Huntkey Green Star 550 W (LW-6550SG) Power Supply Review
By Gabriel Torres on December 9, 2008
If you follow closely our power supply reviews you know that two models we reviewed from Huntkey Green Star series – 400 W, sold in the US as Dynex 400 W, and 450 W – exploded during our tests. So we decided to get a more “powerful” model, 550 W, to see if it has the same fate as its sisters. Is Green Star 550 W a good power supply or it is as flawed as the members from the Green Star family? Check it out.
Updated 12/29/2008: There was a lot of confusion about correctly identifying this power supply. First we thought it was a Green Star model. Then we found out that it had the same part number from the Huntkey V-Power 550 W unit (LW-6550SG) and since Huntkey does not list Green Star products on their website anymore we though we were then facing a V-Power model, so we changed the text to say that this unit was in fact a V-Power model. Then with the help of our reader Travis Chen we could finally correctly id this unit and it is in fact a member of the Green Star series, as you can check here. What kind of company labels different products with the same part number? We've got an e-mail from Huntkey accusing us of reviewing a "fake" unit, since the label from the model we reviewed doesn't have "V-Power" written on it. Funny enough the label from the V-Power 550 W unit posted on their website also doesn't have "V-Power" written on it. Once again, how could we correctly identify this unit if on its label there is no mention to its series, only the "LW-6550SG" part number, which is used by two different products? This makes us speculate that Green Star 550 W and V-Power 550 W are internally the same product (we don't see any other reason a manufacturer using the same part number on two different products). We are going to buy a V-Power 550 W model to review it and clarify this issue. The only real difference we could see between Green Star 550 W and V-Power 550 W labels was the current limit for +12V1, 16 A on Green Star and 18 A on V-Power. Since the unit we reviewed had "16 A" for +12V1 on its label we get the information that we were in fact facing a Green Star unit, not a V-Power one. Another smaller difference was the presence of only two SATA power plugs on the reviewed unit, while V-Power has four of them. Here I ask my most sincere apologies to all our readers, but, once again, we don't have a crystal ball and the manufacturer doesn't help by naming different products using the same name. If we got confused imagine you, a normal user.
By the way, the naming scheme Huntkey uses work like this. "SG" means 140 mm fan and "HG" means 120 mm fan. When the model has a passive PFC circuit then a "P" is added at the end. So an LW-6550HG would be the same unit with a 120 mm fan, and an LW-6550SGP would be the same reviewed unit with passive PFC.
It is good to remember that we have already reviewed a model from a different series (Titan 650 W, sold in the US as Rocketfish 700 W) from Huntkey and it survived our tests. So the problems we had with Huntkey products (power supplies exploding while you try to pull its labeled power) so far only happened with members from their Green Star series.
This power supply is 6 19/64” (160 mm) deep, features a 140 mm fan on its bottom and doesn’t have active PFC circuit, so Huntkey can’t sell this product in Europe (as you can assume from our discussion above, there is a version from this unit with passive PFC). In Figure 1, you can see that it has a voltage selection switch, feature usually present on models without this circuit.
This unit comes with the main motherboard cable using a 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector. This unit also features two 6-pin auxiliary power connectors for video card using independent cables, which is great, one cable containing three peripheral power plugs, one cable containing three peripheral power plugs and one floppy disk drive power plug and one cable containing two SATA power plugs.
The main drawback from this power supply is the presence of only two SATA power plugs, which is insufficient for today’s applications. If you have more than one hard disk drive you will need to convert one of the peripheral power plugs into a SATA power plug using an adapter.
All peripheral cables – including the auxiliary power cables for video cards – use 20 AWG wires, which are thinner than the wires used by other good power supplies on the same power range. The wires on the ATX12V/EPS12V cable and on the main motherboard cable are 18 AWG, though.
Now let’s take an in-depth look inside this power supply.
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.
Even though the printed circuit board had the model name printed on it (LW-6550SG) it also had “350 – 450W” printed on it, which is curious.
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 one extra X capacitors and one extra coil. This power supply has two MOVs located after the rectification bridge (and not before as usual), physically squeezed between the two electrolytic capacitors.
