[nextpage title=”Introduction”]

ST-550P-AM is a 550 W power supply from Seventeam where you can manually control the fan speed – and can even disable it – a feature called “ASM” by the manufacturer. We’ve already tested another model from Seventeam called ST-550P-AG – which achieved a good performance for an entry-level model – and we were curious to see if ST-550P-AM and ST-550P-AG are the same product (since they have similar model numbers) with only the addition of a fan control knob on ST-550P-AM or if they are completely different units. Let’s see.

One funny detail is the sticker in Engrish saying “Breakage Invalid” instead of “Warranty Void if Broken,” a common “feature” on all Seventeam power supplies.

Seventeam ST-550P-AMFigure 1: Seventeam ST-550P-AM power supply.

Seventeam ST-550P-AMFigure 2: Seventeam ST-550P-AM power supply.

Like ST-550P-AG, ST-550P-AM has active PFC and a 120 mm fan on the bottom, being only 5 ½” (140 mm) deep. With the knob available on the rear of the power supply you can control the fan speed. By pressing it you shut the fan down completely and you have a completely noiseless unit. The power supply still has a thermal sensor attached to the secondary heatsink, so if the temperature there goes too high the fan starts spinning even if you turned it off.

The main motherboard cable uses a 20/24-pin connector and it comes with both EPS12V and ATX12V connectors, sharing, however, the same cable.

Seventeam ST-550P-AM comes with five peripheral cables: one with one 6-pin auxiliary power connector for video cards (ST-550P-AG has two connectors; newer shipments from this power supply are coming with two cables with one six/eight-pin connector each), one (or two on newer shipments) with two SATA power connectors, two with two peripheral power connectors and one with two peripheral power connectors and one floppy disk drive power connector.

Even though all wires are 18 AWG – which is the right gauge for a 550 W product – there are two flaws here. The first one is the presence of only two SATA power connectors. Since nowadays you will have at least two SATA devices – the hard disk drive and the optical drive – you will have trouble installing a second hard disk drive (you will need an adapter). Seventeam fixed this on newer shipments, which are coming with a total of four SATA connectors. Also with the distance between these connectors around only 6" (15 cm) you won’t  be able to connect a SATA hard disk drive and a SATA optical unit to this cable at the same time. ST-550P-AG has this same problem.

The second problem is that this power supply has only one power connector for video cards, while all competing products have two (including ST-550P-AG). Seventeam fixed this on newer shipments, which are coming with two cables.

On the aesthetical side only the main motherboard cable uses a nylon sleeving, which comes from inside the power supply housing.

The distance between the power supply housing and the first connector on each cable is of 17 ¾” (45 cm), and the distance between each connector on cables that have more than one plug is of 5 29/32” (15 cm).

Seventeam ST-550P-AMFigure 3: Cables.

Seventeam is one of the few real power supply manufacturers around. They are the company behind of power supplies from XG/MGE and some models from Cooler Master.

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

[nextpage title=”A Look Inside The ST-550P-AM”]

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.

The first thing we could notice is that ST-550P-AM uses bigger heatsinks than ST-550P-AG, which makes sense, as it can operate with its fan turned off.

Seventeam ST-550P-AMFigure 4: Overall look.

Seventeam ST-550P-AMFigure 5: Overall look.

Seventeam ST-550P-AMFigure 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 power supply is flawless on this stage, having two more ferrite coil, two more Y capacitors after the rectifying bridge and two more X capacitors (one of them after the rectifying bridge) than necessary.

Seventeam ST-550P-AMFigure 7: Transient filtering stage (part 1).

Seventeam ST-550P-AMFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the ST-550P-AM.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of ST-550P-AM. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in i
ts primary, capable of delivering 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.

Seventeam ST-550P-AMFigure 9: Rectifying bridge.

The active PFC circuit uses two SPW16N50C3 power MOSFET transistors, each one capable of handling up to 48 A @ 25° C in pulse mode (which is the case) or up to 16 A @ 25° C or 10 A @ 100° C (note the difference temperature makes).

Seventeam ST-550P-AMFigure 10: Active PFC transistors and diode.

The electrolytic capacitor used on the active PFC circuit is Japanese from Matsushita (Panasonic), which is great. It is labeled at 85° C.

On the switching section this power supply uses another two SPW16N50C3 power MOSFET transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above.

Seventeam ST-550P-AMFigure 11: Switching transistors.

The primary is controlled by a FAN4800 active PFC/PWM controller combo installed on a small printed circuit board, a direct competitor to the very popular CM6800 integrated circuit.

Seventeam ST-550P-AMFigure 12: Active PFC/PWM controller.

The primary from ST-550P-AM is identical to ST-550P-AG’s. Let’s see now the secondary.

[nextpage title=”Secondary Analysis”]

The secondary from ST-550P-AM is different from ST-550P-AG’s. ST-550P-AG uses six Schottky rectifiers, while ST-550P-AM uses only four. This is not necessarily a drawback: even though ST-550P-AG uses two rectifiers for the +5 V output and two rectifiers for the +3.3 V output instead of one each like ST-550P-AM, they use a smaller package than the one used on ST-550P-AM (TO-220 vs. TO-247), meaning they can dissipate less power.

