- Jun 11, 2004
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I found an excellent example of why 1 single 12v rail is superior to multiple rails.
Here's a quote from PC Power & Cooling's website:
Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply?s rating. Those losses occur because power literally gets ?trapped? on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.
Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete. [/i]
---Makes perfect sense to me.
So basically a lesson we can take from this is that if we are using multiple rail power supplies the best thing we can do is spread components out across all rails. If all rails on a multiple rail psu are thoughtfully spread across a system this argument could be rendered void however I know there are a great many people who haven't taken this into consideration and even purposefully use as few rails as possible in order to minimize cable clutter.
Here's a quote from PC Power & Cooling's website:
Here are the facts: A large, single 12-volt rail (without a 240VA limit) can transfer 100% of the 12-volt output from the PSU to the computer, while a multi-rail 12-volt design has distribution losses of up to 30% of the power supply?s rating. Those losses occur because power literally gets ?trapped? on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.
Since the maximum current from any one 12-volt rail of a multiple-rail PSU is limited to 20 amps (240VA / 12 volts = 20 amps), PCs with high-performance components that draw over 20 amps from the same rail are subject to over-current shutdowns. With power requirements for multiple processors and graphics cards continuing to grow, the multiple-rail design, with its 240VA limit per rail, is basically obsolete. [/i]
---Makes perfect sense to me.
So basically a lesson we can take from this is that if we are using multiple rail power supplies the best thing we can do is spread components out across all rails. If all rails on a multiple rail psu are thoughtfully spread across a system this argument could be rendered void however I know there are a great many people who haven't taken this into consideration and even purposefully use as few rails as possible in order to minimize cable clutter.