options if PSU too small for new CPU

Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
the Duron with a faster processor (the mobo will take up to a 2400
MHz T'bred).

The existing PSU may turn out to be too small for a faster processor.
If this happens then can I run the FSB at 100 instead of 133 in order
to get the CPU to need less power? (I don't want to get a new PSU.)

Would the CPU's reduced power consumption be proportional to the
reduced FSB speed - would I save about 25% of power supplied to the
CPU if I went from 133 to 100?

Are there any other power saving options I might reasonably consider?
19 answers Last reply
More about options small
  1. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    There is approx 30 watt difference between the two CPUs. Expect about a 4
    watt savings for every 1/10th in vcore reduction.

    "Franklin" <no_thanks@mail.com> wrote in message
    news:95F78CB7E919E71F3M4@130.133.1.4...
    > I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
    > the Duron with a faster processor (the mobo will take up to a 2400
    > MHz T'bred).
    >
    > The existing PSU may turn out to be too small for a faster processor.
    > If this happens then can I run the FSB at 100 instead of 133 in order
    > to get the CPU to need less power? (I don't want to get a new PSU.)
    >
    > Would the CPU's reduced power consumption be proportional to the
    > reduced FSB speed - would I save about 25% of power supplied to the
    > CPU if I went from 133 to 100?
    >
    > Are there any other power saving options I might reasonably consider?
    >
  2. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    "Franklin" <no_thanks@mail.com> wrote in message
    news:95F78CB7E919E71F3M4@130.133.1.4...
    >I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
    > the Duron with a faster processor (the mobo will take up to a 2400
    > MHz T'bred).
    >
    > The existing PSU may turn out to be too small for a faster processor.
    > If this happens then can I run the FSB at 100 instead of 133 in order
    > to get the CPU to need less power? (I don't want to get a new PSU.)
    >
    > Would the CPU's reduced power consumption be proportional to the
    > reduced FSB speed - would I save about 25% of power supplied to the
    > CPU if I went from 133 to 100?
    >
    > Are there any other power saving options I might reasonably consider?
    >

    Telling us what sort of psu and the power rating of it would be a good
    start!
  3. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    On Tue, 08 Feb 2005 13:49:59 +0000, Franklin wrote:

    > Are there any other power saving options I might reasonably consider?

    If you lower the CPU speed you also need to lower vcore to achieve max
    power savings. Just lowering the FSB won't save you near as much as
    lowering vcore along with it. A 2400+ at 100Mhz FSB probably won't need
    more than 1.4v. At least the 2100+ at 100MHz ran fine at 1.4v. That was as
    low as the bios would go.

    --
    Abit KT7-Raid (KT133) Tbred B core CPU @2400MHz (24x100FSB)
    http://wesnewell.no-ip.com/cpu.htm
  4. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    "Franklin" <no_thanks@mail.com> wrote in message
    news:95F78CB7E919E71F3M4@130.133.1.4...
    > I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
    > the Duron with a faster processor (the mobo will take up to a 2400
    > MHz T'bred).

    I assume you mean an Athlon XP 2400+, which IIRC is 2GHz.

    > The existing PSU may turn out to be too small for a faster processor.
    > If this happens then can I run the FSB at 100 instead of 133 in order
    > to get the CPU to need less power? (I don't want to get a new PSU.)

    Yes, if the motherboard allows it.

    > Would the CPU's reduced power consumption be proportional to the
    > reduced FSB speed - would I save about 25% of power supplied to the
    > CPU if I went from 133 to 100?

    Yes, roughly.

    > Are there any other power saving options I might reasonably consider?

    You can try reducing the CPU core voltage if the motherboard allows it.
    (Underclocked, it wouldn't surprise me if it would work at a low enough
    voltage to consume _less_ power than the curren Duron.)

    Unlocking the multiplier may be another option.

    Alex
  5. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    Franklin wrote:
    >
    .... snip ...
    >
    > Would the CPU's reduced power consumption be proportional to the
    > reduced FSB speed - would I save about 25% of power supplied to
    > the CPU if I went from 133 to 100?
    >
    > Are there any other power saving options I might reasonably consider?

    More or less, yes. CMOS logic generally charges and discharges
    lots of dinky little capacitors on each clock cycle. That
    constitutes a charge per unit time, which is a current. Increasing
    the unit of time decreases the current, and thus the power. The
    other factor involved is the voltage to which things are charged.

