1 - 18 of 18 Posts

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
I'm sure this is an exceedingly simply topic for anyone with any electrical experience. Alas, I do not qualify for this demographic. I'm looking to get a computer with an 800 watt power supply. I can't post a link until I post 1 comment, or so the "Preview Post" screen told me, so I'll try to just screencap the info.
Firstly I'd like to know what you all would expect the amps drawn (is that how you put it?) from that will be, because most everything in my 1 bedroom apt is on the same 15 amp circuit. A tad more info: 43 inch TV at 1.2 amps, window AC unit at 4.9, and if I microwave something I always make sure the AC is off for the duration, as nuking draws 7.5 amps, I think. I also have a standard 16" or so fan I run a lot, not sure about its draw. Based on the power supply info, would it be safe to run with the AC and TV, or TV and microwave on a 15 amp circuit? Should I just look for an outlet on a separate circuit? If so, how do you go about determining which outlets are on what circuits?

Any and all advice on this would be greatly appreciated. Thanks for reading.

#### Attachments

• 46 KB Views: 87

#### Jim Port

·
Joined
·
13,492 Posts
To determine amps you divide the watts by voltage (120 or 240).

Motor loads spike higher when starting, but then drop to the running amps.

Your PC is not going to be drawing 800 watts all the time.

Atreyu GoBlesYu

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
PC PSU are rated in watts on the output side which varies from 12V, 5V and 3.3V. In the picture it shows that the unit has an input of 12A/5A depending on the voltage, so you're more likely going to be around the 10A mark with 120V. Actual input appears to be 1200 watts (12Ax100V).

That's full load though so unless you add all of the specs of the PC it's going to be hard to say what it will draw on a regular basis. Personally I'd look for a separate circuit because when the AC kicks in the voltage will drop and could present problems for the PC if you don't have a UPS connected.

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
No real easy way to trace a circuit other than make a drawing, turn the breaker off and see what still works and what doesn't. Never assume outlets next to each other etc are on the same just because it would make sense. Doesn't take very long though with a light or an actual outlet testing. Just make sure whatever you use to test the outlets with doesn't have a battery backup

#### mpoulton

·
##### Semi-Pro Electro-Geek
Joined
·
3,403 Posts
The actual power consumed by the computer depends on the computer parts, not the power supply rating. 800W is the maximum that supply can handle, but it will only consume as much power as the components it is supplying require. That will probably be much less than 800W. You'll need to look at the full-load power ratings of the CPU and graphics card, plus the power used by each of the disk drives in the system, plus a little bit of overhead (maybe 20%) for fans and internal inefficiencies. Most reasonably powerful desktop PCs these days only use a couple hundred watts max. The highest power consumption i& processors use 140W max, and graphics cards run 200-350W for most high performance units, with only a few requiring more.

Atreyu GoBlesYu

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
The actual power consumed by the computer depends on the computer parts, not the power supply rating. 800W is the maximum that supply can handle, but it will only consume as much power as the components it is supplying require. That will probably be much less than 800W. You'll need to look at the full-load power ratings of the CPU and graphics card, plus the power used by each of the disk drives in the system, plus a little bit of overhead (maybe 20%) for fans and internal inefficiencies. Most reasonably powerful desktop PCs these days only use a couple hundred watts max. The highest power consumption i& processors use 140W max, and graphics cards run 200-350W for most high performance units, with only a few requiring more.
Oy, this is a lot to take in. I mean, the spike when you turn it on shouldn't be a big deal, I'd just have to turn it on before I turn anything else on, no biggie. Well, it has a gtx 1080ti, which is pretty up there. Tom's Hardware has an article on its power consumption: http://www.tomshardware.com/reviews/nvidia-geforce-gtx-1080-ti,4972-6.html
Oh, man, this seems like a daunting task just trying to find the max power consumption for all the parts. i7 7700k 4.2ghz processor, 3TB hdd, 240GB ssd, 32GB ram 4x8 configuration 19,300MBps, liquid cooling for the CPU, some MSI motherboard, no optical drive. Yeah, probably best to just try and find another circuit in another room that I never use. I must have one. If worse comes to worst, I guess I can always hire an electrician to re-wire everything. Ugh, why don't all places just have 30 amp circuits?

