Antec SmartPower 2.0 SP-450 ATX Power Supply

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120mm VS. 80mm FANS

120mm fans have become the norm in power supplies, but it has not always been this way. Traditional power supplies use a single rear-mounted 80mm fan, with a straight-through airflow path. However, the 80mm fan has fallen out of favor, probably more because of the successful marketing of the 120mm fan PSU than any compelling technical superiority.

In free air, a 120mm fan produces far more airflow than an 80mm fan at the same speed, so designing a power supply around a 120mm fan seems to make sense. Another reason for using a 120mm fan in a power supply is to help exhaust heat from around the CPU, which sits directly below the power supply in a normal ATX case. This can be helpful, or even necessary in a conventional case, but it is less than optimal when building a quiet system. The reason: The CPU heat must be exhausted through the power supply, which means a higher fan speed ? and thus more noise ? is needed to cool the power supply.

In order to fit a 120mm fan into a standard ATX12V power supply, it must be situated on the bottom. This means that the airflow from the fan must make a 90° turn in order to leave the power supply via the rear exhaust. The airflow impedance is increased and the total amount of airflow correspondingly reduced. Not all of the airflow actually makes the right angle turn; some of simply bounces right back at the fan, causing significant back pressure and turbulence, and further reducing airflow.

The size of the 120mm fan also impinges on the amount of space available for components and for the heatsinks, which has a negative impact on cooling. All other things being equal, the smaller heatsinks required to fit with a 120mm fan make it harder to dissipate the heat.

So there are some serious design considerations for a 120mm fan PSU. Even though a 120mm fan can move more air in free space, its effectiveness inside a power supply is reduced by the impedance and back pressure inside the power supply. In fact, a well-implemented 80mm fan PSU design may produce better cooling for key components in the PSU than a 120mm fan design.


The second fan in the SmartPower 2.0 cannot not increase the maximum potential airflow ? this is limited by the surface area and airspeed of the slower of the two fans ? it does increase the pressure of the airflow. The increase in pressure still results in increased actual airflow through the unit because higher pressure can better force the air to flow around obstacles in its path.

Another benefit of an 80mm power supply is the location of the primary intake at the rear of the power supply. This probaby leads to less heat in the power supply because the intake is a bit farther away from the CPU, and most cases have an exhaust fan directly beneath the PSU to take away some of that CPU-generated heat. It is also possible to create a fresh air intake duct between the power supply and one of the top optical bay drive bays so as to keep the PSU fan speed as low as possible. This technique is almost impossible to pull off with a 120mm fan power supply.

The main benefits, then, of the Smart Power 2's push-pull dual-80mm fan design are:

  • Higher pressure than single fan allows greater effective airflow through the high impedance pathway of a PSU.
  • Straight-through airflow path means less turbulence and back pressure, and improved evacuation of heat.

There are a few disadvantages to the "flow-through" design of the SmartPower 2.0, related to the advantages:

  • The airflow around the CPU that a 120mm power supply provides must be made up with a system exhaust fan.
  • Extra care must be taken not to clutter the small intake area with spare cable sets.


There are a total of seven cable sets plus a fan RPM cable to provide fan speed information to the motherboard:

  • 12" cable for main 20+4-pin ATX connector
  • 13" auxiliary 12V connector for the CPU
  • 13" cable with a 6-pin PCI-e connector
  • 24" cable with three 4-pin IDE drive connectors
  • 24" cable with two 4-pin IDE drive connectors and one floppy drive power connector
  • 2 x 19" cables with two SATA drive connectors each
  • 21" fan RPM monitor cable

There are enough connectors for almost any system. Four SATA connectors is very generous and there is also a 6-pin PCIe connector for use with high powered video cards. Workstations are unsupported, as there is no 8-pin EPS12V connector for dual CPU motherboards. A second PCIe connector would also make SLI more convenient, although most SLI users are likely to want more power.

The main complaint with the cables is the short length, which makes cable management more difficult. It also makes the SmartPower 2.0 unsuitable for use in a case where the motherboard is mounted upside down, such as the SilverStone TJ-06, or where the power supply is not mounted in the standard position, such as the Antec P180.

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