    --
    "If you want to post a followup via groups.google.com, don't use
    the broken "Reply" link at the bottom of the article. Click on
    "show options" at the top of the article, then click on the
    "Reply" at the bottom of the article headers." - Keith Thompson
  6. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    if you are upgrading to a processor that has a higher voltage rated psu
    then the only option is to upgrade your psu. period. cheaping out on
    the psu when you're dropping good cash for a cpu upgrade is not wise.
    many have tried to run a newer machine with a radeon 9800xt and a 230
    watt psu and don't know why the machine is blue-screening and not
    functioning properly?!? HELLO somebody!! Tell this guy what he needs to
    hear not what he wants to hear. why would you even want to lose
    performance by lowering your bus speed 25% to avoid getting a new psu
    which you can find by the way if you shop around for about 50.00 for a
    real GOOD one that will last and which you can use and re-use for later
    projects and upgrades!
    good luck with your decision.
    visit me on the web at http://starfleetscommand.com
    visit us on the web at http;//ezarlodge281.org
    CBFalconer wrote:
    > Franklin wrote:
    > >
    > ... snip ...
    > >
    > > Would the CPU's reduced power consumption be proportional to the
    > > reduced FSB speed - would I save about 25% of power supplied to
    > > the CPU if I went from 133 to 100?
    > >
    > > Are there any other power saving options I might reasonably
    consider?
    >
    > More or less, yes. CMOS logic generally charges and discharges
    > lots of dinky little capacitors on each clock cycle. That
    > constitutes a charge per unit time, which is a current. Increasing
    > the unit of time decreases the current, and thus the power. The
    > other factor involved is the voltage to which things are charged.
    >
    > --
    > "If you want to post a followup via groups.google.com, don't use
    > the broken "Reply" link at the bottom of the article. Click on
    > "show options" at the top of the article, then click on the
    > "Reply" at the bottom of the article headers." - Keith Thompson
  7. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    On Tue, 08 Feb 2005 13:49:59 +0000, Franklin wrote:

    > I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
    > the Duron with a faster processor (the mobo will take up to a 2400 MHz
    > T'bred).
    >
    > The existing PSU may turn out to be too small for a faster processor. If
    > this happens then can I run the FSB at 100 instead of 133 in order to
    > get the CPU to need less power? (I don't want to get a new PSU.)
    >
    > Would the CPU's reduced power consumption be proportional to the reduced
    > FSB speed - would I save about 25% of power supplied to the CPU if I
    > went from 133 to 100?
    >
    > Are there any other power saving options I might reasonably consider?

    Bite the bullet and get an adequate power supply. The last place you
    should cut corners is on the power supply. A marginal power supply can
    give you all sorts of flaky hard to diagnose problems. A power supply
    failure can also take out your entire system. If you can't afford a decent
    power supply now then put off your upgrade until you can. If I were you
    I would add 75W to the size of your current power supply and use that as a
    minimum value for a new one. I bet you'll find that it's not all that
    expensive.
  8. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    In article <1107965008.539607.173790@f14g2000cwb.googlegroups.com>,
    "starfleet40" starfleet40@msn.com says...
    > if you are upgrading to a processor that has a higher voltage rated psu
    > then the only option is to upgrade your psu. period.

    PSUs are specified by the current they can supply on each line, not
    by voltage. The motherboard determines the voltage that's supplied
    to the CPU.

    > cheaping out on
    > the psu when you're dropping good cash for a cpu upgrade is not wise.
    > many have tried to run a newer machine with a radeon 9800xt and a 230
    > watt psu and don't know why the machine is blue-screening and not
    > functioning properly?!?

    That's probably because the GPU draws a considerably higher current,
    not because the CPU uses a few more Watts. The current requirement
    on each line must be met - it's not enough to say e.g. a 500W PSU
    will be sufficient, or a 350W PSU will be insufficient.

    > HELLO somebody!! Tell this guy what he needs to
    > hear not what he wants to hear. why would you even want to lose
    > performance by lowering your bus speed 25% to avoid getting a new psu

    Underclocking is useful for low-noise machines, or using a CPU with a
    higher FSB on a mobo that won't run at that speed.

    > which you can find by the way if you shop around for about 50.00 for a
    > real GOOD one that will last and which you can use and re-use for later
    > projects and upgrades!

    I doubt you'd get much quality for 50.00 - that's a number. If
    you're talking about £50.00 I'd still be doubtful.

