Chapter 7. PSU
There are several important factors to consider when selecting a power supply unit: total power output, +12V line output (combined), quality and efficiency, quietness.Total power output
First you should calculate the total power consumption of your system by using, for example, eXtreme PSU Calculator
. A typical maximum power consumption of each component is:
- CPU: 65W (TDP, thermal design power, of Athlon 64 X2 Brisbane core or Core 2 Duo)
- DDR2 DIMM: 5W
- Motherboard: 40W
- GeForce 7600 GT: 36W (peak 3D), 23W (peak 2D), 15W (idle)
- GeForce 8600 GTS: 47W (peak 3D), 31W (peak 2D), 21W (idle)
- GeForce 8800 GTS 320MB: 103W (peak 3D), 69W (peak 2D), 56W (idle)
- DVD drive: 30W
- SATA drive: 12W
- PCI TV tuner card: 30W (ATI Theater 550 Pro)
- PCI TV tuner card: 44W (NVIDIA DualTV MCE)
- PCI sound card: 10W
- 80mm fan: 2W
For example, if the system consists of 1 x GeForce 8600 GTS card, 2 x DDR2 SDRAM, 1 x DVD drive, 2 x SATA drive, 1 x PCI TV tuner card and 2 x fan, the maximum power consumption is ~245W. This number is obtained simply by adding the maximum power rating for each components. However it is almost impossible for any application to draw, say, 80% of the maximum power from each component simultaneously. Therefore a typical power consumption of such a system when playing back movies are 100W~200W
and a 430W PSU is enough if the PSU is rated honestly.Total power output of an overclocked system
When you overclock the CPU, its power consumption is calculated by the following forumula:
- Power Consumption = Cdynamic x V^2 x Frequency
is a constant dynamic capacity that is determined by the CPU microarchitecture and depends on the number of transistors and their activity during CPU operation (source: Intel Developer Forum; cf. X-bit labs - Getting Ready to Meet Intel Core 2 Duo
), V is the applied voltage, and Frequency is the operating frequency of the CPU. The factor V^2 is just Ohm's law. The factor "Frequency" is due to the so-called switching loss
- the amount of heat emitted from a transistor when it goes from one state to the other (at the order of 10^(-16) joule). Each transistor in the CPU would emit 1 x 10^9 times that amount of heat per second if the CPU frequency were 1GHz and 2 x 10^9 times that amount if the CPU frequency were 2GHz. Thus the total amount of heat is proportional to the frequency.
For example, if you overclock Core 2 Duo E6600 (2.4GHz, 1.25V, 65W) to 3.2GHz with vcore 1.45V, then the power consumption is calculated as follows:
65W x (1.45/1.25)^2 x (3.2/2.4) = 117WQuietness and efficiency
Quietness is one of the essential factors in selecting PSU for a HTPC and higher efficiency is the key to cooler, quieter PSU operation. There are many "quiet" PSU's, but only a few of them are truly quiet. In the following recommendations, I cited efficiency and noise levels measured by Silent PC Review. Please read the SPCR articles in the reference section for their meanings.
- Corsair HX520W
- Specs: 520W, +12V: 40A, 81% & 22dBA@150W, 85% & 22dBA@300W, modular sleeved cables, dual-GPU ready
- Price: ~$105
- Notes: This is simply the best PSU. 620W version is also available.
- Seasonic S12 Energy+550
- Specs: 550W, +12V: 41A, 82% & 20dBA@150W, 84% & 25dBA@300W, sleeved cables, dual-GPU ready
- Price: ~$130
- Notes: 650W version is also available.
- Antec NeoHE 430
- Specs: 430W, +12V: 32A, 79% & 21dBA@150W, 76% & 37dBA@300W, modular sleeved cables
- Price: ~$70
- Notes: 380W, 430W, 500W, 550W versions are available. Super quiet at low power consumption.
- Seasonic S12-430
- Specs: 430W, +12V: 29A, 79% & 22dBA@150W, 80% & 32dBA@300W, sleeved cables
- Price: ~$90
- Notes: 330W, 380W, 430W, 500W, 600W versions are available.
- Antec EarthWatts EA 430
- Specs: 430W, +12V: 30A, 81% & 22dBA@150W, 82% & 37dBA@300W
- Price: ~$60
- Notes: The best budget quiet & efficient PSU. 380W, 430W, 500W versions are available. Performance is akin to NeoHE.