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I got a new power supply/cord for my Asus N550JV-CN191H, after my old one tore. The new one works fine, and the power indicator (Ubuntu 14.04) shows that the battery is charging, except when I play Minecraft, and then the battery is shown to be draining.

Could it be because the output of the new power supply is 4.72A while the old one is 6.32A? Could Minecraft be draining the battery so much that there is net power loss rather than gain? I am not used to mere software having this sort of effect.

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  • That sounds like exactly what it is. 90W devices are chargers for this laptop. You need a 120W device to power it.
    – David Schwartz
    Apr 3, 2015 at 15:34
  • You tell us? You have both chargers in front of you. If the old one provided 33% more Amps then basically you are not providing enough Amperage to your device when its drawing more then 4.72 Amps.
    – Ramhound
    Apr 3, 2015 at 15:51
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    "Mere software" is requiring higher CPU, video, and RAM resources than usual desktop / web browsing / etc. Mere hardware working harder and demanding more power? Yeah, mere software can do that.
    – armani
    Apr 3, 2015 at 16:23

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TL;DR There is a reason your laptop came with a 120W charger. It actually needs it.
I'm also a little jealous

Your battery is draining while under charge because you are no longer supplying it enough power to drive both the battery charging circuitry and the rest of the system at once.

Your new PSU is probably 19V @ 4.7A = ~90W
Your old PSU is 19V @ 6.3A = ~120W

Depending on the components in your system this could well not be enough power.

Looking at your laptop

  • Your high end i7 laptop processor is an i7-4700MQ rated at 47W.
  • Chipsets (processors surrounding the CPU) are approximately 5W.
  • You have a dedicated GPU, an NVIDIA GeForce GT 750M, in the laptop that is rated at 50W. This is quite hungry
  • Hard drives are usually of the order of 10W of power.
  • The screen is also probably between 2W and 8W of power.

Add all this together and under heavy use the components of you laptop could potentially be drawing up to 120W under full load. The charging circuitry also will be wanting a minimum amount of power to charge the batteries efficiently.

If you are only browsing the internet then both the CPU and graphics card will move to a low power state and be drawing much less. The graphics card will move to a low power mode and draw < 10W, probably similar for the CPU. The occasional burst when loading a page will not really affect the charging of the battery by much.

Under very light load your system is probably drawing around 40-50W and so the battery can charge at the same time, under heavy graphics and CPU load it could easily be over 100W, hence your 90W power brick is not going to cut it.

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  • That laptop actually has a HM86, which is more 2.7 W max (TDP is only for full load) - main difference being it's a mobile chipset. Similarly, HDDs only draw their max rated current (commonly 2 A) at spin-up, not constantly - that's why it's specified as a peak load. Still, the CPU and GPU would make up most of the load.
    – Bob
    Apr 3, 2015 at 23:31
  • @Bob I was only aiming for "worst case" figures, and as they are in the vague ballpark I'm not likely to loose sleep over them. The key figures are there and as I hadn't mentioned RAM, CD or other peripherals such as card reader or wifi cards I figure that my estimate is still pretty reasonable.
    – Mokubai ♦
    Apr 3, 2015 at 23:42

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