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New Mobo & CPU - Same PSU - ok or false economy

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New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Mon Jan 15, 2018 10:53 am
by jaminem
Hi all.
Going to upgrade my internals - Mobo, CPU, RAM and cooler to a Z370/8700K
I have a 400W Seasonic from my old 2600K build.

Is it sensible/compatible to retain, or should I upgrade the PSU as well.
The seasonic calc says load is 274W and recommends 324W so its in spec, but its a good 6/7 years old now

Please advise, Thanks in advance

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Mon Jan 15, 2018 8:19 pm
by job
Check the wattage on the 12v line. There may be a sticker on the PSU displaying it. If it's only listed in amps just multiply it by 12 for the wattage. Then refer to the 8700k for power requirements. Remember that other things run off the 12v also so you'll want some headroom, but i think it'll be around 250-300W for the CPU alone at full load when overclocked.

Then just make sure the PSU has all the necessary cables. I think z370 needs both 24 and 8 pin connectors for power. But check your board specs.

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Mon Jan 15, 2018 9:09 pm
by Agharta
If you have anything but a budget Seasonic then it may very well be good for 10+ years of usage.
As for wattage, as long as you aren't over-clocking much 400W should be fine provided you don't have a power hungry GPU.
PSUs are rated for DC output whereas most reviews measure AC input so that gives you some more leeway when you look at figures.
A modern mainstream i7 system with integrated graphics, one drive and the CPU at stock voltage will struggle to consume more than 150W using typical real world workloads.

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Mon Jan 15, 2018 9:13 pm
by ReedySteadyGo
If I was buying new mobo, CPU, RAM & cooler I'd probably also buy a new PSU rather than use an old one. Do you think the old PSU would last another 6/7 years? Is it particularly good and quiet?

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Tue Jan 16, 2018 10:41 am
by jaminem
Hi all, thanks for the replies.

Won't be overclocking, and will be using on-board GPU (which will mean I have a fully passive AMD GPU card up for sale!) 3 drives and 2 UAD cards. I put this spec in the Seasonic calc and it said theory it should be ok

Good point re the connectors I need to check them

Nothing particularly special about the PSU, just trying to save a few quid...

Thanks again...

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Tue Jan 16, 2018 5:22 pm
by job
Agharta wrote:... most reviews measure AC input so that gives you some more leeway when you look at figures.

No they don't man. They generally use DC probes and sometimes compliment it with software. Any AC measure generally comes with 'from the wall' or some other such description.

For example, Tomshardware's current testing for the 8700k was this:

Image

http://www.tomshardware.co.uk/intel-cof ... 037-3.html

...and got 170W for the draw of the 8700k when overclocked, so 150-200 is a reasonable estimate to use when judging viability of this PSU for this CPU. Although since it's not going to be overclocked it hardly matters.

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Wed Jan 17, 2018 4:42 pm
by Indigo2
Please let us know how the new i7-8700k behaves?
Does it run just fine right out of the box?
Or did you have to make some changes to the power management or BIOS with regards to Intel Speed step, turboboost and more?
What's the name of the mobo?

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Sat Jan 27, 2018 6:20 pm
by jaminem
Indigo2 wrote:Please let us know how the new i7-8700k behaves?
Does it run just fine right out of the box?
Or did you have to make some changes to the power management or BIOS with regards to Intel Speed step, turboboost and more?
What's the name of the mobo?

Hi, just built. Mobo is an ASUS Z370 Prime-A
Disabled c-states and speed stepping, left turbo boost on atm.
Initial signs are good, my latest mix that was maxing out my 2600k is less than 25% on the asio performance meter. Boot time noticeably improved.

Went with a Be quiet modular psu in the end.
Onboard graphics work well, which means I have a passive UHD graphics card (Radeon R7 250 ultimate) with display port, hdmi and dvi connection for sale if anyone is interested. Sorry for the ad (hope it’s ok mods? My intentions are entirely honourable) but passive 60hz uhd cards are very hard to come by for a sensible price, so I’m trying to help! PM me if you’re interested

Re: New Mobo & CPU - Same PSU - ok or false economy

PostPosted: Sat Jan 27, 2018 6:33 pm
by Agharta
job wrote:
Agharta wrote:... most reviews measure AC input so that gives you some more leeway when you look at figures.

No they don't man. They generally use DC probes and sometimes compliment it with software. Any AC measure generally comes with 'from the wall' or some other such description.
For example, Tomshardware's current testing for the 8700k was ....

Exactly, measuring from the wall is AC. :thumbup:
We are looking at total system power consumption here so you don't generally need to waste your time on the minority of reviews that look at the DC consumption of individual components.
Unless you are planning to overclock or undervolt that's way more data than you require. :headbang:
Just because TomsAdwareSite uses such techniques that has no bearing on the overall review market. :!: