Thermaltake Smart BM2 750W Power Supply Review

The Smart BM2 750W is a worth considering mid-level power supply from Thermaltake.

Thermaltake Smart BM2 750W
(Image: © Tom's Hardware)

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Primary Rails And 5VSB Load Regulation

The following charts show the main rails' voltage values recorded between a range of 40W up to the PSU's maximum specified load, along with the deviation (in percent). Tight regulation is an important consideration every time we review a power supply because it facilitates constant voltage levels despite varying loads. Tight load regulation also, among other factors, improves the system’s stability, especially under overclocked conditions and, at the same time, it applies less stress to the DC-DC converters that many system components utilize.

Load regulation is satisfactory at 12V, given the competition's performance and tight on the minor rails. 

Hold-Up Time

Put simply; hold-up time is the amount of time that the system can continue to run without shutting down or rebooting during a power interruption.

The hold-up time is low. Thermaltake should use a larger bulk cap, 470uF at least.

Inrush Current

Inrush current, or switch-on surge, refers to the maximum, instantaneous input current drawn by an electrical device when it is first turned on. A large enough inrush current can cause circuit breakers and fuses to trip. It can also damage switches, relays, and bridge rectifiers. As a result, the lower the inrush current of a PSU right as it is turned on, the better.

The inrush current is high, especially with 230V input. With a higher resistance NTC thermistor, this wouldn't be the case. 

Leakage Current

In layman's terms, leakage current is the unwanted transfer of energy from one circuit to another. In power supplies, it is the current flowing from the primary side to the ground or the chassis, which in the majority of cases is connected to the ground. For measuring leakage current, we use a GW Instek GPT-9904 electrical safety tester instrument.

The leakage current test is conducted at 110% of the DUT's rated voltage input (so for a 230-240V device, we should conduct the test with 253-264V input). The maximum acceptable limit of a leakage current is 3.5 mA and it is defined by the IEC-60950-1 regulation, ensuring that the current is low and will not harm any person coming in contact with the power supply's chassis.

Thermaltake Smart BM2 750W

(Image credit: Tom's Hardware)

Leakage current is not as low as the Corsair CX750F, but still is low enough that it doesn't create problems. 

10-110% Load Tests

These tests reveal the PSU's load regulation and efficiency levels under high ambient temperatures. They also show how the fan speed profile behaves under increased operating temperatures.

Swipe to scroll horizontally
Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])Temps (In/Out)PF/AC Volts
14.406A1.994A1.998A0.986A74.96885.455%87125.0 34.09°C0.960
12.112V5.017V3.303V5.071V87.728 36.11°C115.12V
29.849A2.993A3.000A1.186A150.04988.567%87325.0 34.63°C0.976
12.097V5.014V3.300V5.058V169.418 37.43°C115.12V
315.643A3.492A3.503A1.388A225.05989.349%87524.9 35.08°C0.983
12.082V5.013V3.298V5.045V251.887 38.64°C115.12V
421.451A3.993A4.005A1.590A300.08289.095%87724.9 35.58°C0.987
12.068V5.011V3.296V5.033V336.813 40.22°C115.12V
526.895A4.994A5.011A1.794A374.65088.543%87924.9 36.32°C0.989
12.052V5.007V3.293V5.020V423.130 41.76°C115.11V
632.384A5.995A6.016A1.999A449.58987.665%88124.9 36.78°C0.990
12.036V5.006V3.291V5.005V512.847 43.52°C115.11V
737.923A6.998A7.026A2.205A524.92686.351%94727.8 37.56°C0.991
12.019V5.004V3.289V4.990V607.897 45.67°C115.11V
843.478A8.003A8.036A2.411A600.15185.305%115633.7 37.85°C0.992
12.000V5.000V3.285V4.978V703.534 47.55°C115.10V
949.417A8.506A8.529A2.417A674.73083.732%174045.3 38.91°C0.993
11.984V4.998V3.283V4.966V805.824 49.30°C115.09V
1055.370A9.012A9.056A2.523A749.83382.386%212549.4 39.55°C0.993
11.967V4.995V3.280V4.955V910.144 50.61°C115.08V
1161.748A9.016A9.061A2.528A825.04980.824%212049.3 41.46°C0.994
11.949V4.993V3.278V4.946V1020.802 54.28°C115.07V
CL10.116A14.005A13.998A0.000A117.59479.979%694 18.7 36.37°C0.974
12.099V5.003V3.295V5.059V147.031 41.78°C115.12V
CL262.518A1.000A1.000A1.000A761.50482.892%2127 49.4 39.53°C0.993
11.968V5.007V3.287V4.996V918.666 50.03°C115.07V

We didn't go up to 45-47°C as we usually do, since this platform is rated at 40°C for continuous full power delivery. The PSU didn't have any trouble under high operating temperatures, but the fan profile looks weird since up to 525W load, the fan speed is below 1000 RPM. Given the restrictive fan grille and the not top-efficiency platform, the fan speed profile is way too relaxed at moderate loads. 

20-80W Load Tests

In the following tests, we measure the PSU's efficiency at loads significantly lower than 10% of its maximum capacity (the lowest load the 80 PLUS standard measures). This is important for representing when a PC is idle with power-saving features turned on.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])PF/AC Volts

Fan speed is low and the efficiency levels are satisfactory. 

2% or 10W Load Test

Intel plans on raising the ante at efficiency levels under ultra-light loads. So from July 2020, the ATX spec will require 70% and higher efficiency with 115V input. The applied load is only 10W for PSUs with 500W and lower capacities, while for stronger units we dial 2% of their max-rated-capacity.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan Speed (RPM)PSU Noise (dB[A])PF/AC Volts

We didn't expect this unit to achieve over 70% efficiency with 2% of its max-rated-capacity load. 

Efficiency & Power Factor

Next, we plotted a chart showing the PSU's efficiency at low loads, and loads from 10 to 110% of its maximum rated capacity. The higher a PSU’s efficiency, the less energy goes wasted, leading to a reduced carbon footprint and lower electricity bills. The same goes for Power Factor.

With 115V input, the impact on efficiency is notable, especially under higher loads. In general, the platform is efficient for this category, taking the lead from several competing offerings. 

5VSB Efficiency

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Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts

The 5VSB rail is highly efficient. 

Power Consumption In Idle And Standby

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Mode12V5V3.3V5VSBWattsPF/AC Volts

The PSU has minimal energy needs on standby. 

Fan RPM, Delta Temperature, And Output Noise

All results are obtained between an ambient temperature of 37 to 47 degrees Celsius (98.6 to 116.6 degrees Fahrenheit).

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

The fan speed profile shouldn't be as relaxed with moderate loads and high operating temperatures. A more linear fan speed increase would be ideal.

The following results were obtained at 30 to 32 degrees Celsius (86 to 89.6 degrees Fahrenheit) ambient temperature.       

(Image credit: Tom's Hardware)

(Image credit: Tom's Hardware)

For most of its operating range, the PSU is silent, but once you push it and the load exceeds 475-550W (depending on the load on the minor rails), the fan's speed increases notably, and so does noise output.

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Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.