In the next page we will have a more detailed discussion about the components used in the Green Star LW-6550SG.
On this page we will take an in-depth look at the primary stage of Green Star 550 W (LW-6550SG). For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one T15XB80 rectifying bridge in its primary, capable of delivering up to 15 A at 100° C if a heatsink is used – which is not the case – but only 3.2 A at 25° C if a heatsink is not used. The difference is outrageous and Huntkey should have added a heatsink on this component. The current limit for this component is simply too low (3.2 A). At 115 V this unit would be able to pull only up to 368 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver only up to 294 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. This is the same component used on Huntkey Titan 650 W (Rocketfish 700 W), but at least this other product had a heatsink attached to it, which increased the current limit.
LW-6550SG uses two 2SC3320 power NPN transistors on its switching section using the half-bridge design, supporting up to 15 A at 25° C (unfortunately the manufacturer from these transistors do not say how much they can deliver at higher temperatures). These are the same transistors used on Huntkey Titan 650 W (Rocketfish 700 W). These transistors are more “powerful” than the ones used on Green Star 400 W and 450 W. However the use of these transistors was not enough to prevent them from blowing up (we will talk about this is details later).
The two big electrolytic capacitors from the primary are from Teapo (a Taiwanese company) and rated at 85° C.
Huntkey Green Star LW-6550SG has five Schottky rectifiers on its secondary, two for the +12 V output, one for the +5 V output and two for the +3.3 V output.
Since this power supply uses a half-bridge configuration to calculate the maximum theoretical current each output can deliver is easy: all we need to do is to add the maximum current supported by all diodes.
The +12 V output is produced by two STPS20S100CT Schottky rectifiers connected in parallel, each one capable of handling up to 20 A at 100° C (10 A per internal diode). So the maximum theoretical current the +12 V output from this power supply can deliver is of 40 A or 480 W. Of course this math is just an exercise and the actual limit depends on several other factors. It is important to note that this is the same configuration and rating used by Green Star 400 W and Green Star 450 W.
The +5 V output is produced by one S40D40C Schottky rectifier, which is capable of handling up to 40 A at 100° C (20 A per internal diode). So the maximum theoretical current the +5 V output from this power supply can deliver is of 40 A at 100° C or 200 W. This is a different component from the 400 W and 450 W models from Green Star series, which use a 30 A (150 W) rectifier.
The +3.3 V output is produced by two STPS2045CT Schottky rectifiers connected in parallel, which one capable of delivering up to 20 A at 155° C (10 A per internal diode). So the maximum theoretical current the +3.3 V output from this power supply can deliver is of 40 A at 155° C or 132 W. This is a different component from the 400 W and 450 W models from Green Star series, which use a 30 A (99 W) rectifier.
It is always good to remember that the real current/power limit for each output will depend on other factors, like the coils and the width of the printed circuit board traces.
As you can see, what Huntkey did to create their 550 W model was to increase the +5 V and +3.3 V rectifiers and the switching transistors. While replacing the switching transistors was an obvious move, Huntkey should have increased the rectifiers from the +12 V output, not from +5 V and +3.3 V. Nowadays computers consume more current/power from the +12 V line, as the CPU and the video cards are connected to this output, not from the +5 V and +3.3 V ones.
The secondary is monitored by an SG6105, which provides protections such as over voltage (OVP), under voltage (UVP), over power (OPP) and short-circuit (SCP). This integrated circuit is also a PWM controller, being in charge of the switching of the primary transistors.
In Figure 14, you can see the thermal sensor available below the secondary heatsink, in charge of changing the fan speed according to the power supply internal temperature.
In Figure 15, you can see the power supply label containing all the power specs.
This power supply features two +12 V virtual rails distributed like this:
This is of course a very limited distribution, because it assumes that the CPU will be pulling the same amount of current/power than all other devices combined, which isn’t true if you have a high-end video card.
Now let’s see if this power supply can really deliver 550 W.
