55W PC power supply powering the dual-core computer

55W PC power supply powering the dual-core computer

Summary: Most computer builders in the world think I'm nuts for endorsing the use of 330 watt power supplies for a high-end performance computer.  Conventional "wisdom" says that anything under 500 watts is inadequate for an enthusiast PC.

TOPICS: Hardware

Most computer builders in the world think I'm nuts for endorsing the use of 330 watt power supplies for a high-end performance computer.  Conventional "wisdom" says that anything under 500 watts is inadequate for an enthusiast PC.  "My power supply is bigger than your power supply" seems to be a typical mindset for many people but I've always had just the opposite desire to say that "my supply is smaller than yours and it works great".  So when I started building mainstream dual-core computers with 220 watt 80 Plus power supplies, people were shocked that I would even consider such a small power supply.  But since I was able to build a 50W peak power dual-core computer, why not use an even smaller power supply in the sub-100 watt range?

FSP055-50LM SPI 55 watt open frame power supply

Pictured above is the open frame fanless AC input open frame 55 watt FSP055-50LM power supply from Sparkle Power Inc with an MSRP of $39.  Typically when power supplies are this small, people often use DC input power supplies with an external AC brick.  Not so with this model as it's an all in one with the standard AC power connector you get on a normal ATX PC power supply.  It's so small that it doesn't even bother with a fan or metal casing; you have to a system-level fan yourself and provide the bracing and shielding in your computer chassis.  The really nice thing about this solution is that the entire power supply including the AC conversion part is not much bigger than a DC power supply but you don't need an external brick.

Using this 55W power supply, I took a dual-core Intel E2140 along with the bundled ECS945-GM motherboard I bought for $90 and built a computer with it using default clock speed and voltages.  Unfortunately since it was missing a 4-pin power connector for the motherboard, I had to hot-wire a 4-pin CPU power connector from an older power supply to this unit to make it work.  That means 2 12-volt yellow cables and 2 black ground cables had to be soldered in to place and taped up.  Since these cables are safe for 10 amps each which translates to 120 watts per cable, I'm not even close to overloading the cables.

Once the computer came up, the power consumption at the plug peak out at 70W which means the output power is around 52W at 75% efficiency which is 3W under the peak output of the power supply.  That is cutting it a bit close but it shows the extreme worst-case of what this PSU can handle.

In reality, the 55W PSU isn't practical for a mainstream dual-core computer although it would be more than powerful enough for an Intel D201GLY with Celeron 115, D201GLY2 motherboard with Celeron 120, or the Via low-power ITX platforms. The upcoming Intel Centrino Atom platform with the Atom-Diamondville CPU peaks at around 4W TDP so they're even easier to power.

The bottom line is that this is a nice little power supply for small embedded solutions but you'll want to stick with the bigger 80 Plus closed-frame models like the Sparkle SPI220LE 220W or the SPI270LE 270W if you're building a mainstream PC.  Note that the SPI models are 1U power supplies so you'll either need a very custom case or one that uses 1.75" thin power supplies.

Topic: Hardware

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  • Sweet find

    I still think that would be ideal at packing a case with hard drives.

    I always wanted multi tiered file servers and thought that if I build several computers into a single system, I would be better off than if I built a single file server for everyone to start thrashing the hard drives on.
    • Wouldn't be good for hard drives, those take too much peak power

      Wouldn't be good for hard drives, those take too much peak power. Each drive spikes up to 13 watts.
      • Western Digital GP hard drives

        Well George, there's Western Digital GreenPower hard drives:
        Grayson Peddie
  • Watts, volts and amps - oh my

    Great article G.

    Never understood why people buy the marketing hype and put 1200 Watt power supplies in a PC. I guess AMD/INTEL have the GHz war, and PSU manufacturers have the WATT war.

    Computers with a bunch of peripherals (more than 2 HDD) are almost totally reliant on the number of amps on the 12 volt lines, not wattage.

