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ASRock Steel Legend SL-1200GW PSU Review

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 Watt DC load.

We test ambient temperatures at 35C in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:

• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
120W
0.90
3.33
0.93
5.02
8.95
12.04
0.50
5.01
0.20
-12.01
240W
1.62
3.33
1.63
5.01
18.45
12.03
1.00
5.01
0.20
-12.01
600W
3.00
3.33
3.11
5.02
46.78
12.02
1.50
5.01
0.30
-12.01
900W
4.01
3.33
4.05
5.01
70.86
12.01
2.00
5.01
0.30
-12.00
1200W
5.02
3.33
5.20
5.02
94.57
11.99
2.50
5.01
0.30
-12.01

Load regulation is excellent across the board, with minor fluctuation under full load conditions.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
1190W 4.0 3.33 3.0 5.01 88.0 12.01 0.2 -12.01 0.50 5.01
240W 19.0 3.32 22.0 5.00 2.5 12.03 0.2 -12.01 0.50 5.01

The SL-1200GW handled our cross load tests without any issues. When hit with 88A, the +12V rail held at 12.01.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum. ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output
Ripple (mV p-p)
+3.3V
50
+5V
50
+12V1
120
+12V2
120
-12V
120
+5VSB
50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
100W 17 17 25 7
200W 17 20 30 9
400W 23 22 34 11
600W 24 22 33 12
800W 26 21 34 14
1000W 28 22 33 16
1200W 27 23 33 18

Ripple suppression is not bad, it's certainly not the best we have seen in the last year, but it all falls within industry rated tolerances and passed all the tests.

Efficiency (%)
100W
90.9
200W
92.1
400W
93.8
600W
94.4
800W
93.7
1000W 92.7
1200W 91.9

Efficiency is extremely high overall, hitting close to 94.4% at the peak efficiency sector around 50% load. This drops to just over 90% at full load. An excellent set of results for this power supply.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the power supply we have taken it into our acoustics room environment and have set our SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings with real world situations to help describe the various levels.

KitGuru noise guide

10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refrigerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
100W
<28.0
200W
<28.0
400W
<28.0
600W
32.4
800W 33.5
1000W 35.7
1200W 39.7

This is a quality FDB fan but it is quite aggressive in regards to the fan profile. ASRock have set it up to spin quite fast as loads rise closer to 1000 Watts. It's never that annoying, but it is clearly audible at high loads, even above several system fans. Perhaps not ideal if you want a very quiet high end system.

Temperature (c)
Intake
Exhaust
100W
35
38
200W
36
40
400W
38
43
650W
43
47
800W
45
53
1000W 47 57
1200W 50 61

Temperatures are well maintained throughout the load range thanks to the high levels of efficiency of the design and the aggressive fan profile.

Pushing the PSU above its rated limits generates an efficiency of around 89.7%. Not a practical situation in the real world of course.

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