FSP Green PS FSP400-60GLN 400W PSU

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INSIDE THE GREEN PS

The Green PSU is downright scrawny with its top off. No wonder FSP can claim a 25% reduction in weight — there's not much here! The internal components are both fewer and smaller than in most other power supplies. The heatsinks are aluminum plates wedged between the components, and the PCB doesn't occupy the whole space inside the casing. There are fewer coils than usual, a single main capacitor, and even the main transformer is about two thirds the "normal" size.

All in all, the Green PS is a little mysterious. How can a power supply this "small" deliver 400W? How can it be cooled properly by the minuscule (and extremely simple) heatsinks? Is smaller better?

Whatever the answer to these questions, FSP's engineers seem to have taken an unusual approach to the Green PS. Intuitively, it is difficult to believe that the unit can be cooled adequately, but if it had a thermal problem, it would not have passed all of those safety certifications. Whatever the intentions behind the design, I can't help rooting for the little guy.


It's pretty empty inside: Components are few and widely spaced.

What follows is an educated guess about how the internal cooling might work.

In comparison to most power supplies we've seen in the lab recently, component and heatsinks have been minimized, and there is a lot of empty space. The lack of impedance should allow greater airflow through the PSU and perhaps cut down on "hot spots" where there is little or no air movement to evacuate the heat. The shape and careful positioning of the auxiliary exhaust vents seem to be designed to relieve back pressure, and to ensure that there are no dead ends where the air has nowhere to go.

The empty space behind the rear grill means that some of the air from the fan will exit without ever passing over the heat-producing components. This is a short-circuit in the airflow, but it may increase airspeed and minimize back pressure in the rear half. The airflow in the front half will be slower, since there is more impedance, but also higher pressure. It seems plausible that the difference in pressure might be enough to cause a current from the front to the back, thus drawing heat away from the components on the PCB.


This angle shows just how empty it is, about a quarter of the space is unused.

Only the engineers at FSP can confirm my guess about airflow design, but our testing showed that the internal cooling is no worse (but no better) than most of the other power supplies we've tested. Details of the thermal performance can be found on the next page, in the test results.


Skinny, vertically aligned heatsinks offer minimal airflow impedance.


A medium speed, ball bearing fan from a manufacturer known for quiet fans.

The fan is from a manufacturer well known to SPCR: Yate Loon Electronics. It's a medium speed ball bearing model with a rated noise level of 34 dB (no A weighting or measurement distance listed). Yate Loon has an excellent reputation for the low noise of their sleeve bearing fans, but their ball bearing fans are less well known. Hopefully their ball bearing models are as quiet and pleasant sounding.

CABLES AND CONNECTORS

There are a total of seven cable sets.

  • 19" cable for main 20+4-pin ATX connector
  • 20" auxiliary 4-pin 12V AUX connector
  • 26" cable with two SATA drive connectors
  • 2 x 26" cable with two 4-pin IDE drive connectors
  • 32" cable with two 4-pin IDE drive connectors and one floppy connector
  • 20" 6-pin auxiliary power connector for PCI Express


Plain vanilla cables: Not twisted or sleeved.

The Green PS has relatively few output cables, although there are easily enough for most systems. The limiting factor is likely to be SATA connectors, of which there are only two. There is a PCIe connector for a high power video card.

The wires themselves are insulated with an unfamiliar kind of plastic. This is unusual, but not really surprising, since most wire insulation is manufactured with lead. Naturally, the Green PS could not be environmentally friendly if it used lead-based insulation... and it could not meet RoHS requirements either.

The wires are also of several different gauges. 18 gauge wire is almost standard, but the Green PS used no less than three different gauges: Heavy 16 gauge for the PCIe connector, 18 gauge for the +12V AUX connector and most of the wires on the ATX header, and thinner 20 gauge for the IDE and SATA cables.

The rationale behind using different gauges of wire is to minimize voltage drops for the longer cables that carry less current, while ensuring that the highest powered cables don't melt under heavy load. It may also be used as a cost saving measure, since thinner wires are generally a little cheaper.



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