Zalman ZM500-RS Power Supply Review
By Gabriel Torres on December 10, 2009
Zalman has recently released a power supply series based on a resonant switching (RS) design, aptly named RS series. Let’s see if the 500 W model from this series is a good buy.
Like other power supplies from Zalman, ZM500-RS is manufactured by FSP.
Zalman ZM500-RS is only 5 ½” (140 mm) deep, using a 120 mm fan on its bottom and active PFC circuit, of course.
All cables are protected by nylon sleevings, which come from inside the power supply housing. All cables measure 17 ¾” (45 cm) between the housing and the first connector on the cable, and 5 7/8” (15 cm) between connectors on cables with more than one connector. All wires are 18 AWG, which is the correct gauge to be used.
The cables included are:
We didn’t like the cable configuration used on ZM500-RS very much. Although it will probably fit the needs of most users looking for a 500 W product, we’d prefer to see the two video card auxiliary power connectors using individual cables instead of being attached to the same cable and one more SATA/peripheral power connector on each cable, for a total of six connectors from each type instead of only four.
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 flawless on this stage, with two Y capacitors and one X capacitor more than the minimum required, plus an X capacitor after the rectifying bridge.
In the next page we will have a more detailed discussion about the components used in the Zalman ZM500-RS.
On this page we will take an in-depth look at the primary stage of Zalman ZM500-RS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU1006 rectifying bridge in its primary, which can deliver up to 10 A at 100° C. 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.
On the active PFC circuit two FDPF16N50 power MOSFET transistors are used, each one capable of delivering up to 16 A at 25° C or 9.6 A at 100° C in continuous mode (note the difference temperature makes), or up to 64 A in pulse mode at 25° C. These transistors present a resistance of 380 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.
This power supply uses a Taiwanese capacitor from Teapo labeled at 85° C to filter the output from the active PFC circuit.
In the switching section, two STP14NK50ZFP power MOSFET transistors are used, each one capable of delivering up to 14 A at 25° C or 7.6 A at 100° C in continuous mode, or up to 48 A at 25° C in pulse mode, with an RDS(on) of 380 mΩ.
The switching transistors are connected using a design called “LLC resonant,” also known as a series parallel resonant converter, being controlled by an L6598 integrated circuit. So far we’ve seen only a few power supplies using this kind of design, like Seasonic X-Series 650 W, Thermaltake Toughpower 800 W and SilverStone Nightjar 400 W.
The active PFC circuit is controlled by a separated integrated circuit, which we couldn’t read its markings, but we assume it is an ICE1PCS02.
Now let’s take a look at the secondary of this power supply.
This power supply has nine Schottky rectifiers attached to the secondary heatsink. Eight of them are from the model: SBL3040CT (30 A, 15 A per internal diode at 100° C, 0.55 V voltage drop). The ninth rectifier, an SBL1045CT (10 A, 5 A per internal diode at 95° C, 0.55 V voltage drop) is in charge of the +5VSB output.
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%.
The +12 V output is produced by four of the rectifiers, giving us a maximum theoretical current of 86 A or 1,029 W.
The +5 V output is produced by two of the rectifiers, giving us a maximum theoretical current of 43 A or 214 W.
The +3.3 V output is produced by the last two rectifiers, giving us a maximum theoretical current of 43 A or 141 W.
All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.
The outputs are monitored by a PS223 integrated circuit, which supports over current (OCP), under voltage (UVP), over voltage (OVP) and over temperature (OTP) protections. Any other protection that this unit may have is implemented outside this integrated circuit.
Electrolytic capacitors from the secondary are also from Teapo and labeled at 105° C.
In Figure 15, you can see the power supply label containing all the power specs.
This power supply has two virtual rails, distributed like this:
This distribution is perfect since it separated the CPU (ATX12V/EPS12V connectors) from the video card(s).
Now let’s see if this power supply can really deliver 500 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.
The +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester. During this test the +12V1 input was connected to the power supply +12V2 rail while the +12V2 input was connected to the power supply +12V1 rail.
4 A (48 W)
7 A (84 W)
11 A (132 W)
14.5 A (174 W)
18 A (216 W)
3 A (36 W)
7 A (84 W)
10 A (120 W)
14 A (168 W)
18 A (216 W)
1 A (5 W)
2 A (10 W)
4 A (20 W)
5 A (25 W)
6 A (30 W)
1 A (3.3 W)
2 A (6.6 W)
4 A (13.2 W)
5 A (16.5 W)
6 A (19.8 W)
1 A (5 W)
1 A (5 W)
1.5 A (7.5 W)
2 A (10 W)
2.5 A (12.5 W)
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)
% Max Load
Ripple and Noise
Zalman ZM500-RS can really deliver its labeled wattage at high temperatures.
Efficiency was high when we pulled between 40% and 60% from its labeled wattage (i.e., between 200 W and 300 W), being between 84.8% and 85.6%. At light load (20% load, i.e., 100 W) and 80% load (i.e., 400 W) efficiency was still relatively high between 83% and 84%. At full load (500 W) efficiency dropped to 80.8%, still above the 80% mark.
This unit is 80 Plus Bronze certified, meaning that it should present 82% efficiency at full load. This didn’t happen because differently from Ecos Consulting we test power supplies at high temperatures, and efficiency drops with temperature (read our Can We Trust the 80 Plus Certification? article for more details).
Voltages were always inside the allowed range.
Although noise and ripple were inside the allowed range, noise level at +12 V outputs was too high during test five (around 105 mV); during test four it was around 80 mV. The limit is 120 mV and we always prefer power supplies generating half of this or less.
When we tried to overload this power supply noise level at +12 V outputs was outside the maximum allowed value, and we only consider an overloading well succeeded if all parameters are within specs, which was not the case.
Zalman ZM500-RS power supply specs include:
* Researched at Newegg.com on the day we published this review.
If you bought this power supply you won’t face any problems. However, we were expecting more from it, especially because we are talking about a power supply that costs USD 100.
Ripple and noise level at +12 V rails was too high while the power supply was delivering 500 W, at 105 mV, too close to the 120 mV limit. And we didn’t like the cable configuration very much. Although it will probably fit the needs of most users looking for a 500 W product, we’d prefer to see the two video card auxiliary power connectors using individual cables instead of being attached to the same cable and one more SATA/peripheral power connector on each cable, for a total of six connectors from each type instead of only four.
Efficiency was high when we pulled up to 80% of the labeled power (i.e., up to 400 W), but dropped to a little bit above 80% when we pulled the full 500 W from this unit. This power supply is 80 Plus Bronze certified, meaning that it should present 82% efficiency at full load, but as we have exposed on our Can We Trust the 80 Plus Certification? article, Ecos Consulting, the company behind the 80 Plus certification, uses an unrealistic room temperature to test power supplies, and efficiency drops with temperature. Interesting enough on the product box it says that this unit has the standard 80 Plus certification, the 80 Plus Bronze information is available only on the manufacturer website.
But what really kills ZM500-RS is its price. It is unbelievable expensive for a 500 W product. You can buy a 750 W power supply from Seventeam (ST-750P-AF) for the same price and get similar performance, higher number of cables and higher wattage!