Re: power supply questions

Discussion in 'Computer Information' started by Paul, May 16, 2011.

  1. Paul

    Paul Guest

    Fredd Wright wrote:
    > I have a Gateway GT5014 media center PC with a Pentium D 2.80 GHZ and 4GB of
    > RAM (although XP only recognizes 3.25GB) I also have 2 SATA hard drives and
    > an external USB hard drive. About 2 months ago, i installed a Radeon HD
    > 4350 video card so i could run a second monitor. Since then, occasionally,
    > my computer shuts down unexpectedly (maybe 3 or 4 times in the past 2
    > months). Yesterday, my computer shut down and wouldn't boot up - not even
    > with the Sytem Restore CD. I tried everything and as a last resort, yanked
    > out 2 of the memory chips. It booted so i replaced the memory.
    > Today, the computer shut down again without warning. At this point, i'm
    > thinking it's the power supply. I'm running the OEM 300W power supply. My
    > guess is either it's bad or too low for my current setup.
    > Questions are:
    > 1. How much do i need in PS wattage (i'm just looking for an estimate as i
    > realize it's hard to tell these kinds of things)? Would too much be bad?
    > If i got a 600w and the PC didnt' need it, would it matter or could i end up
    > damaging something.
    > 2. With a higher watttage power supply, would there be any cooling issues
    > or would that already be covered with a good quality psu?
    > 3. Any brand/type recommendations?
    > I'm sort of a newbie so please forgive me if these are silly questions.
    > Fredd

    An HD 4350 would use less power than a HD 4550, and you can see here,
    that number is pretty low. It's hard to believe the new video card
    is "tipping over" the supply.

    While the computer is running, I'd try Speedfan and try to get a reading
    of CPU temperature, if that is available from the hardware monitor. It
    could be that the CPU is overheating (heatsink clogged with dust or fan
    not spinning etc). The CPU has THERMTRIP, and if the CPU overheats,
    the logic signal from the processor, turns off the power supply. (a utility to display temp and voltage)


    It could also be, that the power supply is old and weak, and no longer
    able to provide the rated power on the label of the supply. A higher
    rating is OK.

    If you look on the label, it'll say something like "5V @ 20A". What
    that means, is the motherboard can draw any level of current flow
    between zero amperes DC and 20 amperes DC, and the power supply
    can deliver that. The power rating is an "up to" value. So if
    you installed a 630W supply and the internal components of the
    computer need 150W, the power supply produces exactly 150W. The
    power supply can produce any value between zero watts and "up to" 630 watts.

    Virtually every number on the label of the power supply, has a meaning.
    You can select another supply, either by matching or exceeding the
    maximum ratings on the label, or you can do a calculation of the
    power consumed by the components and develop rating numbers that

    12Va @ 18A 12Vb @ 18A
    5V @ 25A -12V @ 0.8A
    3.3V @ 25A +5VSB @ 2A

    +5V & +3.3V up to 180 watts max
    all main rails up to 288W max
    +12Va & +12Vb up to 22 amps max combined

    Now, that label tells you some things about the 12V supply. It is
    split in two pieces. One piece powers the processor. The other
    piece powers the rest of the 12V loads in the computer. The total
    may look like 36 amps, but it isn't. The supply has an upper combined
    limit of 22 amps. That means, you could load 12Va to 18A, 12Vb to 4A,
    and that would be the limit. Or load 12Va to 4A, 12Vb to 18A and again
    be at the limit. Such a rating, gives flexibility in terms of whether
    12Va or 12Vb is the one which is heavily loaded.

    The whole supply works that way - each individual DC output has a high
    rating, in case it is the one supplying most of the power. But the
    overall ratings for the whole supply are low. (In the following,
    power in watts equals volts times amps.)

    To give another example "+5V & +3.3V up to 180 watts max".
    I could load it to 5V @ 25A plus 3.3V @ 16.6A or
    I could load it to 5V @ 19.5A plus 3.3V @ 25A
    but I can't take both rails to the max at the same time.

    You can shop for a new supply, by matching those ratings.

    Now, one problem I have with those ratings, is the 25A rating on
    3.3V and 5V. More modern supplies tend to give 20A on those rails,
    and you end up buying a much larger capacity supply, to try to get
    25A as a rating. For example, I found this one.

    Now, that's too expensive a solution, and this is just intended to
    provide another label to look at.

    The advertising copy, lacks details, so we have to use a picture of
    the label. I had to use an image editor program, and adjust brightness
    and contrast in this picture, to be able to read it!$S640W$

    3.3V @ 24A \___ 130W max, which is less than the other example
    5V @ 24A /
    12V1 @ 24A \___ 576W max, 576/12=48A, so more than double the other supply
    12V2 @ 24A /
    -12V @ 0.8A \___ same ballpark
    +5VSB @ 2.5A /

    That would be close on ratings. I hope the lower rails, really aren't
    drawing 130W.

    Modern supplies put their "effort" into 12Va and 12Vb (12V1 and 12V2).
    Older supplies had more solid 3.3V and 5V, with the 12V being more of
    an afterthought. And that means, buying and matching ratings can be
    a frustrating experience.

