Latitude 5490 - Disabling GPU to Reduce Power Draw 90->65W?

Discussion in 'Dell Latitude, Vostro, and Precision' started by Metal450, Sep 21, 2018.

  1. Metal450

    Metal450 Notebook Enthusiast

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    I'm looking at buying a Latitude 5490, and debating over the discrete graphics option. I understand this increases the power requirements from 65W to 90W.

    For the vast majority of my usage I do not actually need a GPU, but it would be nice to have for those few situations when it would be beneficial. What I'm wondering is, is it possible to disable it - thus configuring the system to use the integrated graphics - and would doing so lower power requirements to the equivalent of a system without a GPU, thus enabling me to use a 65W adapter while it's off? Or does the discrete graphics always draw power (like i.e. a touchscreen digitizer), so having it exist within the system effectively means only the 90W adapter would be usable, whether the GPU is enabled or not?

    I found some discussions about this, but most answers seem to be just guesses (i.e. "you should be able to" or "I think that's how it'd work"). If I can definitively know that it does work that way, it effectively means there's NO downside to ordering the system with discrete graphics - I'd get it & just disable it, & the system effectively becomes the same as a system without it - allowing me to travel with a smaller & lighter 65W adapter. In the instances when I do need to use discrete graphics I'd of course use the 90W adapter, but it would always be optional, with no negative impact when not used.

    Can anyone confirm? :)
     
  2. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    The presence of the dGPU increases the potential maximum power requirement but components will only draw the power that they need. Dell sizes the PSU assuming the worst case of fully loaded CPU + fully loaded dGPU + recharging the battery + power used by other internal and plugged in components.

    The Nvidia dGPU acts as a 3D graphics co-processor for the Intel GPU which handles the 2D graphics and the display output. It stays asleep unless needed and, while there's a set of pre-programmed assumptions (software packages and type of graphics processing) for when dGPU gets to work there is also a control panel for the user to be able to modify those settings. In earlier days the dGPU did continously use power even on idle which meant that battery time took a big hit, but this is no longer the case (at least for Nvidia dGPUs).

    I had a Latitude E7450 with an Nvidia dGPU (specifically bought because I knew this model had a better fan so would run quieter under normal usage) and it travelled with a 65W PSU (less weight). I didn't normally cause the dGPU to wake up but if it did then CPU + dGPU etc (but excluding battery charging) was well within 65W. In addition, the BIOS was programmed to manage any battery charging so that the total power drain was within the PSU capacity. I doubt if Dell has intentionally changed that feature.

    I now use a Precision 5510 which has an Nvidia dGPU. The notebook is shipped with a 130W PSU but I've travelled with a 90W PSU (plus 65W PSU as backup) and haven't had problems - 65W will keep the machine running under non-dGPU conditions although any battery charging may be slow (varying according to how much power the CPU is using).

    The one investment I would recommend is mains power meter so that you can see for yourself how much power is drawn from the outlet under different operating conditions (but note that the PSU is likely to be 85% to 90% efficient so a fully loaded 65W PSU will draw 70 to 75W from the outlet).

    John
     
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  3. Metal450

    Metal450 Notebook Enthusiast

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    Awesome, thanks so much for the detailed reply!

    I actually do have a mains power meter...but of course, no E5490 here to test as I'm only considering buying it. And once I've bought it, I'd like to avoid the situation where I test & then realize it can't work & have to return it. But from what you say, it sounds like it will likely work just fine :)

    My only real intended use for the GPU is rendering in Adobe Premiere, which I don't do all that often. In all other cases it's 2D only business applications.

    Good to know that I don't even need to disable the GPU - it just goes to sleep when not in use. My primary concern was being able to get by on the extremely small Finsix Dart charger that I travel with, which they only make in a 65W version. It sounds like as long as I'm not stressing the CPU+GPU, it should be just fine :) (I do actually max out the CPU fairly often - code compiling at the like - but in this case the GPU would be off, so it sounds like it should still be fine as they sell the non-GPU version with a 65W adapter by default).

    Thanks again! :)
     
  4. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    The BIOS will probably warn you that you are connecting an under-rated PSU but shouldn't stop you using it. Dell Power Manager has several Alert options:
    Dell Power Manager Options.jpg
    John
     
  5. Metal450

    Metal450 Notebook Enthusiast

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    Cool, thanks again :)
     
  6. mr_handy

    mr_handy Notebook Evangelist

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    I'd be concerned that it will throttle the CPU when on an underpowered (or not keyed) adapter even if it doesn't actually need more power. My 5491 isn't bothersome when it throttles on a power bank that reports itself as 65W (one of Dell's "Power Companion" although I don't remember the model) but it does throttle, and some older models were pretty much useless when throttling.
     
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  7. Metal450

    Metal450 Notebook Enthusiast

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    Yeah, that would suck.

    I was actually considering the 5491 vs the 5490, but leaned towards the 5490 because I figured its 45W CPU using 3x the power of the 5490's 15W would be even less likely to get away with a 65W adapter...and I really don't want to have to travel with a 90W. Plus, I can only assume the 91's battery life would be quite a bit less too, as it's running such a beefier CPU off the same battery. Any thoughts, since u have direct experience with the 91?
     
  8. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    I've just run wPrime on my Precision 5510 connected to a 65W PSU (but no dGPU being loaded and no battery being charged) and the i7-6820HQ CPU sustained 3.2GHz throughout the test with the maximum CPU package power being 32W when running 4 threads. Trying to run 8 threads resulted in 40W power drain and thermal throttling which reminded me that I need to repaste the CPU. However, there was no hint of power-related throttling as the maximum CPU speed is the same as when using the 130W PSU. However, there's a chance that Dell might have changed the tolerance to un-powered PSUs on the newer notebooks but there's no rational reason for doing so that comes to my mind.

    John
     
  9. Metal450

    Metal450 Notebook Enthusiast

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    Cool...also hints that it should be fine :)
     
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