General knowledge / electricity questions

[Amp34]

I know there used to be a few around that were up to date, and these would give you a pretty accurate measure of the overall draw of your components (non exact fans, HDDs and such really don't matter as half-one W here and there really aren't going to make a difference.). I don't know specific websites now however.

My 75-90% statement may be a little out however, just looking at http://www.silentpcreview.com again (very good at showing efficiency for PSU's) the true range of efficiency is probably actually a little lower, however the true draw of a system is usually a lot lower than you expect (as they point out in a review a couple of months ago a worst case system would probably only draw a little over 300W max (unless of course it has 20 HDD's or is majorly overclocked)).

 

[kylew]

400, it's rated to supply up to 600 (at peak load)

What it draws from the wall and what it outputs are different things.

What it draws from the wall we don't know until we know the PSU's efficiency.

What it is able to output to components though is the peak, so while it can output 600w to the components, at full pelt it could be drawing over 600w from the wall.

 

[megakid]

-My ipod, running from its battery, is plugged into my speaker system. The speakers are plugged into the mains (on) and are at full volume. Does a change in volume on the ipod change the amount of electricity being used from the mains?[/I]

I'm going to disagree with Jez here too but maybe in a different way than div0.
If you're plugging your speakers into the headphone socket then Jez is correct, as you increase the ipod volume, you will need more amplification to get the louder sound. But I'd argue that typically ipods are docked using their proprietary ipod connection which has a line out stereo connection. This line out signal does not change amplitude when you increase the ipod's volume, (if nothing is plugged into the headphone socket of the ipod, it won't use any more battery as you increase the volume), therefore the sound you hear won't get any louder from your speakers and you won't be using any more electricity.
EDIT: Just read your description, if your ipod is running from its batteries then I'd assume you don't have it docked and would be using the headphone socket instead of the proprietary stereo line out signal - in which case, yes, as you increase it, the ratio of amplification stays constant but in absolute terms, the amplification increases therefore requiring more power. Your ipod will also drain it's own battery quicker since it's own internal amplifiers will be doing more work (to push out bigger amplitude sound into your speakers where it is amplified even more).

 

[trackrat]

A slight deviation off of this topic, but a point I've always wondered, but is there any reliable way to estimate the power draw of a system before you have all the parts to hand, like an online calculator? I know I've seen these kinds of things before, but they were never really up-to-date with components and/or used far too generic components/terminology.

How do people get a feel for what level of PSU they need, or is it just one of these things you make an educated stab at? Do people get an idea for power draw through looking at benchmarks of similar systems when comparing product reviews and so on? It's for this very reason I've always overestimated the power draws of my system, but after reading this it seems kind of counter productive if you aren't going to utilise that extra power with a future upgrade.

http://extreme.outervision.com/psucalculatorlite.jsp