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Question about PSU's
I bought a new bare-bones system some two months ago, and have blown
two new 400W PSU's now. I think I need to go for a stronger PSU. I notice my M3A78-CM motherboard has a larger so-called 4PX20 connection plus another separate 4P square connection. I pulled one of my old PSU's out of the close that has just a 20pin connector and the separate 4P. I connected it to the motherboard and things are running fine. So I guess I can go with this until I get a new PSU. But I have two questions. 1) What calamity am I apt to suffer because I have left the one 4P connector (on the 4PX20) open? 2) What spec do I look for as I shop for a replacement stronger (say, 600W) PSU? I want to be sure the new PSU has both the 4P connectors. Thanks Duke |
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Question about PSU's
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Question about PSU's
wrote:
I bought a new bare-bones system some two months ago, and have blown two new 400W PSU's now. I think I need to go for a stronger PSU. I notice my M3A78-CM motherboard has a larger so-called 4PX20 connection plus another separate 4P square connection. I pulled one of my old PSU's out of the close that has just a 20pin connector and the separate 4P. I connected it to the motherboard and things are running fine. So I guess I can go with this until I get a new PSU. But I have two questions. 1) What calamity am I apt to suffer because I have left the one 4P connector (on the 4PX20) open? 2) What spec do I look for as I shop for a replacement stronger (say, 600W) PSU? I want to be sure the new PSU has both the 4P connectors. Thanks Duke When I look at the picture here, I see a 24 pin main connector, and a 2x2 ATX12V connector for processor power. http://ae.asus.com/999/images/products/2341/2341_l.jpg The four pins on the end of a 24 pin connector, have four different colored wires. The wires carry redundant 3.3V, 5V, 12V1, and GND. http://www.formfactors.org/developer...public_br2.pdf What purpose do redundant wires serve ? They increase the ampacity of the interconnect. Each pin of the connector, can safely handle 6 amps of current flow (the exact number may depend on the gauge of wire leading to the pin). There are five red wires in the 24 pin wiring harness, which all carry +5V. 5 wires times 6 amps each, gives 30 amps maximum that the motherboard could draw, without burning the connector. In practice, a motherboard designer would likely try to avoid going all the way to 30A, since the current sharing in a motherboard isn't perfect. (Some pins carry more current than others. One motherboard I checked, the spread is +/- 1 amp.) The most important pin of the new ones, is the extra 12V1 pin. Since the 24 pin connector now has two wires carrying 12V1, up to 12A can be drawn from that rail. On your motherboard, there is one video card slot, and the most slot power I've heard of in a video card slot, was a load of 4.35A. So 4.35 amps doesn't exceed the single wire on a 20 pin connector. There could be an issue if two video cards were present, as 2*4.35 = 8.7A, and then you would benefit from the use of a 24 pin connector. ******* In terms of power supply shorting, there are a couple cases to consider. The motherboard could have a (partial) short, between a rail and ground. That would strain the power supply, and bring it close to its limits, causing it to heat up internally. Or, if the overcurrent detection in the supply was actually working, it might shut off the supply, at about 30% over its rating. A second kind of fault, would be rail to rail. Say the +5V rail on the motherboard, had a partial short to 3.3V. Current from +5V would flow into the 3.3V rail. The ATX power supply is not "push-pull" and has no way to compensate for that. The 3.3V rail voltage will rise, the feedback system will hit the wall, the supply will make its maximum possible correction to the disturbance, but the 3.3V will still be rising. If the power supply is well equipped, it will have OVP. The supply will shut off, if the 3.3V rises high enough. If it doesn't have OVP, then perhaps the motherboard components will be fried by the out of spec voltage. ******* When a motherboard pops two supplies, either the calculation of required power is wrong, or the system is drawing more power than it should be. To check that, you can use a clamp-on DC ammeter. (I have the 380947, in this document.) http://www.extech.com/instrument/pro...41_942_947.pdf To use it, I place the five red wires in the ATX power supply bundle, all within the jaws of the meter. Set the meter to 40A DC max range, then take a measurement. The meter sums the magnetic field around the five wires, so is able to measure the combined current flow. In that way, I can determine whether the loading is "normal" or not. If I take the meter, and clamp it around an AC cord, it reads zero, because the magnetic field around the two power carrying conductors cancels. To measure AC power, you need a "cheater" cord, where