Reduce max TDP of i5-4670K by undervolting/underclocking?

[phositadc]

I'm thinking about doing a mini-ITX build in an Antec ISK-110, which has a built-in PSU of only 90W (might be able to swap it out with a 150W PicoPSU). I've read success stories from people using cpus with max 65W TDP in the ISK-110. So at first I was thinking I would get an i5-4670S or even an i5-4670T, but then I started thinking I could get a 4670K and just undervolt and underclock it down to a max TDP of < 65W.

Is it safe to assume that I could achieve that? Or is some 4670K silicon not capable of running stable on an undervolt? I read that a 0.1v undervolt would result in a max TDP of 69W.... so if I could get 0.11-0.12v undervolt, that would get pretty close to 65W.

Anybody know how realistic that is? Or would I be better off just going with a 4670S or 4670T to get the guaranteed lower max TDP?

Also, it's been awhile since I've done a custom build. Would the best means of achieving this simply be to do a voltage offset of -0.1x to achieve the max TDP that I desire?

Any thoughts greatly appreciated!

 

[Headfoot]

This should be theoretically possible but consider that it will probably boot to regular full TDP in the first place, before you can undervolt it. You don't want to overload the PSU immediately. If you took care to attach no peripherals until you had successfully undervolted, this would be feasible. Given that Intel has idle states that aggressively undervolt and underclock, you should be able to do the same without much hassle. You could most likely undervolt and reduce consumption quite a bit without lowering clocks much or at all, given that voltage is the primary driver of power consumption with clock speed a distant second

Also consider getting low-power HDDs/SSDs, lower voltage RAM as well. There are 1.35v ddr3 kits out there that would save you some consumption on that end as well.

I personally would be most comfortable using the 150w supply if I were using the full 4670k, considering total consumption after all peripherals and not knowing the efficiency of the power supply

 

[BSim500]

I read that a 0.1v undervolt would result in a max TDP of 69W.... so if I could get 0.11-0.12v undervolt, that would get pretty close to 65W.

Anybody know how realistic that is? Or would I be better off just going with a 4670S or 4670T to get the guaranteed lower max TDP?

It's entirely possible, though if you're undervolting and not OC-ing, you don't really need a K chip. You could just buy a regular i5-4670. Forget T chips - they're too GHz crippled for the price. S chips are good if you don't want to fuss about undervolting, or if you want to save some $ on a non-Z motherboard. Also the quoted 84w TDP's are just the absolute peak that the worst binned chips will typically draw. To give you an idea:-

- I can sustain a -0.1v undervolt on my i5-3570 up to 4.0GHz. Despite being OC'd from 3.4 -> 4.0Ghz, it's real power draw at this speed & voltage is barely 62w (vs 77w of a "stock" i5-3570 @ 3.4GHz). That's a 15w (20%) drop in TDP even with a mild 600mhz overclock. Even at peak 4.2GHz OC and no undervolting, it draws under 70w (10% less than quoted 77w).

- At pure stock 3.4GHz, I can get it down to -0.125v undervolt (resulting in humorously low 0.896v load voltages). At this speed & undervolt, it draws around 49w (36% less than a theoretical listed 77w).

NB: All above load figure are totally maxed out running Prime. Real world usage figures are 5w lower when running, eg, x264 still fully loading all 4 cores. General apps and games are much lower - often just 20-40w load on the CPU itself. Each chip also has different "binning" though, and your mileage may vary, but the real key is getting a "good" CPU with low stock voltage then pushing it downwards further. If you bought a regular i5-4670 (non K non S), kept it at stock, and undervolted it, it's highly unlikely you'll pull over 60-65w.

