Question Sizing PSU for build

[marcplante]

I'm building a PC that will be used for some VR PC gaming. Specs:

MSI Mini ITX 370 motherboard
i7-8700k Processor
32GB of RAM (4x8)
2 M2 SSDs (128GB and 512 GB)
Assume a 2070 super or 2080 GPU
Running in an InWin Mini tower which seems well ventillated, but is small. (4 fans+ CPU cooler fan)

The specs are fairly steep since I run a driving simulator (Though I tend to run with just a couple cars on the track).

Using a Power supply sizer, I get a sizing in the 450-500w range. If I buy a larger PSU (650w-700W) would it run cooler as it is using less of its capacity? Or am I just buying capacity for more peripherals? I don't mind spending more on a larger gold unit if it helps with temperatures.

Thanks

Marc

 

[UsandThem]

Nvidia recommends a 650w unit for both of those cards, and that would be enough for the rest of your stuff. That size would be a good balance for your build. You could also get a quality 550w (as long as it has enough connectors for your needs), and it would be fine as well. However, I would personally get a 650w unit.

Using a Power supply sizer, I get a sizing in the 450-500w range. If I buy a larger PSU (650w-700W) would it run cooler as it is using less of its capacity? Or am I just buying capacity for more peripherals? I don't mind spending more on a larger gold unit if it helps with temperatures.

Generally the "rule of thumb" for power supplies, is to keep the maximum load in the 40% - 70% range as that's usually when they are at their most efficient (the sweet spot), and at their quietest outside of stopping the fan altogether under very low loads on some models).

If you buy too small of a power supply, and if you put a solid 70%+ load on it, it will usually be less efficient and cause more heat (more noise as well from the PSU fan).

 

[marcplante]

Thanks. My thoughts were actually about possibly going to to 750 to keep the psu at the lower end of it's range. My case will be a little small as it will be in a shelf under my tv, and I'm trying to minimize heat where I can. I suppose a 650 will be ok and I can spend the difference on a fan.

 

[LukeSavenije]

If you buy too small of a power supply, and if you put a solid 70%+ load on it, it will usually be less efficient and cause more heat

you're not entirely wrong, but let's get an example here



as you can see here, the difference between the efficiency in overload and peak efficiency is at best 3% on 230v and 4% on 115v.


that i compare with the 850w model of the psu, which shows a similar thing

i put a 550w load on both, resulting in a efficiency of about 90 and 92 percent for the 850w
and 89 and 91 percent for the 750w

which would then be 55/44w vs 60.5/49.5w of lost energy under this load

the problem you do generally get with power supplies beyond 650w is that they can have a lot of current on a single rail. i keep a personal limit of 60a/rail, which would make a 750w still somewhat acceptable, but beyond i recommend multirail units. since they're not very wide spread they'll likely cost more, and so on

I'd rather look at the quality of the unit and with that the fan itself rather than wattage for this reason

 

[marcplante]

OK, so I bought a Corsair RM650X I was thinking about a 750, but figured that was overkill. My thought was minimizing heat, but I'll get a lot more heat out of the CPU and GPU, so I shouldn't worry beyond the fact that I bought a decent PSU.

Thanks for the sanity check.

Marc

 

[UsandThem]

you're not entirely wrong, but let's get an example here

As long as I'm not totally wrong, lol.

Of course it depends on the unit, but a heavily loaded PSU is less efficient, runs hotter, and is noisier.

Also from the review you referenced:

 

[LukeSavenije]

Of course it depends on the unit, but a heavily loaded PSU is less efficient, runs hotter, and is noisier.

again, you're not wrong

i just wanted to show that the difference is in my eyes minor