Clevo P750ZM: Overclocking Power Requirements

Increasing performance though overclocking will always increase power draw (all other variables being the same), which is part of the concern with overclocking notebooks. On a desktop where you can easily upgrade the power supply and cooling, there are ways to deal with the higher power requirements and increased heat. With a notebook, you’ll want something with a good amount of headroom just to be safe. Thankfully, the P750ZM provides just what we need.

System Power Draw

Typically when overclocking components, there’s a point where the power (voltage) requirements start to increase rapidly for increasingly small performance improvements. Our two overclocking targets represent about a 10% and 20% overclock of the GPU core, and both increase the power requirements. However, the aggressive overclock uses almost 20% more power than the moderate overclock on average, which in turn uses a bit less than 10% more power than the stock clocks. Overall, we’re increasing the power draw by nearly 30% for a 20% increase in performance.

Keep in mind that the higher power draw when overclocked isn’t just coming from the GPU – the CPU will end up working harder to feed the faster GPU, so many of the components in the system will use more power. Still, the majority of the power is almost certainly being funneled into the GTX 980M.

The scaling of performance vs. power with our aggressive overclock is actually not too shabby, but it does raise a concern. When it comes to power, this is going to be one of the limiting factors with overclocking certain notebooks. The P750ZM we received from Eurocom includes the beefier 330W AC adapter, so it’s not a problem, but assuming 85% efficiency on the power bricks the 230W AC adapter would be very close to 100% load. Other laptops (e.g. the Gigabyte P35W v3) come with 180W adapters, which we could easily surpass – never mind the difficulty of cooling an overclocked 980M in a slim chassis.

There’s also the question of temperatures, both internal and external, which is what we’ll look at next.

Clevo P750ZM: Overclocking Performance Clevo P750ZM: Stress Testing
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  • The_Assimilator - Friday, March 20, 2015 - link

    "... but then that part [i7-4790] has a lower maximum clock of 4.0GHz, so on the whole the i7-4790K is still going to be faster."

    Apparently not, considering your stress tests. Since the CPU is so thermally limited, it can't be overclocked past or boost higher than 4GHz, which means that you might as well save the cash and get the non-K.

    Despite what Clevo claims about the thermal interface used, I'd like to see you guys open up the laptop and inspect what kind of job they did. If not a good one, repasting the CPU and retesting would surely be a welcome follow-up.
    Reply
  • Stuka87 - Friday, March 20, 2015 - link

    I agree, and mentioned the same in the original review. The 4790K is not worth the cost because they already run warm. A slightly slower i5 would perform nearly the same due to not throttling as often. Reply
  • Refuge - Friday, March 20, 2015 - link

    I would like to see the headroom on overclocking one of these with an i5k skew now that you mention it. I mean if this is a gaming laptop, and it is using desktop sku processors (No dual core i5 issues) then the i7 was a waste of money to begin with.

    The worst part about all of this? Is that I never even thought about it until I read your comment.

    Hey Jarred, is it possible to get one of these with a Devils Canyon i5k for testing? I imagine probably not, but it doesn't hurt to ask! :D
    Reply
  • JarredWalton - Friday, March 20, 2015 - link

    @Assimilator: Remember the max turbo is 4.0 GHz on i7-4790, and you're not going to hit max turbo with all cores active. Hence, my assumption is with 4790 you will actually clock closer to 3.6GHz vs. ~3.9GHz on 4790K. And if you max out the fan speed, of course you're going to hit 4.1GHz on the 4790K even under stress conditions.

    Regarding the i5-4690K, it's a reasonable alternative that will save $100 or so. How much slower would it be? Well, unless it overclocks to 4.0-4.4GHz, the 4790K will certainly be faster. Stock clocks are 3.5-3.9GHz. If you're buying a Eurocom P5 Pro, the the i7-4790 and i5-4690K are the same price while the i7-4790K is $91 more. On a top performance $2500+ notebook (assuming 16GB RAM, 512GB SSD, 980M) is it worth saving $91 on the CPU? I don't think so.
    Reply
  • Refuge - Friday, March 20, 2015 - link

    Apologies for not being clear, the money savings was just icing on the cake. Just wasn't sure if you could use an i5 in place of the i7 while still being able to feed the GPU. Maybe allow for a bit more thermal headroom or at least less long term stress from some possibly lower sustained temps.

    are i5's having a hard time feeding 980's in desktops? If not then it should have no problem feeding a 980m right?
    Reply
  • extide - Saturday, March 21, 2015 - link

    Top end i5's are actually suggested for desktop who primarily game, as there is generally no frame rate increase going from the i5 to the i7. All you are getting is essentially hyperthreading, as all of the haswell chips overclock to similar levels (if they are unlocked). Reply
  • Goodstorybra - Tuesday, March 24, 2015 - link

    We have people on NBR already running @ 4.5ghz on stress testing @ 77C so that fear of heat is moot at this point. Reply
  • Goodstorybra - Tuesday, March 24, 2015 - link

    Don't forget that Anandtech has 0 clue what proper thermal pasting is, as well as what tweaking even is, so they will tear anything down that exceeds their standard knowledge of "power on and push" Reply
  • nunomoreira10 - Friday, March 20, 2015 - link

    Undervolting the processor with an ofsett if possible could really help lower the temperature, and more extreme, a deliding would also help a lot. Reply
  • JarredWalton - Friday, March 20, 2015 - link

    Assuming the system can stably undervolt of course, which isn't guaranteed. I'll give it a shot and see. Any suggestion on a suitable undervolt offset? Reply

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