Run a Power Supply without a Fan?

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What Are Temps with Low Airflow Fan?

The above results begs the question of what temperatures are reached when a Panaflo 80mm L1A or other low noise, low airflow fan is substituted for the loud, fast stock fans in most PSUs. As the thermal probe for the Veriteq was already jammed in place, it was a simple matter of removing the 80mm fan and speed adjustment assembly, drop in a Panaflo, connect it to an IDE connector, replace the cover with a closed one (instead of one with a hole) to better simulate conditions inside a case, and start recording. All other conditions, including the CPU stress program, were the same as before.

The results are shown on the graph below. The room temperature was slightly lower than before - 20C instead of 22C. The stress test was begun at about 16:03 with the Panaflo at 12V. At 16:06, the fan was switched to 5V. The temperature rose steadily, then hits 34C in about 20 minutes, at which point it stabilized.

Open Air vs. Tunnel Effect

There has been conjecture that the quiet effectiveness of the Zalman PSU is related to its relative lack of intake ventilation holes. Unlike many PSU that have many ventilation slots, the Zalman has them only on the side opposite the exhaust fan. Some believe this cause a kind of tunnel effect in which the air is forced to follow a narrower path through the PSU, thus causing a kind of tunnel effect in which the airflow is actually accelerated, with the assistance of natural warm air convection.

A simple test of this theory was conducted by taking the top cover (with no holes) off. The resulting graph is shown below.

On the surface of it, the theory seems to be confirmed here, as the temperature jumps 10 degrees in 5 minutes after the cover is removed and climbs all the way to 48C before stabilizing. Putting the cover back on has the even more amazing effect of lowering the temperature dramatically by 10C in 5 minutes.

This data makes me question the validity of the first set of data, run fanless and with the cover off. Perhaps I need to rethink the effect of convection.

No Fans, Second Try

This time, after removing all fans and putting the solid cover on, I positioned the PSU so that both back (outside) and front (inside) vents were unobstructed. The back became the top, and the front became the bottom. This way, as hot air rose, cooler air could be drawn in from the bottom. How did it work? Same conditions, here is the graph.

It's much better, taking half an hour to reach 52C. Nearly 20 minutes beyond this graph, it was still hovering around 52.5C, so certainly, the temperature seemed to have stabilized. Still, 52C is a pretty high temperature, and with all the added heat, there is definitely a higher chance of earlier failure.

In-case Simulation

Yet another experiment was to simulate what happens with a modded Enermax PSU when installed inside a typical tower PSU over a hot CPU. In this case the CPU was not that hot, being a VIA C3-933 that only dissipates around 10W. Still, it was cooled by a passive heatsink only, and a fair amount of heat could be felt around the CPU. I removed the 92mm fan from the cover, put the cover on the PSU, then placed the assembly so that the 92mm hole was about 1" directly over the CPU / heatsink.

The result? No graph is shown because the effect was very simple: Temperature rose 5 degrees in about 10 minutes, then stabilized at 42C temperature.

Conclusions

It was a little disappointing to discover that this Enermax does not appear well suited for operation without fans. Considering the designers equipped it with two fans, perhaps I should not be surprised. In the nutshell:

  • The EG-365P-VE probably should not be run without at least a little bit of airflow.
  • A modification to increase the heatsink area of this PSU may make it more suitable for convection-only cooling. Positioning the unit for optimal convection airflow over the hot components is very important. NOTE: my sample did not have live voltage on the heatsink.
  • A Panaflo FBA08A12L 80mm fan at 5V probably provides ample cooling for most PSUs in most cases. At 5V, it is inaudible except from within one foot. This fan is rated for 21 dBA and 24 cfm at 12 VDC. At 5V, I would guess the airflow is down to 12 cfm or less, and the noise is below 10 dBA.
  • Very hot processors and/or systems loaded with hot components will likely require greater airflow.
  • The concept of directing fan airflow through a specific path by using vents only where needed has substantial merit and appears to result in improved cooling when compared to open vents everywhere.

There's little question that long term reliability would be affected if fanless operation increases operating temperature from a nominal 30C to over 50C. As to what happens if /when a PSU fails, I have one friend who says a PSU "took out" his motherboard when it died. More on this topic another time.

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