Cold Test Results

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.

Seasonic PRIME Titanium Efficiency
(~25ºC Ambient Temperature Testing)
% Titanium
650TD 750TD 850TD
10 90% 93.1% 93.2% 92.9%
20 94% 94.2% 94.2% 94.1%
50 96% 96.3% 96.2% 96.1%
100 91% 94.8% 94.8% 94.8%

We usually expect to see an 80Plus Titanium certified unit to borderline pass or even fail the certification requirements during our testing. This is because we are supplying 230V AC to the unit and most models have been optimized for an 110V AC input, as the certification requirements are significantly lower and makes it slightly easier for the designer to meet them. Seasonic positively surprised us because all three of the new PRIME Titanium units are extremely efficient, easily meeting the stricter 80Plus Titanium performance requirements with an input voltage of 230V AC. The top efficiency of all three units is ~96.2% when operating at 50% capacity, with a nominal load range (20%-100%) efficiency average of 95.1% (650W model) to 95.3% (750W/850W models). The low load efficiency with the PRIME Titanium PSUs operating at 10% capacity is above 84.5%, which is much higher than the peak efficiency many low-cost PSUs can hope to achieve. Still, the efficiency of the units once they reach 20% capacity is so high that the thermal losses actually seem to drop instead of increasing.

Please note that we had the hybrid fan mode disabled during our testing in order to showcase the low load noise levels with the fan turned on. With the hybrid mode turned on, the fan starts when the load reaches about 20-25% of the unit’s rated capacity.

The internal operating temperatures of the Seasonic PRIME Titanium are very low, which is to be expected with such an efficient design. The cooling fan initially appears to have a “ladder” behavior, increasing its speed in steps in relation to the load, but the thermal control circuit is actually linear. When the units are operating in an ambient temperature environment, the speed increases are just very small in relation to the fan’s operating range, which appears as a step-like behavior on a chart. The fan of any of the three units did not even reach 50% of its rated speed at maximum load under these operating conditions, operating way below its optimal range and barely reaching audible sound pressure level figures.

The hybrid fan mode is the only thing that does not make much sense with these three units. If the setting is set to off, the fan will start as soon as the PSU is powered on regardless of the load, but will still retain its minimum possible rotational speed until the thermal control circuit decides that it needs to spin faster. The fans of the PRIME Titanium units are inaudible when running at such low speeds. If the setting is turned on, the fans will start before the point they become audible with the setting turned off, meaning that there is no practical difference at low loads whether the fan is spinning or not. Considering that the fans of the units are inaudible when spinning at their minimum speed, it might be wise to keep the hybrid mode turned off. Lower operating temperatures can only increase the longevity of a PSU, even one as good as this one.

External and Internal Design Hot Test Results: Hot Box at 45-50ºC
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  • TEAMSWITCHER - Saturday, April 8, 2017 - link

    This site isn't nearly as useful as it once was....
  • Ian Cutress - Monday, April 10, 2017 - link

    Care to elaborate?
  • crashtech - Saturday, April 8, 2017 - link

    All these need is a Hobbs meter, they sound like a rock you can build many a system upon.
  • Stele - Sunday, April 9, 2017 - link

    Well-written review as usual, offering a good balance between technical detail and readability. I have however noticed that you use the term "primary conversion bridge" in your PSU reviews. I believe you're referring to the component which converts AC to DC; if so, it's properly called a "bridge converter". That aside, do keep up the good work!
  • surt - Sunday, April 9, 2017 - link

    In what country? Around here primary conversion bridge is definitely the correct term.
  • Stele - Monday, April 10, 2017 - link

    Actually in many if not most English-speaking countries. Countries aside - it's also used by the semiconductor industry, including manufacturers themselves. For just a few examples:-

    And in standard electronic texts - try Cedra & Smith, Microelectronic Circuits (any edition).

    I was an electrical engineer :)
  • Stele - Monday, April 10, 2017 - link

    I hasten to add my original post was itself erroneous - I meant to say "bridge rectifier" not "bridge converter". Not enough coffee!
  • mobutu - Sunday, April 9, 2017 - link

    The only thing I'm interested in from this series is the minimum wattage option, the 600W fanless.
    And also hope that seasonic will offer lower wattage also in this product line. (like 300-500W range)
    I'll never use more than one GPU so have no use for PSUs more than 500-600W, even overclocked.
  • Hxx - Monday, April 10, 2017 - link

    for the price they should have included paracord cables
  • Laststop311 - Monday, April 10, 2017 - link

    I have the 750 watt version and it's a work of art. Either than fan has never spun up or i cant hear it. Even with a 5.0ghz overclock 7700k cooled with a nh d15s and thermal grizzly liquid metal with the ultra low speed adapters for the fans. Inside a fractal define r5 with 2x 140mm venturi HF intake fans and 1x 140mm fractal exhaust that comes with it. controlled with asus fanxpert. System is dead quiet and powers everythng like a boss. paired with an rx 480 overclocked to the max since i have a free sync monitor. im happy with 144hz 1920x1080 gaming on a curved 27" acer predator. Thank you seasonic for making the best PSU ever made.

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