pros and cons of using more powerful PSU than required wattage ?

[eighthwonder]

Hi,
1) if i use a 650 PSU for a basic system that needs (according to wattage calculator) less than 200 watts, what are the disadvantages and advantages ?
i want to use a good PSU like 80+Gold with longer warranty but they are not available in low wattage like 300 to 400 watts here in India so i have no choice but buy more than what i need.
2) what is your opinion about this PSU ?
Thank you in advance

http://www.primeabgb.com/online-price-reviews-india/corsair-rm650x-650w-fully-modular-power-supply-cp-9020091-eu/

 

[BadActor]

That's a very good PSU. The disadvantages to using a larger PSU would be the cost and loss of efficiency since it will be loaded below the desired range. The loss of efficiency shouldn't be great enough to to make a major impact on your electricity costs. The benefits include being cooler and quieter since it won't being working as hard and the fan speed should remain low. It may also have more longevity because of this. An additional benefit is already having a capable PSU should you decide to upgrade your graphics card.

 

[joex444]

Your system would at peak draw 200W of DC power, but the PSU draws AC power. If you used a 350W PSU that had maximum efficiency of 88% then this 200W DC would be 200/0.88 W = 227W AC. If you used a 650W PSU that was 90% efficient at its peak but at 200W was only 83% efficient then it would draw 200/0.83 W = 241W which would be 14W more power. This means you use a bit more electricity, about 6% more at peak. The 350W would need to dissipate 27W of heat, while the 650W would need to dissipate 41W which is 52% more heat but if we consider the 650W's ideal output of 400W @ 90%, this would be 444W input and 44W of heat. This means the PSU is designed to handle the 41W or so very easily, but in this hypothetical scenario a PSU that's 83% efficient at 200W and 90% efficient at 400W ends up producing very similar amounts of heat.

What you would want to do in particular is look up the efficiency vs power curve for the 650W PSU you're interested in and the lower wattage one. It may be that the lower wattage one, despite not having an 80+ Gold certification, is more efficient at your intended draw and would therefore use less power, generate less heat and be a better purchase.

 

[geofelt]

I have no problem overprovisioning a PSU a bit.
It will run cooler, quieter, and more efficiently in the middle third of it's range.
A PSU will only use the wattage demanded of it, regardless of it's max capability.

1) If a psu is grossly overpowered, I see two disadvantages.
a. you will have paid more than you deeded to.
b. If the psu is truly loafing at 20% of capacity, it will not be as efficient.
on the other hand, I see a couple of plusses.
a. You will not need to buy a stronger psu whenever you upgrade your graphics configuration.
b. Because the psu is loafing, the fan will not need to run as fast, if at all. This makes it quieter.

Sizing a psu is easy; it all depends on your graphics.
Here is a chart:
http://www.realhardtechx.com/index_archivos/Page362.htm

2) Looks ok to me.
Here is one tiered list of psu quality:
https://community.newegg.com/eggxpert/computer_hardware/f/135081/t/45344.aspx?Redirected=true

 

[eighthwonder]

Your system would at peak draw 200W of DC power, but the PSU draws AC power. If you used a 350W PSU that had maximum efficiency of 88% then this 200W DC would be 200/0.88 W = 227W AC. If you used a 650W PSU that was 90% efficient at its peak but at 200W was only 83% efficient then it would draw 200/0.83 W = 241W which would be 14W more power. This means you use a bit more electricity, about 6% more at peak. The 350W would need to dissipate 27W of heat, while the 650W would need to dissipate 41W which is 52% more heat but if we consider the 650W's ideal output of 400W @ 90%, this would be 444W input and 44W of heat. This means the PSU is designed to handle the 41W or so very easily, but in this hypothetical scenario a PSU that's 83% efficient at 200W and 90% efficient at 400W ends up producing very similar amounts of heat.

What you would want to do in particular is look up the efficiency vs power curve for the 650W PSU you're interested in and the lower wattage one. It may be that the lower wattage one, despite not having an 80+ Gold certification, is more efficient at your intended draw and would therefore use less power, generate less heat and be a better purchase.

joex444 thanks for the reply and the explanation
the PSU that i am interested in does provide a good efficiency at 150 to 200 watt draw, check this out and correct me if i am wrong and tell me if i should go for it or look for something else i am very biased on this one because of 7 year warranty + semi-passive cooling and good reviews every where

http://www.tomshardware.com/reviews/corsair-rm750x-power-supply,4303-5.html

 

[eighthwonder]

I have no problem overprovisioning a PSU a bit.
It will run cooler, quieter, and more efficiently in the middle third of it's range.
A PSU will only use the wattage demanded of it, regardless of it's max capability.

1) If a psu is grossly overpowered, I see two disadvantages.
a. you will have paid more than you deeded to.
b. If the psu is truly loafing at 20% of capacity, it will not be as efficient.
on the other hand, I see a couple of plusses.
a. You will not need to buy a stronger psu whenever you upgrade your graphics configuration.
b. Because the psu is loafing, the fan will not need to run as fast, if at all. This makes it quieter.

Sizing a psu is easy; it all depends on your graphics.
Here is a chart:
http://www.realhardtechx.com/index_archivos/Page362.htm

2) Looks ok to me.
Here is one tiered list of psu quality:
https://community.newegg.com/eggxpert/computer_hardware/f/135081/t/45344.aspx?Redirected=true

thanks for the reply, geofelt, tier 1 PSUs are very rare and expensive here in India and all are available @ higher wattage only no good 350 to 450 watt PSUs are sold in my country 🙁

 

[eighthwonder]

That's a very good PSU. The disadvantages to using a larger PSU would be the cost and loss of efficiency since it will be loaded below the desired range. The loss of efficiency shouldn't be great enough to to make a major impact on your electricity costs. The benefits include being cooler and quieter since it won't being working as hard and the fan speed should remain low. It may also have more longevity because of this. An additional benefit is already having a capable PSU should you decide to upgrade your graphics card.

thanks for the reply