Why you can trust Tom's Hardware Our expert reviewers spend hours testing and comparing products and services so you can choose the best for you. Find out more about how we test.
Efficiency, Temperature And Noise
Efficiency
Our efficiency testing procedure is detailed here.
Using the results from the previous page, we plotted a chart showing the ZM750-EBT's efficiency at low loads, and loads from 10 to 110 percent of the PSU's maximum-rated capacity.
Efficiency trails the competition in this category, and Zalman falls to last place in the light and normal load graphs. Given the modern design of this platform, we expected much higher performance.
Efficiency At Low Loads
In the following tests, we measure the efficiency of Zalman's ZM750-EBT at loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60 and 80W. This is important for representing when a PC is idle, with power-saving features turned on.
| Test # | 12V | 5V | 3.3V | 5VSB | DC/AC (Watts) | Efficiency | Fan Speed (RPM) | Fan Noise (dB[A]) | PF/AC Volts |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1.188A | 0.480A | 0.475A | 0.191A | 19.63 | 64.28% | 850 | 38.5 dB(A) | 0.922 |
| 12.276V | 5.114V | 3.365V | 5.172V | 30.54 | 115.0V | ||||
| 2 | 2.405A | 0.968A | 0.980A | 0.384A | 39.74 | 76.34% | 960 | 38.9 dB(A) | 0.968 |
| 12.275V | 5.109V | 3.360V | 5.167V | 52.06 | 115.0V | ||||
| 3 | 3.618A | 1.459A | 1.488A | 5.161A | 59.84 | 80.78% | 1080 | 42.1 dB(A) | 0.980 |
| 12.272V | 5.105V | 3.356V | 5.161V | 74.08 | 115.0V | ||||
| 4 | 4.828A | 1.962A | 1.968A | 0.775A | 79.82 | 83.02% | 1190 | 43.2 dB(A) | 0.986 |
| 12.267V | 5.100V | 3.351V | 5.155V | 96.15 | 115.0V |
At light loads, Zalman's offering falls significantly behind the other Gold-rated 750W PSUs. Even SilverStone's ST75F-GS V2, which uses exactly the same platform with a few different components, easily beats the ZM750-EBT.
5VSB Efficiency
The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher efficiency with 100mA of load, 60 percent or higher with 250mA of load and 70 percent or higher with 1A or more of load.
We will take four measurements: one each at 100, 250 and 1000mA, and one with the full load the 5VSB rail can handle.
| Test # | 5VSB | DC/AC (Watts) | Efficiency | PF/AC Volts |
|---|---|---|---|---|
| 1 | 0.102A | 0.53 | 72.60% | 0.098 |
| 5.178V | 0.73 | 115.1V | ||
| 2 | 0.252A | 1.30 | 75.58% | 0.191 |
| 5.176V | 1.72 | 115.1V | ||
| 3 | 1.002A | 5.18 | 79.33% | 0.319 |
| 5.166V | 6.53 | 115.1V | ||
| 4 | 3.002A | 15.39 | 76.57% | 0.380 |
| 5.128V | 20.10 | 115.1V |
The 5VSB rail achieves close to 80 percent efficiency in the third test. However, under full load, its efficiency drops significantly. This is a clear sign that 3A on this rail are close to its limit. Most likely, this is why ripple suppression is so lousy at higher loads. Zalman should probably keep the max current output on this rail at 2.5A to offer better performance.
Power Consumption In Idle And Standby
| Mode | 12V | 5V | 3.3V | 5VSB | Watts | PF/AC Volts |
|---|---|---|---|---|---|---|
| Idle | 12.265V | 5.120V | 3.372V | 5.178V | 11.18 | 0.702 |
| 115.1V | ||||||
| Standby | 0.08 | 0.012 | ||||
| 115.1V |
In the table above, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).
Vampire power is very low, especially with 115V input.
Fan RPM, Delta Temperature And Output Noise
Our mixed noise testing is described in detail here.
The first chart below illustrates the cooling fan's speed in RPM, and the delta between input and output temperature. The results were obtained at 34 °C (93.2 °F) to 47 °C (116.6 °F) ambient temperature.
The next chart shows the cooling fan's speed (in RPM) and output noise. We measured acoustics from one meter away, inside a small, custom-made anechoic chamber with internals completely covered in sound-proofing material (be quiet! Noise Absorber kit). Background noise inside the chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 34 °C (93.2 °F) to 47 °C (116.6 °F) ambient temperature.
The following graph illustrates the fan's output noise over the entire operating range of the PSU. The same conditions of the above graph apply to our measurements, though the ambient temperature was between at 28 °C (82.4 °F) to 30 °C (86 °F).
At normal conditions and up to 400W load the PSU is quiet enough, though not silent. Under higher loads, however, its fan quickly speeds up. Naturally, output noise increases as well. At close to 600W, the fan's noise becomes annoying. Look for another PSU if you're out to build a quiet PC.
