Wattage questions?

When I built this machine 4 years ago, I used a 550W that has been working great. But now the motherboard 12v rails have dropped to about 10.6, burning out two CPUs in a row.

My questions:

1. Is the PSU failing because I should have used one with a higher output?

2. Considering the components being powered exactly the same, does a 700W PSU use more power than a 550W? Meaning, if I get a bigger PSU than I actually need, will my power bills be unnecessarily higher? And I guess chewing a bigger hole into the environment is something to keep in mind.

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  1. I'm not sure the 10.6 V reading is the explanation for your trouble, but that's not important if you've already decided to replace the PSU, anyway. To your second question, go ahead and don't worry. In general a 700 W PSU that is actually only supplying 400 W to a mobo will use only a tiny bit more power from the wall than a 500 W PSU would use IF all else is the same. But in fact some of the better larger PSU's have designs with better efficiency and that more than makes up for other small differences. Think of it this way:

    1. The spec of "700 W" is the MAXIMUM it can supply, not the actual consumption at all times.
    2. The Efficiency of a PSU (output to the mobo versus power consumed from the wall) changes only a little bit over a wide range of actual outputs; at 400 W output the efficiency is almost the same as at 650 W output.
  2. thank you. also good to know about better efficiency on higher output units. besides, i'm yet to see an improved component technology that takes less power than the one it replaces. the only way is up. 700W it is then.
  3. Paperdoc said:
    I'm not sure the 10.6 V reading is the explanation for your trouble, ...

    No, but that is way out of tolerance. You're allowed 5%. That's 11.4 to 12.6 volts. You should not have been able to boot at that level.
  4. I had another thread here dealing with the processor issue. In a nutshell, the machine stopped going into post, I tried everything else, including a new motherboard. As a last resort, I bought a used processor on ebay, and that did the trick. Three days later, the machine went dead again, putting me back exactly where I started. CPU temperatures were solid the whole time, 29 C cool and 39 C under load. Since the motherboard is new, the problem has to be the PSU (the 10.6 reading doesn't help its case).

    My new replacement CPU came yesterday so I'm putting everything back together this afternoon.
  5. just to close this thread--the problem was definitely with the PSU. ever since i changed it, the machine has been running like a song for 4 months.

    thanks to everyone who helped here.
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