LEPA B850W Power Supply Review

1. Introduction2. LEPA B850W Power Supply (Bundle & Cables)3. LEPA B850W Power Supply (External)4. LEPA B850W Power Supply (Internal)5. Testing Methodology and Results6. Closing Thoughts7. View All Pages

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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