Seventeam ST-750P-AF Power Supply Review

[nextpage title=”Introduction”]

Seventeam is slowly entering the US market and ST-750P-AF is one of the few products from them available around here. Is it a good product? Can it deliver its labeled power? Check it out.

Seventeam P-AF and Z-AF series are internally identical, with the difference being the presence of a modular cabling system on Z-AF. So while we tested ST-750P-AF, the results are also valid for ST-750Z-AF. Both models are 80 Plus Bronze certified, meaning a minimum efficiency of 82% under light (20% i.e., 150 W) and full loads (750 W), and minimum efficiency of 85% while delivering half of the labeled wattage (i.e., 375 W). Seventeam also advertises this power supply as having Japanese capacitors inside, while we discovered that this isn’t entirely true (more on this later).

New models from SilverStone Element series (ST65EF, ST75EF and ST85EF) are in fact Seventeam P-AF power supplies. So numbers from this test can also be used for evaluating SilverStone Element ST75EF. It is very important to notice that other models from this series are manufactured by FSP and not by Seventeam.

Seventeam trademark is the sticker in Engrish saying “Breakage Invalid” instead of “Warranty Void if Broken.” By the way, we’ve just got this e-mail from Seventeam: "Since you and other media have mentioned several times about the seal label "Breakage Invalid", we will change it to "Warranty void if Broken" in the near future, after our old Breakage Invalid stock is cleared out.". Isn’t it great when manufacturers actually do something when you point out that there is something wrong?

Figure 1: Seventeam ST-750P-AF power supply.

Figure 2: Seventeam ST-750P-AF power supply.

ST-750P-AF is a small 750 W unit, being 6 ½” (16.5 cm) deep, using a 135 mm fan (which actually measures 130-mm) on its bottom and featuring active PFC, of course.

Only the main motherboard cable is protected by a nylon sleeving, which doesn’t come from inside the power supply housing. Cables are somewhat long, measuring 19 11/16” (50 cm) between the housing and the first connector on the cable, and 5 ½” (140 mm) between connectors on cables with more than one connector. All wires are 18 AWG, which is the correct gauge to be used.

The cables included are:

• Main motherboard cable with a 24-pin connector (no 20-pin option).
• One cable with one EPS12V connector and one ATX12V connector.
• Two auxiliary power cables for video cards with one six/eight-pin video card auxiliary power connector each (the unit we reviewed had four cables, but it was a "special edition", differing from the product found on the market).
• Two SATA power cables with three SATA power connectors each.
• One peripheral power cable with three standard peripheral power plugs and one floppy disk drive power connector (the unit we reviewed had two cables, but it was a "special edition", differing from the product found on the market).

With only two power connectors for video cards this power supply does not offer direct support for SLI or CrossFire using two high-end video cards, since each one requires two connectors each.

Figure 3: Cables.

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

[nextpage title=”A Look Inside The ST-750P-AF”]

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.

Seventeam says that this power supply has Japanese capacitors, however only the big electrolytic capacitor from the primary is Japanese (from Rubycon). All others are Chinese from Samxon. This wouldn’t be a problem if Seventeam didn’t use the word “capacitors” in the plural on the box and on their website. As far as we know, this is false advertising.

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.

This stage from ST-750P-AF is flawless, with two Y capacitors and one ferrite coil more than the minimum 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 Seventeam ST-750P-AF.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Seventeam ST-750P-AF. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply use
s one GBJ2506 rectifying bridge in its primary, which can deliver up to 25A at 100° C  if a heatsink is used, which is the case. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 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 SPW20N60S5 power MOSFET transistors are used, each one capable of delivering up to 20 A at 25° C or 13 A at 100° C in continuous mode (note the difference temperature makes), or up to 40 A in pulse mode at 25° C. These transistors present a resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

Figure 10: Active PFC transistors.

This power supply uses a Japanese capacitor from Rubycon labeled at 85° C to filter the output from the active PFC circuit. Although Seventeam advertises this power supply as having “Japanese capacitors,” only this capacitor is Japanese: all other are Chinese. As far as we understand this is false advertising.