    > good luck with your decision.
    > visit me on the web at http://starfleetscommand.com
    > visit us on the web at http;//ezarlodge281.org
    > CBFalconer wrote:
    <snip>
    Learn about the proper use of a signature separator, and how not to
    top-post.
  9. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    On 08 Feb 2005, jacoby wrote:

    > There is approx 30 watt difference between the two CPUs. Expect
    > about a 4 watt savings for every 1/10th in vcore reduction.

    Forgive me, but I am not entirely clear on your what you are saying.

    When you say a 4 watt savings for every 1/10th in vcore reduction,
    are you saying that for every 1/10th of a volt which vcore is reduced
    by then there will be approx a 4W saving?
  10. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    *** Rude and foolish top-posting fixed ***

    starfleet40 wrote:
    > CBFalconer wrote:
    >> Franklin wrote:
    >>>
    >> ... snip ...
    >>>
    >>> Would the CPU's reduced power consumption be proportional to the
    >>> reduced FSB speed - would I save about 25% of power supplied to
    >>> the CPU if I went from 133 to 100?
    >>>
    >>> Are there any other power saving options I might reasonably
    >>> consider?
    >>
    >> More or less, yes. CMOS logic generally charges and discharges
    >> lots of dinky little capacitors on each clock cycle. That
    >> constitutes a charge per unit time, which is a current. Increasing
    >> the unit of time decreases the current, and thus the power. The
    >> other factor involved is the voltage to which things are charged.
    >
    > if you are upgrading to a processor that has a higher voltage rated
    > psu then the only option is to upgrade your psu. period. cheaping
    > out on the psu when you're dropping good cash for a cpu upgrade is

    If you are changing supply voltages you are probably destroying
    something. Components expect to operate at certain rated supply
    voltages.

    > not wise. many have tried to run a newer machine with a radeon
    > 9800xt and a 230 watt psu and don't know why the machine is
    > blue-screening and not functioning properly?!? HELLO somebody!!

    I only heard a question about how to control power consumption.
    The only one mentioning 9800xt and 230 watts is you. Try to get
    out a little more.

    > Tell this guy what he needs to hear not what he wants to hear. why
    > would you even want to lose performance by lowering your bus speed
    > 25% to avoid getting a new psu which you can find by the way if you
    > shop around for about 50.00 for a real GOOD one that will last and
    > which you can use and re-use for later projects and upgrades!

    Maybe he wants to run from a battery and extend life. Don't make
    so many silly assumptions. Try to learn some elementary
    netiquette, including how to post and snip properly. Also crack
    some elementary books on electricity, the care and feeding of.
    Some people actually know what they are talking about and what they
    don't know, and I suspect this applies to Franklin.

    --
    "If you want to post a followup via groups.google.com, don't use
    the broken "Reply" link at the bottom of the article. Click on
    "show options" at the top of the article, then click on the
    "Reply" at the bottom of the article headers." - Keith Thompson
  11. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    On Wed, 09 Feb 2005 19:29:52 GMT, Franklin
    <no_thanks@mail.com> wrote:

    >On 08 Feb 2005, jacoby wrote:
    >
    >> There is approx 30 watt difference between the two CPUs. Expect
    >> about a 4 watt savings for every 1/10th in vcore reduction.
    >
    >Forgive me, but I am not entirely clear on your what you are saying.
    >
    >When you say a 4 watt savings for every 1/10th in vcore reduction,
    >are you saying that for every 1/10th of a volt which vcore is reduced
    >by then there will be approx a 4W saving?

    wattage is proportional to the square of the voltage and the
    frequency. To calculate this use C as a constant for the
    CPU to be determined (calculated) based on the manufacturer
    specs (which can be seen per each CPU from their respective
    manufacturer datasheets, the following is a fictional CPU
    for example purposes only:

    [ frequency * (voltage)² ] / C = Wattage

    As an example, if a particular CPU is spec'd to run at 1.5V
    and 2.0 GHz (2000 MHz), which radiates 100W heat, (uses 100W
    power), then from above equation we have:

    [2000 * (1.5)² ] / C = 100

    Solved for C,
    C = 45

    Now taking same CPU where C= 45, but running it at 1.3V and
    1600MHz-

    [ 1600 * (1.3)²] / 45 = Wattage

    Wattage = 60.1
  12. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    On Tue, 08 Feb 2005 13:49:59 GMT, Franklin
    <no_thanks@mail.com> wrote:

    >I have an SD-RAM motherboard with a 700 MHz Duron. I want to replace
    >the Duron with a faster processor (the mobo will take up to a 2400
    >MHz T'bred).
    >
    >The existing PSU may turn out to be too small for a faster processor.
    >If this happens then can I run the FSB at 100 instead of 133 in order
    >to get the CPU to need less power? (I don't want to get a new PSU.)
    >
    >Would the CPU's reduced power consumption be proportional to the
    >reduced FSB speed - would I save about 25% of power supplied to the
    >CPU if I went from 133 to 100?
    >
    >Are there any other power saving options I might reasonably consider?

