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1 computer, 2 PSUs - feasible?
Is it possible to use two cheap low-power PSUs instead of a
single premium unit? Even in the remote area where I live, computers have become an essential part of everyday life, but many computer owners have had to dig deep into their savings to buy an entry-level machine. They either don't know about PSU quality and actual capacity, or can ill afford to spend that extra $50-150 for a good PSU. It's hard to blame them as I've personally known literally hundreds of $10 PSUs last for years. (The $ here meaning the equivalent in US currency). There's nothing available in between the $10 types and the $50 models. Forget about build quality and load regulation, etc. for the time being. Is it at all feasible to use one cheap PSU for, say, a power-hungry graphics card and another one for the rest of the system? What about these factors - 1. Syncing. It shouldn't be hard to make a simple adaptor to switch two PSUs from the same motherboard. But there may be a difference of a fraction of a second in the times taken by the two PSUs to power up and power down. 2. Partial PSU breakdown. If one PSU breaks down while the other is still operating, could that cause damage to the rest of the system? |
#2
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1 computer, 2 PSUs - feasible?
"pawihte" wrote in message ... Is it possible to use two cheap low-power PSUs instead of a single premium unit? Even in the remote area where I live, computers have become an essential part of everyday life, but many computer owners have had to dig deep into their savings to buy an entry-level machine. They either don't know about PSU quality and actual capacity, or can ill afford to spend that extra $50-150 for a good PSU. It's hard to blame them as I've personally known literally hundreds of $10 PSUs last for years. (The $ here meaning the equivalent in US currency). There's nothing available in between the $10 types and the $50 models. Forget about build quality and load regulation, etc. for the time being. Is it at all feasible to use one cheap PSU for, say, a power-hungry graphics card and another one for the rest of the system? What about these factors - 1. Syncing. It shouldn't be hard to make a simple adaptor to switch two PSUs from the same motherboard. But there may be a difference of a fraction of a second in the times taken by the two PSUs to power up and power down. 2. Partial PSU breakdown. If one PSU breaks down while the other is still operating, could that cause damage to the rest of the system? Feasible? Of Course. Practical? Not Really - for both technical and non-technical reasons Sensible? Definitely Not Just work out what power your PC will need and get a no-frills PSU to suit. PA |
#3
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1 computer, 2 PSUs - feasible?
On 08/18/2010 12:48 PM, pawihte wrote:
Is it possible to use two cheap low-power PSUs instead of a single premium unit? Even in the remote area where I live, computers have become an essential part of everyday life, but many computer owners have had to dig deep into their savings to buy an entry-level machine. They either don't know about PSU quality and actual capacity, or can ill afford to spend that extra $50-150 for a good PSU. It's hard to blame them as I've personally known literally hundreds of $10 PSUs last for years. (The $ here meaning the equivalent in US currency). There's nothing available in between the $10 types and the$50 models. Forget about build quality and load regulation, etc. for the time being. Is it at all feasible to use one cheap PSU for, say, a power-hungry graphics card and another one for the rest of the system? What about these factors - 1. Syncing. It shouldn't be hard to make a simple adaptor to switch two PSUs from the same motherboard. But there may be a difference of a fraction of a second in the times taken by the two PSUs to power up and power down. 2. Partial PSU breakdown. If one PSU breaks down while the other is still operating, could that cause damage to the rest of the system? There are some servers specifically built with redundant PSU capabilities... but what you wish to do is not terribly practical. You'd be best off just to get a *single* good quality supply. What you propose is of course possible however and you could supply the aux. power to your graphics card and HD's and or DVD's from a second supply... but I don't recommend doing so |
#4
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1 computer, 2 PSUs - feasible?
