Question about power supply calculators + wattages

[btng]

I just used https://outervision.com/power-supply-calculator to find out how much wattage my new build would need and what is recommended. The calculator says that the load wattage of my future system is 641W and recommends a PSU wattage of 691W. However, just under those results they recommend a 850W PSU (with a link to Amazon). Why don't they recommend a 700W or 750W PSU there? 

 

So what is actually recommended for my system that has a load wattage of 641W? Will a 750W PSU do?

[The_Tron]

3 minutes ago, btng said:

I just used https://outervision.com/power-supply-calculator to find out how much wattage my new build would need and what is recommended. The calculator says that the load wattage of my future system is 641W and recommends a PSU wattage of 691W. However, just under those results they recommend a 850W PSU (with a link to Amazon). Why don't they recommend a 700W or 750W PSU there? 

 

So what is actually recommended for my system that has a load wattage of 641W? Will a 750W PSU do?

Yes. They might have suggested 850w at the time as it may have been the cheapest, or for efficiency, which wont matter too much for you. BTW it would help if you could give us a parts list.

[seon123]

If the calculator suggests it needs 640W, I'll recommend a good 450W. The calculators are crap and overestimate by a ton.

[Annual Toe]

You never know if there was a sponsor or slight bias towards a certain manufacturer in the recommendations. Only use calculators to get a basic idea of what your aim should be.

Most builds will only need 500W quality power supply.

[btng]

2 minutes ago, The_Tron said:

Yes. They might have suggested 850w at the time as it may have been the cheapest, or for efficiency, which wont matter too much for you. BTW it would help if you could give us a parts list.

Part list:

CPU: Threadripper 2950X

CPU Cooler: Enermax Liqtech TR4 240

MB: ASRock - x399 Taichi ATXZ TR4

RAM: 4x G.Skill Trident Z 32GB DDR4 3000MHz

Storage: Samsung EVO 970 1TB M.2

GPU: RTX 2080 TI

 

Threadrippers eat lots of electricity.

[The_Tron]

yeeah 750w will do but wid liddle room 4 oc

[ZFGeek]

The 750 watt PSU would probably be fine, you always want to give yourself some headroom when picking PSU.

[Dedayog]

7 minutes ago, btng said:

Part list:

CPU: Threadripper 2950X

CPU Cooler: Enermax Liqtech TR4 240

MB: ASRock - x399 Taichi ATXZ TR4

RAM: 4x G.Skill Trident Z 32GB DDR4 3000MHz

Storage: Samsung EVO 970 1TB M.2

GPU: RTX 2080 TI

 

Threadrippers eat lots of electricity.

When you actually build the system, do a wattage test at the wall to see what she really eats.  For now, you're just blowing wishes.  

 

We'll see if you build it.   If you were going to invest in something like that and had any idea the parts you were buying, you'd know what PSU to buy as well.

[btng]

1 hour ago, jstudrawa said:

When you actually build the system, do a wattage test at the wall to see what she really eats.  For now, you're just blowing wishes.  

 

We'll see if you build it.   If you were going to invest in something like that and had any idea the parts you were buying, you'd know what PSU to buy as well.

 

Well, I would not have asked here if I knew.

[STRMfrmXMN]

3 hours ago, btng said:

Part list:

CPU: Threadripper 2950X

CPU Cooler: Enermax Liqtech TR4 240

MB: ASRock - x399 Taichi ATXZ TR4

RAM: 4x G.Skill Trident Z 32GB DDR4 3000MHz

Storage: Samsung EVO 970 1TB M.2

GPU: RTX 2080 TI

 

Threadrippers eat lots of electricity.

The RTX 2080 Ti isn't out yet, but we'll say it uses 50W more than a 1080 Ti. So, I would recommend a 650W unit for that. A Corsair RM650i would be a nice pairing with your black and white motherboard.

[Stefan Payne]

11 hours ago, btng said:

Threadrippers eat lots of electricity.

Only when Overclocked.
For that, without OC a good quality 550W is enough.

