Load testing the PSU

Load Testing The PSU

Testing a power supply is a challenge, and you need professional load testers to check the PSU’s behavior the right way. 

The first basic test is performed with a simple power supply tester. It doesn’t load the PSU with more than a couple of Watts, but it helps to determine if the power supply unit is operational at all. There’s a self-check indicating if the voltages are at the proper levels. As you can see, there have been no issues with the Lian Li SP750 unit.

The following setup was used for the remainder of the testing:

• Voltcraft VC-870 Digital Multimeter - voltage measurement (+ Fluke 97 scope meter)
• Oscilloscope - GW INSTEK GDS 3154
• DC load - original solution
• Fluke 97 Scope meter (a measurement of voltage and ripple),
• Voltcraft SL-451 decibel meter (volume measurement)
• ACUVIM-IIRF – for measuring active power (input from the socket).
• PCE Instruments PCE-DT 50 tachometer – for the measurement of the rotational speed of the fan.

Efficiency

In our power supply reviews, we emulate real-world usage by creating such loads as a power-hungry, multi-GPU setup with a powerful CPU would generate. Older components used to require more power, but there has been some progress in this area. In a typical configuration, reaching over 500-600 Watts of power draw is difficult. Let’s take a look at the SP750’s efficiency first. Checking efficiency is a relatively easy thing to accomplish.

It does look great even at low loads (e.g., 10%, equaling 75 W), which is quite typical of the idle state in modern PCs.

Maximum load

Next up is the maximum wattage that this unit can hold before switching off.

Efficiency looks excellent, even above 100% load. 808 Watts is a good value, but you really wouldn’t want to come close to that for very long.

ErP Lot 6 Power Off wattage

We looked at the powered-off status (ErP/EuP), productivity mode (when we stress the CPU), and finally gaming. The lower the wattage, the more efficient the PSU. It is that simple.  

This is well below the 0.5 W requirement.

Ripple testing

First up is the ATX12V V2.2 specification for DC output ripple:  

The Lian Li SP750 achieved the following results:

The values are very well within tolerance. Even in the worst-case scenario (100% load), it is not even a quarter of the allowed number, so this is not worrying at all.