pawihte wrote:
Is it possible to use two cheap low-power PSUs instead of a single premium unit? Even in the remote area where I live, computers have become an essential part of everyday life, but many computer owners have had to dig deep into their savings to buy an entry-level machine. They either don't know about PSU quality and actual capacity, or can ill afford to spend that extra $50-150 for a good PSU. It's hard to blame them as I've personally known literally hundreds of $10 PSUs last for years. (The $ here meaning the equivalent in US currency). There's nothing available in between the $10 types and the $50 models. Forget about build quality and load regulation, etc. for the time being. Is it at all feasible to use one cheap PSU for, say, a power-hungry graphics card and another one for the rest of the system? What about these factors - 1. Syncing. It shouldn't be hard to make a simple adaptor to switch two PSUs from the same motherboard. But there may be a difference of a fraction of a second in the times taken by the two PSUs to power up and power down. 2. Partial PSU breakdown. If one PSU breaks down while the other is still operating, could that cause damage to the rest of the system? Find a copy of the latest ATX spec from formfactors.org (in the Specifications and Guides section). PS_ON# is an input, and is wired-OR type. It has a pullup, and a driving device pulls down with an open collector. If you join two power supplies together, you'd put their PS_ON# signals in parallel. The motherboard would then end up driving the pullup resistors on both PSUs, which is twice the load. PWK_OK is an active high output from the supply. The ATX spec doesn't specify it is wire-OR logic with open collector drive (which is essential for safely tying together a set of outputs without damaged). At least, I couldn't see that suggested there. The specification also seems to be worded, as if they expect you to tie a pulldown to the circuit (to guarantee PWR_OK is logic 0 when the power supply is not working at all). And that suggests totem-pole drive, with an external resistor pulldown to guarantee logic 0 when the supply is off. If I look at the schematic on this site, it looks like PWR_OK comes from an LM393 comparator, with a 680 ohm pullup, so this supply happens to implement it in such a way, that it can be tied together to another supply. This design fails to include the 1K to common, to force the output to logic 0 when the supply is off. Again, there is the issue, that the LM393 would be driving 5V/340 ohms = 15ma. The datasheet doesn't suggest it works that well at high current (poor logic 0). http://www.pavouk.org/hw/en_atxps.html http://www.national.com/ds/LM/LM193.pdf The DC output characteristic of the ATX supply, is a voltage source, and it is a "push-only" design. It is not "push-pull". For example, if you short the 5V rail to the 3.3V rail, the 3.3V rail would be lifted, and the power supply would not actively fight it. If the supply had OVP (and not all of them do), the supply would shut off once the 3.3V went too far out of spec. But the supply doesn't actively pull down on that rail, to try to bring it back into spec. Since the power supply is a voltage source, you can't tie it in parallel with another supply. You would get current hogging if you did (effectively, one supply can take all the load, while the other one just sits there). The outputs can be kept independent from one another, and be used to power things known to be independent inside the computer. (Redundant power supplies, have a different output design, and do current sharing, so are safe to connect in parallel. The designers know in advance, that the supplies will be paralleled. When both supplies are present, they each deliver 50% of the current, plus/minus about one percent.) The ATX12V used by the motherboard, is independent (except on some Biostar motherboards, where it was discovered their motherboards would run with only the main power connector in place). The PCI Express external connectors (2x3, 2x4) are supposed to be independent as well. Those are examples of things you could power. The independent things, all seem to be using 12V. (Independence of PCI Express rails is on page 9.) http://www.pcisig.com/developers/mai...c6 65ac770768 An example of a power supply designed to operate as a "second supply", is the Fortron Booster. It senses the presence of 12V, and enables its 12V output milliseconds later. The 12V it produces, is suitable for independent load inputs. It does not tie into PWR_OK, neither does it use PS_ON# for control purposes. The wiring provided, is for powering the PCI Express auxiliary connectors on a pair of video cards. So if you had some 150W video cards, you might run two of them off that thing (leaving a little capacity left over). If the unit failed, it could potentially remain on, while the other supply is off. But PCI Express video cards, as far as I know, are supposed to be able to take it. http://www.newegg.com/Product/Produc...82E16817104054 It may be acceptable to try your experiment on your own home rig, but if you do it on a paying customer's machine, remember you're responsible for the insurance liability. If someone's house burns down because of some fault with the two supplies, there will be a knock at the door, and some lawyers to answer to. The only thing that should go into a customer machine, is approved circuit configurations. Where you can claim, "everything I've done is standard industry practice". Then, if they want to sue someone, it'll be the power supply manufacturer. One other small benefit of the $50 supply, is the potential for it to be 80% efficient, versus the 68% efficiency of the $10 supply. Over the years, that will give enough savings on the power bill, to pay for the $50 supply. So it isn't all bad. 80% efficient supply for $45 http://www.newegg.com/Product/Produc...82E16817371033 Paul |
#5
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1 computer, 2 PSUs - feasible?
