The BitFenix Whisper M 450W & 850W PSU Review

Cold Test Results (Room Temperature)

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M  40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs - 2014 Pipeline post.

Both the 450W and the 850W version of the BitFenix Whisper M PSU honored their 80Plus Gold certification without issues. The 450W version actually fared a little better, with an average nominal load range (20%-100%) efficiency of 91.2%. It is only slightly higher than that of the 850W version (91%), but we can see the 850W version only barely surpassing the 92% mark at 50% load, where the 450W version exceeded it with ease, peaking at 92.5%. We can also notice that the 450W model is substantially more efficient with loads lower than 300 Watts. This is not an issue of any kind; the narrow power range of the 450W model simply allows it to perform much better when lightly loaded. The powerful 850W model technically reaches its nominal load range with a load of 170 Watts and above, in the range where the 450W model is already moving towards peak efficiency.

With loads lower than 300 Watts, the higher efficiency of the 450W model allows it to maintain lower internal operating temperatures, but not lower noise levels. The fans of both units seem to copy each other, with the fan of the 850W model simply speeding up further with loads above 450 Watts. Regardless, the sound pressure level with loads below 300 Watts is below 34 dB(A) with both units, which corresponds to a very soft humming noise if one gets an ear very close to the PSU.