    I have a couple dandy Enermax supplies I bought on sale within the last
    couple of years, but they don't make those models any more. Mine are
    rated at 3.3V @ 30A and 5V @ 30A and 160W combined, which is pretty good.
    I expect I could use one of those as a substitute for your old supply
    without worrying. I suspect the 130W combined is enough to do the job

    On my old P4 based system, the measured load (using a clamp-on DC ammeter)
    at the motherboard was:

    3.3V @ 14.4A, 5V @ 0.55A, 12V @ 5.6A

    and from that, the combined load on lower rails is around 50W. So
    having a combined lower rails rating of 180W is kinda overkill in
    that example. Even a combined of 130W would have been enough.
    There is a tiny bit more 5V used by storage devices, but not enough
    to change the picture drastically. The technology on your motherboard
    would be similar enough, for me to estimate your lower rails would
    be around 50W combined for 3.3V/5V rails to run the motherboard.
    Maybe 70W total for the whole computer, on lower rails.

    So something like this, with lower rails 24A and combined 130W is
    likely to be good enough. And overall wattage high enough to run
    your PC. I'd be more concerned, if the combined 3.3V/5V power rating
    dropped below 100W.

    I picked this one last example, as an extreme. What is special about
    this supply, is it is more efficient (kicks out less waste heat)
    than any other supply. But look at the lower rails. It has a
    20A rating (which would still meet my 14.4A load), but the combined
    is only 100W for 3.3V/5V. Again, this would probably work with
    your motherboard, but would not be my first choice. More run of the
    mill and less expensive supplies, would offer more loading margin
    on the lower rails. The less efficient supplies would come with
    the 130W lower rail rating.$S640W$

    And lastly, one of my favorite pictures of an ATX supply,
    demonstrating how *not* to market a supply :) One of the products
    this company makes, is rated for 500W, yet won't run a computer
    with a P4 processor in it. And that's why a proper label with
    combined ratings information is important, to make sure it really
    is the right supply. That particularly bad supply, couldn't even
    deliver 15A on 12V to run a P4. So you can't just go out and
    buy a "500W" supply and hope for the best. In some cases, the
    supply is so poorly designed, it won't run half the computers
    out there that are really only drawing 150-200W. Using the
    overall wattage rating in selecting a supply, is not enough.
    Looking at the other numbers, shows how well balanced and matched
    to the computer the supply is.

    Paul, May 16, 2011
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  2. Paul

    Paul Guest

    Fredd Wright wrote:
    >> While the computer is running, I'd try Speedfan and try to get a reading
    >> of CPU temperature, if that is available from the hardware monitor. It
    >> could be that the CPU is overheating (heatsink clogged with dust or fan
    >> not spinning etc). The CPU has THERMTRIP, and if the CPU overheats,
    >> the logic signal from the processor, turns off the power supply.

    > thanks. I installed Speedfan and the two hard drives show temps of 34C and
    > 37C but the CPU, internal and remote temp all show 0C. Does that mean that
    > the program is not configured right?
    > Fredd

    Hard drive temperature is measured by querying SMART feature set on
    the hard drive itself. The hard drive has an internal temperature
    sensor. (At least, quite a few drives do now. There have been
    cases, where the temperature of the drive never moves, and those
    are bogus. In that case, there is no physical sensor.)

    On virtually all the motherboards I have here, the SuperI/O chip
    has a Hardware Monitor interface. It measures voltages, such as
    3.3V, 5V, 12V, and measures motherboard temperature (via a thermistor),
    CPU temperature (diode method, via a diode on the substrate of the
    CPU silicon). It also measures fan speeds on anywhere from three to
    five fans.

    Since yours read zero, you should go back and look at the detection
    process Speedfan is using, and see if the log shows it has actually
    located a hardware monitoring device of some kind. I think you could be
    right, in that it isn't configured correctly. If you check
    the site, there are some tables of systems and comments
    from users. But it might not be enough to tell you what is going on.

    A second alternative, for an older system, is MBM5 (motherboard
    monitor version five). Years ago, the developer gave up on it,
    but you could still download it for a year or more afterwards.
    It requires a bit more "adjustment" by the user than Speedfan.
    But conversely, it might be easier to fix than Speedfan. If
    you can find a copy, you can give that a try.

    OK, so the program is here.

    The developer site used to be here, but a cybersquatter uses this now.
    Don't bother clicking this. I tried to find an archive of the table
    here ("mobolist"), but it isn't on . It has information on
    which sensor display is which.

    There is another one here, but I haven't tried this yet. I
    use the CPU-Z program from this site, quite a lot, and have
    tried many different versions of that. This developer does
    good work, and who knows, maybe this will work for you.

    Writing those programs is a thankless job. At one time,
    it required custom tables for every motherboard, and if
    you're doing this as a hobby, doing 10,000 of those
    would suck big time. It would only be "fun" for the first
    couple hundred.

    I got the vague impression, that the BIOS has some way of
    indicating the scale factors for the sensors. So maybe there
    is some way on the more modern boards, for the program to
    ferret out the details without human intervention. A good deal
    of this, the respective developers keep to themselves, because
    some day, they may wish to sell a library for accessing
    hardware measurements, to other developers.

    A few motherboard manufacturers provide their own utilities.
    Asus has Asus Probe. Abit may have had uGuru (with their own
    hardware solution). But I've really stopped investigating those,
    because they're nothing to write home about. Sometimes,
    developers are too intent on "making a nice skin" and forget
    what the program is for :)

    Paul, May 16, 2011
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