SilverStone Element ST50EF-Plus 500 W Power Supply Review

[nextpage title=”Introduction”]

SilverStone Element power supply series is being out for some years now, and we were curious to review their popular 500 W model, ST50EF-Plus. It is important to know that models from SilverStone Element series can be manufactured by two distinct companies: models up to 600 W are manufactured by Enhance Electronics, while models starting at 650 W are manufactured by Seventeam. SilverStone uses a lot of different manufacturers for their power supplies. Besides Enhance and Seventeam, units from their Decathlon series are manufactured by Impervio and units from their Strider series are manufactured by FSP. Phew!

Enhance Electronics is the manufacturer behind power supplies from Akasa, Real Power Pro series from Cooler Master, TruePower Quattro series from Antec and some models from BFG, just to name a few. Keep in mind that not all models from these brands are manufactured by Enhance.

Figure 1: SilverStone Element ST50EF-Plus power supply.

Figure 2: SilverStone Element ST50EF-Plus power supply.

Element ST50EF-Plus is small 5 ½” (140 mm) power supply, having a 120 mm fan on its bottom and active PFC, of course.

Only the main motherboard, EPS12V and video card cables use nylon protections, which don’t come from inside the power supply housing, as you can see in Figure 2. The included cables are:

• Main motherboard cable with a 24-pin connector (no 20-pin option).
• Cable with one EPS12V connector.
• Two auxiliary power cables for video cards with six-pin video card power connectors.
• Two SATA power cables with three SATA power connectors each.
• Two peripheral power cables with three standard peripheral power plugs and one floppy disk drive power connector each.

The number of cables is good enough for an entry-level or mainstream PC, but we think that SilverStone should have used a six/eight-pin connector on one of the video card auxiliary power cables, in order to allow you to install a very high-end video card that requires one eight-pin power connector and one six-pin power connector at the same time.

All cables have 21 5/8” (55 cm) between the power supply housing and the first connector on the cable. On the peripheral power cables there is 5 7/8” (15 cm) between connectors, but on the SATA power cables there is 9 7/8” (25 cm) between connectors, being the cables with the longest space between connectors we’ve seen to date. Most wires are 18 AWG, which is the correct gauge to be used, but the main motherboard cable and the EPS12V cable use 16 AWG wires (i.e., thicker), which is always great to see.

Figure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The ST50EF-Plus”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

Figure 4: Overall look.

Figure 5: Overall look.

Figure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

On this power supply this stage is flawless, with two X capacitors (one of them after the rectifying bride), one ferrite coil and two Y capacitors more than required.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the SilverStone Element ST50EF-Plus.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of SilverStone Element ST50EF-Plus. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in its primary, which can deliver up to 10 A at 100° C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Figure 9: Rectifying bridge.

On the active PFC circuit two STW20NK50Z power MOSFET transistors are used, each one capable of delivering up to 17 A at 25° C or 10.71 A at 100° C in continuous mode (note the difference temperature makes) or 68 A in pulse mode at 25° C, presenting a resistance of 270 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Taiwanese from Teapo and labeled at 105° C, which is great (on the majority of power supplies this component is rated at 85° C, the higher temperature rating the better – it translates into a higher life-span for the product).

In the switching section, two STW14NK50Z power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 14 A at 25° C or 7.6 A at 100° C in continuous mode (note the difference temperature makes) or 48 A in pulse mode at 25° C, with a maximum RDS(on) of 380 mΩ.

Figure 10: Switching transistors, active PFC diode and active PFC transistors.

The primary is controlled by a CM6800 PFC/PWM combo controller.

Figure 11: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply uses three Schottky rectifiers on its secondary.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by one STPS60L45CW Schottky rectifier, which has a maximum current limit of 60 A (30 A per diode at 135° C, 0.50 V voltage drop). This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

The +5 V output is produced by another STPS60L45CW Schottky rectifier, giving us a maximum theoretical power of 214 W for this line.

