Enermax Liberty DXX 500W Power Supply Review
By Gabriel Torres on April 13, 2008
Liberty DXX 500 W, a.k.a. ELT500AWT, is one of the most popular power supplies from Enermax, featuring active PFC, high efficiency, modular cabling system, 120 mm fan and two video card auxiliary power cables for you feed your SLI or CrossFire system. We completely disassembled this unit and also tested to see if it can really deliver its labeled 500 W. Check it out.
As you can see, this power supply uses a big 120 mm ball bearing fan on its bottom (the power supply is upside down on Figures 1 and 2) and a big mesh on the rear side where traditionally we have an 80 mm fan. We like this design as it provides not only a better airflow but the power supply produces less noise, as the fan can rotate at a lower speed in order to produce the same airflow as an 80 mm fan.
This power supply has active PFC, which provides a better usage of the power grid and allowing Enermax to sell this product in Europe (read more about PFC on our Power Supply Tutorial). As for efficiency, Enermax says that this product has 80% efficiency. Of course we will measure this to see if what the manufacturer claim is true. The higher the efficiency the better – an 80% efficiency means that 80% of the power pulled from the power grid will be converted in power on the power supply outputs and only 20% will be wasted. This translates into less consumption from the power grid (as less power needs to be pulled in order to generate the same amount of power on its outputs), meaning lower electricity bills.
The main motherboard cable uses a 20/24-pin connector and this power supply has two ATX12V connectors that together form one EPS12V connector.
On this power supply you can monitor the speed of its fan through your computer, a feature not commonly available. If you want to use this feature, you have to install the fan cable that comes from inside the power supply (shown in Figure 2) on any unused three-pin fan power connector on the motherboard.
As mentioned this power supply uses a modular cabling system, with the cables coming inside a pouch, shown in Figure 3. We like modular cabling systems as you need only to attach the cables you will really use, improving the internal PC airflow by having fewer cables inside the computer.
This power supply comes with six peripheral power cables: one auxiliary power cable for video cards with a 6-pin connector attached, one auxiliary power cable for video cards with a 6/8-pin connector attached, two cables containing two standard peripheral power connectors and two SATA power connectors each and two cables containing two standard peripheral power connectors, two SATA power connectors and one floppy disk drive power connector each. As you can see this an unusual configuration, as usually manufacturers don’t put SATA power connectors and standard peripheral power connectors on the same cable.
So this power supply has a total of eight SATA power connectors and eight peripheral power connectors, which is far more than any average user will ever need. The problem, though, is that is hard to use the SATA power connectors and the peripheral power connectors that are installed on the same cable at the same time, since they are too close to each other. For example, if you have two SATA hard drives and one optical unit that still uses the standard peripheral power connectors, you will need to use at least two cables, as the cable used to feed the two hard drives isn’t long enough to feed the optical drive at the same time.
It is interesting to note that Enermax sells additional cables for this power supply, if you need a different cable configuration.
On this power supply all wires are 18 AWG, which is perfect for this power supply power range.
On the aesthetic side Enermax used nylon sleeving on all cables, coming from inside the power supply housing on the motherboard cables.
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.
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.
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 impeccable, bringing one extra ferrite coil and two extra Y capacitors, on this stage, plus one additional X capacitor after the rectifying bridge and two ferrite beads, one on the main AC cable and another on the cable connecting the transient filtering to the main printed circuit board (on this power supply the transient filtering stage is located on a separated printed circuit board, see Figure 7). On this unit the MOV is installed after the rectifying bridge, a configuration that is typical with units using older projects.
In the next page we will have a more detailed discussion about the components used in the Liberty DXX 500 W.
Now let’s take an in-depth look inside Enermax Liberty DXX 500 W. For a better understanding of what we are talking here and in the next page, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU10J rectifying bridge in its primary stage, which can deliver up to 10 A (rated at 100° C). This bridge is attached to a heatsink. 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.
click to enlarge
Figure 9: Rectifying bridge.
On the active PFC circuit this power supply uses two IRFP460A power MOSFET transistors, each capable of handling up to 20 A at 25° C or 13 A at 100° C (here you can see the difference temperature makes).
In the switching section, two 2SK2746 power MOSFET transistors are used, each one capable of delivering up to 7 A at 25° C continuously or 21 A at 25° C in pulse mode.
Here lies the main different between this power supply and other good power supplies available on the market today. Even though the switching section has two transistors, they don’t use the traditional two-transistor forward configuration, but instead the two transistors are connected in parallel using a single-transistor forward configuration.
The switching transistors, active PFC transistors, active PFC diode and +5VSB switching transistor are located on the same heatsink.
The active PFC circuit is controlled by a UCC3818 integrated circuit, which is located on a small printed circuit board attached to the main printed circuit board.
This power supply uses four Schottky rectifiers on its secondary, however they are connected on a way that is different from other power supplies.
Nowadays on power supplies with four rectifier packs we usually have two of them connected in parallel rectifying the +12 V line, one rectifying the +5 V and another rectifying the +3.3 V line. This reflects the current usage of power supply, where most of the power is pulled from the +12 V outputs. In the past most of the power was concentrated on the +5 V outputs.
