Zalman ZM600-ST Power Supply Review

[nextpage title=”Introduction”]

So far Zalman has only two models on their ST power supply series, 500 W and 600 W. Let’s see if the 600 W model is a good product.

Figure 1: Zalman ZM600-ST power supply.

Figure 2: Zalman ZM600-ST power supply.

Zalman ZM600-ST is 5 ½” (140 mm) deep, using a 120 mm fan on its bottom and featuring active PFC circuit, of course.

This unit does not have a modular cabling system. All cables have nylon protections, which come from inside the unit. All cables use 18 AWG wires, which is the correct gauge to be used. The cables included are:

• Main motherboard cable with a 20/24-pin connector, 22” (56 cm) long.
• One cable with two ATX12V connectors that together form an EPS12V connector, 21 5/8” (55 cm) long.
• One cable with one six-pin connector and one six/eight-pin connector for video cards, 19 ¾” (50 cm) to the first connector, 5 7/8” (15 cm) between connectors.
• Two cables with three SATA power connectors each, 20 7/8” (53 cm) to the first connector, 5 7/8” (15 cm) between connectors.
• One cable with three standard peripheral power connectors, 20 ½” (52 cm) to the first connector, 5 7/8” (15 cm) between connectors.
• One cable with three standard peripheral power connectors and one floppy disk drive power connector, 20 ½” (52 cm) to the first connector, 5 7/8” (15 cm) between connectors.

The length of the cables and the number of SATA connectors is satisfactory for a 600 W power supply, but we didn’t like that the two video card power connectors are installed on the same cable. It is always better to see them attached to individual cables.

Figure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The Zalman ZM600-ST”]

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 4: Overall look.

Figure 5: Overall look.

Figure 6: 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), 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 two X capacitors more than the minimum required, plus an X capacitor after the rectifying bridge.

Figure 7: Transient filtering stage (part 1).

Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Zalman ZM600-ST.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Zalman ZM600-ST. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge, which supports up to 10 A at 100° C if a heatsink is used, which is the case. 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 itself out. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Figure 9: Rectifying bridge.

The active PFC circuit uses only one transistor, an SPW35N60C3, capable of delivering up to 34.6 A at 25° C or 21.9 A at 100° C in continuous mode (note the difference temperature makes) or up to 103.8 A at 25° C in pulse mode. This transistor presents a maximum resistance of 100 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. Usually power supplies use two transistors on this stage and not only one.

The electrolytic capacitor used to filter the output from the active PFC circuit is Japanese from Matsushita (Panasonic) and labeled at 105° C. The product webpage says “Japanese capacitors” (in the plural), but this information is wrong, as there is only one cap present on the primary.

The reviewed power supp
ly uses two STP25NM50N power MOSFET transistors on its switching section, installed on the traditional two-transistor forward configuration. Each transistor can handle up to 22 A at 25° C or up to 14 A at 100° C in continuous mode, or up to 88 A at 25° C in pulse mode, with a maximum RDS(on) of 140 mΩ.

Figure 10: Switching transistors, active PFC diode and active PFC transistor.

The primary is controlled by a CM6806 PFC/PWM combo controller.

Figure 11: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply has four Schottky rectifiers on its secondary heatsink.

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 two 40CPQ060 Schottky rectifiers, each one supporting up to 40 A (20 A per internal diode at 125° C, 0.68 V maximum voltage drop). This gives us a maximum theoretical current of 57 A or 686 W for the +12 V output.

The +5 V output is produced by one STPS60L45CW Schottky rectifier, capable of delivering up to 60 A (30 A per internal diode at 135° C, 0.73 V maximum voltage drop), giving us a maximum theoretical current of 43 A or 214 W for the +5 V output.

The +3.3 V output is produced by another STPS50L45CW Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

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.

Figure 12: +3.3 V, +5 V and +12 V rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports over voltage (OVP), under voltage (UVP), over temperature (OTP) and over current (OCP) protection (with two +12 V channels).

Figure 13: Monitoring integrated circuit.

All capacitors from the secondary are from Teapo.

[nextpage title=”Power Distribution”]

In Figure 14, you can see the power supply label containing all the power specs.

Figure 14: Power supply label.

This power supply has two +12 V rails (the monitoring integrated circuit really provides monitoring for two +12 V channels and we could clearly see the two current sensors installed on the printed circuit board, see Figure 15), distributed like this:

• +12V1: All cables but the video card power cable.
• +12V2: The video card power cable.

This distribution is perfect, as it put the CPU and the video card on separated rails.

Figure 15: The two current sensors (“shunts”) for the +12 V rails.

Now let’s see if this power supply can really deliver 600 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 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 +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test the +12VA input was connected to the power supply +12V1 and +12V2 rails, while the +12VB input was connected to the power supply +12V1 rail (EPS12V connector).