The +3.3 V output is produced by one 40CPQ060 Schottky rectifier, which supports a maximum current of 40 A (20 A per diode at 120° C, 0.49 V voltage drop), giving us a maximum theoretical current of 29 A or 94 W for the +3.3 V output.

What is unique about this power supply is the use of a MOSFET transistor to rectify the -12 V output (it is used an IRF2807 transistor, which is capable of handling up to 58 A at 100° C in continuous mode).

Figure 12: +5 V and +3.3 V rectifiers and -12 V transistor.

Figure 13: +12 V rectifier.

This power supply uses a WT7517 monitoring integrated circuit, which is in charge of the power supply protections. It supports over voltage (OVP), under voltage (UVP), over current (OCP) and over temperature (OTP) protections. This power supply really implemented the over temperature protection, which we could confirm by the presence of two thermal sensors, one for controlling the fan and one for this circuit. In most power supplies the monitoring integrated circuit supports over temperature protection but this protection isn’t activated, as the thermal sensor necessary for this protection to work is not installed.

Figure 14: Monitoring integrated circuit.

Electrolytic capacitors from the secondary are from Teapo and Su’scon and labeled at 105° C.

[nextpage title=”Power Distribution”]

In Figure 15, you can see the power supply label containing all the power specs.

Figure 15: Power supply label.

This power supply uses a dual-rail design distributed like this:

• +12V1 rail: Main motherboard, SATA and peripheral power cables and half of the EPS12V connector.
• +12V2 rail: Half of the EPS12V connector and video card power cables.

We prefer when the CPU (EPS12V connector) and the video cards are in separated rails.

Now let’s see if this power supply can really deliver 500 W.[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests the +12V1 input was connected to both +12V1 and +12V2 rails,
the same thing happening with the +12V2 input.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12V1	4 A (48 W)	7 A (84 W)	11 A (132 W)	14.5 A (174 W)	18 A (216 W)
+12V2	3 A (36 W)	7 A (84 W)	10 A (120 W)	14 A (168 W)	18 A (216 W)
+5V	1 A (5 W)	2 A (10 W)	4 A (20 W)	5 A (25 W)	6 A (30 W)
+3.3 V	1 A (3.3 W)	2 A (6.6 W)	4 A (13.2 W)	5 A (16.5 W)	6 A (19.8 W)
+5VSB	1 A (5 W)	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 W)
-12 V	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)
Total	102.0 W	193.1 W	294.5 W	392.8 W	490.9 W
% Max Load	20.4%	38.6%	58.9%	78.6%	98.2%
Room Temp.	46.9° C	45.9° C	46.8° C	47.9° C	50.0° C
PSU Temp.	50.1° C	49.6° C	49.2° C	50.8° C	55.4° C
Voltage Stability	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	125.1 W	230.8 W	355.6 W	487.2 W	633.0 W
Efficiency	81.5%	83.7%	82.8%	80.6%	77.6%
AC Voltage	112.4 V	111.1 V	109.5 V	106.7 V	105.6 V
Power Factor	0.924	0.962	0.975	0.977	0.971
Final Result	Pass	Pass	Pass	Pass	Pass

SilverStone Element ST50EF-Plus can really deliver 500 W at 50° C, which is really good. Efficiency when we pulled between 40% and 60% from its maximum labeled power (between 200 W and 300 W) was really good, between 82.8% and 83.7%. At 80% load (400 W) efficiency dropped to around 80% and at full load it dropped below the 80% mark, at 77.6%. It is very important to remind that our tests are tougher than the ones promoted by the 80 Plus organization, which test power supplies at a room temperature of only 23° C, a temperature impossible to be achieved inside a typical PC. Since efficiency drops with temperature and we pulled 500 W at more than double the temperature used by 80 Plus our result was lower than the one provided by this institution. In our opinion our results are more realistic.

There are two claims on Element ST-50EF-Plus that we must check whether they are true or not. The first one is the “±3% cross regulation.” The ATX specification says that all outputs must be within 5% of their nominal values, except for the -12 V output, which has a 10% tolerance. So SilverStone is claiming that this power supply has a tighter regulation than required by the ATX specification. This proved to be true, expect for the -12 V output, which was always outside this 3% range.

