[nextpage title=”Introduction”]
ST-550P-AG is an entry-level 550 W power supply from Seventeam, featuring active PFC, a 120 mm fan and only two SATA power connectors. Let’s see if this unit can really deliver 550 W and whether it is a good product or not.
One funny detail is the sticker in Engrish saying “Breakage Invalid” instead of “Warranty Void if Broken.”
Figure 1: Seventeam ST-550P-AG power supply.
Figure 2: Seventeam ST-550P-AG power supply.
This power supply is very small, being only a 5 ½” (140 mm) deep. It uses one brushless 120 mm fan on its bottom and as you know this cooling solution is better than using one or two 80 mm fans, as a 120 mm or bigger fan can produce a bigger airflow rotating at a lower speed, what reduces the noise produced by the fan.
Funny enough Seventeam’s website does not feature this product, but we could find the original spec sheet here. According to the manufacturer this power supply has a 78% maximum efficiency.
As mentioned, this power supply features active PFC, what enables Seventeam to sell this product in Europe.
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-AG comes with five peripheral cables: one with two 6-pin auxiliary power connectors for video cards, one with two SATA power connectors, two with three 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). This may indicate that this unit uses an older project from when SATA peripherals were not the norm (we will see if our suspicion holds true after disassembling it and analyzing its project).
The second problem is that even though this power supply has two auxiliary power connectors for video cards, they are attached to the same cable. Ideally each connector should use its own cable.
On the aesthetical side only the main motherboard cable uses a nylon sleeving, which comes from inside the power supply housing.
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-AG”]
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 3: Overall look.
Figure 4: Overall look.
Figure 5: 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, yellow component on the pictures below) 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 coils (one of them is behind the printed circuit board in Figure 6), four more Y capacitors (two of them can’t be seen in Figure 6) and two more X capacitors than necessary.
Figure 6: Transient filtering stage (part 1).
Figure 7: Transient filtering stage (part 2).
In the next page we will have a more detailed discussion about the components used in the ST-550P-AG.
[nextpage title=”Primary Analysis”]
On this page we will take an in-depth look at the primary stage of ST-550P-AG. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU1006 rectifying bridge in its primary, capable of delivering up to 10 A at 100° C. This is more than adequate rating for a 550 W power supply. The reason why is that 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.
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).
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 two other SPW16N5
0C3 power MOSFET transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above.
Figure 8: Rectifying bridge and switching transistors.
Figure 9: Active PFC transistors and diode.
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.
Figure 10: Active PFC/PWM controller.
[nextpage title=”Secondary Analysis”]
Seventeam ST-550P-AG uses six Schottky rectifiers on its secondary, using an updated design – meaning that the rectifiers for the +12 V outputs are more powerful than the ones used for the +5 V and +3.3 V outputs. So our suspicion that this power supply would use an outdated design just because it has only two SATA power connectors was completely wrong. This shows us the importance of analyzing the circuit used by a given product instead of assuming things based on its external appearance.
For the +12 V rectification two SBL3060PT Schottky rectifiers connected in parallel are used. Each one is capable of handling up to 30 A at 95° C (15 A per internal diode). The maximum theoretical current the +12 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 514 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +5 V output is produced by two SBL3040CT Schottky rectifiers connected in parallel, each one capable of handling up to 30 A (15 A per internal diode) at 100° C. The maximum theoretical current the +5 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
The +3.3 V output is produced by two other SBL3040CT Schottky rectifiers. The maximum theoretical current the +3.3 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 141 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.
On the secondary heatsink we also found the voltage regulator integrated circuit for the -12 V output (LM7912), which has a current limit of 1.5 A.
Figure 11: -12 V voltage regulator, +12 V rectifier, +5 V rectifier and +3.3 V rectifier.
Figure 12: +3.3 V rectifier, +5 rectifier and +12 V rectifier.
The secondary from this power supply is monitored by a PS223 integrated circuit, which is physically installed on a separated small printed circuit board (see Figure 13). This integrated circuit features the following protections: over current (OCP), over temperature (OTP, not implemented on ST-550P-AG), over voltage (OVP) and under voltage (UVP). As you see the only protection missing is over power protection (OPP), but for an entry-level product this power supply has a very satisfactory number of protections.
Figure 13: Monitoring integrated circuit.
The electrolytic capacitors from the secondary are from Capxon and Samson, two Taiwanese companies, and labeled at 105° C.
[nextpage title=”Power Distribution”]
In Figure 14, you can see the power supply label containing all the power specs.
Figure 14: 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 connectors.
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.[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 valu
e 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).
The power supply label says that each +12V rail can deliver up to 18 A but combined they can deliver only up to 384 W. This is, in our opinion, a value that is too low for a 550 W product since nowadays most current/power is drawn from the +12 V outputs. So we used two different load patterns for our 100% load test. On the first one (test five) we respected the limits stated on the power supply label, where we were pulling far more power from +5 V and +3.3 V than a real PC would do. On the second pattern (test six) we increased current on +12 V and lowered on +5 V and +3.3 V. The results you can see below.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 | Test 6 |
| +12V1 | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 15.5 A (186 W) | 16 A (192 W) | 18.5 A (222 W) |
| +12V2 | 4 A (48 W) | 8 A (96 W) | 12 A (144 W) | 15.5 A (186 W) | 16 A (192 W) | 18.5 A (222 W) |
| +5V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 6 A (30 W0 | 18 A (90 W) | 10 A (50 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 17 A (56.1 W) | 10 A (33 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) | 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) | 0.8 A (9.6 W) | 0.8 A (9.6 W) |
| Total | 114.4 W | 217.1 W | 329.8 W | 429.8 W | 554.1 W | 540.4 |
| % Max Load | 20.8% | 39.5% | 60.0% | 78.1% | 100.7% | 98.3% |
| Room Temp. | 46.8° C | 47.9° C | 48.6° C | 47.4° C | 49.6° C | 50.4° C |
| PSU Temp. | 49.7° C | 50.9° C | 52.1° C | 50.1° C | 50.1° C | 53.9° C |
| Voltage Stability | Pass | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass | Pass |
| AC Power | 142 W | 262 W | 402 W | 533 W | 723 W | 705 W |
| Efficiency | 80.6% | 82.9% | 82.0% | 80.6% | 76.6% | 76.7% |
| Final Result | Pass | Pass | Pass | Pass | Pass | Pass |
Seventeam ST-550P-AG presents efficiency above 80% if you pull up to 80% (440 W) from it. This is not the best result in the world but it isn’t the worst either. A power supply not being able to maintain efficiency above 80% at full load is very common. For its market segment (low-end) it has a very adequate efficiency.