    Also - when comparing two power supplies, it's always good to look for specifications that rate "continuous" power at normal room temps, rather than peak power ratings that come from marketing departments that live in a freezer.

    I add up the component amps requirements, and then find the most efficient solution. The PSU is almost always the last item on my list to purchase.

    I practice what you preach. I'm currently running a Core2 rig with a 300W supply (I could have used a 250, but the 300 was on sale), and an X2, 8Gig, dual raid1 server on a 500W supply.

    I read disinformation constantly in forums with advice such as "get the biggest power supply you can, and you'll be okay"

    I like your advice. "get the most efficient power supply based on the components you have in your rig"

    Never thought about building a 55W rig though.... neato.
    • I am sure you are aware but P = VI

      "are almost totally reliant on the number of amps on the 12 volt lines, not wattage."

      You can't make such a distinction. If voltage is fixed, then the number of amps flowing determines the wattage consumed. So if there are 3 amps at 12 V you have 36 watts. You can't pit one against another.

      Ultimately all "power" consuming devices need just that power. Power is expressed in watts. For many non-electronic devices you can (within limits) actually reduce the number of amps consumed by boosting the voltage. That's why motors can pop circuit breakers during brown-outs. They need X power but the voltage is low, so they compensate by pulling more amps.
      • While you are correct about the formula...

        PSU makers wattage ratings are based on the total wattage from all outputs 5/+12/-12v, not just the 12v, so in order to determine if a given supply will support the number of hard drives your system has you need to look at only the +12v current and to some degree the +5v.
        • Some drives pull 2.8A on the 12V rail

          I too wonder if this power supply has enough reserve to spin up some of the more current hungry 3.5" drives. Seagate drives pull 2.8A on the 12V rail, plus some on the 5V. Can this PS consistently handle spinning up the HDD while also powering the motherboard and other peripherals?
      • Wrong!

        • Re: Wrong!

          P=VI, P=IV, P=IE, P=EI, Watts=Volts x Amps....

          All the same thing.
      • Point taken...

        I append my comment to read,

        "...are almost totally reliant on the number of amps on the 12 volt lines, not the advertised total PSU wattage."
  • Mini File Server might need a splitter?

    If I were to build a Mini File Server... Would I be safe to split their one adapter into two plugs? We are talking probably 2 hard drives with a D201GLY
    • Yeah you can do that, but not recommended with this PSU

      Yeah you can do that, but not recommended with this PSU. There's no 4-pin. Use the SPI220LE which is only a little more money. I bought one for $49.
      • Just trying to save on space

        If I can cut down space, I can reduce the size of the case. We are basically talking considering super small custom system. The fact that I want to use SATA hard disks is debatable.
        • The SPI220LE is already extremely small

          The 80 Plus SPI220LE is already extremely small and it's just as efficient at the lower loads as this 55W PSU.
  • Will a 500W PSU consume 500W all the time?

    If I buy a 500W PSU and only hookup lets say 150W of equipment to it. Will the PSU still consume 500W during normal use? Or Will it use only 150W? I understand peak numbers may be higher. I guess I am trying to determine if I should buy a larger PSU because I might some day add a discrete graphics card to my system and I want the PSU that I am about to buy to support it. But at the same time I don't want it drawing power unnecessarily until I actually add the additional card.
    • Couple of things

      Most gaming PCs even with a highend video card will have a 0%-5% of around 90 watts of actual power consumption which translates to about 112 watts at the plug because of conversion inefficiencies.

      For a good 80 Plus efficient 500 watt power supply, you need at least 100 watts of loading to maintain the 80% efficiency. You start dipping below 80% and the efficiency drops quickly. Non 80 Plus PSUs are even worse.

      For a PC using the cheapest Intel 45nm quad-core CPU and an NVIDIA 9600 graphics card, you can expect idle power consumption down to the 60 watt range so 500 watt or above PSU is a waste.

      Your best bet for a new computer system is a good 80 Plus Seasonic 330W power supply.
      • unless you're a high end gamer

        yes, true - you almost never need a huge PSU unless you're a high end gamer - dual nVidia 9800 GX2s in SLI requires an enormous 850Watts according to nVidia specs (the vendor numbers are a bit lower - i.e. XFX recommends 680W).

