Huntkey Green Star 550 W (LW-6550SG) Power Supply Review

Introduction

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.

Figure 1: Huntkey Green Star 550 W (LW-6550SG).

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.

Figure 2: Huntkey Green Star 550 W (LW-6550SG).

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.

Figure 3: Overall look.

Figure 4: Overall look.

Figure 5: Overall look.

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.

Figure 6: Isn’t this marking 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.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

Figure 9: Transient filtering stage (part 3).

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.

Figure 10: Rectifying bridge.

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).

Figure 11: One of the two switching transistors.

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.

Figure 12: The two +12 V rectifiers, the +5 V rectifier and one of the +3.3 V rectifiers (the other one is on the other side of the heatsink).

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.

Figure 13: Monitoring integrated circuit.

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.

Figure 14: Thermal sensor.

The electrolytic capacitors from the secondary are from KSC, Teapo and Fcon and labeled at 105° C, as usual.