In the switching section, two SPW16N50C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 16 A at 25° C or 10 A at 100° C in continuous mode (note the difference temperature makes), or up to 48 A in pulse mode at 25° C. These transistors present a maximum RDS(on) of 280 mΩ.

Figure 11: Switching transistors.

The primary is controlled by a FAN4800I PFC/PWM combo controller.

Figure 12: 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 six 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 four of these rectifiers. Two SBR30A60CT (30 A, 15 A per internal diode at 110° C, typical voltage drop of 0.53 V) connected in parallel are in charge of the direct rectification part, while two PFR60L45PT (60 A, 30 A per internal diode) connected in parallel are in charge of the “freewheeling” part (i.e., discharging the coil). For our math we need to consider the path with the lower current limit, which is the direct rectification one. This gives us a maximum theoretical current of 86 A or 1,029 W for the +12 V output.

By the way, we are now talking about the voltage drop presented by the rectifiers. This parameter shows how much voltage is wasted by the rectifier. The lower this number is, the better, as less voltage is wasted, increasing efficiency.

The +5 V output is produced by one SBL6040PT Schottky rectifier (60 A, 30 A per internal diode at 100° C, typical voltage drop of 0.55 V), giving us a maximum theoretical current of 43 A or 214 W for this output.

The +3.3 V output is produced by another SBL6040PT Schottky rectifier, so the maximum theoretical power this output can deliver is of 141 W.

All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.

Figure 13: Rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports under voltage (UVP), over voltage (OVP), over current (OCP) and over temperature (OTP, not implemented on this power supply) protections. Any other protection that this unit may have is implemented outside this integrated circuit.

Figure 14: Monitoring integrated circuit.

Electrolytic capacitors from the secondary are Chinese from Samxon 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 has two virtual rails, distributed like this:

• +12V1 (yellow with black stripe wire): ATX12V/EPS12V connectors.
• +12V2 (solid yellow wire): All other cables.

For a better distribution this power supply needed to have four virtual rails, not only two.

Now let’s see if this power supply can really deliver 750 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 beha
ved 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 the power supply +12V2 rail and the +12V2 input was connected to the power supply +12V1 rail.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12V1	5 A (60 W)	11 A (132 W)	16 A (192 W)	22 A (264 W)	27 A (324 W)
+12V2	5 A (60 W)	10 A (120 W)	16 A (192 W)	21 A (252 W)	27 A (324 W)
+5V	2 A (10 W)	4 A (20 W)	6 A (30 W)	8 A (40 W)	10 A (50 W)
+3.3 V	2 A (6.6 W)	4 A (13.2 W)	6 A (19.8 W)	8 A (26.4 W)	10 A (33 W)
+5VSB	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 W)	3 A (15 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	149.8 W	303.0 W	455.3 W	606.4 W	749.9 W
% Max Load	20.0%	40.4%	60.7%	80.9%	100.0%
Room Temp.	45.5° C	47.2° C	47.8° C	49.0° C	48.3° C
PSU Temp.	48.2° C	48.5° C	49.4° C	51.1° C	56.2° C
Voltage Stability	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Fail on -12 V
AC Power	181.9 W	356.2 W	539.5 W	733.0 W	934.0 W
Efficiency	82.4%	85.1%	84.4%	82.7%	80.3%
AC Voltage	112.9 V	111.2 V	108.8 V	106.2 V	104.1 V
Power Factor	0.991	0.997	0.998	0.999	0.998
Final Result	Pass	Pass	Pass	Pass	Pass

Efficiency was high between 84.4% and 85.1% when we pulled between 40% and 60% from this power supply labeled capacity (i.e., between 300 W and 450 W). Under light load (20% load, i.e., 150 W) and 80% load (i.e., 600 W) efficiency dropped to between 82% and 83%, not a bad number. Under full load (750 W) efficiency dropped to 80.3%, still above the 80% mark. This unit is 80 Plus Bronze certified, meaning that according to 80 Plus organization it presents efficiency of at least 82% under full load. The difference between what we achieved and what they achieved can be easily explained: they collect data at a room temperature of only 23° C, a temperature that is impossible to be seen inside a PC, and efficiency decreases with temperature (click here for more information).

