On Mon, 23 Mar 2009 20:53:38 -0700 (PDT), YKhan wrote:

On Mar 23, 5:33*pm, daytripper wrote:
It's nothing that involved - there's no "trapped" electrons, and there's no
real effect on "efficiency" in any classic sense. That whole spiel simply
points out the effect of "partitioning" 12V capacity into multiple isolated
rails, verses having all 12V capacity on a single rail.

And you mentioned that UL & CSA safety requirements don't allow for
more than 240VA, which would mean a maximum of 20A @ 12V. So I don't
see how they can avoid having multiple rails if they want more than
240VA on the system?

For instance, say you have a single-rail supply with 36A of 12V capacity, and
another supply with 2 12V rails rated at 18A each. Now build a system that
requires 12A of 12V for the motherboard and peripherals, plus a pair of 12A
graphics cards.

Both supplies are rated at 36A of 12V, but hooking up the dual-rail supply is
probably going to be more challenging than the single rail supply. In fact, it
probably could not be done - hence you would have unusable ("trapped")
capacity in the dual-rail supply...

But that's probably why they have triple rail power supplies.

Yousuf Khan

And more, even. As we all know, "size matters" ;-)

Bottom line is you can't simply buy capacity - a box of watts - without
understanding potential partitioning effects as applied to a given system
build...

/daytripper