question about PSU and heat inside a case

Roughly, what percentage of the heat inside a case is generated by the
PSU?

Have manufacturers tried to move the PSU to a stand-alone external unit
to reduce cooling requirements inside a case and/or provide more room
for other stuff inside the case?

These questions arose because I was looking at my old laptop and
thinking about the heat the ac/dc power converter generates when I'm
using the laptop.

John

On Mon, 28 Sep 2015 17:58:51 +0000 (UTC), "Yes"
wrote:

Roughly, what percentage of the heat inside a case is generated by the
PSU?

Have manufacturers tried to move the PSU to a stand-alone external unit
to reduce cooling requirements inside a case and/or provide more room
for other stuff inside the case?

These questions arose because I was looking at my old laptop and
thinking about the heat the ac/dc power converter generates when I'm
using the laptop.

John

None. PS is self contained and self evacuating.

Laptops, however, you can't ask that question as it's a design
efficiency of the manufacturer and an integral of the unit. Unless
you ask the manufacturer. They make they own rules concerning some
aspects of standardization (as do a few PC manufacturers).

Yes wrote:
Roughly, what percentage of the heat inside a case is generated by the
PSU?

Have manufacturers tried to move the PSU to a stand-alone external unit
to reduce cooling requirements inside a case and/or provide more room
for other stuff inside the case?

These questions arose because I was looking at my old laptop and
thinking about the heat the ac/dc power converter generates when I'm
using the laptop.

John


The information is frequently available at the time of purchase.

ATX power supplies with unspoken efficiency, might be around 65% efficient.

As a worked example, say the DC load presented by the components is 100W.
(65W CPU, 10W motherboard, 25W storage devices, just for laughs).

100W DC output * ( 1 ) = 154W
-----
0.65

And that means that 100W of heat come from the CPU, motherboard, storage devices.
While 54W comes out of the ATX power supply.

Some power supplies of that type, you could actually feel the heat on
the side panel of the computer case, as well as "hot screws" on the back
of the machine. And such power supplies would not have had a quiet fan
on them either, since the fan needs to move that 54W.

Modern supplies come with bronze, gold, platinum ratings, which are
80 percent or higher efficiency. Now, rework the numbers in the
above equation with 0.87 for the efficiency, and see how much of
an improvement that makes.

https://en.wikipedia.org/wiki/80_Plus

Power supplies with Active PFC (a stage in front
of the primary side of the power supply), that reduces
the efficiency by a percentage point or so. But is
included for European regulatory reasons. North American
customers are not billed for reactive power, so we don't
have a financial incentive to have Active PFC. But Active PFC
is probably universal with the 80 Plus designs.

The 80_Plus designs are intended for *modern* computers. One
of the reasons they get to 80 percent, is because the power
supply is actually two-stage. The main power path is +12V only,
and an expectation of the supply design is that most of the
raw watts of power are drawn by +12V loads (CPU/GPU). The 3.3V and
5V rails are not intended to be loaded. That's why they typically
only have a rating of 20A, instead of a higher number. For example,
my old AthlonXP motherboard, the measured load on +5V was 25 amps
when gaming. So the 80_Plus supplies are not a good match for
such loading. My AthlonXP, most of the power comes from +5V,
and going through a two-stage supply drops the efficiency
*way down*. It would also cause the separate +3.3V/+5V
converter module to get pretty hot.

So what an 80_plus supply is intended for, is a computer
with most of the loading on the +12V rail. And less loading
on some of the other rails. The efficiency numbers assume
a certain loading pattern, as otherwise, if all the power
came from the (weak) +5V rail, the efficiency would be pretty
poor, and two stages of conversion inside the PSU would be
generating heat. Instead of just one stage, if you load up the
+12V first stage instead.

Paul

Yes wrote:

Roughly, what percentage of the heat inside a case is generated by the
PSU?

Have manufacturers tried to move the PSU to a stand-alone external unit
to reduce cooling requirements inside a case and/or provide more room
for other stuff inside the case?

These questions arose because I was looking at my old laptop and
thinking about the heat the ac/dc power converter generates when I'm
using the laptop.

Without knowing the efficiency and load on the PSU, no one can tell you
how much heat (in percentage) the PSU is generating compared to the heat
produced by all the other components (RAM, video, CPU, drives, etc).
You might have a cheap PSU with low efficiency under high load. You
might have a good PSU with high efficiency under low load. Your PSU
might have 2 fans instead of 1, and the 2nd may not be running all the
time (it's thermo controlled by a sensor inside the PSU).

There are cases you can buy where the PSU is at the bottom of the case.
Vents in the case ensure that cool fresh air intake goes directly into
the PSU instead of the top-mounting standard setup where the air is
already pre-heated by the RAM, CPU, video, drives, etc. There is still
a fan at the top of the case for exhausting the air heated by the other
components but the PSU [mostly] gets it own supply of cooler outside
air. There are 2 exhausts: one for the PSU (that gets it own intake)
and the other for air heated by the other components.

Because the PSU is at the bottom of the case but the drive bays are
still at the top, you have to ensure the cables from the PSU at the
bottom will reach the drives at the top, and the 20/24 connector from
the PSU will reach the header on the motherboard without interference by
the CPU or chipset heatsinks or daughtercards (e.g., video card).

On 2015-09-28 13:58, Yes wrote:

Roughly, what percentage of the heat inside a case is generated
by the PSU?

None (or very little radiating heat). In the ATX standard, where the PSU
is at the top, the fan inside the PSU pulls hot air in and shoots it
outside; none of the heat that the PSU generates ends-up inside the
case. As Vanguard pointed out, many new cases have the PSU at the
bottom, so it doesn't help at cooling the case, but it still will not
send its heat inside the case.

Have manufacturers tried to move the PSU to a stand-alone external unit
to reduce cooling requirements inside a case and/or provide more room
for other stuff inside the case?

As stated above, the standard is for the PSU to *help* evacuate heat
from the case; it doesn't help to put the PSU outside, since you will
need a fan at the top of the case anyway. But I'm pretty sure you can
find tiny computers with the PSU outside.

These questions arose because I was looking at my old laptop and
thinking about the heat the ac/dc power converter generates when I'm
using the laptop.

John

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