On this power supply, however, the two rectifiers that are connected in parallel are in charge of the +5 V outputs and they are used, at the same time, for helping the rectification on the +12 V line. This is the first time we’ve seen such exotic configuration. To help you to understand this configuration, we have drawn a simple schematics of the secondary from this power supply in Figure 13.
All four Schottky rectifiers are the same: DF40S4. Each pack can handle up to 40 A at 106° C (20 A per internal diode). Because of this different design, calculating the maximum theoretical currents is not so easy.
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 (or by the freewheeling diode, whichever has lower current limits). Just as an exercise, we can assume a typical duty cycle of 30%.
Since the +3.3 V doesn't share rectifiers with the other outputs it is the easiest one to calculate: 20 A rectifying diode, 29 A maximum current [20 A/(1 - 0.30)] and thus 94 W maximum theoretical power.
From what we understood the +5 V output is produced by the two rectifying diodes drawn on the bottom of the schematics with the two freewheeling diodes drawn in the middle of the schematics. This would give us a 40 A rectifying diode (20 A x 2), 57 A maximum current and thus 286 W maximum power.
Calculating the maximum theoretical values for the +12 V output is hard, and we may be wrong. We will consider only one rectifying diode (the top one), which would give us a 29 A maximum current and thus 343 W maximum power.
This power supply uses a thermal sensor on its secondary heatsink (see Figure 16; to take this picture we removed the secondary heatsink), which is used to control the fan speed according to the power supply internal temperature.
This power supply uses a PS223 monitoring integrated circuit (see it in Figure 16), which is in charge of the power supply protections, like OCP (over current protection). This IC also provides over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP), but not over power protection (OPP).
The active PFC capacitor is Japanese from Chemi-Con and rated at 85° C, while the electrolytic capacitors from the secondary are rated at 105° C.
In Figure 17, you can see the power supply label containing all the power specs.
As you can see this power supply has two virtual +12 V rails, +12V1 and +12V2 and inside the power supply we could clearly see that each rail is separately connected to the monitoring integrated circuit, which is in charge of the over current protection (OCP). During our tests, however, we couldn’t make this circuit to shut down the power supply, as we will talk about later.
On this power supply each virtual rail is connected like the following:
This is the traditional distribution for power supplies with two virtual rails. We, however, don’t think this is the best distribution for a system with two video cards, because the cards are connected to the same rail and if you use high-end models they can make the power supply to shut down (by activating the power supply’s over current protection) even if they are running inside their specs.
The modular cabling system is connected to the main printed circuit board using two 18 AWG wires for the +3.3 V line, four 18 AWG wires for the +5 V line, two 12 AWG wires for the +12 V line and three 12 AWG wires for the ground signal. These 12 AWG wires are really thick, which is great.
Now let’s see if this power supply can really deliver 500 W of power.
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 six 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. This was the same load pattern we used for other 500 W power supplies we’ve tested recently like Antec EarthWatts 500 W.
For the 100% load test we used two patterns. On the first one, test number five, we respected the maximum combined limit for the two +12 V rails printed on the power supply label (384 W). In order to respect this limit, however, we were testing the power supply with more current on the +5 V and +3.3 V lines than we wanted. So we included a sixth pattern also pulling 500 W from Liberty DXX 500 W but pulling more current from +12 V and less current from +5 V and +3.3 V, using the same pattern used on the test of the abovementioned power supply from Antec, but pulling more current (and thus power) that the two +12 V rails could officially deliver together.
In the table below we list the load patterns we used and the results for each load.
+12V2 is the second +12 V input from our load tester and was connected to the power supply EPS12V connector. Since on this unit the only device connected to its +12V2 rail is really the EPS12V connector, on this review +12V1 and +12V2 on the tables and graphs below really represent the +12V1 and the +12V2 rails from the power supply.
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.
4 A (48 W)
8 A (96 W)
11 A (132 W)
14 A (168 W)
16 A (192 W)
17 A (204 W)
3 A (36 W)
6 A (72 W)
10 A (120 W)
14 A (168 W)
16 A (192 W)
17 A (204 W)
1 A (5 W)
2 A (10 W)
4 A (20 W)
6 A (30 W)
12 A (60 W)
9 A (45 W)
1 A (3.3 W)
2 A (6.6 W)
4 A (13.2 W)
6 A (19.8 W)
11 A (36.3 W)
9 A (29.7 W)
1 A (5 W)
1 A (5 W)
1.5 A (7.5 W)
2 A (10 W)
3 A (15 W)
3 A (15 W)
0.5 A (6 W)
0.5 A (6 W)
0.5 A (6 W)
0.5 A (6 W)
0.6 A (7.2 W)
0.6 A (7.2 W)
% Max Load
Ripple and Noise
The main problem with this power supply is efficiency, as you can see. It could only maintain efficiency above 80% on tests one (20% load or 104 W), two (40% load or 196 W) and three (60% load or 297 W). Just to remember, on Corsair VX450W and Antec EarthWatts 500 W (which are internally the same power supply) we saw an efficiency of 82% when the power supply was delivering 500 W and reaching above 85% on patterns one, two and three, where this unit from Enermax could only reach up to 82.5%.