Voltage stability was great, with all voltages inside spec all the times.
Ripple and noise were also at very good levels. Noise level at +12 V outputs was always below half of the maximum limit (except +12V2 at tests five and six, which was at 63.2 mV and 62 mV, respectively). Noise level at the +5 V was below half the maximum limit on all tests but test five, where it peaked 31 mV (still inside the 50 mV limit). Noise level at +3.3 V was the highlight of this product, below 10 mV (the limit is 50 mV) if you pull up to 80% (440 W) of the labeled maximum capacity.
We were only disappointed with ripple on -12 V output. Since this power supply uses a voltage regulator integrated circuit for this output we expected to see very little ripple, which wasn’t the case (between 70 mV and 76 mV depending on the load and still inside ATX specs). But this doesn’t change the good impression we had about this product.
Below you can see noise level when we were pulling 554 W (test number five) from this power supply. Just to remember, the maximum allowed for the +12 V outputs is 120 mV peak-to-peak and the maximum allowed for the +5 V and +3.3 V outputs is 50 mV peak-to-peak.
Figure 15: Noise level at +12V1 input from our load tester with the reviewed unit delivering 554 W (42.2 mV).
Figure 16: Noise level at +12V2 input from our load tester with the reviewed unit delivering 554 W (63.2 mV).
Figure 17: Noise level at +5 V input from our load tester with the reviewed unit delivering 554 W (31 mV).
Figure 18: Noise level at +3.3 V input from our load tester with the reviewed unit delivering 554 W (14.8 mV).
Now let’s see if we could pull even more power from Seventeam ST-550P-AG.
[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.
Even though OCP was clearly active, we think that it was configured at a value that is too high, since the label states an 18 A limit for each rail. Maybe the value is too high on purpose, since the +12V2 rail is connected to the CPU (EPS12V/ATX12V connector) and to the video cards at the same time, what would shut down the power supply under normal working conditions. In our opinion Seventeam should have moved the video card or the CPU connector to +12V1 and configured OCP at a lower value.
Then starting from test six we increased currents on +12 V, +5 V and +3.3 V to the maximum we could with th
e 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 | 23 A (276 W) |
| +12V2 | 23 A (276 W) |
| +5V | 10 A (50 W) |
| +3.3 V | 10 A (33 W) |
| +5VSB | 2.5 A (12.5 W) |
| -12 V | 0.8 A (9.6 W) |
| Total | 630 W |
| % Max Load | 114.15% |
| Room Temp. | 48.6° C |
| PSU Temp. | 53.4° C |
| AC Power | 880 W |
| Efficiency | 71.6% |
[nextpage title=”Main Specifications”]
Seventeam ST-550P-AG power supply specs include:
- Nominal labeled power: 550 W.
- Measured maximum power: 630 W at 49° C.
- Labeled efficiency: 80% maximum.
- Measured efficiency: Between 77% and 83%.
- Active PFC: Yes.
- Modular Cabling System: No.
- Motherboard Power Connectors: One 20/24-pin connector, one EPS12V connector and one ATX12V connector (sharing the same cable).
- Video Card Power Connectors: Two 6-pin connectors (sharing the same cable).
- Peripheral Power Connectors: Eight in three cables.
- Floppy Disk Drive Power Connectors: One.
- SATA Power Connectors: Two in one cable.
- Protections: Over voltage (OVP, not tested) and over power (OPP, not tested). Even though not listed by the manufacturer, the monitoring integrated circuit supports under voltage (UVP) and over current (OCP, tested and working). Short-circuit protection present and active.
- Warranty: N/A.
- Manufacturer website: https://www.seventeam.com.tw
- More Information: https://www.scribd.com/doc/427599/ST550PAG
- Average price in the US: We couldn’t find the reviewed product being sold in the US.
[nextpage title=”Conclusions”]
We were somewhat impressed by the performance of Seventeam ST-550P-AG 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 630 W from it at 49° C. Not bad at all.
Differently from Seventeam ST-420BKV the reviewed model uses an updated design with active PFC, power MOSFET transistors on the switching section and rectifiers for the +12 V output that are bigger than the ones used on the +5 V and +3.3 V outputs.
Efficiency is good (i.e., above 80%) if you pull up to 80% (440 W) of its labeled power. If you, however, pull 550 W or more from it you will see efficiency below the 80% mark.
But honestly we don’t think someone buying this power supply would ever come close to its labeled power, so this should not be an issue for the user this power supply is targeted to.
The only real problem with this power supply is the extremely low number of SATA power connectors – only two. If you want to install more than two SATA devices you will have to use adapters to convert standard peripheral power plugs into SATA power plugs.
If this limitation doesn’t bother you, this unit provides a terrific cost/benefit ratio, mainly because of its price. Of course more expensive models will provide more features, like modular cabling system, more SATA power connectors and even more video card power connectors.
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