        I believe most laptop hardware is specc'd for 80W max, though some like my current laptop will use up to 110 when the dedicated graphics card is getting heavy use. I wasn't surprised by a 55W machine because if you base on hardware essentially designed for laptops or embedded you can probably do that easily - the strange thing is you didn't - the E series is specc'd at 55-75W (more on that below), so you could probably add more hardware if you use a chip designed for laptops like the T Series or any of the lower powered series. I recall reading the Core 2 Duo U7500 actually rated at 10 Watts (which I only remember because I have its big brother - a T7500). Intel's codes are (I'm 90% sure) X=>75W, E=55-75W, T=25-55W, L=15-25W, U=<15W.

        That said, the largest power supply I've owned is 450W and I only needed that because it was the cheapest that had the special Intel power connectors my graphics card required at the time (I've stripped and rebuilt that box once since then and it's due for an upgrade, but I still have room to grow - my last graphics card was rated at 180W and the system uses at most 100-150).
      • I actually went with the Seasonic 380

        Although I was going with an older Q6600 CPU, but still considering the newer 9600 GPU.

        When I consider going with an SLI rig, I might have to go with the 500 W Seasonic, but again, for what its worth, you really don't want to go too cheap on your components.
      • A couple more

        George, I usually buy a PS somewhat larger than I figure that I need, for a couple of reasons. First, the extra capacity means that I don't have to upgrade the PS later if I expand the system. I have had some namebrand systems blow the PS when I added RAM or upgraded the video card. Building in some extra capacity allows for future changes. Also, consider the number of devices that we power from USB ports now.

        Second, especially with cheaper PSs, I find that they run hot when pushed close to the limit, while a higher wattage unit will run cool at the reduced load.

        I would also expect less voltage fluctuations from the unit running at a fraction of its rated capacity. If a PS is taxed to its limit and a device requires a transient burst of power (powering up a HD that had gone into standby, for example), something else must give to supply that power.

        All things considered, though, I agree with your premise. Most system builders over buy on the PS, some ridiculously so. Anyone who buys a 1000+ watt PS and then plugs into a standard outlet is just fooling themselves.
      • These Couple Of Things Are Potentially Inaccur.

        I have a PC with dual core 65nm CPU, 9600GSO video, 4GB memory, 3 hard drives, 1 optical, 1 (~8W) tuner/capture card and when measured by a Kill-A-Watt meter it uses upwards of 240W at the wall, and NEVER idles under 120W including when 2 out of the 3 hard drives are spun down, but clearly the power management is working as it does drop considerably below it's non-idle wattage and CPU utilization is reported between 0-1%.

        The numbers you are claiming are doubtful, even some old Pentium 3 based systems with a single hard drive and power miser video card consume more than 60W idle. The 9600 video card alone will consume over 20W, probably closer to 35W just sitting at the 2D desktop (no Vista Aero either) and you then claim 60W for entire system.

        Your best bet for a computer running at around 200W may be a good quality 330W PSU but "good quality" is the key, quite often the lower capacity PSUs aren't just lower in capacity, they are also built to a price point to the extent that they are shorter lived even within their rated load capability. Some of them won't even allow a system to initialize because the rise-time for the power rails is too slow, too long.

        Ultimately the point should be that a quality 330W PSU doesn't cost much if any less than a similar quality 400 to 500W PSU, so unless there is significantly worse efficiency which there might be, but not necessarily, it is not a useful thing to try and get the psu that has less margin between system load and it's capacity.

        Then there's upgradability and reuse, nobody wants to have to trash a PSU when they do an upgrade because they tried to match it with too little margin, and PSU function degrades over time as the capacitors drift in spec. even if it uses quality capacitors instead of the questionable ones so often found in lower wattage rated PSU.

        THAT is why wise builders put a 500W PSU in a system consuming only ~ 180 to 300W.