Zalman ZM600 heatpipe-cooled modular power supply

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The cooling of the ZM600-HP worked well considering the high power draw of the test system. Temperature rise remained reasonable until the 200W mark, where it rose above 10°C. At full load, it rose to 16°C, which is probably to be expected of such a high power draw. With 170W of power being dumped into the thermal simulation box, a 16°C rise is acceptable.

The internal temperature of the thermal simulation box was somewhat lower than in recent previous tests of power supplies at similar loads. We're fairly sure this is due to the higher fan ramp up speed, and the larger 120mm exhaust fan in the thermal simulation box.

Does the use of heatpipes make the ZM600 a better cooled power supply? It's hard to say. The Antec Earth Watts 430 used the same exact test rig configuration (bigger 120mm fan), and at the same power output levels (150~450W), the temperature inside the thermal simulation box was 3-4¬įC higher with the ZM600. This is explained by the higher speed and larger size of the fan in the Zalman PSU; it evacuates the heat from the box more quickly, thus keeping the internal box temperature lower. This difference is also seen at the exhaust temperatures. However, the temperature rise through the power supply was similar.

What does all this mean? The Zalman's heatpipe heatsink works, but we cannot say whether it works any better than a conventional heatsink scheme.

One word of warning: Our new test bench uses a larger 120mm fan that provides a more realistic simulation of the kinds of low-noise systems that are in use today. As a result of this change, thermal results are not directly comparable to earlier tests. Previously tested power supplies will likely exhibit a slightly shallower fan speed / temperature curve in the new setup because a bit more of the heat in the box is evacuated by the 120mm fan.


The fan started at 5.0V, higher than many other quiet power supply fans. The system was easily audible at 1m, but was not unpleasant. A slight buzzing sound could be heard when there was very little load on the +5V lines. Applying a small amount of load on the 5V lines made this buzz go away.

As the load increased, so did the fan voltage. One would hope that the fan voltage remain constant at low loads, and rise only when there is risk of damaging the internal components. With the ZM600-HP, the fan voltage increased more or less linearly, as did the noise levels. At 200W, the noise levels were 29 [email protected] , which is already a bit too high a value for a quiet system. With the other noise sources in a typical PC, the net SPL would certainly climb over 30 [email protected] with this PSU at this load. This is considerably noisier than the best quiet high power power supplies SPCR has tested.

As any change to airflow also affects noise, the same caveat as the temperature data applies to our noise results: They are not directly comparable to earlier reviews. We do not believe that the change is large, but the larger fan will certainly have an effect; the increase in airflow can be expected to delay the point when the fan increases in speed. Cooler temperatures inside the test bench mean that the power supply doesn't have to work as hard to keep cool, and it can therefore run more quietly. Another possible change is that the larger fan may let out more noise from the box than previously.


During testing, the system simply shut down when we were testing it at or close to the maximum load. This happened a number of times, with the unit coming back on immediately when reset or with a very minor reduction in 12V load. It was undoubtedly the result of the current limiting on the "four independent lines". We have only two independent loads, one for 12V1 (main ATX cable and 4-pin peripheral power cables) and one for 2x12V, so at maximum load, we had 18A and 19A on those lines. Zalman cites 16A maximum on each 12V line. We expect that Intel's ATX12V v2.2 guide of 18A current limiting for the 12V lines was used.

The good thing is that the 12V overcurrent protection circuit definitely works. The bad thing is that the OCP works, so this means if you do have a high power system, you'll have to take some care to distribute the 12V load evenly. You may have to experiment with different cable combinations to avoid this issue with very high power systems.


Each of these recording have 10 seconds of silence to let you hear the ambient sound of the room, followed by 10 seconds of the product's noise.

No recordings were made at higher levels; it got a bit too loud.

Sound Recordings of PSU Comparatives


These recordings were made with a high resolution, studio quality, digital recording system, then converted to LAME 128kbps encoded MP3s. We've listened long and hard to ensure there is no audible degradation from the original WAV files to these MP3s. They represent a quick snapshot of what we heard during the review. Two recordings of each noise level were made, one from a distance of one meter, and another from one foot away.

The one meter recording is intended to give you an idea of how the subject of this review sound in actual use — one meter is a reasonable typical distance between a computer or computer component and your ear. The recording contains stretches of ambient noise that you can use to judge the relative loudness of the subject. For best results, set your volume control so that the ambient noise is just barely audible. Be aware that very quiet subjects may not be audible — if we couldn't hear it from one meter, chances are we couldn't record it either!

The one foot recording is designed to bring out the fine details of the noise. Use this recording with caution! Although more detailed, it may not represent how the subject sounds in actual use. It is best to listen to this recording after you have listened to the one meter recording.

More details about how we make these recordings can be found in our short article: Audio Recording Methods Revised.


The ZM600-HP is clearly targeted at the high performance gaming market. The high power output, good voltage regulation, and excellent power factor correction make it a solid candidate for a new dual core, dual video card setup. The price tag also matches that of systems that might have such a high power requirement. The modular sleeved cables are also another nice touch for those that demand tidyness or want to show of their rig to their gamer friends.

Unfortunately, a gaming rig is typically not the realm of quiet computing. The unit performed quietly only at <150W load, and would most likely be amongst the loudest components in a typical "quiet" system. It's strange, since Zalman's product pages are littered with talk about "ultra-quiet" systems — maybe they're talking about ultra-quiet relative to the typical high-end gaming rig. Their ZM460B-APS power supply boasts a feature Zalman calls CNPS (Computer Noise Prevention System) that is supposed to keep the fan running slowly until the internal temperatures reach 30°C, but the ZM600-HP has no indication of such a feature on their website. Our results suggest that the absence of such a claim is no accident.

One possible source of the problem lies in the tight spacing of the heatsink fins on the heatpipe. With such a small gap between the fins, the fan needs to spin faster in order to provide sufficient pressure to sufficiently cool the device. For high airflow systems, this provides more efficient cooling, but it significantly reduces performance in low airflow situations. Although the heatpipe heatsink is interesting, it has not helped Zalman to produce a PSU that uses less airflow for cooling. Or one that's quieter than the competition.

In the end, if the ZM600-HP is used in a system where the CPU fan, hard drives and/or graphics card are loud, then yes, you could call this PSU "ultra-quiet". If silence is your goal, there are several other PSUs even in this high power category that are better choices.


SPCR Articles of Related Interest:
Power Supply Fundamentals & Recommended Units
Power Distribution within Six PCs
SPCR PSU Test Rig V.4
Enermax Liberty EL500AWT & EL620AWT
Seasonic M12-700
Seasonic S12 Energy Plus: Efficient Power for Connoisseurs

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