Paul wrote:
pawihte wrote: Is it possible to use two cheap low-power PSUs instead of a single premium unit? Even in the remote area where I live, computers have become an essential part of everyday life, but many computer owners have had to dig deep into their savings to buy an entry-level machine. They either don't know about PSU quality and actual capacity, or can ill afford to spend that extra $50-150 for a good PSU. It's hard to blame them as I've personally known literally hundreds of $10 PSUs last for years. (The $ here meaning the equivalent in US currency). There's nothing available in between the $10 types and the $50 models. Forget about build quality and load regulation, etc. for the time being. Is it at all feasible to use one cheap PSU for, say, a power-hungry graphics card and another one for the rest of the system? What about these factors - 1. Syncing. It shouldn't be hard to make a simple adaptor to switch two PSUs from the same motherboard. But there may be a difference of a fraction of a second in the times taken by the two PSUs to power up and power down. 2. Partial PSU breakdown. If one PSU breaks down while the other is still operating, could that cause damage to the rest of the system? Find a copy of the latest ATX spec from formfactors.org (in the Specifications and Guides section). PS_ON# is an input, and is wired-OR type. It has a pullup, and a driving device pulls down with an open collector. If you join two power supplies together, you'd put their PS_ON# signals in parallel. The motherboard would then end up driving the pullup resistors on both PSUs, which is twice the load. PWK_OK is an active high output from the supply. The ATX spec doesn't specify it is wire-OR logic with open collector drive (which is essential for safely tying together a set of outputs without damaged). At least, I couldn't see that suggested there. The specification also seems to be worded, as if they expect you to tie a pulldown to the circuit (to guarantee PWR_OK is logic 0 when the power supply is not working at all). And that suggests totem-pole drive, with an external resistor pulldown to guarantee logic 0 when the supply is off. If I look at the schematic on this site, it looks like PWR_OK comes from an LM393 comparator, with a 680 ohm pullup, so this supply happens to implement it in such a way, that it can be tied together to another supply. This design fails to include the 1K to common, to force the output to logic 0 when the supply is off. Again, there is the issue, that the LM393 would be driving 5V/340 ohms = 15ma. The datasheet doesn't suggest it works that well at high current (poor logic 0). http://www.pavouk.org/hw/en_atxps.html http://www.national.com/ds/LM/LM193.pdf The DC output characteristic of the ATX supply, is a voltage source, and it is a "push-only" design. It is not "push-pull". For example, if you short the 5V rail to the 3.3V rail, the 3.3V rail would be lifted, and the power supply would not actively fight it. If the supply had OVP (and not all of them do), the supply would shut off once the 3.3V went too far out of spec. But the supply doesn't actively pull down on that rail, to try to bring it back into spec. Since the power supply is a voltage source, you can't tie it in parallel with another supply. You would get current hogging if you did (effectively, one supply can take all the load, while the other one just sits there). The outputs can be kept independent from one another, and be used to power things known to be independent inside the computer. (Redundant power supplies, have a different output design, and do current sharing, so are safe to connect in parallel. The designers know in advance, that the supplies will be paralleled. When both supplies are present, they each deliver 50% of the current, plus/minus about one percent.) The ATX12V used by the motherboard, is independent (except on some Biostar motherboards, where it was discovered their motherboards would run with only the main power connector in place). The PCI Express external connectors (2x3, 2x4) are supposed to be independent as well. Those are examples of things you could power. The independent things, all seem to be using 12V. (Independence of PCI Express rails is on page 9.) http://www.pcisig.com/developers/mai...c6 65ac770768 An example of a power supply designed to operate as a "second supply", is the Fortron Booster. It senses the presence of 12V, and enables its 12V output milliseconds later. The 12V it produces, is suitable for independent load inputs. It does not tie into PWR_OK, neither does it use PS_ON# for control purposes. The wiring provided, is for powering the PCI Express auxiliary connectors on a pair of video cards. So if you had some 150W video cards, you might run two of them off that thing (leaving a little capacity left over). If the unit failed, it could potentially remain on, while the other supply is off. But PCI Express video cards, as far as I know, are supposed to be able to take it. http://www.newegg.com/Product/Produc...82E16817104054 It may be acceptable to try your experiment on your own home rig, but if you do it on a paying customer's machine, remember you're responsible for the insurance liability. If someone's house burns down because of some fault with the two supplies, there will be a knock at the door, and some lawyers to answer to. The only thing that should go into a customer machine, is approved circuit configurations. Where you can claim, "everything I've done is standard industry practice". Then, if they want to sue someone, it'll be the power supply manufacturer. One other small benefit of the $50 supply, is the potential for it to be 80% efficient, versus the 68% efficiency of the $10 supply. Over the years, that will give enough savings on the power bill, to pay for the $50 supply. So it isn't all bad. 80% efficient supply for $45 http://www.newegg.com/Product/Produc...82E16817371033 Paul Thanks, Paul. I've been down with a severe case of the flu for 3 days now. Still don't have the energy to go through the points you raised and continue the discussion. Will be back later. |
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