AX760i | AX1200i PSU - Quieter one?
AX760i | AX1200i PSU - Quieter one?
This post is a comparative study between the AX760i and AX1200i PSU to see which one is quieter. The specifications of the hardware used are given below. Note that the article was originally written at the Corsair blog on June 18, 2014. All credit goes to them. A link to their page is available as the end of this post. The article is as follows:
A few weeks ago, we presented the
question: "does a bigger PSU mean a quieter PSU"? Using an AX760i and
an AX1200i in the same PC, we found that the AX1200i was significantly quieter
when presented with a 600W load. Of course, the AXi product line is the absolute
top of the line and the differences between the AX760i and the AX1200i go far
beyond how the fan controller is programmed. So this week we're going to do the
same thing, but with a different set of power supplies.
Because we recycle systems at Corsair
quite often, the build is a little different:
Motherboard: ASUS Z97-WS
CPU: I7-4770K @ 4.3GHz 1.25Vcore
CPU Cooler: Corsair H100i with stock
2x 120mm fans
RAM: 16GB (4x4GB) Corsair Dominator
Platinum DDR3-2800 CAS12
Graphics card: AMD Radeon HD 7990
6GB GDDR5 (Reference)
OS drive: 120GB Corsair Force GT SSD
Drive: 240GB Corsair Force LS SSD
OS: Windows 7 SP1 x64
Chassis: Obsidian 450D Case w/ stock
2x 140mm intake fans and 1x 120mm exhaust fan
Room temperature has been measured
as low as 24.7°C and as high as 25.8°C.
To make sure we're fully loaded,
we're running Prime95 (two threads) and the
Unigine Valley benchmark simultaneously.
Because the RM series power supplies
are not digital, the monitoring capabilities are limited compared to that of
the AXi series. By using an analog to digital bridge , we can monitor the +12V
load on the PSU and the fan RPM. We'll log the CPU temperature to illustrate
the PC's activity.
You can click on any of these graphs
to get a better view.
We'll start with the RM550....
If we look at the "12V
current" line in blue, we can see that we peak out at almost 37A. That
equates to around 444W, so we're pretty close to fully loading this power
supply.
Now, we can't measure the PSU
temperature with the RM Series, but we're still going to log the CPU
temperature so we have an idea of how hot things are. The CPU gets up to
82.1°C. Using a K-Type thermal probe taped to the housing of the PSU, we find
that the ambient temperature by the PSU is around 33.5°C.
The fan almost immediately starts up
and fluctuates between 250 and 650 RPM before settling in on an average fan
speed of 650 RPM.
Now we'll swap out the 550W for the
RM650 and wait about an hour for the ambient temperatures to drop to under
24°C.
You can see that our +12V load is
pretty much the same, as it should be as we're running all of the same
benchmarks on the same hardware, and we see the fan once again fluctuating
between 250 and 650 RPM.
This time, however, the fan goes up
to 800 RPM once the inside of the PC reaches over 30°C according to our K-type
thermometer. We hit temperatures inside the PC as high as 30.7°C. which is a
good 2.8°C lower than the first test, despite the fact that room temperature is
only 1.2°C cooler at the most. The CPU temperature is slightly lower too, which
leads us to believe that the higher fan RPM is reducing temperatures inside the
case and helping reduce CPU temperatures.
Now let's try the RM750. While the
RM550 and 650 are based off of the same platform, the RM750 is a completely
different animal internally.
And here we can see that with a
completely different platform comes completely different results.
The fan stays off longer, at first,
and for the next six minutes, the fan switches from off to spinning 690 RPM.
Finally, the fan settles on an average RPM of around 680 RPM. So while
initially the RM750 is quieter, it only takes a matter of time before it's the same
as the 550W.
But what about the RM850? It's based
on pretty much the same platform as the RM750...
The RM850 doesn't seem to be too
different than the RM750 in terms of fan speed. Once again, we see the PSU
trying to hang onto Zero-RPM mode for a much longer duration than the RM550 or
RM650, but it eventually does kick in and spin at 650 RPM average. Only
slightly slower than the 690 RPM we logged with the RM750.
Finally, we're going to install an
RM1000 in this PC. The RM1000 is a different platform still. Different than the
RM450 and RM550 and different from the RM750 and RM850 as well. Let's see how
it does!
A typical user would assume that
their fan isn't working at all! After more than 20 minutes, the outer surface
of the PSU housing reaches 40.9°C, the hottest we've seen, and this causes the
fan to immediately spin up to 900 RPM. Of course, the fan only stays up here
for less than a minute before spinning back down and leveling off at 620 RPM
where it stays for almost two minutes before shutting off again.
Not only was the RM1000 the quietest
of the bunch, we also found it was the most efficient. We could only log the
+12V load in Link with the RM series power supplies nd not total DC output. And
we certainly aren't able to log AC input and calculate and log efficiency on
the fly like we can with the AXi series. But we used a Watts-Up meter to
measure and log the AC load at the wall. The RM450 and RM550 consumed 547W from
the wall. The RM750 and RM850 consumed a little less at 541W. The RM1000
consumed the least amount of power at 534W. Of course, this makes sense as a
power supply tends to be the most efficient at 50% of its capability and less
so at lower and higher loads.
Once again, we've shown that a
larger PSU can potentially be a quieter unit, though the actual difference can
be minimal when looking at models that are only a few wattages apart and
certainly within the same platform. More importantly, PSU choice should be
purpose driven. If you know your PC will be used primarily for office
applications and typically used around the neighborhood of 100 to 150W, it
doesn't make sense to buy a 1000W, 850W or even a 750W if you're only going to
be occasionally gaming. Even if you have a killer graphics card installed just
for the occasional game and the PSU is 3% more efficient at 50% load than at
10% or 20% load, you're not going to see much of an ROI buying a larger PSU if
less than 10% of your computer's usage is gaming. And it's likely the low noise
at high load benefit won't be that noticeable as the graphics card fan is
typically A LOT louder than any PSU fan. On the other hand, if you're someone
that has a PC strictly for gaming and 90% of the time that PC is in game, it
makes sense to get a PSU that's more than you need so it can run more
efficiently, quieter and allow for plenty of overhead if you plan to either add
an additional graphics card or replace your existing one with a more powerful
card some time down the road.
Source:
http://www.corsair.com/en/blog/2014/june/rm_fan-speed
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