    IMO, it is a false economy to underclock the CPU for the
    sole benefit of reusing your current PSU. Moreso than many
    devices, power supplies do eventually fail, especially when
    ran near their max output, which seems to be what you're
    trying to accomplish. Otherwise, to get about same power
    consumption from a newer CPU, you'd not be getting THAT much
    more performance.

    If you wish to get the maximum out of your current PSU _AND_
    your motherboard has multiplier adjustment capability,
    choose a mobile Athlon XP, which has lower voltage
    requirements, and then consider reducing the multiplier
    moreso than the FSB speed. Your board MUST support
    muliplier changes to use one though, otherwise it will be
    stuck at 6X default multiplier unless you used hacks to burn
    bridges, solder leads or wire-wrap pins to get some other
    multiplier. Frankly I suggest you just buy another PSU.

    Since you have such an old board, it's most likely using 5V
    power for CPU. A fairly good budget range PSU for higher 5V
    current would be a Thermaltake 420W, Newegg frequently has
    them for $36-40 on sale.
    http://www.newegg.com/app/viewproductdesc.asp?description=17-153-006&DEPA=0
  13. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    Yes. The 2400 draws max 41 amps.
    "Franklin" <no_thanks@mail.com> wrote in message
    news:95F8C657DB3DD71F3M4@130.133.1.4...
    > On 08 Feb 2005, jacoby wrote:
    >
    > > There is approx 30 watt difference between the two CPUs. Expect
    > > about a 4 watt savings for every 1/10th in vcore reduction.
    >
    > Forgive me, but I am not entirely clear on your what you are saying.
    >
    > When you say a 4 watt savings for every 1/10th in vcore reduction,
    > are you saying that for every 1/10th of a volt which vcore is reduced
    > by then there will be approx a 4W saving?
  14. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    Rob Morley <nospam@ntlworld.com> wrote in message news:<MPG.1c745243f14a607798a767@news.individual.net>...
    > In article <1107965008.539607.173790@f14g2000cwb.googlegroups.com>,
    > "starfleet40" starfleet40@msn.com says...
    > > if you are upgrading to a processor that has a higher voltage rated psu
    > > then the only option is to upgrade your psu. period.
    >
    > PSUs are specified by the current they can supply on each line, not
    > by voltage. The motherboard determines the voltage that's supplied
    > to the CPU.
    >
    > > cheaping out on
    > > the psu when you're dropping good cash for a cpu upgrade is not wise.
    > > many have tried to run a newer machine with a radeon 9800xt and a 230
    > > watt psu and don't know why the machine is blue-screening and not
    > > functioning properly?!?
    >
    > That's probably because the GPU draws a considerably higher current,
    > not because the CPU uses a few more Watts. The current requirement
    > on each line must be met - it's not enough to say e.g. a 500W PSU
    > will be sufficient, or a 350W PSU will be insufficient.
    >
    > > HELLO somebody!! Tell this guy what he needs to
    > > hear not what he wants to hear. why would you even want to lose
    > > performance by lowering your bus speed 25% to avoid getting a new psu
    >
    > Underclocking is useful for low-noise machines, or using a CPU with a
    > higher FSB on a mobo that won't run at that speed.
    >
    > > which you can find by the way if you shop around for about 50.00 for a
    > > real GOOD one that will last and which you can use and re-use for later
    > > projects and upgrades!
    >
    > I doubt you'd get much quality for 50.00 - that's a number. If
    > you're talking about £50.00 I'd still be doubtful.
    >
    > > good luck with your decision.
    > > visit me on the web at http://starfleetscommand.com
    > > visit us on the web at http;//ezarlodge281.org
    > > CBFalconer wrote:
    > <snip>
    > Learn about the proper use of a signature separator, and how not to
    > top-post.

