kony wrote:
> Tomaz Cedilnik <tcedilnik@ntlworld.no.spam.please.com> wrote:
>
>> I'm a bit confused. Looking on dabs.co.uk they cost anything
>> between 15 and 150 pounds (ok, the top end are those that output
>> 700+, but even exactly 500 can cost anything between 20 and 110
>> pounds).
>>
>> Seems there is much more to a PSU that the wattage... What do I
>> need to look for in a PSU so it will work with my machine? I've
>> got an Athlon XP 2000+ (1.67 GHz).
>>
>> About wattage - it only draws as much power from mains as needed
>> considering the components that have to be powered at that
>> moment, doesn't it? How do I find out what wattage I need?
>
> List all major parts in your system, including motherboard
> make, model, and hopefully a link to the product page or at
> least a (link to a) larger picture of it (need not be a
> picture you took, only of same thing).
>
> With this we can approximate a ballpark figure with at least
> some margin. From the age of your CPU there were many
> motherboards still using 5V power for CPU subcircuit so it
> could make a significant difference what motherboard you
> have, towards which PSU spec is the most cost effective,
> then from there further narrowing down potential candidates.
> Then there is the issue of whether there is any chance you
> might want to reuse the PSU on your next system rebuild, if
> that is the case then you may need a fairly high wattage
> "IF" it currently uses 5V rail for CPU subcircuit, as it
> would later need 12V rail for that, so a fairly high(er)
> total wattage unit would be necessary to cover both
> scenarios.
>
> Avoid the lowest cost PSUs which tend to be quite overrated,
> generally most people can use a median priced unit unless
> their system was particularly well endowed, but some
> prettied-up generics also sell for more than they're worth,
> name brands can help but first you'll need to consider the
> specific parts in the system.

Or you can measure it by using the wattmeter method I outlined in
another thread.

I suggest people build suitable test loads. You can use 12V
automotive bulbs for the 12V supply, but you may have problems
finding suitable 3.3v and 5V bulbs. Now make a breadboard with a
suitable number of bulb sockets wired in parallel.

When someone offers an XXX watt PSU, load up sufficient bulbs to
dissipate XXX watts, distributed between the various lines
according to the mfg spec for max load. Connect, turn the PS on,
and wait. I predict 90% of PSUs will self destruct in 30 min or
less. So do this test at the sellers location, before buying. If
it passes, buy it. :-)

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>