Power Supplies
Power Supplies
First, Let me explain a myth. If you are buying a 400 Watt PSU, you're not getting 400 Watts, maybe 250, but that depends on who and how they made it -- But don't get worried yet. A 400-2000 MHz CPU takes between 40-60 Watts (Peak). A P4 3.2Ghz takes 89-103Watts (Depending on CPU model). A video card takes about 30-60 Watts, unless you're getting the latest NVidia 5x00, 4x00 that takes about 90 Watts (Peak). Hard drives take about 5-10 Watts. Your motherboard takes about 10 Watts. Fans take 2-5 Watts. A typical computer system takes in total about 190 Watts Peak, 160 Watts average/idle.
A normal switching type power supply is only 50%-60% efficient and so can only handle 50%-60% of the wattage the power supply is made for. If you have a 350Watt power supply, you can safely get about 210 Watts out of it. Solid state power supplies can be over 70% effecient and will let you put a higher load on it without over stressing the power supply, but they are much more expensive and rarely used for computers. All power supplies have an optimal power load where they are the most efficient. If you draw too much power they get extremely warm and hot electronics are not as efficient and don't last as long. If the power draw is too low you really waste power.
You might be surprised what you can get out of smaller power supply. I thought that a 250 Watt power supply I was using was staying too warm because too much power being pulled through it (Running an AMD XP 2600 and 1 hard drive). When I bought a new case with a 350 Watt power supply and I was surprised to find that it was even slightly warmer than the 250 Watt power supply and I was using more power and money to power the same system. This was because the 250 Watt PSU could output enough DC power to run the system, probably close or over it's recommended load. The 350 Watt PSU had plenty of extra power and converting that extra power, even though it was not used, caused more heat.
In mid 2004, I reviewed the Silverstone ST46F PSU in my search to find a safe HTPC case when needing to have 4-8 hard drives to hold a fair amount of HDTV recordings. The power supply worked very well but when a brief power outage hit an APC 350VA UPS (Which outputs up to 180 Watts) no longer would keep the system up, even for a split second. Again, increasing from a 380 Watt Power supply (About 250 Max Watt output) that I was using before the ST46F and keeping the same hardware ended up with the HTPC drawing more power. Luckily, Office Depot had a special a week later for a 500VA APC battery backup that was free after rebates. The one exception to the normal rule when getting a larger PSU is that the ST46F ran cooler than than every PSU I have used, including the old 250Watt. The ST46F is one of the most effecient PSU's on the market, but it still took in 460 Watts, which means more money to power it. I have yet to find a PSU that only draws the power that it needs.
Now back to figuring out which PSU is right for you. I decided to do a bit of research to found out how many Watts a computer or HTPC really needs. The reason there are now certified power supplies is because power supply companies had cut corners in the past and didn't provide enough power for some outputs from the power supply. The amount of power that was sent to the motherboard (Vs. hard drives and fans) was not enough to run the latest video cards and CPU's at the same time and it caused new systems to be unstable when needing peak performance from both at the same time. In my situation, the first 250 Watt power supply I was using had enough output in Watts for the CPU and video card. Buying a new power supply only provided me with the option to add more devices like hard drives. Even later yet, I have found that manufacturers are still cutting corners.
At the beginning of 2004 I went to use my HTPC one day to find it was off and would not power on. It turned out my power supplied had been fried (I was using 3 drives at this point) and had taken one of the hard drives out with it. (And the irony I have to note, is I don't believe in burning CD's, so I kept all my pictures, programs I've written, and everything critical on two hard drives in 2 machines. It just so happened that before I had the system back up I lost the other 10GB Western Digital drive. To be fair, I don't know if the drive went out taking the power supply with it, or the other way around, but I will probably never know.) Regardless, I learned not to trust just any power supply because bad QA, bad design, or many other things will cause power problems in a computer and that is not acceptable when you care about the hardware or content it is holding.
In the past, looking back now, I thought having a quiet power supply was the most important. I had recommended to find power supplies that were the quietest and to pick one you can afford and buy that. I was wrong. The power supply you get can be very important. The power supply is one the second or third highest heat producers of heat in a computer. In many cases, having a cool power supply means it won't be raising the ambient temperature in the case. Also, having a good fan that can cool the power supply well also means it is pulling a lot of air through the computer case to keep other computer components cool.
The best designed power supplies I have seen are the ones with a 120mm fan on the inside of the case, next to the CPU. The SilverStone power supply designs are an example of this. Having the fans on the inside of the case moves a lot of air and are fairly quiet because they use a larger fan that rotates slower to keep noise down. They still move as much or more air than the noisy power supplies with a smaller fans just on the back of the power supply. These type of PSU's are not silent, but right now I don't believe silent is the way to go unless you have a low end HTPC.
As for what size of power supply you need, it depends on your case, your hardware, and internal components. A 350 Watt power supply is fine for a lower end HTPC. If you plan on having 4+ drives, a high-end video card, and building a system like mine I recommend getting 380Watts or higher. Pay attention to how much current (Amps) a power supply supports for it's +12 Voltage as this is what hard drives run off of. Most hard drives take up to 2 Amps of current. The +5 Voltage rail is for things such as PCI cards. I recommend looking at Toms Hardware and other sites if you don't go with a SilverStone or Antec power supply that I trust and recommend. I have researched and tested these and I know they can be trusted. Both of these companies are leagues ahead of other PSU companies. The Antec True Power line will guarentee you won't have lack of power between hardware at peak performance while still staying with a lower wattage PSU. The SilverStone gives you much, much more airflow at a quiet speed and high effeciency. Also to note, SilverStone does have lower wattage PSU's than the ST46F and they also have the same effeciency and design. As for comparing voltages, read my review of the ST46F. Both Antec and SilverStone have fairly solid voltages, with the ST46F being slightly more stable and especially under system load.
So what is quiet and what determines how loud a power supply or system is? Quiet usually means it has a decibel rating of less than 40, but silent is below 27 (The loudness of a whisper). Anandtech has a recent review and noise test levels for their power supplies and so does Toms Hardware. You should also be aware that many power supply and cases are advertised with their lowest noise level. If the CPU is not idle then what they claim goes completely out the door. I can't hear anything from an Antec Sonata case when it's idle, but when you start running that system hard it becomes very noticable because of the CPU fan.
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