Noise level at +12V1 was very high (102.8 mV) during test five, almost touching the 120 mV limit, while -12 V output presented a 138 mV noise, surpassing the maximum allowed. All other outputs were inside the maximum allowed, but we wanted to see lower levels specially on +5 V and +5VSB, which presented 41 mV and 43.6 mV noise levels, respectively. You can see the results below for test number five. All values are peak-to-peak figures and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +5 V and +3.3 V outputs.

Figure 16: +12V1 input from load tester at 749.9 W (102.8 mV).

Figure 17: +12V2 input from load tester at 749.9 W (46.6 mV).

Figure 18: +5V rail with power supply delivering 749.9 W (41.0 mV).

Figure 19: +3.3 V rail with power supply delivering 749.9 W (25.8 mV).

Now let’s see if we could pull more than 750 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 configured the +12V1 input from our load tester (which was connected to the power supply +12V2 rail) with a low current and configured our load tester to pull 33 A from the power supply +12V1 rail. The power supply turned on, meaning that either OCP is disabled or configured at a value above 33 A.

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. When we tried to increase one more amp at any output ripple would go to the roof, meaning that the unit stopped working correctly.

The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn and when we tried to pull far more than it could deliver it would shut down, so this unit passed on this test.

Input	Maximum
+12V1	30 A (360 W)
+12V2	30 A (360 W)
+5V	13 A (65 W)
+3.3 V	12 A (39.6 W)
+5VSB	3 A (15 W)
-12 V	0.5 A (6 W)
Total	845.9 W
% Max Load	112.8%
Room Temp.	48.3° C
PSU Temp.	56.2° C
AC Power	1,083 W
Efficiency	78.1%
AC Voltage	102.2 V
Power Factor	0.999

[nextpage title=”Main Specifications”]

Seventeam ST-750P-AF power supply specs include:

• ATX12V 2.2
• Nominal labeled power: 750 W.
• Measured maximum power: 845.9 W at 48.3° C.
• Labeled efficiency: 80% minimum (80 Plus Bronze certified)
• Measured efficiency: Between 80.3% and 85.1% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• Motherboard Power Connectors: One 24-pin connector, one ATX12V connector and one EPS12V connector.
• Video Card Power Connectors: Two six/eight-pin connectors.
• Peripheral Power Connectors: Three in one cable.
• Floppy Disk Drive Power Connectors: Two.
• SATA Power Connectors: Six in two cables.
• Protections: Over voltage (OVP, not tested), under voltage (UVP, not tested), over current (OCP, tested and not working) and over power (OPP, not tested). Short-circuit protection (SCP) present and working.
• Warranty: N/A.
• More Information: https://www.seventeam.com.tw
• Average price in the US*: USD 130.00.

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

[nextpage title=”Conclusions”]

It is good to see Seventeam finally entering the US retail market. From our experience their products are honest and present a good cost/benefit ratio for the mainstream user.

Talking specifically about ST-750P-AF, it presents high 84%-85% efficiency when you pull between 40% and 60% from its labeled capacity, i.e., between 150 W and 450 W from it. Under other loads efficiency isn’t the best in the world, but at the same time isn’t the worst.

The number of available cables is enough for the user building PC with one high-end video card. If you want to install two or three video cards you will either need adapters or a different product, as each high-end video card needs two connectors each to operate.

The only drawback from this power supply is the electrical noise level. Even though it was below the maximum allowed, we wanted to see noise and ripple at lower levels. Usually power supplies with high noise levels we give our Silver Award, but considering that this unit costs only USD 130 it presents an outstanding cost/benefit ratio for the user looking for an honest 750 W power supply, and that is why we are giving this unit our Golden Award seal.

We’d like to remember that internally this power supply is identical to Seventeam ST-750Z-AF and SilverStone ST75EF, so all performance considerations are also valid for these other two products.

The only feedback we need to give to Seventeam is for them to fix their website and product box and replace "Japanese capacitors" by "Japanese capacitor on primary" or similar wording, as "capacitors" lead the consumer to think that all capacitors inside the power supply are Japanese, which is not the case.

Here is the answer from Seventeam regarding this issue: "this is actually a translation mistake by our part, it was described in Chinese as Japanese Big Capacitor, but somehow translated into plural description in English. But thank you for pointing this out, we will correct this mistake."