what power supply to buy

Discussion in 'Computer Information' started by Travis, Mar 19, 2009.

  1. Travis

    Travis Guest


    My current Dell computer has a 250 watt power supply in it, and I
    think that that is not providing enough power to run my 2 hard drives
    and 2 DVD drives and 4 PCI cards, not to mention 6 USB energy requring

    I'm looking at new power supplies on tigerdirect but am unsure of what
    wattage to get, I don't want to buy something that is still
    underpowered but dont' want to buy something that is redundant if I'll
    never use 1000Watts.

    Also if I buy a higher wattage power supply, it doesn't necessarily
    draw that much power when it's running, only when it needs it? Would
    putting a 1000watt PSU in this computer that originally had 250 mean
    my energy bill will go up 4 times?
    Travis, Mar 19, 2009
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  2. Travis

    Paul Guest

    Your first problem, is whether the Dell uses a standard power
    supply or not. Recent Dells probably do. But there are
    probably some older ones that do not. You can either examine the
    wiring harness colors, to get some idea, or just buy the
    supply from a company that can assure you it is compatible.
    (PCPower seems to be discontinuing some of their models.)


    To calculate how much power to provide, you need to know the
    processor being used, the video card (either integrated into
    the motherboard, or a separate plug-in card), with the other
    loads being secondary.

    A hard drive is 12W. The optical drive might be 20-25W,
    but only with media spinning at high speed in it, and
    in the middle of doing a burn. (My optical is 17W, measured.)
    PCI cards are usually a small number of watts, and 1W to 3W
    is probably plenty to account for the average card. USB devices
    can draw 5V @ 0.5A max or a total of 2.5W. Things like your USB
    mouse would be 0.5W or so. There is no reason for a keyboard
    to draw a lot of power, so maybe another 0.5W or less.

    In summary, the current supply may be plenty. But I
    cannot say for sure, because I don't know the
    processor (35W up to 144W) or the video card (12W up to
    265W or so). The details are important to the determination.
    We know the processor and video cannot be more than 250W total,
    because the company puts enough power supply to run them. It's
    a matter of figuring out, whatever extra loads you've added,
    have pushed the total load over the limit.

    Since some Dell models have hardware options, if you
    do post back details, include all the hardware you
    know about or can figure out. Using the model number
    alone, it may not be possible to work out exactly
    what is in the box. A model could have integrated
    (motherboard) video, but also include a low end
    AGP or PCI Express video card.

    Paul, Mar 19, 2009
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  3. Travis

    trav10854 Guest

    I have a Dell Dimension 1100. Not sure of the exact manufacture year,
    but I think it is 2005 or 2006, as it is an older system. Here are the
    rest of the specs

    Intel Celeron D 2.8Ghz Processor
    nVidia GeForce FX 5500 PCI graphics card (256MB Video RAM)
    Hauppauge WinTV Tuner
    Western Digital WD5000AVJB 500GB Harddrive (EIDE)
    Seagate Barracuda ST380011A 80GB Harddrive (EIDE)
    512MB DDR RAM
    Integrated SoundMAX Audio
    3.5" Floppy Drive

    The reason I think I am having trouble with my power supply is because
    occasionally USB devices will malfunction when there are too many
    connected. (There are 6 available ports, I generally have 4/6 in use
    but if I plug in a fifth it will begin to cause problems).

    I do believe this computer is of the MicroATX form factor?

    Thank you for your reply.
    trav10854, Mar 19, 2009
  4. Travis

    gnu / linux Guest

    how about a powered USB hub ?
    gnu / linux, Mar 20, 2009
  5. Travis

    Paul Guest


    3.3V @ 18A, 5V @ 22A, 12V @ 16A, -12V # 1A, +5VSB @ 2.0A
    <---- 150W max ---->
    <------------------------- 250W ----------------------->

    The P4 connector in the Dell diagram is non standard. It is a
    2x3 connector with NC,COM,COM,3.3,5,12V on it. Regular ATX supplies
    don't have that. And I don't see a spot on the motherboard where
    that plugs in. If it is not being used for anything, then the
    rest of the connectors are standard, so a standard supply could
    replace it. If the 2x3 connector is plugged into something, then
    it would be interesting to understand why that connector is
    necessary. (The signal names on the 2x3 suggest power for a
    SATA drive, but the connector is the wrong shape. Are they using
    an adapter cable ?)

    From an Ebay advert for a Dimension 1100 motherboard I get

    microATX 9.60 x 8.20 inches (I see three PCI slots in the picture)
    Pentium 4 processor S478 FSB400/533/800
    Celeron D processor S478 FSB400/533 <--- yours could be 2.8Ghz/FSB533
    Two 184-pin DDR DIMM sockets (DDR 400/333/266)
    Intel 865GV Chipset (means no AGP slot, integrated graphics available)
    On Board 3D Stereo Sound Card

    Your processor is 73W at the socket. With 90% efficient Vcore
    conversion, that is 73/0.9 = 81W at the 2x2 power connector.
    That comes from the 12V rail (via the 2x2 connector), so would
    be 12V @ 6.8A.

    For older graphics cards, this archived copy of an old web
    site has some numbers. There is nothing for FX5500 though.
    The FX5500 could be pretty close to the FX5200, and if
    I throw in a few more watts, it might be about 30 to 35W
    or so. The power would come from the lower voltage rails.