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	4 A (48 W)	9 A (108 W)	13 A (156 W)	17.5 A (210 W)	21.5 A (258 W)
+12VB	4 A (48 W)	9 A (108 W)	13 A (156 W)	17.5 A (210 W)	21.5 A (258 W)
+5V	1 A (5 W)	2 A (10 W)	4 A (20 W)	6 A (30 W)	8 A (40 W)
+3.3 V	1 A (5 W)	2 A (6.6 W)	4 A (13.2 W)	6 A (19.8 W)	8 A (26.4 W)
+5VSB	1 A (5 W)	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	3 A (15 W)
-12 V	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)
Total	112.3 W	237.9 W	348.2 W	469.4 W	598.8 W
% Max Load	18.7%	39.7%	58.0%	78.2%	99.8%
Room Temp.	45.3° C	44.6° C	46.6° C	47.6° C	46.9° C
PSU Temp.	46.4° C	46.2° C	48.5° C	50.4° C	47.8° C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	133.1 W	275.9 W	411.4 W	570.1 W	757.0 W
Efficiency	84.4%	86.2%	84.6%	82.3%	79.1%
AC Voltage	109.6 V	108.5 V	107.4 V	105.2 V	104.4 V
Power Factor	0.958	0.956	0.964	0.973	0.980
Final Result	Pass	Pass	Pass	Pass	Pass

Zalman ZM600-ST can really deliver its labeled power at high temperatures.

Efficiency was really high between 84% and 86% when we pulled between 20% and 60% from the labeled wattage (between 120 W and 360 W). At 80% load (480 W) efficiency dropped to 82%, still a pretty decent number. At full load, however, efficiency dropped below the 80% mark. This unit has only the standard 80 Plus certification and it is always good to keep in mind that the 80 Plus numbers are collected with the power supply running at 23° C and since we test power supplies at temperatures of at least 45° C, our efficiency numbers are usually lower than those presented by 80 Plus (efficiency drops with temperature).

Voltages were always within the allowed range.

Power factor was between 0.95 and 0.98, which is below the numbers we usually see (0.97 to 0.99), because the active PFC circuit from this unit has only one transistor instead of two.

Noise and ripple levels were within the allowed range, but a little bit higher than we’d like to see, especially during test five, as you can see below. The maximum allowed is 120 mV on +12 V and 50 mV on +5 V and +3.3 V. All these numbers are peak-to-peak figures.

Figure 16: +12VA input from load tester at 598.8 W (96.4 mV).

Figure 17: +12VB input from load tester at 598.8 W (92.4 mV).

Figure 18: +5 V rail with power supply delivering 598.8 W (31.6 mV).

Figure 19: +3.3 V rail with power supply delivering 598.8 W (29.6 mV).

Now let’s see if this unit can deliver more than 600 W.

[nextpage title=”Overload Tests”]

Below you can see the maximum we could pull from this unit. If we increased one amp on any given output ripple/noise levels would get above the maximum allowed at +12 V (during this test noise level was around 118 mV).

Input	Overload Test
+12VA	25 A (300 W)
+12VB	25 A (300 W)
+5V	8 A (40 W)
+3.3 V	8 A (26.4 W)
+5VSB	3 A (15 W)
-12 V	0.5 A (6 W)
Total	654.4 W
% Max Load	109.1%
Room Temp.	46.8° C
PSU Temp.	48.4° C
AC Power	836.0 W
Efficiency	78.3%
AC Voltage	106.4 V
Power Factor	0.980

[nextpage title=”Main Specifications”]

Zalman ZM600-ST power supply specs include:

• ATX12V 2.3
• Nominal labeled power: 600 W.
• Measured maximum power: 654.4 W at 46.8° C.
• Labeled efficiency: 86% at typical load (i.e., at 300 W) at 230 V, 80 Plus Standard certification
• Measured efficiency: Between 79.1% and 86.2% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector.
• Video Card Power Connectors: One six-pin connector and one six/eight-pin connector on the same cable.
• SATA Power Connectors: Six in two cables.
• Peripheral Power Connectors: Six in two cables.
• Floppy Disk Drive Power Connectors: One.
• Protections: Information not available. Although not listed by the manufacturer, this unit supports Over Voltage (OVP), Under Voltage (UVP), Over Current (OCP) and Short-Circuit protections.
• Warranty: Three years.
• More Information: https://www.zalman.com
• Average price in the US*: USD 95.00.

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

We were quite disappointed with this power supply. Although it can deliver its rated power at high temperature and high efficiency between 84% and 86% if you pull up to 360 W from it, efficiency drops below the 80% mark at full load. We also didn’t like the high noise/ripple levels when the unit was delivering its full 600 W (although they were still inside specs), the two video card connectors attached to the same cable and its price. For USD 25 less you can buy OCZ ModXStream Pro 600 W, which provides better performance, comes with a modular cabling system and has video card connectors on separated cables. This unit from OCZ also has presented noise/ripple levels a little bit above what we’d like to see, but lower than ZM-600ST’s.

Honestly, we don’t know what is happening with Zalman. They used to carry only top-notch power supplies at prices that were a little bit above the competition, but not by much. This is changing, and all units from them we reviewed lately are overpriced and some prone to high noise/ripple levels (see the reviews from ZM500-RS and ZM600-RS).