X-650: Seasonic hits Gold

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The removal of four screws allowed the fan panel to be removed. Compared to previous Seasonic models, some very significant differences are visible:

  • There is only one large heatsink, way off to one side. No wonder it was not visible from the outside.
  • The connector to the fan is 4-pin, as expected for PWM control.
  • Airflow impedance looks to be modest.
  • The isolation of the lower voltage circuitry to the daughter PCB appears to have minimized clutter on the board; that plus the absence of multiple soldered output cables.
Postscript Note, Nov 5/09: It was pointed out to us by a sharp-eyed reader that the internal photos shown below are from an X750. We had just received the X750 sample when this review was being posted, and photos of both PSUs were taken at the same time. The photos of the two samples got mixed up accidentally; the two PSUs look identical internally except for the value of some of the capacitors, which are all rated 105°C. Rest assured that there was no confusion or mixup about the test results; they are for the X650 we tested and the conclusions remain unchanged.

Only one large heatsink, oddly almost out of the airflow path of the fan.

The fan has good geometry and rugged bearing housing, identical in design to the excellent fan used in the M12D series. The current rating of 0.13A suggests both modest speed and high energy efficiency. A rubber pad lies between the fan and the intake grill panel, presumably to minimize vibration transfer from the fan.

All of the circuitry on the main PCB has to do with conversion from AC to 12VDC; the DC/DC conversion to the lower voltages takes place on the daughter board which also holds the output connectors.

Note 105°C KMR primary filter capacitors and main step-down transformer. The vertically positioned PCB is the DC/DC Connector Module with Integrated VRM.

A close-up of both sides of the DC/DC Connector Module board supplied to reviewers.

One of the most important aspects of the DC/DC Connector Module is that it keeps the outputs at 12VDC through most of the PSU. By making the conversion from 12VDC to 5VDC and 3.3VDC on this module, the losses inherent in low voltage electricity transfer are minimized. Only the 12VDC line has to run from the main PCB to the DC/DC Connector Module, which keeps internal wiring and soldering (both sources of higher energy loss) to an absolute minimum. The illustration below from Seasonic explains the difference between the X-series design and conventional modular output PSU design.

As with the fan in the M12D, the quality of the fan seems more than skin deep. This Sanyo Denki has extremely low friction bearings. Some basic free air tests on the spare fan were run to glean a bit more information.

Sanyo Denki San Ace S1212P4M61 fan
32 dBA

PWM speed control will allow this fan to start and run at extremely low speed, probably below 500rpm. Seasonic's term, Hybrid Silent Fan Control, attempts to explain that the fan only starts when necessary and stops when it's not. The following is Seasonic's explanatory illustration.

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