Re: [TCLUG:22867] Athlons and power supplies

[Philip C Mendelsohn <mend0070@tc.umn.edu>]

On Thu, 19 Oct 2000, Thomas T. Veldhouse wrote:

> Yeah - but it is quite simple.  You are going to have a 120V (this is a
> fixed value)

Put a meter on your wall outlet, and see how fixed it is, especially in
the summer.  Plus or minus 10% is very acceptable, and 20% isn't unheard
of.  You never know when NSP is going to sag a little or a lot.

> across the power supply unless there is a short.  Thus, the
> only thing that changes is Amperage availability.

This assumes that the switcher is working in the first place.  If your
switch clock freq. isn't within tolerances, the integral of the voltage
w.r.t. time varies, and so does the output voltage.  If you have problems
with filter caps (and caps are the *least* predictable component
made) your output voltage will vary.

In a linear mode supply, there's a few ways that the regulator can get out
of whack too.

> Assuming the power supply
> is not shorted or open and it is actually producing 250W, you can be sure
> you have the power required (which is at most 250W).  It doesn't take
> electrical engineering to get that far (P = I*V = I^2*R).

You don't take into account the stiffness of the regulator or the dynamics
of the load -- hard drives spinning up and down, fans, what have
you.  It's not a binary on/off situation.

I'm still not saying that you're going to run into trouble by buying the
right size P.S. at (insert store here).  But, I've repaired gear with both
linear and switched mode power supplies, and seen problems occur.  I've
even seen problems when someone puts what they think is a brand-new, good
P.S. in a box, but it turns out that some ancillary spec was not
sufficient -- so there are some 250W supplies that *might* not work in
certain circumstances.  These *STILL* should be non-issues in everyday
life, but I don't agree that every one will *never* have *any*
problem.

It ain't that big a deal.

Cheers,
Phil

-- 
"To misattribute a quote is unforgivable." --Anonymous