the outer insulation of the cord is removed, leaving the three insulated wires inside loose. By grabbing the hot wire, and clamping around that, it is possible to make an AC measurement. I have a couple cheater cords I made myself, as I'm too cheap to buy one from the meter company. I've also used that meter to work on the car. When my car was having trouble starting on a cold morning, I used that meter to measure the peak current consumed, and it measured 150A on the 400A DC scale. So the meter can be used for more than just motherboards. I also use it for checking the current draw on the central air conditioner. (The fan on my central air, draws twice the rated current, and some day, it is going to burn out.) Is it worth investing money in a specialized meter like that ? Probably not. But it does have the advantage, of allowing a "non-contact" method of measuring current. No fuses to pop, no accidents. Inside the device, is a Hall probe, which is what converts the magnetic field into a voltage. The jaw design is a flux concentrator, that helps the device only measure the magnetic field encircled by the jaws. Fields outside the jaws are ignored. http://en.wikipedia.org/wiki/Hall_probe To make a current measurement with a conventional multimeter, would require 1) Measure individual wires, one at a time, due to the 10 amp limit of the highest range on a cheap multimeter. 2) Purchase a 24 pin to 24 pin extension cable, and chop each wire in two, then insert the multimeter between the two ends, then turn on the computer and make a measurement, while the computer is running your favorite test case (Prime95 perhaps). So it is possible to make some measurements, but by measuring the individual wires, there could be additional measurement error. And with that many wires, I'd probably buy crimp terminals and a terminal block, to make it easier to manage all the cut ends of the wires. To measure currents over 10 amps, you can make your own shunt out of manganin wire. You have to set the shunt resistance low enough, such that the manganin doesn't get too hot. Manganin is selected for its low temperature coefficient of resistance, which is why it would be preferably to using some nichrome wire scavenged from your toaster. http://en.wikipedia.org/wiki/Manganin A Hall probe based meter, avoids some of those issues, and makes it much quicker to measure system power consumption on a per rail basis. Paul |
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Question about PSU's
"Paul" wrote in message ... When I look at the picture here, I see a 24 pin main connector, and a 2x2 ATX12V connector for processor power. http://ae.asus.com/999/images/products/2341/2341_l.jpg The four pins on the end of a 24 pin connector, have four different colored wires. The wires carry redundant 3.3V, 5V, 12V1, and GND. http://www.formfactors.org/developer...public_br2.pdf What purpose do redundant wires serve ? They increase the ampacity of the interconnect. Each pin of the connector, can safely handle 6 amps of current flow (the exact number may depend on the gauge of wire leading to the pin). There are five red wires in the 24 pin wiring harness, which all carry +5V. 5 wires times 6 amps each, gives 30 amps maximum that the motherboard could draw, without burning the connector. In practice, a motherboard designer would likely try to avoid going all the way to 30A, since the current sharing in a motherboard isn't perfect. (Some pins carry more current than others. One motherboard I checked, the spread is +/- 1 amp.) The most important pin of the new ones, is the extra 12V1 pin. Since the 24 pin connector now has two wires carrying 12V1, up to 12A can be drawn from that rail. On your motherboard, there is one video card slot, and the most slot power I've heard of in a video card slot, was a load of 4.35A. So 4.35 amps doesn't exceed the single wire on a 20 pin connector. There could be an issue if two video cards were present, as 2*4.35 = 8.7A, and then you would benefit from the use of a 24 pin connector. ******* In terms of power supply shorting, there are a couple cases to consider. The motherboard could have a (partial) short, between a rail and ground. That would strain the power supply, and bring it close to its limits, causing it to heat up internally. Or, if the overcurrent detection in the supply was actually working, it might shut off the supply, at about 30% over its rating. A second kind of fault, would be rail to rail. Say the +5V rail on the motherboard, had a partial short to 3.3V. Current from +5V would flow into the 3.3V rail. The ATX power supply is not "push-pull" and has no way to compensate for that. The 3.3V rail voltage will rise, the feedback system will hit the wall, the supply will make its maximum possible correction to the disturbance, but the 3.3V will still be rising. If the power supply is well equipped, it will have OVP. The supply will shut off, if the 3.3V rises high enough. If it doesn't have OVP, then perhaps the motherboard components will be fried by the out of spec