Power Supply Requirements

Discussion in 'A+ Certification' started by Joe, Dec 20, 2003.

  1. Joe

    Joe Guest

    Can anyone help me figure out
    1. Tell me if a specific system I have in mind would work without problems
    with a 350 watt power supply.
    2. What happens if you use too low of a power supply with a system.
    3. How to measure or determine the right power supply for a given system.
    Details follow.

    1. Basically, I'm trying to get a new system for myself (while keeping
    costs as low as possible). The current place I'm considering buying from
    offers me a 350 Watt Power Supply by default. I'd love to get it to 420
    watts, however, the way this place is set up, I'd have to change the case to
    get which raises the price by almost $50 which I rather not do unless I have
    to. The system is Athlon 2800 XP with 3 case fans (or 2 LED case fans if
    that matters). 2 hard drives. 1 DVD-ROM. 1 Flash Media Card Reader.
    Quite possibly also 1 CD-RW (I can leave this off as I have another system
    with a CD-RW I can use to burn CDs with). The case doesn't come with all
    the glowing neon lights everywhere...but considering it's only a few
    dollars, I might add some in IF it won't boost my power supply requirements
    by any noticeable amount. It will of course have video card (GeForce5600),
    fax/modem, etc. as well. So, with this system, am I safe with a 350 watt
    power supply (remember the CD-RW and any LED lights are optional for me if
    they present a problem)? Or must I have a 420 or higher watt power supply?

    2. So what happens, generally speaking, if you use a power supply that is
    too low for all your system needs? Will it still turn on? Does it have any
    possible chance of causing damage? Will the system perform at 100%
    functionality and if not, how will it be reduced?

    3. I vaguely remember there being some sort of rule of thumb for
    determining how big of a power supply is needed based on type or number of
    devices as well as a more exact way of measuring how much power your devices
    will take and buying the corresponding power supply to match it. If my
    vague memories are right, you also have take into account about the extra
    power the devices might draw at boot up as well as their normal drain.
    Unfortunately, it's all vague and been a while. Can someone tell me exactly
    how it all works for both the rule of thumb version as well as the more
    exact version? If the exact version requires, though, knowing the exact
    power each device draws, it won't help as I haven't bought the system in
    question.

    Thanks!
     
    Joe, Dec 20, 2003
    #1
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  2. Joe

    MF Guest

    "Joe" <> wrote in message
    news:NyVEb.159674$_M.741229@attbi_s54...

    answers in line.

    > Can anyone help me figure out
    > 1. Tell me if a specific system I have in mind would work without

    problems
    > with a 350 watt power supply.
    > 2. What happens if you use too low of a power supply with a system.
    > 3. How to measure or determine the right power supply for a given

    system.
    > Details follow.
    >
    > 1. Basically, I'm trying to get a new system for myself (while

    keeping
    > costs as low as possible). The current place I'm considering buying

    from
    > offers me a 350 Watt Power Supply by default. I'd love to get it to

    420
    > watts, however, the way this place is set up, I'd have to change the

    case to
    > get which raises the price by almost $50 which I rather not do

    unless I have
    > to. The system is Athlon 2800 XP with 3 case fans (or 2 LED case

    fans if
    > that matters). 2 hard drives. 1 DVD-ROM. 1 Flash Media Card

    Reader.
    > Quite possibly also 1 CD-RW (I can leave this off as I have another

    system
    > with a CD-RW I can use to burn CDs with). The case doesn't come

    with all
    > the glowing neon lights everywhere...but considering it's only a few
    > dollars, I might add some in IF it won't boost my power supply

    requirements
    > by any noticeable amount. It will of course have video card

    (GeForce5600),
    > fax/modem, etc. as well. So, with this system, am I safe with a 350

    watt
    > power supply (remember the CD-RW and any LED lights are optional for

    me if
    > they present a problem)? Or must I have a 420 or higher watt power

    supply?

    It sounds like 350 watts is plenty for that system. Including a cd
    burner.

    > 2. So what happens, generally speaking, if you use a power supply

    that is
    > too low for all your system needs? Will it still turn on? Does it

    have any
    > possible chance of causing damage? Will the system perform at 100%
    > functionality and if not, how will it be reduced?


    Things go awry. Strange days ensue. You become perplexed and the
    problem of troubleshooting takes on a whole new dimension, until you
    finally figure it out. More specifically, all kinds of things happen.
    Failures to start. Spontaneous reboots. Memory errors, processor
    errors. Bad data writes. Freezes. Often, if the PS is almost strong
    enough, it'll start up okay and seem fine until you try to use two
    devices at once that draw a lot of power, like copying from hd to hd
    or to CD. Then crashes and reboots and possible lost data. So that
    kind of damage is possible. Electronically inclined people will also
    tell you that prolonged underpower will damage certain devices, but
    you may well have figured out you have a problem before that happens.

    > 3. I vaguely remember there being some sort of rule of thumb for
    > determining how big of a power supply is needed based on type or

    number of
    > devices as well as a more exact way of measuring how much power your

    devices
    > will take and buying the corresponding power supply to match it. If

    my
    > vague memories are right, you also have take into account about the

    extra
    > power the devices might draw at boot up as well as their normal

    drain.
    > Unfortunately, it's all vague and been a while. Can someone tell me

    exactly
    > how it all works for both the rule of thumb version as well as the

    more
    > exact version? If the exact version requires, though, knowing the

    exact
    > power each device draws, it won't help as I haven't bought the

    system in
    > question.
    >


    You discover the current drawn by each device in your system and
    compare it to the current provided by the power supply. Example, I'm
    looking at an old, dsyfunctional 250 watt PS. Under each voltage
    +5,+12,-5,-12, it shows the maximum current available in that line.
    In amps. Amperage. or A. So under 12 volts it shows a max of 10 A.
    To find out if the PS is adequate, you add up all the current draws of
    your 12 Volt devices, mainly the motors in the computer, drives, fans,
    etc. if the total is 9 or less (less than 10 percent less than ten),
    you can feel sure you're okay. And then your 5 volt devices, 3.3 volt
    devices and so on. You do not need to think about the negative
    voltages.

    And that is how you do it, and yes, you can do it without having the
    computer, because many manufacturers list the current draws of their
    devices on their websites where you can look it up, AND there are also
    lists of typical draws by device on various websites. I don't have
    any links handy or I'd give you one. Go to google and look it up. As
    to the various formulas, the only one I remember consistently is Watts
    over Volts = Amps. Reason I remember it is that 2000 watts over 120
    volts equals 16.6 amps, usually enough to blow the fuse in an older
    house; so when you're lighting a movie scene and you want 2000 or more
    watts of light for the scene(which you usually do), you need to be
    careful to put your lamps on separate circuits. That's the one I
    learned the hard way, so that's the one I remember :) - (but the rest
    are equally simple).

    You should be okay with 350. Good luck.
    > Thanks!

    That'll be $75.00, please.
    Just kidding.
     
    MF, Dec 20, 2003
    #2
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