ocaholic - PSUs > be quiet! Pure Power L8 730W CM Review

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Photo Gallery

Page 2 - Photo Gallery

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Delivery and Specifications

The Pure Power L8 CM 730W is a semi modular PSU.

Non modular cables
Cable	Length
1 x ATX 20+4 pin	45 cm
1 x EPS/ATX 12V (4+4) pin	45 cm

Modular cables
Cable	Length
2 x PCI-E 6+2 + 6 pin	45, 45 cm
2 x 2x SATA + 1x Molex + 1x Floppy	45, 60, 75, 90 cm
2 x 3x Molex	45, 60, 75 cm
2 x 3x SATA	45, 60, 75 cm

Connectivity is decent for the PSU of this class as it offers four PCI-Express 6+2 +6 power connectors on two separate cables, ten SATA and four Molex connectors, enough for most mid- to higher-end setups. The cables are the 18 AWG. High-end PSUs normally use better 16AWG or even better cables.

Specifications
Voltage	Current	Power
+ 3.3 V	25 A	150 Watt	730 Watt (Total)
+ 5.0 V	20 A	150 Watt
+ 12 V	55 A	660 Watt
- 12 V	0.3 A	3.6 Watt
+ 5 Vsb	3.0 A	15 Watt

As it does not use the single +12V rail design it should be taken into an account that it actually provides 55Amps on both rails, 30Amps on 12V1 and 30Amps on the second one. Most PSU makers are currently going back to the single +12V rail design, but we are sure this one does well unless you are pushing for extreme multi-GPU setups that require much higher-end PSUs.

The Pure Power L8 CM 730W has been 80Plus Bronze certified. This means, that the efficiency of this PSU should be above 82% at 20% load, above 85% at 50% load and above 82% at 100% load.

As you can see from the list below, the rest of the features include standard protections, standard dimensions and a 3-year warranty which is pretty much what you get with a mid-range class PSU.

80Plus Bronze
OVP, UVP, OCP, SCP, OPP, OTP
Dimensions (W x H x D): 150 mm x 86 mm x 160 mm
120 millimeter fan
Warranty: 3 Years
Price: 100 CHF

Page 3 - Delivery / Specs

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A Look Inside

BeQuiet's Pure Power L8 CM is based on a HEC OEM design. The first hint for a high-quality power supply you can get from the transient filtering stage.

On the primary side you find a rectifier. We can find a PCB housing the CM6800. The CM6800 controls the PFC Booster and the Push-Pull converter. This PSU has a Push-Pull topology using two Mosfets and two Diodes according to the following primary sided principle: link
This is an old school standard topology; simple and proven, but it won't achieve new efficiency records. Because this topology requires hard switching from the Mosfets (Switching Mosfets under voltage and current generates losses) this topology is more and more replaced in the PC PSU market by resonant topologies. The transformer has on the secondary side two coils one for 12V and one for 5V. 3.3V is generated from the 5V Coil. This is the classic old PSU topology.

The APFC Capacitor with 470uF at 400V and 85°C from Teapo. The PFC Booster uses a BCY10-600 Hyperfast recovery diode and 3 60R190C6 Mosfets. This is ok for a PSU in this price range; SiC Diodes are still quite expensive. For rectifying the secondary side Schottky diodes are used. The Output filter Capacitors are from Teapo. 105°C is written on them.

The OCP, UVP, OVP is done by a WT7527.

Page 4 - A Look Inside

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Input/Output Power and Efficiency

Page 5 - Input/Output Power and Efficiency

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Result Analysis and Discussion

Efficiency 115V
Load	Pin(W)	Pout(W)	Efficiency
20 %	174.1	148.51	85.30 %
50 %	425.6	368.84	86.66 %
100 %	871.6	728.74	83.61 %

The 80Plus Bronze certification requirements (82% - 85% - 82%) are surpassed especially at 20% Load. This is the case with most of todays PSU's an it mainly originates from the reason of lower losses in the AC filtering stage and the PFC at 230V AC.

Output Stability
Load	Rail	Loading(A)	Output(V)
20 %	5V	1.61	5.40
	3.3V	1.58	3.33
	12V	9.91	12.06
	5VSB	1.00	5.08

50 %	5V	2.97	5.02
	3.3V	2.90	3.34
	12V	26.57	11.98
	5VSB	1.54	5.03

100 %	5V	5.10	5.02
	3.3V	5.11	3.25
	12V	54.02	11.86
	5VSB	3.00	4.97

The stability of the output voltages and the outcome of the crossload tests (results not shown here) are not perfect but still with margin within the norms and absolutely satisfactory (especially when you consider the Topology used in this PSU).

Noise
Load
20 %	Silent
50 %	Audible
100 %	Noisy

Noise level results are decent and mostly attributed to be quiet!'s choice to use its own high-quality thermally controlled 120mm fan with rifle bearing, but we would prefer that it is much less noisy under full load.

Noise/Ripple
Voltage	Noise/Ripple Vpp
5V	0.023
12V	0.054
-12V	0.032
3.3V	0.030
+5VSB	0.036

The noise values are within the ATX norm. This is a perfect example for the quality difference between Japanese and non Japanese capacitors. The topology used in this PSU is filter friendly and Teapo capacitors are used in a high amount. However the filter performance is worse compared to high end PSUs using Japanese capacitors. Transient loads are a big issue for this topology. In modern PCs transient load changes often occur. This can end in a output Voltage not within the norm for a short moment. This again can end up in system instability.

Page 6 - Result Analysis and Discussion