    The 865GV and RAM, could be using 3.3V @ 12A (based on a similar
    generation motherboard here, which I measured). That is in
    dual channel mode with two sticks of RAM, doing something
    like memtest.

    OK. On storage, we have two hard drives, with 12V @ ~0.6A each.
    The optical drives would be 1.5A each, if you were copying a
    DVD from one drive, onto the other DVD drive. That may not be a
    realistic scenario. Your cooling fans could use 12V @ 0.5A.
    Total there is 4.7A, which gets added to the 6.8A for the
    processor. The total, 11.5A, is less than the 16A limit.
    So your 12V rail is OK.

    The 3.3V rail is probably pretty close to its limit.
    (But it doesn't power the USB.)

    Now, time to try a total power calculation.

    81W for processor
    35W graphics card
    40W motherboard and RAM estimate
    12W + 12W + 25W + 25W + 6W (2 HDD, 2 ODD, fans)
    10W max USB can draw
    -------------------------- ----------------
    246W Total
    -------------------------- ----------------

    OK. So what is wrong with that calculation ? We
    can toss out about one DVD drive, which brings it
    down to 221W. And not all subsystems go to max
    at the same time. If you were gaming, you wouldn't be
    copying a DVD from one drive to the other. The
    motherboard and RAM might be a bit lower than stated.
    It is still pretty close.


    USB power on a motherboard can come from either the main
    +5V rail (plenty of amps) or from the +5VSB (only 2 amps).
    If the mouse light stays on when the computer is "sleeping",
    then that USB port is powered by +5VSB.

    One way to reduce the electrical load on whatever rail powers
    the USB, is to use a powered USB hub. They come with a wall
    wart 5V supply, and the current generation are not too
    generous with current. I've seen some older ones that came
    with a 5V @ 3.0 amp supply. The adapters now tend to be a bit
    more lightweight. (None of the externally powered hubs
    on Newegg have that good a customer rating, so I cannot recommend
    any of them.)

    If you want to replace the ATX power supply

    1) Check where that 2x3 connector goes. If it is used
    to power SATA drives, then a regular ATX with real
    SATA (wafer) power connectors could be substituted.
    2) Check the dimensions of the power supply. If the
    power supply is smaller than a standard supply,
    it may be harder to replace. ATX is standard in two
    dimensions, and the length is variable. Super high
    power supplies may be a couple inches longer than
    others. Check some supplies on Newegg, as they list
    3) Check you've got enough cables for the job.
    Check cable length. Some brands (Fortron) can
    be a bit tight with the cable length. Some are
    absurdly long (good for computer cases that
    mount the PSU at the bottom, instead of the top).
    4) Verify the mechanical details. Sometimes the faceplate
    of the supply doesn't fit. Or the features are in the
    wrong place. Or the supply has tabs or lips that get
    in the way. Inspect the pictures on Newegg for the
    supply, to see whether the holes and stuff line up
    with your Dell.

    This one from PCpower is listed as "compatible" with your
    Dell 1100 (whatever that means these days). It doesn't have
    the goofy 2x3 connector with COM,COM,3.3,5,12V signals on it.
    So that better not be important. (It has a 2x3 for PCI Express,
    with signals COM,COM,COM,12V,12V,12V, which is not the same thing.)
    I only mention this one, as a means to cut down on the selection
    process (since there are so many brands out there). There are
    plenty of brands that are crap, so shopping can be tough if
    all you look at is price.


    It is $95 USD here.
    http://www.ncixus.com/products/30164/PPCS500D/PC Power & Cooling/

    And nicely rebated here. But please read the reviews. Many users have
    mechanical problems - it is a "one size fits all" so cannot possibly
    always properly align with the holes in the case. Look at the pictures
    carefully for mechanical details. Some of the customers writing the
    reviews here, are pissed.

    http://www.newegg.com/Product/Product.aspx?Item=N82E16817703016&Tpk=pc power dell 500w

    The specs on the supply are:

    +3.3V @ 24A, +5V @ 24A, +12V @ 35A, -12V @ 0.8A, +5VSB @ 2.5A

    So, how does that help you ? Your 3.3V is no longer marginal (6 more amps
    to work with). 5V wasn't a problem before, as near as I can tell.
    Bigger supplies have more +12V than you'll ever use (you're using
    11.6 amps), so the 35A isn't really helping you. The -12V is not
    usually called on for more than a few milliamps for something like
    a serial port. The +5VSB *may* be used to power the USB, and
    now you've got a whole extra 0.5A to work with (big deal).
    I don't know if that is enough to tip the balance or not.

    My current supply would fit you better than that one.

    It is an Enermax EG465P-VE FMAII. Specs...

    3.3V @ 30A, 5V @ 30A, 12V1 @ 22A, 12V2 @ 20A, -12V @ 0.6A, +5VSB @ 3A
    <------ 150W ------> <-- 384W combined -->
    <--------------- 437.8W ------------------>
    <----------------------------- 460W -------------------------------->

    I purchased that one as a "crossover" supply. It was used
    to power a "5V pig" motherboard of a previous generation,
    before I did my current build. My current computer uses
    more +12V, and I'm well covered there. I tried to get the
    FMA, which I think was the previous generaton single rail
    12V supply, but my local retailer handed me the FMAII instead.
    It turned out to do the job for me as well. Even the FMAII
    seem to be pretty hard to find now.

    Paul, Mar 20, 2009
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