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 out tests the +12V1 input was connected to the power supply +12V1 (main motherboard cable, peripheral power connectors and video card auxiliary power connector), while the +12V2 input was connected to the power supply +12V2 rail (EPS12V connector). Thus on this review+12V1 and +12V2 really represent the power supply rails with the same name.
For the test number five we had to respect the current limits for the +12 V outputs, so we had to pull more power from +5 V and +3.3 V outputs than we’d like to.
4 A (48 W)
8 A (96 W)
12 A (144 W)
16 A (192 W)
16 A (192 W)
4 A (48 W)
8 A (96 W)
12 A (144 W)
16 A (192 W)
18 A (216 W)
1 A (5 W)
2 A (10 W)
4 A (20 W)
5 A (25 W)
15 A (75 W)
1 A (3.3 W)
2 A (6.6 W)
4 A (13.2 W)
5 A (16.5 W)
15 A (49.5 W)
1 A (5 W)
1 A (5 W)
1 A (5 W)
1.5 A (7.5 W)
2 A (10 W)
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)
% Max Load
Ripple and Noise
This power supply exploded when we tried to pull 550 W from it (test number five). On the next page we posted the video and pictures showing this.
During our tests this power supply could only achieve good results when we pulled up to 60% (330 W) from it. Under this circumstance efficiency was between 82.9% and 85.3%, which isn’t bad at all.
The problem was when we pulled 80% from its labeled capacity (440 W) efficiency dropped to 77% and noise and ripple skyrocketed to values far above the maximum allowed. Noise and ripple at +12V1 jumped to 157 mV (from 81.4 mV during test three), jumped to 115 mV (from 51.2 mV during test three) at +12V2 and jumped to 58.1 mV (from 23.6 mV) at +5 V. At +3.3 V noise and ripple was within spec (24 mV). All these numbers are peak-to-peak values and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +5 V and +3.3 V outputs. It is interesting to note that Huntkey says this power supply can have a maximum noise level of 200 mV for +12 V and 100 mV for +5 V and +3.3 V. This is ridiculous, as this violates the ATX specification.
Below you can watch the video from test number five with Huntkey Green Star LW-6550SG.
What exploded were the two switching transistors. When the power supply explodes it means that the primary side is under dimensioned. When the secondary side is under dimensioned the power supply dies silently, because when a rectifier burns the short-circuit protection enters immediately in action shutting down the power supply.
So Huntkey should have used more powerful transistors and added a heatsink to the rectifying bridge, plus using rectifiers with higher current limits for the +12 V output.
Below we have some pictures of the power supply and the switching transistors after the explosion.
Huntkey Green Star 550 W (LW-6550SG) power supply specs include:
Huntkey Green Star 550 W is as flawed as the other members from the Green Star family: LW-6550SG exploded when we tried to pull its labeled power.
When we pulled 80% of the labeled capacity (around 427 W in our tests) efficiency was low at 77% and ripple and noise were above the maximum admissible (157 mV at +12 V and 58 mV at +5 V).
The manufacturer clearly plays with the fact that someone buying this power supply probably won’t pull near half of its labeled capacity (a typical PC with a good video card pulls between 100 W and 150 W). However when we buy a product labeled “550 W” we want it to be able to deliver its labeled power, it doesn’t matter if we are going to pull this amount or not. This is called false advertisement.
And it only provides two SATA power connectors.
Internally it uses the exact same rectifiers for the +12 V outputs as the 400 W and 450 W models from Green Star series. This is ridiculous. Current limits were increased at +5 V and +3.3 V with the use of rectifiers with higher current limit, but nowadays we need more current at +12 V, not at +5 V and +3.3 V. This model uses more powerful switching transistors than these 400 W and 450 W models, but they are still under dimensioned, as they exploded.
If you are looking for a true 550 W power supply don’t buy this product. Take a look on the list of power supplies we already tested and that got an award seal for choosing a good product that won’t explode or damage your equipment.
Keep in mind that this problem seems to be specific with the Green Star product line, as we reviewed Huntkey Titan 650 W (Rocketfish 700 W) and it didn’t explode. We will try to review other power supplies from this manufacturer in the near future.