With, only the sky is the limit...

[btng]

So what would be the downsides (except having to buy a more expensive PSU) of having say an 850W PSU instead of a more reasonable 550-650W?

[WoodenMarker]

2 hours ago, btng said:

So what would be the downsides (except having to buy a more expensive PSU) of having say an 850W PSU instead of a more reasonable 550-650W?

A physically larger psu might mean less space for cabling and a smaller relative load might mean not hitting the peak of efficiency curve as often and wasting more electricity. 

[btng]

2 minutes ago, WoodenMarker said:

A physically larger psu might mean less space for cabling and a smaller relative load might mean not hitting the peak of efficiency curve as often and wasting more electricity. 

But according to that graph, a PSU of 750-850W might not be a such a bad idea for me anyway if I want to reach peak efficiency with system loads about 50% (350-425W)? 

[WoodenMarker]

1 minute ago, btng said:

But according to that graph, a PSU of 750-850W might not be a such a bad idea for me anyway if I want to reach peak efficiency with system loads about 50% (350-425W)? 

Most systems outside of render farms rarely hit peak power draw. Most of the time, general use and a bit of gaming pull a fraction of that. 

[Stefan Payne]

4 hours ago, btng said:

So what would be the downsides (except having to buy a more expensive PSU) of having say an 850W PSU instead of a more reasonable 550-650W?

higher fan speed

more damage when something goes wrong due to more energy inside the circuit and higher OCP/OPP

lower efficiency under lower load situations.

 

@WoodenMarker

The Efficiency Curves from the Manufacturers or 80plus are rather bad because they only have like 3, maybe 4 datapoints. And that is 20, 50 and 100% Load, sometimes 10%.

Because the Efficiency "curve" isn't one, its more like a slightly falling line and less of a curve these days.

For example:

https://www.tweakpc.de/hardware/tests/netzteile/corsair_rm850x_white/s03.php

https://www.tweakpc.de/hardware/tests/netzteile/corsair_rmx_2018/s03.php

[btng]

So people in here are recommending a PSU with a wattage of 450W on the low end and 850W on the high end. I am still a bit confused

[Stefan Payne]

33 minutes ago, btng said:

So people in here are recommending a PSU with a wattage of 450W on the low end and 850W on the high end. I am still a bit confused

Its easy:
No OC: 550W

Hardcore no tomorrow OC: 750 or even 850W.

 

 

[awesomegamer919]

1 hour ago, Stefan Payne said:

Its easy:
No OC: 550W

Hardcore no tomorrow OC: 750 or even 850W.

 

 

Depending on the board it may not want to boot without 2 EPS cables plugged in, in which case there are few650w and even fewer 550w units that would work. 

[Stefan Payne]

6 minutes ago, awesomegamer919 said:

Depending on the board it may not want to boot without 2 EPS cables plugged in, in which case there are few650w and even fewer 550w units that would work. 

That's the first time I've heard that.

And the Manufacturers usually also don't mention that.

 

Do you have more information?

[Dedayog]

2 hours ago, btng said:

So people in here are recommending a PSU with a wattage of 450W on the low end and 850W on the high end. I am still a bit confused

Or you can look at people's rigs and see what they are actually using perfectly fine...

 

It's like buying a truck.  400ft/lbs of torque for regular people, 500+ for towing boats, 600+ for a 5th wheel, etc.  It's all relative.  

 

Buy something, use it. It'll work.

[Gedgn]

9 hours ago, Stefan Payne said:

That's the first time I've heard that.

And the Manufacturers usually also don't mention that.

 

Do you have more information?

I second it, that doesn't make any sense.

 

 

@btng Wattage calculators are garbage, don't trust them.

 

550W is fine if not OC'ing, a 650W-750W if you are OC'ing, depending on your overclock.

[zassou]

i generally dont trust calculators. a high end single card rig rarely need more than 300w, but since most psu work at max effeciency at about 50% load. for a high end gaming rig(non-hedt, non-oc) would recommend a 400-500w psu from reputable brands.