Introduction

We would like to thank Seasonic for supplying the review sample.


Seasonic is among the few OEMs offering fanless power supplies. Building a PSU without any active cooling is challenging, especially if high-wattage, since thermal loads have to be as low as possible to ensure it operates properly under all operating conditions. Such a PSU usually uses parts that far exceed requirements to ensure increased temperatures don't cause failures if these parts are stressed. It goes without saying that all protection features should operate flawlessly, including over temperature protection.

The Prime Fanless 700 W is the strongest passive power supply that money can get you today. It uses the Prime Titanium platform with a vast wattage overhead. In essence, the platform can deliver way more than 700 W, but is set to 700 W because there is no cooling fan to remove the heat, and the higher the power output, the higher the thermal load. The best way to build a passive PSU is to use a highly efficient, strong platform and limiting power output to where the parts won't have a problem handling the heat for prolonged periods of time even without any cooling. You also have to pay extra attention to the chassis and its airflow. Hot air goes up, so you either use a beefy heatsink on top or make the top cover look like Swiss cheese. Finally, keep in mind that you should not install passive PSUs on their side or with the top exhaust grille facing down because it will trap the hot air internally, which puts a lot of stress on parts and shuts the PSU down by triggering OTP. As such, not all cases are suitable for passive PSUs, including those with a PSU shroud without any ventilation holes.

Specifications