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%. Of course the maximum current (and thus power) this line can really deliver will depend on other components, especially the coil.

The +12 V output is produced by two SBL3060PT Schottky rectifiers, each one supporting up to 30 A (15 A per internal diode at 95° C), so we have a maximum theoretical current of 43 A (15 A x 2 / 0.70), which corresponds to 514 W.

The +5 V output is produced by one SBL4040PT Schottky rectifier, capable of handling up to 40 A (20 A per internal diode at 100° C). This translates into a maximum theoretical current of 29 A or 143 W.

The +3.3 V output is produced by another SBL4040PT Schottky rectifier, so the maximum theoretical power for this output is of 94 W.

Seventeam ST-550P-AMFigure 13: +12 V rectifier and +5 V rectifier.

Seventeam ST-550P-AMFigure 14: +3.3 V rectifier and +12 V rectifier.

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

Seventeam ST-550P-AMFigure 15: Monitoring integrated circuit.

The electrolytic capacitors from the secondary are from Samxon, with some Japanese caps from Rubycon also being used, which is really nice to see.

[nextpage title=”Power Distribution”]

In Figure 16, you can see the power supply label containing all the power specs.

Seventeam ST-550P-AMFigure 16: Power supply label.

As you can see this power supply has two +12 V rails, which are distributed like this:

  • +12V1 (solid yellow wire): Main motherboard cable, peripheral power connectors and SATA power connectors.
  • +12V2 (yellow with black stripe wire): ATX12V/EPS12V and auxiliary video card power connector.

In our opinion the outputs from this power supply are not well distributed. Today a typical PC pulls more current/power from the ATX12V/EPS12V and video card auxiliary connectors, and all these outputs are concentrated on the same rail, while +12V1 has only components that do not demand a lot of current/power.

A better distribution would be moving the EPS12V/ATX12V cable or the auxiliary video card power cable to +12V1.

Now let’s see if this power supply can really deliver 550 W.– page break —

[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 &ldq
uo;% 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 the power supply +12V1 (main motherboard connector and peripheral power connectors) and +12V2 (video card power connector) rails at the same time, while the +12V2 input was connected to the power supply +12V2 rail (EPS12V connector).

All tests were conducted with the fan from the power supply manually set to its maximum speed. This was done so the results wouldn’t be biased by a fan speeding on different speeds during each test.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 4 A (48 W) 8 A (96 W) 12 A (144 W) 16 A (192 W) 20 A (240 W)
+12V2 4 A (48 W) 8 A (96 W) 12 A (144 W) 16 A (192 W) 20 A (240 W)
+5V 1 A (5 W) 2 A (10 W) 4 A (20 W) 5 A (25 W) 6.5 A (32.5 W)
+3.3 V 1 A (3.3 W) 2 A (6.6 W) 4 A (13.2 W) 5 A (16.5 W) 6.5 A (21.45 W)
+5VSB 1 A (5 W) 1 A (5 W) 1 A (5 W) 1.5 A (7.5 W) 2 A (10 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 115.2 W 219.0 W 331.8 W 436.9 W 545.8 W
% Max Load 20.9% 39.8% 60.3% 79.4% 99.2%
Room Temp. 45.4° C 46.5° C 47.3° C 48.2° C 49.6° C
PSU Temp. 46.6° C 47.5° C 48.1° C 49.5° C 50.3° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power (1) 137 W 255 W 391 W 526 W 675 W
Efficiency (1) 84.1% 85.9% 84.9% 83.1% 80.9%
AC Power (2) 143.4 W 263.7 W 401.2 W 536.7 W 684.0 W
Efficiency (2) 80.3% 83.0% 82.7% 81.4% 79.8%
AC Voltage 113.2 V 111.3 V 109.4 V 108.6 V 106.9 V
Power Factor 0.969 0.988 0.993 0.996 0.997
Final Result Pass Pass Pass Pass Pass

Updated 06/24/2009: We re-tested this power supply using our new GWInstek GPM-8212 power meter, which is a precision instrument and provides accuracy of 0.2% and thus presenting the correct readings for AC power and efficiency (results marked as "2" on the table above; results marked as "1" were measured with our previous power meter from Brand Electronics, which isn’t so precise as you can see). We also added the numbers for AC voltage during our tests, an important number as efficiency is directly proportional to AC voltage (the higher AC voltage is, the higher efficiency is). Also, manufacturers usually announce efficiency at 230 V, which usually inflates efficiency numbers. We added power factor (PF) numbers as well. These numbers measure the efficiency of the power supply active PFC circuit. This number should be as close to 1 as possible. Under light load (20% load, i.e. 110 W), the active PFC circuit from this unit isn’t as good as when operating under higher loads, but 0.969 is still a good number.

Seventeam ST-550P-AM presents a good efficiency around 83% when you pull between 40% and 60% from its labeled load (betwen 220 W and 330 W). At light load (20% load, i.e., 110 W) it delivers 80.3% efficiency – low, but still above 80% – and when you pull 80% from its labeled capacity (440 W) it shows 81.4% efficiency. The only problem is when fully loaded efficiency drops below the 80% line (but by very little).

