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28-11-2007, 05:29 PM

In article news:<fihj1i$6u6$1@tree.broomstick.com>, Arthur Hagen wrote:
> The total wattage is irrelevant. You need to measure the
> current polled /per rail/.

You do indeed -- and I'm sorry I forgot to say so.

However, my own over-spec'd PSU gives at least twice what's needed on
all rails ... and that really *is* more than is necessary.

What I was trying to warn the OP of is that -- just as buying a cheap
PSU is a false economy (which is to say no economy at all) -- spending
more to buy a higher power PSU of no better quality is a complete waste
of money.

Yes, the PSU does have to be sufficiently powerful to run the system,
but I know of several people who advocate 480W and 600W (and even more
powerful) PSUs for systems that, on closer inspection, would run
perfectly well on a good quality 350W (or even smaller) unit.

You *can* buy 1kW PSUs ... but it's fairly hard to spec a system that
needs anything like that (having two top-whack graphics cards would get
you almost half-way, but using the other half would be hard).

> Also beware of rounded numbers. If the label says 20A, 10A, 5A for
> three rails, it's likely to be numbers rounded *up* to the nearest
> multiple of 5, and 20A might in reality mean anything from 16-20A,
> and for 16A, that's a 48W difference for a 12V rail.

That's something I haven't come across. I think that the Trades
Descriptions Act (or whatever stands in its place, nowadays) here in
the UK would mean that anyone selling a PSU claiming to provide 20W on
some rail when it only provided 16W would quickly be required to
withdraw it from sale.

> That said, there's no point in buying a PSU that's much bigger than
> what you will /actually/ need on each rail, keeping in mind that the
> specs are likely overrated (yes, even with "top quality" PSUs) and
> that you add a little extra for reduced efficiency as the PSU gets
> older and/or hotter,

So ... how much overcapacity would YOU allow on each rail, when
spec'ing a PSU?

> ... and any peripherals you might want to add in the future (like
> an extra HD or a PCI card).

Allowing slack for expansion is a different matter, of course.

Cheers,
Daniel.

28-11-2007, 05:29 PM	#23
Daniel James Guest Posts: n/a	Re: Need HW advice for new PC - Which CPU In article news:<fihj1i$6u6$1@tree.broomstick.com>, Arthur Hagen wrote: > The total wattage is irrelevant. You need to measure the > current polled /per rail/. You do indeed -- and I'm sorry I forgot to say so. However, my own over-spec'd PSU gives at least twice what's needed on all rails ... and that really is more than is necessary. What I was trying to warn the OP of is that -- just as buying a cheap PSU is a false economy (which is to say no economy at all) -- spending more to buy a higher power PSU of no better quality is a complete waste of money. Yes, the PSU does have to be sufficiently powerful to run the system, but I know of several people who advocate 480W and 600W (and even more powerful) PSUs for systems that, on closer inspection, would run perfectly well on a good quality 350W (or even smaller) unit. You can buy 1kW PSUs ... but it's fairly hard to spec a system that needs anything like that (having two top-whack graphics cards would get you almost half-way, but using the other half would be hard). > Also beware of rounded numbers. If the label says 20A, 10A, 5A for > three rails, it's likely to be numbers rounded up to the nearest > multiple of 5, and 20A might in reality mean anything from 16-20A, > and for 16A, that's a 48W difference for a 12V rail. That's something I haven't come across. I think that the Trades Descriptions Act (or whatever stands in its place, nowadays) here in the UK would mean that anyone selling a PSU claiming to provide 20W on some rail when it only provided 16W would quickly be required to withdraw it from sale. > That said, there's no point in buying a PSU that's much bigger than > what you will /actually/ need on each rail, keeping in mind that the > specs are likely overrated (yes, even with "top quality" PSUs) and > that you add a little extra for reduced efficiency as the PSU gets > older and/or hotter, So ... how much overcapacity would YOU allow on each rail, when spec'ing a PSU? > ... and any peripherals you might want to add in the future (like > an extra HD or a PCI card). Allowing slack for expansion is a different matter, of course. Cheers, Daniel.