Thermaltake Smart BM2 750W Power Supply Review

To learn more about our PSU tests and methodology, please check out How We Test Power Supply Units. 

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.

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Results 1-8: Load Regulation

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.

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Results 9-12: Hold-Up Time

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.

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Results 13-14: Inrush Current

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.

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.

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.

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.

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.

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Results 15-18: Efficiency

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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Results 19-20: 5VSB Efficiency

The 5VSB rail is highly efficient. 

Power Consumption In Idle And Standby

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Results 21-22: Vampire Power

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).

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.       

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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