The second claim present on the power supply label is “PFC > 0.96.” As you can clearly see on the table above, power factor was below this value during test one, with the power supply delivering 20% of its labeled power (100 W).

Ripple and noise levels were always below the maximum allowed (120 mV for +12 V and -12 V outputs and 50 mV for +5 V and +3.3 V outputs). During test number five, with the power supply delivering 490.9 W, noise level at +12V1 input was of 68.6 mV, at +12V2 it was of 74.8 mV, at +5 V it was of 24.2 mV, at +3.3 V it was of 26.6 mV and at -12 V it was of 47.8 mV. All numbers are peak-to-peak figures.

Now let’s see if we could pull more than 500 W from this unit.

[nextpage title=”Overload Tests”]

Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.

In order to do that we increased current on the +12V2 rail until the power supply shut down. This happened when we tried to pull more than 20 A from it.

Manufacturers always leave a margin between what is written on the label (18 A in this case) and the level the OCP circuit is really configured (20 A in this case). We always like to see this margin as tight as possible, like happened with this power supply.

Then starting from test five we increased currents to the maximum we could with the power supply still running inside ATX specs. The results are below. After only a couple of minutes running under this configuration the power supply exploded, and we couldn’t finish collecting data. After disassembling the power supply we could see that the transistors from the active PFC circuit were the components that burned (see Figure 10).

Of course you are not suppose to pull more than the power supply labeled power from it, however we do that to see if some protection will kick in and prevent the unit from burning or exploding, which didn’t happen with this power supply.

Input	Maximum
+12V1	19 A (228 W)
+12V2	19 A (228 W)
+5V	21 A (105 W)
+3.3 V	12 A (39.6 W)
+5VSB	2.5 A (12.5 W)
-12 V	0.5 A (6 W)
Total	590.0 W
% Max Load	118.0%
Room Temp.	48.0° C
PSU Temp.	56.6° C

[nextpage title=”Main Specifications”]

SilverStone Element ST50EF-Plus power supply specs include:

• ATX12V 2.2
• Nominal labeled power: 500 W.
• Measured maximum power: 500 W at 50° C.
• Labeled efficiency: 80% minimum (80 Plus certified)
• Measured efficiency: Between 77.6% and 83.7% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• Motherboard Power Connectors: One 24-pin connector and one EPS12V connector.
• Video Card Power Connectors: Two six-pin connectors in two cables.
• SATA Power Connectors: Six in two cables.
• Peripheral Power Connectors: Six in two cables.
• Floppy Disk Drive Power Connectors: Two in two cables.
• Protections: Over current (OCP, tested and working), over voltage (OVP, not tested), no load (NLO) and short-circuit (SCP, tested and working). Over temperature protection (OTP) is present but not listed by the manufacturer.
• Warranty: Information not available.
• Real Manufacturer: Enhance
• More Information: https://www.silverstonetek.com
• Average price in the US*: USD 90.00.

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

SilverStone Element ST50EF-Plus is a decent mainstream 500 W power supply that can really deliver its labeled power at 50° C, providing a decent efficiency between 82.8% and 83.7% if you pull between 200 W and 300 W from it. At full load, however, efficiency was below 80%. It is very important to remind that our tests are tougher than the ones promoted by the 80 Plus organization, which test power supplies at a room temperature of only 23° C, a tempe
rature impossible to be achieved inside a typical PC. Since efficiency drops with temperature and we pulled 500 W at more than double the temperature used by 80 Plus our result was lower than the one provided by this institution. In our opinion our results are more realistic.

The main positive voltages were really within 3% from their nominal values, as promised by the manufacturer. Translation: voltages were closer to their nominal values than required under ATX specification, which is great.

Ripple and noise levels were always below the maximum allowed.

In summary, you won’t have any problems when using this unit.

It exploded while we overload it (at 590 W), but you have to keep in mind that this is an extreme situation that obviously show not be attempted. Of course we prefer when a protection from the power supply kicks in preventing this kind of thing from happening.