    A touch arrogant Rob.
  15. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    [top-posting fixed]
    "jacoby" <jacobykjh@comcast.net> wrote in message
    news:BvCdnRy9BOhnZpffRVn-ow@comcast.com...
    > "Franklin" <no_thanks@mail.com> wrote in message
    > news:95F8C657DB3DD71F3M4@130.133.1.4...
    > > On 08 Feb 2005, jacoby wrote:
    > >
    > > > There is approx 30 watt difference between the two CPUs. Expect
    > > > about a 4 watt savings for every 1/10th in vcore reduction.
    > >
    > > Forgive me, but I am not entirely clear on your what you are saying.
    > >
    > > When you say a 4 watt savings for every 1/10th in vcore reduction,
    > > are you saying that for every 1/10th of a volt which vcore is reduced
    > > by then there will be approx a 4W saving?
    >
    > Yes. The 2400 draws max 41 amps.

    But if the voltage is changed, the current will change too, by a similar
    factor. If you assume the same factor (a close approximation, AFAIK), you
    get the result kony gave: power proportional to square of voltage (all else
    being constant).

    Alex
  16. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    "Alex Fraser" <me@privacy.net> wrote in message
    news:37133oF55t1e2U1@individual.net...
    >>
    > But if the voltage is changed, the current will change too, by a similar
    > factor. If you assume the same factor (a close approximation, AFAIK), you
    > get the result kony gave: power proportional to square of voltage (all
    else
    > being constant).
    >
    > Alex
    >
    This is true. So a 0.25 reduction in volts will not exactly equate to a 10
    watt power reduction. I was merely pointing out that there is only a 30 watt
    difference in the two cpus and a only slight reduction in power consumption
    may be obtained by lowering voltage, thus lowering the difference between
    the two cpus. As Kony stated your mb most likely feeds the cpu from the
    3.3/5 volt rail. If your mysterious psu has been stable running the Duron,
    the question is weather or not the additional 25 to 30 watt increase will
    render instability issues. How many watts does your current psu supply to
    the combined 3.3/5 volt rail?
  17. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    In article <56f50d64.0502100030.42ae7d62@posting.google.com>,
    "Mescalito" Digging4fire@hotmail.com says...
    <snip>
    >
    > A touch arrogant Rob.
    >
    Just a touch?
  18. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    "jacoby" <jacobykjh@comcast.net> wrote in message
    news:baOdnX5ILqdqH5bfRVn-hA@comcast.com...
    > "Alex Fraser" <me@privacy.net> wrote in message
    > news:37133oF55t1e2U1@individual.net...
    > > But if the voltage is changed, the current will change too, by a
    > > similar factor. If you assume the same factor (a close approximation,
    > > AFAIK), you get the result kony gave: power proportional to square of
    > > voltage (all else being constant).
    >
    > This is true. So a 0.25 reduction in volts will not exactly equate to a
    > 10 watt power reduction.

    Nor will it necessarily equate to anything like a 10W power reduction. It's
    not linear; it depends what voltage you are reducing it from.

    I think 10W is a significant underestimate for a reduction of 0.25V from the
    default core voltage of the CPU in question (an XP 2400+).

    > I was merely pointing out that there is only a 30 watt difference in the
    > two cpus and a only slight reduction in power consumption may be obtained
    > by lowering voltage, thus lowering the difference between the two cpus.

    I was merely pointing out that your original 4W per 0.1V figure was
    apparently based on a false premise (that the current does not change), and
    as a consequence liable to be wrong.

    Alex
  19. Archived from groups: alt.comp.hardware.overclocking.amd,uk.comp.homebuilt,alt.comp.hardware (More info?)

    ok, fine. I do not have time to delve into such trivial matters. Either get
    the new cpu and roll the dice your current psu will be sufficient or get a
    new psu or do nothing. Jeewiz. I am out!

    "Alex Fraser" <me@privacy.net> wrote in message
    news:371lbmF56ru8eU1@individual.net...

    > Nor will it necessarily equate to anything like a 10W power reduction.
    It's
    > not linear; it depends what voltage you are reducing it from.
    >
    > I think 10W is a significant underestimate for a reduction of 0.25V from
    the
    > default core voltage of the CPU in question (an XP 2400+).
    >
    > > I was merely pointing out that there is only a 30 watt difference in the
    > > two cpus and a only slight reduction in power consumption may be
    obtained
    > > by lowering voltage, thus lowering the difference between the two cpus.
    >
    > I was merely pointing out that your original 4W per 0.1V figure was
    > apparently based on a false premise (that the current does not change),
    and
    > as a consequence liable to be wrong.
    >
    > Alex
    >
    >
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