voltage. ******* When a motherboard pops two supplies, either the calculation of required power is wrong, or the system is drawing more power than it should be. To check that, you can use a clamp-on DC ammeter. (I have the 380947, in this document.) http://www.extech.com/instrument/pro...41_942_947.pdf To use it, I place the five red wires in the ATX power supply bundle, all within the jaws of the meter. Set the meter to 40A DC max range, then take a measurement. The meter sums the magnetic field around the five wires, so is able to measure the combined current flow. In that way, I can determine whether the loading is "normal" or not. If I take the meter, and clamp it around an AC cord, it reads zero, because the magnetic field around the two power carrying conductors cancels. To measure AC power, you need a "cheater" cord, where the outer insulation of the cord is removed, leaving the three insulated wires inside loose. By grabbing the hot wire, and clamping around that, it is possible to make an AC measurement. I have a couple cheater cords I made myself, as I'm too cheap to buy one from the meter company. I've also used that meter to work on the car. When my car was having trouble starting on a cold morning, I used that meter to measure the peak current consumed, and it measured 150A on the 400A DC scale. So the meter can be used for more than just motherboards. I also use it for checking the current draw on the central air conditioner. (The fan on my central air, draws twice the rated current, and some day, it is going to burn out.) Is it worth investing money in a specialized meter like that ? Probably not. But it does have the advantage, of allowing a "non-contact" method of measuring current. No fuses to pop, no accidents. Inside the device, is a Hall probe, which is what converts the magnetic field into a voltage. The jaw design is a flux concentrator, that helps the device only measure the magnetic field encircled by the jaws. Fields outside the jaws are ignored. http://en.wikipedia.org/wiki/Hall_probe To make a current measurement with a conventional multimeter, would require 1) Measure individual wires, one at a time, due to the 10 amp limit of the highest range on a cheap multimeter. 2) Purchase a 24 pin to 24 pin extension cable, and chop each wire in two, then insert the multimeter between the two ends, then turn on the computer and make a measurement, while the computer is running your favorite test case (Prime95 perhaps). So it is possible to make some measurements, but by measuring the individual wires, there could be additional measurement error. And with that many wires, I'd probably buy crimp terminals and a terminal block, to make it easier to manage all the cut ends of the wires. To measure currents over 10 amps, you can make your own shunt out of manganin wire. You have to set the shunt resistance low enough, such that the manganin doesn't get too hot. Manganin is selected for its low temperature coefficient of resistance, which is why it would be preferably to using some nichrome wire scavenged from your toaster. http://en.wikipedia.org/wiki/Manganin A Hall probe based meter, avoids some of those issues, and makes it much quicker to measure system power consumption on a per rail basis. Now *THAT* is how to answer a posted question. Well done, Paul! |
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Question about PSU's
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#6
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Question about PSU's
On Sat, 02 May 2009 11:55:38 -0400, kony
wrote: But I have two questions. 1) What calamity am I apt to suffer because I have left the one 4P connector (on the 4PX20) open? None usually, a conservative 6A per connector pin estimate and two pins for 12V and two for ground will allow 12A * 12V, 144W which you can multiply by the typical CPU VRM power circuit efficiency of roughly 93% to arrive at 0.93* 144 = 134. So long as your CPU's max rated power is 134W or less, and/or if you overclock it you stay below 134W, and assuming the power supply contacts and mating socket are in good condition, there is no need to use more than a 2x2, 4 pin plug with that. I probably misread what you wrote, ignore the above reply but the situation is similar, that a typical system with the board you have will not need the extra current a 24 pin plug offers over a 20 pin plug. The extra 4 pins are redundant to decrease resistance through more supply lines and connector pins for systems that need more than average current while a system with typical components and an efficient motherboard like yours will use less current than a typical system that runs fine off a 20 pin connected PSU. |
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Question about PSU's
On Sat, 02 May 2009 08:47:45 -0500, philo wrote:
What brand were the ones that blew? Not all brands are equal...avoid the cheapie off brand types OKIA 450ATX |
#8
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Question about PSU's
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