Ripple and noise were at excellent levels. Noise level at +12 V outputs was always below a quarter of the maximum limit. Noise level at the +5 V was always below 15 mV (the maximum allowed is 50 mV) and at +3.3 V was always below 13 mV (the maximum allowed is also 50 mV). These numbers are peak-to-peak figures and are far better than the ones presented by ST-550P-AG.

Below you can see noise level when we were pulling 545.8 W (test number five) from this power supply.

Seventeam ST-550P-AMFigure 17: Noise level at +12V1 input from our load tester with the reviewed unit delivering 545.8 W (25.6 mV).

Seventeam ST-550P-AMFigure 18: Noise level at +12V2 input from our load tester with the reviewed unit delivering 545.8 W (28.8 mV).

Seventeam ST-550P-AMFigure 19: Noise level at +5 V input from our load tester with the reviewed unit delivering 545.8 W (14.4 mV).

Seventeam ST-550P-AMFigure 20: Noise level at +3.3 V input from our load tester with the reviewed unit delivering 545.8 W (12.2 mV).

Now let’s see if we could pull even more power from Seventeam ST-550P-AM. [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 first removed the auxiliary video card power cable from our load tester to make the +12V1 from the power supply to be connected on the +12V1 input from our load tester and the +12V2 from the power supply to be connected on the +12V2 input from our tester (with the video card cable connected the +12V1 input was connected to both +12V1 and +12V2 rails from the power supply).

Then we configured our load tester with a low (1 A) current on +12V1 and increased current at +12V2 until the power supply shut down. This happened when we tried to pull more than 28 A from +12V2.

The label states that each rail has a 20 A limit, so OCP was configured 8 amps above that. Usually manufacturers configure OCP circuit at a value higher than
what is printed on the label, but we personally like to see OCP configured at a value as close as possible to what is printed on the label.

Starting from test five we increased currents on +12 V, +5 V and +3.3 V 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.

Input Maximum
+12V1 25 A (300 W)
+12V2 25 A (300 W)
+5V 8 A (40 W)
+3.3 V 8 A (26.4 W)
+5VSB 2 A (10 W)
-12 V 0.5 A (6 W)
Total 671 W
% Max Load 122%
Room Temp. 47.7° C
PSU Temp. 48.8° C
AC Power (1) 864 W
Efficiency (1) 77.6%
AC Power (2) 871.0 W
Efficiency (2) 77.0%
AC Voltage 104.9 V
Power Factor 0.997

Consider the results marked as "2", as they are the correct ones, measured with our precision power meter.

[nextpage title=”Main Specifications”]

Seventeam ST-550P-AM power supply specs include:

  • Nominal labeled power: 550 W.
  • Measured maximum power: 671 W at 47.7° C.
  • Labeled efficiency: 80% minimum at full load.
  • Measured efficiency: Between 79.8% and 83.0% 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 EPS12V connector and one ATX12V connector (sharing the same cable).
  • Video Card Power Connectors: One six-pin connector (two six/eight-pin connectors on newer shipments).
  • Peripheral Power Connectors: Six in three cables.
  • Floppy Disk Drive Power Connectors: One.
  • SATA Power Connectors: Two in one cable (Four in two cables on newer shipments).
  • Protections: Over current (OCP, tested and working), over voltage (OVP, not tested), under voltage (UVP, not tested), over power (OPP, not tested) and short-circuit (SCP, tested and working).
  • Warranty: N/A.
  • Em português: 1 ano se comprada em revenda autorizada do distribuidor oficial.
  • More Information: https://www.seventeam.com.tw
  • Average price in the US: We couldn’t find the reviewed product being sold in the US.

[nextpage title=”Conclusions”]

We were impressed by the performance of Seventeam ST-550P-AM in our tests. Even though this is a low-end product it could not only really deliver its labeled power at 50° C, but we could pull up to 671 W from it at 47.7° C. Not bad at all.

We thought ST-550P-AM would be internally identical to ST-550P-AG but we were wrong: this is a different product, with different rectifiers on the secondary (the primary from both units is identical).

Efficiency was around 83% when we pulled between 40% and 60% from the labeled capacity (between 220 W and 330 W). The problem was during full load, where efficiency was a little bit below 80%, at 79.8%.

Ripple and noise level were at very low levels all the time.

The only real problem with this power supply is the extremely low number of SATA power connectors – only two – and the presence of only one video card auxiliary power connector. If you want to install more than two SATA devices, more than one video card or a high-end video card that requires two power connectors you will have to use adapters. Fortunately Seventeam corrected this issue on the newer shipments from this power supply, adding two SATA power cables with two connectors each and two cables for video cards.

If this limitation doesn’t bother you, this unit provides a terrific cost/benefit ratio. Of course more expensive models will provide more features, like modular cabling system, more SATA power connectors and more video card power connectors.

The low number of connectors and the efficiency a little bit below 80% at full load are the reasons we are giving it our “Silver Award” instead of our “Golden Award.”