Well, any further advice anyone has will, of course, be greatly appreciated.

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
One thing I don't get is if America usually has 120v circuit, and you divide the wattage by the voltage to get amps, wouldn't 800w / 120v be 6 2/3? Where does the ~10 amps number come from? Why is electrical engineer more mysterious and difficult to understand for me than cosmology?

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
It's way easier than it used to be to calculate this stuff. Outervision, SeaSonic and several others all have component level calculators.

The link below pretty much has all of the components you just listed and draws around 433 watts. This assumes stock clocks and voltages. Overclocking these will easily put you in the 500 watt range. You could get away with a 600 watt PSU with no problems for this rig.

If you go SLI with the 1080 and overclock then you'd be needing a bigger PSU like 900 to 1000 watts.

https://outervision.com/b/bRsCKn

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
One thing I don't get is if America usually has 120v circuit, and you divide the wattage by the voltage to get amps, wouldn't 800w / 120v be 6 2/3? Where does the ~10 amps number come from? Why is electrical engineer more mysterious and difficult to understand for me than cosmology?
Read above, 800 watts is the output on the DC side of the PSU, not the input. If you were to have 800 watts on the input side you'd be getting more like 550 output on the DC side. A computer power supply converts 120V AC to 12V DC, 5V DC and 3.3V DC. Each one of these voltages is defined as a rail on the PSU sticker.

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
By the way, nice rig! Still running a Q6600 oc'ed to 3.2 with a 460 GTX. Desperately need an upgrade.

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
Read above, 800 watts is the output on the DC side of the PSU, not the input. If you were to have 800 watts on the input side you'd be getting more like 550 output on the DC side. A computer power supply converts 120V AC to 12V DC, 5V DC and 3.3V DC. Each one of these voltages is defined as a rail on the PSU sticker.
Whew, I might as well be looking at hieroglyphics. How does it decide to switch btw 12, 5, and 3.3v dc? Or does it do all 3 at once? Christ, feels like I'm climbing a mountain of new information.

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
Whew, I might as well be looking at hieroglyphics. How does it decide to switch btw 12, 5, and 3.3v dc? Or does it do all 3 at once? Christ, feels like I'm climbing a mountain of new information.
The plugs only fit one way :vs_cool:

Don't sweat it, it's like grown up Lego's. It all depends on what device you plug in and how it needs to use the proper voltage but that's built into the device, no leg work on your part. You'll mostly have a 24 pin ATX power plug for the MOBO, then some 4 pin molex for older drives, devices and possibly your water cooling. 6 pin PCI power for the graphics and SATA plugs for your drives. Take your time and DON'T force anything into place. Sometimes you need to push things in but don't force anything because you'll break it and need to replace a whole lot more than just a plug. MOBO's are easy to crack if you put too much force on them - ie wrong component in wrong slot + Hulk smash = \$\$\$

Toms used to have a lot of good info, haven't visited them in awhile.

#### Paulusgnome

·
##### Registered
Joined
·
91 Posts
Read above, 800 watts is the output on the DC side of the PSU, not the input. If you were to have 800 watts on the input side you'd be getting more like 550 output on the DC side. A computer power supply converts 120V AC to 12V DC, 5V DC and 3.3V DC. Each one of these voltages is defined as a rail on the PSU sticker.
I would expect much greater efficiency from a modern switchmode computer PSU than this. It would be a fairly poor PSU that gave less than 90% efficiency, and I'd expect better than 95%. Hence, if your PSU was drawing the full 800W that it is rated for, it should be wasting around 40W and delivering the remaining 760W to the PC internals.

As others have said, the PSU will be overframed so that the power it is actually supplying will be quite a bit less than its maximum rating.

