

The subject of your research is a difficult one. The mathematics is quite simple. For each of the supply voltages you need to determine the current to be taken by each device. watts = Volts x amps. Add up each wattage for each supply and you will get the total wattage. For any supply, you should have specified the wattage available from each voltage as well as the total wattage for the supply. Remember the supply may not be able to deliver the maximum for each voltage simultaneously without overheating.

The difficult part is determining the power taken by each part of the system. This is not always specified by the manufacturer. The power will depend on the clock rate and how much data is being processed. A CMOS device takes very little power when it is static, but start clocking it and putting a signal through it and the power taken increases rapidly. This is because each gate is essentially a capacitor. When static the capacitor takes virtually no power, but when it is clocked the capacitor is repeatedly charged and discharged. This is where the power is being used.

The PCI spec allows 25W to each card click here. If you have 6 PCI cards this adds up to 150W. I don't think there is any PC system that actually uses that power which illustrates why you cant use this simplistic way of specifying the power supply for a computer. Have a look at what AMD have to say about specifying a power supply in this document click here, and for other guides on using the Athlon have a look at this list of documents click here^1065,00.html.

click here

  Gongoozler 21:41 19 Mar 03

Sorry about the spare "click here" it came from editing the posting. I'm afraid you'll have to put the last bit of the broken link into your browser address window manually.

  King Diamond 00:05 20 Mar 03

Thanks a million Gongoozler, that was a great help and greatly appreciated.

Woodchip - Yes I do know how to research and posting on here is part of that. I'm almost finished my HNC and have done very well.

BTW...put a '?' at the end of your question, as maybe you could do with researching your English.

  Cordy13 00:48 20 Mar 03

If you want further replies I'd suggest that you don't insult the intelligence of those replying! And yes, I put an exclamation point in.

This thread is now locked and can not be replied to.

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