Voltage regulation during all our tests was excellent, with all outputs within 3% of their nominal voltages – ATX specification defines that all outputs must be within 5% of their nominal voltages – except on +5 V, which was between 5.16 V and 5.17 V during all our tests. These numbers, however, are still inside the 5% margin that is set by the ATX spec for this output. Of course we always want to see values closer to the nominal voltage.
The main highlight from this product was noise and ripple, which were at a very low level. However when we moved from 80% load to 100% load the noise level at +12 V outputs almost doubled, jumping from 18 mV to 32.4 mV at +12V1 and jumping from 21.4 mV to 34.4 mV at +12V2 (results for pattern number five). Even with this increase noise level was still very low and far away from the 120 mV limit. Noise level at +5 V was 16.2 mV and at +3.3 V was 15 mV, also for pattern number five. Pattern number six presented similar results, which are also similar to the results presented by Antec EarthWatts 500 W and Corsair VX450W.
Now let’s see if we could pull more power from this product.
As usual we pushed this power supply over its official limits to see what happens.
First we tried to see if over current protection was active and at what level. To test this we removed all power supply cables from our load tester leaving only the main motherboard cable and increased current on +12V1 to 28 A. The power supply didn’t shut down. Since the label says that each +12 V rail has a limit of 22 A, the power supply should have shut down when we pulled 28 A. Since we could really see that each rail was physically connected to the monitoring integrated circuit in charge of OCP, we guess that OCP was set at a value that was higher than what was printed on the label. We could keep increasing the current on +12V1 but +12 V voltage started dropping.
Our next move was to discover what was the maximum amount of power this unit can deliver still working inside its specs.
Starting from pattern number six (see previous page) we increased current on both +12 V rails to 24 A and current on +5 V and +3.3 V rails to 10 A each. With this pattern we were pulling 681.2 W from the unit but voltages were outside specs – voltage on +12V1 was at 10 V, for example. Under voltage protection (UVP) didn’t enter in action like it should, so it is either disabled (which we don’t think it is the case as the monitoring chip supports this feature) or it is configured to enter in action only when voltages are too far away from their nominal values (which is more probable).
Then we configured both +12V1 and +12V2 rails to pull 22 A, keeping +5 V and +3.3 V at 10 A. At this configuration the power supply was delivering 617 W and we were pulling 852 W from the wall, so efficiency was at 72.4%. After two minutes working at this configuration the power supply shut down, so one of its protections entered in action.
So we decreased current on +12V1 and +12V2 to 21 A, making the power supply to deliver 596 W and pull 819 W from the power grid – so efficiency was at 72.8%. The problem was that after one and a half minutes under this configuration the power supply silently died. After opening the power supply and testing all its major components we could see that the +12 V rectifier burned.
Enermax says that this product has over power protection (OPP or OLP; both acronyms mean the same thing), however the monitoring integrated circuit does not provide this feature. If this power supply really has this feature implemented outside this chip (which doesn’t seem to be the case), it is configured at a value that is too high and that we couldn’t see it in action.
Because the power supply burned so fast we couldn’t check noise level for all outputs (we could only see for +12V1, which was at 47 mV).
So we couldn’t determine if power supply can deliver more than 500 W continuously.
Short circuit protection (SCP) worked fine for both +5 V and +12 V lines.When the power supply fan is running slowly it is really quiet, but as soon as it starts spinning at its full speed noise level becomes very high.
Enermax DXX 500 W power supply specs include:
* Researched at Shopping.com on the day we published this review.
To be completely honest we were somewhat disappointed with Enermax Liberty DXX 500 W, as we expected more from it. Even though it has a 120 mm fan, a modular cabling system supporting two auxiliary power cables for video cards – one of them with a 6/8-pin connector –, more power connectors than the majority of mainstream power supplies, a very low noise and ripple levels and could really deliver 500 W at 48.5° C, its efficiency was somewhat low, being below 80% if you pull more than 300 W from it.
This power supply uses a different design on its secondary, which showed to be not so good. Together with the decision of using a single-transistor forward design on the primary instead of the traditional two-transistor forward, the design used by this power supply proved not to be the best for efficiency.
Also almost all protections failed during our tests, showing that they are either disabled or configured with a value that is too high: this power supply didn’t survive our overload tests.
We know that average users won’t probably overload their units, but it is always nice to know that the power supply will turn off if an overloading situation occurs, instead of just burning.
Users building a mainstream PC won’t probably pull more than 300 W from their PCs, so if you are such user you probably won’t face the efficiency or overloading issues we are commenting. However, when you think that both Corsair VX450W and Antec EarthWatts 500 W are cheaper and better products – both are internally the same power supply and can provide a far higher efficiency and have their protections working just fine – it makes no sense buying Enermax Liberty DXX 500 W today.
Keep in mind that this power supply is already on the market for quite a while and this doesn’t mean that all Enermax products have the same issues. Don’t worry: we will review their latest power supplies very soon.