Power Supply Desktop PC

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SpartanVXL

1317 posts

Uber Geek

#2668409 5-Mar-2021 16:51

A 2060 super has a power limit of 180W, you’d be find with a 450-500W even if you raised that limit.

Without going into much detail on what a cheap psu does over an expensive one, no you don’t need excess capacity. A good psu will deliver what it says on the box to your parts, the efficiency rating is what it actually draws from the wall eg. A 750W with 90% will draw 833W from the wall at full load, not that you’d do this of course.

kiwis

832 posts

Ultimate Geek

#2668479 5-Mar-2021 17:22

Thanks everyone for the replies.

jpoc

1043 posts

Uber Geek

#2668661 6-Mar-2021 07:40

Dial111:
fe31nz: If you put a 2000 W power supply on a system that is normally only using less than 200 W, it will be working below 10% of its capacity and will be badly inefficient, increasing your power bill and heating the room it lives in.

Your computer will only draw what it needs from the psu not the other way around, it's totally fine to use higher rated psu's there is no wasted power draw

That is not correct. While the computer will just take the power that it requires, the power supply will be operating well outside its optimum range.

If you look at the specifications for power supply efficiency ratings, you will see that the requirement is that the PSU is measured for peak efficiency at a load of 50% of its rated power.

The efficiency is also measured at 20% and 100% of rated power and is permitted to be lower. The only standard that has a requirement outside that range is the 80 plus Titanium standard which also states the required efficiency at a 10% load.

Since that is the only one for which we have a specification at such a load factor, consider two computers which both have a 200W power draw. With a 400W 80 plus Titanium supply, the PSU efficiency is 96%. A 2000W supply with the same efficiency rating is only required to be 90% efficient when delivering 10% of its rated power. At NZ power prices, the 2000W 80+Ti supply will cost an extra $30 a year as opposed to a 400W supply with the same efficiency rating. That is if the computer is switched on 24/7.

If you look across the range of 80 plus specs and consider a computer with a 400W power drain running off a PSU with a power rating of 400W or 800W you will see that the 800W PSU running at its most efficient load will save $15 a year compared to the same computer with a 400W PSU. That is assuming a computer that is turned on for 12 hours a day with power supplies that have the same 80 plus rating. Alternatively an 80 plus silver PSU rated at 800W will cost the same to run as a 400W 80 plus platinum unit.

SomeoneSomewhere

1804 posts

Uber Geek

Lifetime subscriber

#2668676 6-Mar-2021 09:05

Example graph of efficiency:

source

Larger power supplies have larger standing losses, which is the power drawn even when no power is being supplied, and efficiency is by definition zero.

You can see that peak efficiency is at about (a bit under in this case) 50%. If your computer was expected to be running at full power 24/7 (like a mining rig or render farm), you might size the PSU to run at around 50-60% capacity.

However, if your PC spends most of its time at idle, most of its power draw is going to be around that 50W mark. It might reach peak efficiency occasionally but rarely, and the efficiency is going to be relatively poor the rest of the time.

Things that happen with an undersized PSU:

Ripple and noise generally increases as load increases, but decent PSUs will be well within spec even at full load. A good PSU fully loaded is likely to perform better than a cheap one at 30% load.
It runs hotter which shortens its lifespan - but it rarely reaches or stays at full load for hours in consumer use.
Overcurrent protection cuts in and turns off your computer, at least if it's a good quality one.

K8Toledo

1014 posts

Uber Geek

#2669715 7-Mar-2021 20:55

kiwis: When I upgraded my PC last year I used an old 500W PSU.

At the time I was told to get a 650+ and see many gaming rigs with feedback to get a 700 or 750W PSU.

Two questions

1) What does the higher PSU give you? Is there a performance boost or what’s the reason?

2) If I was upgrade - what am I looking for? Specs below. Current PSU is all plug and play. Easy to install from unit to components

B450 Pro Board
3600X CPU
RTX 2060 Super GPU
16GB RAM (may go to 32GB)
2x 1TB SSD
2x 3TB HDD
Fan cooling

Maximum load plus some headroom factored in means the PSU doesn't have to work as hard over it's lifetime therefore (should) last longer. I usually allow for about 20%.

So for example if max load is likely to be around 500W I'd personally go for ~700W PSU. Single rail preferably. Also when looking at output look at amps not watts.

SomeoneSomewhere

1804 posts

Uber Geek

Lifetime subscriber

#2669732 7-Mar-2021 21:22

Single rail is BS. Essentially, multi-rail PSUs have individual short circuit protection on groups of output wires, so it trips if you pass more than 20-30A on each set, depending on model.

A single rail PSU will happily feed the full rated current down a single wire, which is a bit of a hazard if you have a larger PSU that can provide 70A+ - it's quite likely it will never detect a short circuit.

A properly designed multi-rail PSU isn't ever going to trip on a normal load, or if it does, you're probably misusing it (using chained PCIe splitters to feed all your GPUs from one cable, for example).

richms

28191 posts

Uber Geek

Trusted

Lifetime subscriber

#2669835 8-Mar-2021 09:32

IME not having per wire current limiting is negligent on PSUs since they can easily get one of the wires up to smoking temperatures. Paralleling up a low current connectors pins for high current is an absurd way to do it, but I dont expect that we will see modular power supplys with anderson connectors on them anytime soon, despite thats basically what they should be with the move to 12v only.

Richard rich.ms

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