Wednesday, October 9, 2013

[Article] There is an advantage of going with an overkill PSU for you PC

A while back I wrote this article in which I talked about how 80Plus Rating of a PSU didn't really mean that much in reality. You should read reviews, if possible, multiple reviews before going with a particular product, not the 80Plus rating.

There are two very important things to check before you choose a PSU. The manufacturer and the capacity. You are almost certain to get a very good PSU, regardless of the 80Plus-ness, if you go with a reputed brand. One can argue that if you go with a PSU that has a high 80Plus rating (gold or platinum), you would get better internal components. Yes, that is correct, but I would pick a 80Plus Bronze rated PSU made by Corsair or Seasonic over a 80Plus Platinum rated PSU made by an unknown manufacturer. You are definitely paying a price premium for the brand name and the higher 80Plus rating, but it is better not to cheap out on PSUs. Cheap out in terms of 80Plus rating, and not the brand.

Capacity is the next point. You definitely want to have some headroom for future expansion. But how much? The GPU is the most power hungry component in a typical high-end PC (unless of course you are going with a AMD FX-9370 and overclock it further), so you can get a rough idea about how much power you need. For a high-end gaming PC with a single graphics card, even when overclocked, won't use 500W. For two graphics card, 750W should suffice. I'm talking about a typical high-end users. Not the ones who want to break overclocking records. Even for a couple of NVidia Titans, 850W PSUs would be more than enough. If you want triple or quad graphic card, you are looking at 1200-1500W to be safe. That is, only if you are going with the most power hungry GPUs. (i.e. Titan)

Now, going overkill not only costs you a lot of initial capital that will never pay off, but will also cause your power bills to go up. It won't be THAT noticeable though. See, the thing is, there is a wattage range where the PSU can perform very efficiently. When too less power is drawn from it as well as too much power is drawn from it, the efficiency goes down the toilet. Usually 20% to 80% range is where the PSU is efficient, and around the mid point is the peak of the efficiency curve. Since most PCs are sitting there idle most of the time, the PSU's operating point will be below 20%. 20% of 850W is about 160W. Most current generation PCs idle well below 100W, even with a graphics card on. Even though the PC is only using about, say, 100W, because the effiency of the PSU is low at below 20% load, the PSU might be running at 70% efficiency. This would result in the PSU pulling like 142W from the walls even though the PC is actually only using 100W. Now, if you had a PSU that has a capacity of 400W, it will be perform decently at 100W load. Perhaps you might get like 85% efficiency and that would pull only 117W from the walls. 25W difference between a 400W PSU and a 850W PSU at idle. So basically, getting a PSU that fits your PC's load is ideal in terms of the initial capital you put into the PSU and the eventual power bill. Remember though, that the difference in power consumption would be smaller when the load increases. If the 400W is too low, you might actually see better efficiency with the 850W PSU.

But going overkill has it advantages as well. The chances of failure is less because the components inside the PSU won't be stressed as much as in the case of a lower capacity PSU. That not only prolongs the lifespan of the PSU, but also allows it to run cooler and quieter. If you like silent computing, like myself, you should probably go slightly overkill in terms of the capacity of the PSU. 

By all means, get a PSU that has modular cabling.

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