Mint said:
I was wondering why so much heat comes from the power supply fan.
Is the conversion from 120 Volt to the lower voltages that
inefficient ?
Thanks.
It doesn't have to be that way.
Power supplies on the order of ten years old, are designed
to be 68% efficient. That isn't very efficient at all. If a
supply like that has a moderate load on it (say a couple video
cards), the heat coming from the power supply will be withering.
The best modern supplies, now offer 80+ percent efficiency. The
air coming from a supply like that, will be at a lower velocity, and
won't be quite as warm as one of those 68% supplies. The efficiency
also allows the supply to have smaller heatsink assemblies internally.
I think one supply, managed to hit around 87% efficiency, but the
trick for doing that, is the supply is a two stage design. First,
they convert 120VAC to 12V DC. And then, a small printed circuit
board is used to convert the 12V DC, to 5V and 3.3V. Such a supply
hits 87% efficiency, as long as the 5V and 3.3V loads are only a
few amps. Some modern motherboards are like that, and complement the
design of the power supply well. But if you were to plug your
old Athlon S462 motherboard, the one with the 5V @ 25A loading,
that supply would no longer be able to hit the 87% number.
The supply would get hotter, and it's possible it would even shut off,
as it can't supply 25 amps on 5V.
So, yes, you can fix it. You can probably combine an 80% efficiency
number, with good overall current ratings on all rails. If you shoot for
a product with an even higher efficiency number, that works out as long as the
new motherboard draws most of its current from the +12V rail.
You can assume, that a supply which doesn't state the efficiency on the
label, is a 68% one. Ones that do better than that, you usually pay
more for them, and they're more likely to print the details on the
label, to convince you to buy it.
As an example of what you can do with super-efficient designs, there
is a 400W power supply with no cooling fan inside. And that is
possible, because it doesn't generate a lot of heat. You can't actually
draw the 400W number, as it will likely shut off if you try. But it does
show, that the manufacturer was willing to give it a try (run fanless).
Usually, there are enough other fans in the computer, that some air
is always moving through the power supply.
Paul
