On Fri, 2004-09-03 at 14:52, Harvey Alaric wrote:
>I plan to buy a PC case with power supply. I see some advertised
>with a 550 Watt power supply, which seems like a lot. Is more
>better or is it possible to have too many Watts?

Hi Harvey

First of all, the power output from a power supply depends on
the temperature inside the power supply. A power supply rated as
550 Watts at 25 degrees Centigrade may only supply 366 Watts at
40 degrees C., which is not an unrealistic temperature for the
inside of a PC power supply.

Secondly, power supplies are more efficient and reliable when
loaded to less than 70% of maximum capacity. So a 550 watt
supply might be ideal for a system that only needs 275 watts
but is hot inside the case.

Thirdly, different power supplies supply differing amounts of
power at the various voltages needed by the computer. (I'm
talking about 3.3 volts, 5 volts, and 12 volts.) A computer
with a large number of hard drives, CD-Rom or DVD-Rom drives,
CD or DVD burners, etc. probably needs extra power on the
12 volt lines. (The drive motors run off 12 volts.) A computer
with a super video card or power hungry CPU might need more
power from the 3.3 volts and 5 volt lines. (The logic stuff
on the motherboard, video card, PCI cards, inside the
processor(s) and in the circuitry of the disk drives uses 3.3
and/or 5 volts.)

An older 600 watt power supply meant for a system with a ton
of disk drives may not supply enough power at 3.3 volts and 5
volts for today's P4 or Athlon systems and high performance
video cards.

A system with ten disk drives might not get enough power from
a power supply that supplies a disproportionate amount of its
power supply at 3.3 volts and 5 volts.

So the safest solution might be to get a power supply that
seems overpowered. It should run more efficiently and would
hopefully supply sufficient power at all voltages.

For an idea of how much power you need for the components
inside your computer, check out the following webpage:

http://www.pcpowercooling.com/maxpc/cases.htm

You could keep count of the power needed at each voltage and
compare the three totals to the specification sheets of
prospective power supplies. To answer your question, you can
never have too large a capacity power supply.

Final comments: Over the years, I've come to hate cheap or
insufficiently powered power supplies. Most of the troubles
I've had inside my computers have been power related. All the
disk drive problems I've ever had have been due to bad power
cables or insufficient power. Same with power to the motherboard.
Reoccurring Windows blue screens have been solved by replacing
the power supply.

I've had power supplies slowly die over the course of a month
or two and I've had power supplies die suddenly with a loud
crack and smell of smoke.

I suspect however that few people are willing to spend the
money for a high quality large capacity power supply.

Regards,
Bill

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