Is a 300w power supply enough for my system?

On Thu, 26 Jan 2006 11:47:42 GMT, Sean Cousins
wrote:

On 26 Jan 2006 01:41:28 -0800, wrote:


With few exceptions, the rating is meant to indicate maximum continuous
power output. The exceptions include very bad and cheap supplies, such
as Q-tec, and Q-tec at least admits that its ratings are for peak power.

That's not what I read just yesterday. Can't find the link now but it
said most PSU's only have about 75% efficiency and only the elite
PSU's can sustain their rated output: PC Power and Cooling, Seasonic,
OCZ etc. These PSU's can run above their rated power output at peak.

You are confusing terms. Continuous power would be running
24/7 for life. They cannot do that.

What you're calling continuous would be more apprpriately
termed peak, and what you're calling peak, momentary.

Sean Cousins wrote:

http://www.extremeoverclocking.com/a..._Guide_11.html

Power Supply Efficiency:

A power supply's efficiency rating is determined by the ratio of AC
power going in to the DC power going out.

They could have simply said, "power going in to the power going out,"
but they wanted to show off and impress the ignorant.

Generally this comparison is done using Watts as a common unit of
measurement.

Again, they're mentioning units that don't matter.

kony wrote:
On Thu, 26 Jan 2006 12:28:23 -0600, David Maynard
wrote:



That is true, but not necessarily useful for your purpose.
The point of the 3V+5V rating is a guide to relative
amperage capacity on 5V rail as some supplies overrate it by
far too much, while the combined 3V+5V rating tended to
remain a more accurate indicator.

The "combined power" spec wasn't really a matter of 'over rating'. At the
time there was a significant difference between system types as to how much
3.3 vs 5 volt power they needed so the power supply would be able to handle
more on one, or the other, as long as the total for the two fell within the
combined power rating.


That is true, but in retrospect we can often see the
secondary benefit when some PSU will spec it higher than
others. In other words, in the non-antec designs it is
common to give a cetain # of amps on 3V, but the 3V+5V was
actually a better indicator of what the max 5V was actually
capable of as 3V was derived from it, so you get closer to
5V sustainable rating rather than instantaneous.

Neither of the numbers were 'instantaneous' in the combined power rating,
either individually or combined. You could continuously pull any
combination from either up to the combined rating as long, as you didn't
exceed the individual max either.

On Thu, 26 Jan 2006 22:25:46 -0600, David Maynard
wrote:


Neither of the numbers were 'instantaneous' in the combined power rating,
either individually or combined. You could continuously pull any
combination from either up to the combined rating as long, as you didn't
exceed the individual max either.


In theory, yes.
problem is when reality doesn't meet theory...
when long-term use makes it fail.

kony wrote:
On Thu, 26 Jan 2006 22:25:46 -0600, David Maynard
wrote:



Neither of the numbers were 'instantaneous' in the combined power rating,
either individually or combined. You could continuously pull any
combination from either up to the combined rating as long, as you didn't
exceed the individual max either.



In theory, yes.
problem is when reality doesn't meet theory...
when long-term use makes it fail.

As I said in the original reply, it's possible for an unscrupulous
manufacturer to lie about anything but the premise itself was technically
sound, and for good reason, just as total PSU watts is technically sound,
it's just that unscrupulous el-cheapo makers lie about it.

Sean Cousins wrote:
On 26 Jan 2006 16:09:17 -0800, wrote:

The article actually makes you lose credibility since the author
obviously doesn't know the difference between real power and apparent
power. Power factor correction circuitry actually decreases efficiency
slightly since its circuitry wastes some power, and the only practical
benefit from active PFC that a smaller UPS can be used.

The moral is: Don't rely on technical information written for
pretentious nontechnical business types.

And what are your credentials?

You don't have to believe me; believe companies like Unitrode, Linear
Technology, and International Rectifier, which make PFC controller
chips. Their data sheets and application notes, while written for
engineers, are easy for anyone with a high school education to
understand. Your physics class back then should have taught you about
the differences between reactive power/apparent power and real power.
Why do you think transformers and UPSes are rated for VA and not just
watts?

Sean Cousins wrote:
On 26 Jan 2006 18:33:36 -0800, wrote:

"A power supply's efficiency rating is determined by the ratio of AC
power going in to the DC power going out."

They could have simply said, "power going in to the power going out,"
but they wanted to show off and impress the ignorant.

Ignorant is being a dickhead for no good reason.

Absurd, as there is never a good reason for being such a person.

"Generally this comparison is done using Watts as a common unit of
measurement. "

Again, they're mentioning units that don't matter.

VxA=W You saying that doesn't matter?

But efficiency is watts/watts, a unitless number. Also simply
multiplying average volts and amps will result in a product
higher than the actual power consumption if the voltage and
current are out of phase with each other, as they usually
are with inductive or capacitive loads, which include motors
and power supplies.

Sean Cousins wrote:
On 23 Jan 2006 02:15:20 -0800, wrote:

I've read that you shouldn't exceed a PSU's wattage by 80%, and
I also should have some "extra" wattage in case I add more components
in the future. So do you think my 300w power supply is enough?

Many PSU's have about a 75% efficiency and the 300w rating is only
peak rating.

I'm not sure why you mention efficiency here because the reason keeping
below 80% of maximum power rating has nothing to do with efficiency but
with the limits of the power supply's components.

The 300W rating is not a peak or other short term rating but a
continuous one. Whether or not it's accurate is another matter.

wrote in message
ups.com...
They could have simply said, "power going in to the power going
out,"
but they wanted to show off and impress the ignorant.

Ignorant is being a dickhead for no good reason.

Absurd, as there is never a good reason for being such a person.


California's Teachers Union.