M12D-850W: Seasonic joins the Power Race

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INSIDE

The removal of four screws provided access to the innards of the clamshell design. Compared to previous M12 and other Seasonic models, a few visible difference stand out:

  • The heatsinks appear blockier, with less spacing in between them.
  • There are two "daughter" PCBs attached to the main printed circuit board.
  • The San Ace 120 is obviously not an Adda, the fan brand Seasonic has used consistently for years.
  • A small plastic baffle reduces the airflow "short circuit" from fan to exhaust, and forces the air to blow across more of the components before exiting.


Standard clamshell casing design.


One of the two main heatsinks has the interleaved design of previous Seasonics.


The other heatsink has one main bank of fins. In between are the main transformer, the main 105¬įC Nippon Chemi-Con capacitors, and near the output cables, the back side of the DC-to-DC converter PCB is visible.


Here's that nifty little DC-DC circuit.


All the visible caps in the secondary stage are also Nippon Chemi-Con. Note 2-conductor fan connector on right.


The fan has good geometry, struts not parallel with the trailing edges of the blades, which are swept forward more than usual, deeply scooped, and nicely rounded to minimize turbulence noise.


The plastic material is hard and perhaps a bit brittle, rather than low resonance.


The end of the fan shaft looks impressive; it can be oiled if necessary. Ball bearings are used, for longer life in high temperature conditions.

The overall impressive look and feel of the fan is more than skin deep. When a 120mm DC fan is manually rotated by hand, it "clicks" into position from one magnetic pole position to another. A finger flick of the blades rarely keep the fan spinning for more than about 1.5 seconds. This Sanyo Denki moves from one "click" position to another more smoothly than any other fan I've encountered, and a finger flick keeps it spinning 3~4 seconds. This suggests extremely low friction bearings.

A technical specification sheet included some basic data about the fan. It is rated for a very high 82 CFM (in free air).

Sanyo Denki San Ace S1212H403 fan
used in Seasonic M12D-850
Rated Voltage
12 VDC
Air flow
82 CFM
min. Noise
<36 dBA

We ran some basic free air tests on the fan to glean a bit more information about its performance.

Sanyo Denki San Ace S1212H403 fan
MEASURED DATA
Voltage
RPM
2.1V (min)
320
3V
770
4V
1120
5V
1370
7V
1870
9V
2160
11V
2370
12V
2500

The fan started consistently at an amazingly low 2.1V, with an ambient temperature of 21°C, spinning at 320rpm. At this speed, it still moves a bit of air, and is essentially silent. The start voltage / speed is superbly low for a fan rated at 2500rpm. PWM speed control is increasingly used these days for its ability to start and keep a fan spinning at a lower speed. A PWM control fan has no advantage over this San Ace; its low speed capability with straight voltage control is already much better than most 2500rpm PWM fans can achieve. We'd bet the super wide speed range is directly related to the smooth low friction bearings.



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