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LEPA B850W Power Supply Review

Additional technical assistance: Peter McFarland and Jeremy Price.

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. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 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

12V output is combined for our testing.

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
100W
1.56
3.35
1.78
5.06
6.64
12.14
0.50
5.03
0.20 -12.14
225W
3.72
3.33
3.85
5.04
15.53
12.12
1.00
5.02
0.20 -12.12
450W
7.52
3.31
8.32
5.03
30.68
12.06
1.50
5.01
0.30 -12.11
675W 11.32 3.30 12.35 5.01 47.47 11.89 2.00 4.97 0.50 -12.10
850W
1.42
3.28
1.17
4.98
63.29
11.76
0.50
4.95
0.20 -12.10

The LEPA B850W delivered strong load regulation via +3.3V and +5V output. These are good results and the +3.3V and 5V rails remained firmly within +/-2% of the nominal voltage instead of the recommended +/-5%. There is slightly more fluctuation on the +12v output (0.38).

LEPA B850W Maximum Load
904W

We managed to get the PSU to hit 904W before it would shut down. delivering around 54W 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
760W 1.0 3.31 1.0 5.02 60.0 11.77 0.2 -12.02 0.50 5.00
165W 15.0 3.26 18.0 4.96 2.0 12.12 0.2 -12.04 0.50 4.97

The overall view is that the cross loading results are very healthy indeed. With +3.3V and +5V holding well within expected parameters. The +12V rail exhibited a little more variance, but it is still within safe parameters.

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 5 5 25 5
225W 10 10 35 5
450W 10 10 50 10
675W 10 10 60 10
850W 15 10 75 10

Ripple results are extremely impressive across the +3.3V and +5V rails. The +12V is slightly less impressive, however it is still well within the rated tolerance guidelines. +12 V output peaked at around 75mV under full load.

Efficiency (%)
100W
83.21
225W
84.45
450W
86.76
675W
85.59
850W 82.70

For a 80 Plus Bronze specified unit, these results are very good, showing a maximum efficiency rating well over 86%. At maximum load this drops to just under 83%, which is again, a great result.

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 Digital Sound Level Noise Decibel Meter Style 2 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 Refridgerator
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
28.3
225W
29.4
450W
34.8
675W
35.9
850W 37.2

The power supply is fairly quiet until around 45% of total load and becomes audible, peaking at a rather noticeable 37 dBa at full load.

Temperature (c)
Intake
Exhaust
100W
36
38
225W
38
42
450W
40
46
675W
43
52
850W
45
56

Exhaust temperatures are good in the lower end of the spectrum, rising to a 11c above ambient result at full load.

Maximum load
Efficiency
904W
81.5%

For those interested, we measured efficiency when stressing the unit to breaking point. Over 81% at 904W … hardly practical, but interesting regardless.

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