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combining 2 power supplies

Discussion in 'Electronic Repair' started by lee, Mar 26, 2006.

  1. lee

    lee Guest

    Hi,

    Over the years, I've kept a few ATX power supply from old computers. Now,
    I'm thinking about upgrading my computer and add more hard disks. The
    problem is the current power supply might not be able to support so many
    hard disks running at the same time. Instead of buying a new, more powerful
    power supply, I am planning to use one old piece (350w) to serve the
    motherboard, CD, and 3 hard disks, then another power supply (350w too) to
    serve 3 to 4 more hard disks. All components are connected to the same
    motherboard. I need to know how I could turn on both power supply with a
    single press of the power button on the case.

    In other words, only one power supply can plug to the motherboard, how can I
    jam the wires together so that the second power supply receive the power-on
    signal when I press the button? I was thinking about the Power-On (Green),
    Power-Good (Gray) and 5 VSB (Purple) wires. the second power supply would
    only support the hard disks and nothing else, but I need them to be powered
    up at the same time other hardware are up (and down when it's shut down).

    Thanks.
     
  2. crazy frog

    crazy frog Guest

    green wire to black ground starts them up, but put
    a load on them first like youre drives.
    only the motherboard needs power good.
    if running with no load, use a 5watt 100ohm resistor
    accross the 5v+ to black ground for a dummy load.
     
  3. 100 ohms may be too high. 5 ohms probably better. But an automotive
    taillight (incandescent) or dead harddrive also should work.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
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  4. Ian Stirling

    Ian Stirling Guest

    Do the numbers.
    Only 8 should not be a problem, if it's a real 350W.

    15W * 8 = only 120W.
    Add another 100W for the motherboard, and you're pretty much fine.

    Also.
    You'll want to do the numbers on life cycle cost.
    Yes, you may have 3 80G drives spare, that you can stick into a system.
    If you're going to be leaving them on (which increases drive life), then
    in some places, you'll pay for a new 240G drive in a couple of years.
     
  5. lee

    lee Guest

    Thanks and I did my numbers:

    I'm thinking a P4 9xx CPU and it draws around 100w alone, new display cards
    (ATI x series) also draws a lot of power. More than 1 web site said hard
    disks draws 25w so I use that in my calculation to be on the safe side.
    Plus RAM, DVD-RW, fans, and USB devices that might connect to the machine
    every now and then. Each of those costs little but they add up. 350w might
    not be sufficient all the time. In addition, I don't trust the PSU will
    produce 350w as claimed by the manufacturer.

    In the meanwhile, thank you for everyone's help in this.

    Best regards.
     
  6. James Sweet

    James Sweet Guest


    There's a lot of wattage inflation these days, following the stereo
    equipment makers in the 80s. The fact of the matter is that if you have
    a *quality* 300 or 350W power supply, it should run just about anything
    you can fit in the computer. I've measured a number of computers with a
    power analyzer and I have yet to see one which draws more than 250W from
    the wall under full load, most typical single CPU computers are down
    around 160-180W even with multiple hard drives.
     
  7. Don't fight it. People think that adding power supplies multiples the
    speed of the PC by the number of power supplies added. No way to talk
    them out of it. :)

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  8. crazy frog

    crazy frog Guest

    im useing a supply with no mobo
    and 100ohm works fine.
     
  9. crazy frog

    crazy frog Guest

    got the info from silicon chip.
     
  10. And so you think this applies equally well to ALL power supplies? :)

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  11. crazy frog

    crazy frog Guest

    no not all, look at silicon chips artical
     
  12. crazy frog

    crazy frog Guest

    how do you think my power supply is working.
     
  13. Perhaps a link?

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  14. crazy frog

    crazy frog Guest

    cant fined the old article on pc power
    supplies.
    thay hav a new one on useing them as a 13v
    high power unit without a pc connected.
     
  15. crazy frog

    crazy frog Guest

    you can use a 10ohm 10watt for heavy load.
    a 100ohm 5watt is ok for lite dummy load, connect
    whatever you want, a 10ohm will get hot and
    you hav to cool it with something.
     
  16. What article?

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  17. Lets do a bit of maths.

    5 V across 100 Ohms is 5^2 / 100 = 25 / 100 = 0.25 W. So you would only need 1/4
    W restor, not a 5 W one.

    However, like someone else, i think that would be totally inadequate as a
    minimum load.




    --
    Dave K MCSE.

    MCSE = Minefield Consultant and Solitaire Expert.

    Please note my email address changes periodically to avoid spam.
    It is always of the form: [email protected] Hitting reply will work
    for a couple of months only. Later set it manually.
     
  18. But I don't belive that 250 W drawn from the mains is a likely maximum now.

    I was doing some calculuations the other day based on a pair of Opterons.
    According to AMD, they are about 100 W each. A very mediocre graphics card is
    probably 30 W. Disks take more when they spin up.

    350 W is probably adequate for most things I would agree. My main PC (I don't
    use PCs much) has a 235 W power supply in it, but a pair of 450 MHz Pentiums and
    a 10,000 rpm SCSI disk. That seems to be OK

    A more elegant solution if there are multiple disks might be to build a timer
    that delays the starts on them, as the power when running is probalby only half
    that when starting.

    Personally, I think I'd just rather buy a bigger psu - they are not that
    expensive now.


    --
    Dave K MCSE.

    MCSE = Minefield Consultant and Solitaire Expert.

    Please note my email address changes periodically to avoid spam.
    It is always of the form: [email protected] Hitting reply will work
    for a couple of months only. Later set it manually.
     
  19. Franc Zabkar

    Franc Zabkar Guest

    I've measured ~175W for my single HDD, Athlon XP 2500+ system.

    These are my idling and standby power consumption data:
    http://groups.google.com/group/alt.comp.hardware.homebuilt/msg/96de737e37e64526?dmode=source&hl=en

    - Franc Zabkar
     
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