Psu overpower?

[orphan]

Is it possible to get a power supply with too much wattage or is it safe to go overboard? Also, how do i know what powersupply is right for my system?
My chasis is ATX if that's all that matters...

 

[jaguarskx]

Is it possible to get a power supply with too much wattage or is it safe to go overboard? Also, how do i know what powersupply is right for my system?
My chasis is ATX if that's all that matters...

There is no danger in buying an overpowered PSU for a PC because the PC will only draw the power that it needs. However, an underpowered PSU is dangerous because the PC can draw more power than the PSU can supply. At best your system will just freeze or maybe reset. At worst your PSU will die and take the rest of the PC with it. Meaning you'll need a whole new PC.

Here is a link to a popular site that has a Power Comsumption Calculator. There are people who have criticized the site for high estimates, but I suppose it is better to guess higher power requirements than lower power requirements. As an example of the site's high estimates, the Athlon X2 3800+ is rated to consume 89w at 100% load. That is incorrect 89w is the max TDP of the X2 3800+, not power consumed. Basically that is how much heat the CPU will generate under the worst conditions. Power consumption is more like 65w, which is done by actually measuring how much power the CPU itself is consuming.

Here is a link to some actual CPU power consumption measurements. If you overclock the CPU or GPU it will naturally draw more power. Also note that Pentium 4 draws much more power than an Athlon 64. That is why on some video card boxes there is a minimum PSU power requirement. ATI and nVidia recommends high wattage for some cards because they don't know if you are running an Athlon 64 or Pentium 4. Intel's next CPU, Conroe, should be more in line with the Athlon 64s.

In the old days the CPU almost always draws more power than the video card (GPU). That is no longer true. Very powerful GPU draws more power than a CPU, this is especially true of ATI cards. Therefore, ATI GPUs can have larger power requirements than nVidia GPUs. Here is a link to GPU Power Consumption measurements.

Regarding the physical size of a PSU, ATX PSUs are for ATX cases. m-ATX PSUs are for m-ATX cases. There are some m-ATX cases that do take ATX PSU though, the case's specs will tell you.

There is one bad thing about buying a PSU that is more powerful than what you actually need, besides paying too much. That's inefficiency. In general the lower the load on a PSU the less efficient they will be. PSU are typically at thier most efficient when the load is between 50% - 90% of the maximum power the PSU can deliver.

Okay, what the hell does that mean? Power Supplies have a maximum efficiency rating listed somewhere in the specs. The higher the efficiency the better because that means less power is being drawn from the AC outlet.

For example, PSU #1 is 65% efficient, PSU #2 is 85% efficient and the both PCs draws 200w of power from there PSUs. Because PSU #1 is only 65% efficient, it will draw 308w from the AC outlet (308 = 200/0.65). PSU on the other will only draw 235w from the AC outlet (235 = 200/0.85). Big difference, huh? Wait, it gets better. As I said before, at lower loads the PSU is not as efficient as they can be. Let's say both PSU are 600w units, the PC will only draw a max of 200w. That means that best the PSUs will only provide 33.33% of thier maximum load, so they are running below thier max efficiency. Let's say PSU is only 60% efficient and PSU is on 80% efficient at 33.33% load. Doing that math that means PSU #1 will be drawing 333w from the AC outlet, and PSU#2 will be drawing 250w from the AC outlet, yet your PC actually uses only 200w.

The "wasted power" is lost due to heat and the inefficiency of the PSU to convert AC to DC. That difference can add up to a lot if you leave your PC on 24/7.

So how do you know if a PSU is good or not? While it's good to get suggestions from people, it is better to read hardware reviews about the PSU you want to buy. Unfortunately, PSUs are not reviewed as much as other products so it is very possible that the PSU you want has no hardware reviews at all.

Hardware review sites:

SilentPCReview

PCStats.com

ExtremeOverclocking.com

Systemcooling.com

A good primer is this article:

Power Supply Fundamentals & Recommendations

 

[orphan]

Wow, thanks for the info. I'll be sure to find a power supply that isn't too little or too much keeping all of this in mind.