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
The plugs only fit one way :vs_cool:

Don't sweat it, it's like grown up Lego's. It all depends on what device you plug in and how it needs to use the proper voltage but that's built into the device, no leg work on your part. You'll mostly have a 24 pin ATX power plug for the MOBO, then some 4 pin molex for older drives, devices and possibly your water cooling. 6 pin PCI power for the graphics and SATA plugs for your drives. Take your time and DON'T force anything into place. Sometimes you need to push things in but don't force anything because you'll break it and need to replace a whole lot more than just a plug. MOBO's are easy to crack if you put too much force on them - ie wrong component in wrong slot + Hulk smash = \$\$\$

Toms used to have a lot of good info, haven't visited them in awhile.
Oh, there's no way I'd build this myself, plus I've checked the individual prices of all components and, even if it were cheaper to build one (which it doesn't look like it is), the headache saved by not worrying about accidentally breaking something is well worth whatever extra money I'd plunk down for a prebuilt model. I remember putting a GTX 960 with a blower fan into my current PC. Had to have a friend walk me thru it in a call on my laptop, and that's probably the SIMPLEST part to install.

Maybe I shoulda just linked this earlier for reference, but this is the model I want to get, just not from this website. CyberPowerPC Desktop - Intel Core i7 - 32GB Memory - NVIDIA GeForce GTX 1080 Ti - 3TB Hard Drive White SLC8602OPT - Best Buy

I'm still not sure how to properly calculate amps now. How do you get the 10 amps number? Walk me thru it like I'm 7 years old, if you don't mind.
I would expect much greater efficiency from a modern switchmode computer PSU than this. It would be a fairly poor PSU that gave less than 90% efficiency, and I'd expect better than 95%. Hence, if your PSU was drawing the full 800W that it is rated for, it should be wasting around 40W and delivering the remaining 760W to the PC internals.

As others have said, the PSU will be overframed so that the power it is actually supplying will be quite a bit less than its maximum rating.
I've seen data on a 1080ti alone when pushed to its limit that say it runs in the neighborhood of 300 watts. The cpu nears 140w at its limit. I wouldn't be surprised if the average modern game with high end graphics running on this rig require 600w on average. Man, this is really stressing me out.

#### Fish_Stick

·
##### Registered
Joined
·
220 Posts
If you're not going to build it yourself then don't overthink all of the above.

For calculating the input amps (out of the wall) there's a sticker on the side of the power supply. The one you have in the screenshot shows the following: AC Input - 100-240V 12/5A. So take the voltage times the amps and you'll get watts. 100Vx12A=1200 watts. Then to find out the amps on a regular 120V circuit, divide the watts by the voltage. So 1200 watts / 120V = 10 amps. So that answers the maximum number of amps that the PSU will use. Always calculate it though based on the sticker values for the listed voltages.

A lot of modern games aren't going to max out everything though, the CPU can run below 100% in alot of cases and depending on the monitor you hook up you might not even max the card. Several of the tests I found were on 4K and that hit the 300 watts. Long story short - I thought you were building the pc so gave you more info. Buying prebuilt though don't sweat it. They match the PSU to the components. It'll run out of the box without any issues.

#### ddawg16

·
##### JOATMON
Joined
·
15,307 Posts
Whew, I might as well be looking at hieroglyphics. How does it decide to switch btw 12, 5, and 3.3v dc? Or does it do all 3 at once? Christ, feels like I'm climbing a mountain of new information.
It's a switching power supply. It takes the incoming 120Vac....chops it up into a high freq signal....then produces the 3 DC voltages your computer uses using solid state devices vs conventional transformers.

Typical efficiency will be 90% or better.....which is better than a typical transformer.

As others noted, the 800W is the output power. Even with a 90% efficiency, you are not going to get close to 10A on the input.

I deal with power draw by computers all the time (UPS sizing). In my experience, a typical PC is going to pull 1.5-2.5A under normal operation.

#### dmxtothemax

·
##### Registered
Joined
·
5,468 Posts
QUOTE - How does it decide to switch btw 12, 5, and 3.3v dc?

ANSWER - Or does it do all 3 at once?

yes the power supply has multiple secondaries
so it will provide many voltages simultaniously !

:glasses:

#### Atreyu GoBlesYu

·
##### Registered
Joined
·
7 Posts
Discussion Starter
QUOTE - How does it decide to switch btw 12, 5, and 3.3v dc?

ANSWER - Or does it do all 3 at once?

yes the power supply has multiple secondaries
so it will provide many voltages simultaniously !

:glasses:
Thanks, I definitely appreciate the help.

I think I also need to get a good UPS before I even turn it on, but maybe I'm just being paranoid about a fairly major buy.

1 - 18 of 18 Posts