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FSP Twins 500W Redundant Power Supply 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 run ambient temperatures of 35c in this 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
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• 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
50W
0.92
3.30
0.85
5.01
3.13
12.00
0.50
5.07
0.20
-12.01
100W
1.60
3.29
1.65
5.01
6.70
11.98
1.00
5.05
0.20
-12.01
250W
2.95
3.27
2.90
5.00
18.00
11.96
1.50
5.04
0.20
-12.02
375W
4.05
3.27
4.10
4.98
28.00
11.90
2.00
5.00
0.30
-12.03
500W
5.00
3.27
5.35
4.96
37.32
11.87
2.50
4.97
0.30
-12.03

Load regulation is pretty good across the range of figures however compared to some of the latest desktop power supplies we have reviewed, they are a little disappointing. That said, this is a very different style of power supply comprising parallel units running in tandem, so this is to be expected to a certain extent. Results do remain within industry rated tolerance guidelines.

To simulate a unit failure, we unplugged one of the power supply bays power connectors. The single unit handled the task well with only minor fluctuations. The fall back redundancy feature certainly seems to work well.

FSP Twins 500W Redundant Power Supply Maximum Load
545 watts

We managed to get the PSU to deliver 545 watts before it would shut down, delivering around 45 watts more than the rated specifications.

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
390W 2.0 3.29 2.0 5.03 30.0 11.88 0.2 -12.00 0.50 5.00
170W 18.0 3.24 12.0 4.92 4.0 11.99 0.2 -12.01 0.50 5.03

The unit passed our cross load test without any major issues.

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
50W 10 10 40 5
100W 15 10 45 5
250W 15 15 45 10
375W 15 15 50 10
500W 20 15 55 10

Ripple suppression falls within industry rated parameters with the +3.3V and +5 output peaking at 20mV and 15mV respectively. The 12V output peaks at 55mV under full load – well within industry rated parameters, although higher than what we would consider an average of our review samples taken in the last year.

Efficiency (%)
50W
71.23
100W
81.44
250W
91.23
375W
90.32
500W
89.45

Efficiency is actually very good, hitting a peak around 91.2% – and dropping to close to 89.5% at 100% load.

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 in 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)
50W
33.7
100W
34.4
250W
38.8
375W
40.6
500W 51.1

Unfortunately, running two 40mm fans at high speed is going to get noisy. The fans sound like mini helicopters at close to full load and they will drown out any case or cooler fans in most systems if you are driving close to 400 watts or higher.

I found this power supply difficult to deal with with a demand over 350 watts if I was being honest – the two 40mm fans spin up to compensate for rising heat levels inside, and they become intrusive and very annoying. Nothing FSP can do about this really, they are forced to use super small fans to accommodate the diminutive dual bay structure of this unit.

Temperature (c)
Intake
Exhaust
50W
36
39
100W
39
45
250W
42
51
375W
43
56
500W
46
61

The tiny fans have to work hard to maintain the FSP thermal profile, but they actually handle it all very well. If you can deal with the noise that is.

Maximum load
Efficiency
545W
88.8

For those interested, we measured efficiency when stressing the unit to breaking point. 88.8 percent efficiency at 545W … hardly practical, but interesting regardless.

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