Other things to think about:-

- Buy a Haswell i3 instead. They run 54w max, and can be heavily under-volted often by over -0.1v as well, bringing their typical max loaded TDP down to under 35-45w making them perfect for compact Mini-ITX cases with sub-100w PSU's. You can expect 2/3rds of the performance vs an i5 (often with better performance than a 2.3GHz i5-4670T) in general apps, and 4/5 to 9/10 of the performance in most games (though with a 90w PSU, you won't be using GFX cards anyway so the difference there will be virtually zero). i3-4330/4340 are the best choice due to having the same HD4600 GFX unit as the i5 whereas the i3-4130 uses the HD4400 if that makes any difference. If you have very low usage needs (just office / internet work / playing DVD's & Blu-Ray, etc), you could save a lot of money by buying a Pentium G3420 (54w - again probably nearer 35-40w undervolted).

- Use SSD's or at least 2.5" HDD's (which draw up to 6w less power than 3.5" HDD's).

- Low voltage RAM might knock off 2-3w of power, depending on motherboard support.

- Disable any unwanted stuff on the motherboard. Eg, serial ports, stuff like Virtu-MVP, etc.

 

[phositadc]

Thanks to both of you for the responses. Very helpful.

I will definitely be using low voltage RAM and a low power SSD (planning on a Samsung 840 EVO, which I understand is among the lowest power consuming SSDs available).

I'll go ahead and rule out the "T" model and either just get a 4670 or 4670S. Maybe the S would be safer since it has the same turbo boost speed as the regular 4670 but a max TDP of 65W, so by undervolting I would be guaranteed to be substantially below even that, which would virtually assure that the 90W PSU would be fine.

Thanks again for the responses.

 

[coffeejunkee]

Well, my 3570K wasn't stable with 0.1V undervolt so I wouldn't count on it.

I'd either get a case with bigger psu, a T model or an i3.

 

[NTMBK]

You can always get a Pico-PSU- they go up to 160W.

 

[BSim500]

Thanks to both of you for the responses. Very helpful.

I'll go ahead and rule out the "T" model and either just get a 4670 or 4670S. Maybe the S would be safer since it has the same turbo boost speed as the regular 4670 but a max TDP of 65W, so by undervolting I would be guaranteed to be substantially below even that, which would virtually assure that the 90W PSU would be fine.

No problem. If you insist on keeping your 90w PSU, then I'd suggest getting an i5-4570S/4670S or i3-4330 for overhead just in case you can't undervolt a standard i5-4670 by very much. Again I'd just like to reiterate - just as not all i5-4670K's can OC to 4.6GHz - likewise, not all i5-4670's are guaranteed to undervolt by exactly the same -0.1v (for exactly the same reason - the quality of each chip & stock voltage varies for each CPU on a die, and there's no telling what it can do until after you've bought it). Also double check that your motherboard CAN adjust voltages before you buy. Not all of the cheaper non-Z boards can!

120-160w PicoPSU's are another option, though obviously, you need a 160w brick in addition to the actual pico-PSU bit you plug in. Even with a 160w PSU, it's still worth getting a lower powered CPU to avoid heat build-up / fan noise in those tiny cases with slimline coolers.

 

[coffeejunkee]

Maybe just tell us what the intended use is? I mean, do you really need quadcore power in the tiniest box possible?

Also, I'd look into a nuc or brix type pc.

 

[GlacierFreeze]

If low power usage is most important factor here then get an i3.

 

[Yuriman]

I don't think TDP is being used correctly. A simplified explanation is that a 65w TDP chip is guaranteed to work with a cooler that can dissipate 65w. Motherboards allow for peak draw over 65w for brief periods, and lower TDP variants aren't necessarily more efficient, they just throttle to stay below that average heat output figure. Undervolting and underclocking are your tools to reduce peak draw.

 

[phositadc]

Maybe just tell us what the intended use is? I mean, do you really need quadcore power in the tiniest box possible?

Also, I'd look into a nuc or brix type pc.

A NUC or Brix would suffice for my needs, as far as power is concerned, but for literally like $50 more than I would pay for a NUC, I can build my own, and it would be quad-core and user-upgradeable, unlike the NUC. Also, I could probably make it quieter.

Also, the hobbyist in me just wants to build my own.

Thanks to all for the responses.