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Dual 12V PSU Shootout
Author: JonnyGuru
Date Posted:21/07/2005 13:42.03
| AMS Mercury PP-44603 SLRating: |  |
| Seasonic S-12-430 SLRating: | |
| Thermaltake TWV500 SLRating: | |
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Bottom Line:
The three of these power supplies really don\'t shoot-out each other. If you want cheap, the AMS. If you want quiet, the Seasonic. If you want modular, the Thermaltake.
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Introduction
It's that time again. I've
got three more power supplies with dual 12V rails and a power supply tester
waiting to test them.
I changed some of my loads
from the last review. I didn't blow anything up, so I figured I'd
Test 1: .I've got
+12V1 and +12V2 at 12A. I figured this
was a good
"base" test.
Test 2: The +12V1 and +12V2 are juiced up to 14A to emulate a
higher than average load. This may be above spec for some power supplies.
Test 3: This test
throws the power supply a bit off balance +12V1
goes up to 16A, while +12V2 goes back down to 12A. The 5V is brought
up to 16A
Test 4: This test
is the opposite of three. +12V2
is now at 16A and +12V1 at 12A. The 5V is still at 16A.
Test 5: This test
is rather balls to the wall. The 5V is brought down to 14A, but both
12V rails are whacked with a 16A load. This is a 32A, or 384W, on the
12V combined rail. This is out of spec for most power supplies, but
I find many can handle this I then move the rails up to a combined wattage
of 408W. This can be done by putting 17A on each rail or 16A and 18A...
depending on how the power supply is spec'd.
The only exception I made
for this test is the Seasonic. Since the Seasonic was only
a 430W power supply (I take what I can get) the 12V load was so out of spec
the overload protection immediately kicked when I applied it. For the
fifth and final test, the Seasonic gets a 14A load on 12V1, a 15A load on
12V2, a 14A load on the 5V rail and a 10A load on the 3.3V.
What is a 12V rail and why are there two of them?
I suppose we should break
down what we're talking about here.... The
rails (named after steel rails that carried power to electric trains) are what
each different colored wire (yellow for +12V, red for +5V, etc.) derive it's
power from. With the demand on +12V becoming greater and greater, Intel
decided it would be "safer" to split the duty of supplying +12V across two
rails. It's "safer" because inexpensive transistors capable of supplying
more amperage (say more than 34A) at any kind of decent efficiency (70% or
better) are subject to blowing up. :-) That's not very safe. ;-)
To split the duty up between
two +12V rails, one can use cooler running, cheaper transistors to supply
the power. Furthermore, this
isolates devices on one rail from another, so EMI introduced by lighting
inverters and drive motors
can be isolated from sensitive components like the CPU and video card.
(14 * 12) + (16 * 12)
= 336? What is this? NEW math?
You'll often find that
the capabilities of the +12V rails combined almost never equal what is listed
for each rail individually added together. This
is because, although the two +12V rails are on separate transistors, they're
still being fed by the same, single transformer and rectifier. So one
rail might be able to pull off 168W if loaded up by itself, and the other might
be able to pull off 192W if loaded up by itself, but the amount of juice that
can even get to those transistors (safely) isn't more than 336W, so you simply
CAN NOT fully load both rails to their maximum capabilities. And when
I say "can not" load them, I mean load them without overloading them and staying
within the tolerance of the rated rail. I mean, I put 16A loads on 14A
rails all day long... that doesn't mean it's recommended. ;)
So back to the testing!
So we have our 5 tests,
and we also have a +5VSB test that looks at the power factor and efficiency
of a power supply when it's idle. Power factor
and efficiency will also be measured under all loads. All loads are run
for 15 minutes prior to deriving a reading and are run for 30 minutes before
determining a pass/fail. The usual stuff.
Noise will not be measured
on a technical level. As before, I will just give a "judgment" on
how loud a power supply is. If it can drown out my 2 1/2 year old dancing
around to the Wiggles in the other room, it's loud.
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