Windows rMBP pulling more power than it can handle in Bootcamp while gaming

Dazmatze

macrumors newbie
Original poster
Mar 24, 2011
25
0
UK
Hello,

Just want to check with some folks here that my rMBP is behaving normally.

So when I'm playing graphically intensive games in Bootcamp (Tomb Raider, Bioshock Infinite etc...) After about 20-30 mins of gaming time, the light on my charger will change between green and orange every 10 seconds or so, after about 10 minutes of this happening, the charger will then return to green.

After researching similar issues, I believe this to be the fact that the rMBP is pulling more power than it can handle and therefore the charger is struggling to keep up, therefore it feels it needs to charge the battery (hopefully that somewhat makes sense)

If anyone with some knowledge on this, could just confirm this to be (fairly) normal and/or explain why the light is changing colour so often, that would be greatly appreciated.

Thanks.
 

gnasher729

macrumors P6
Nov 25, 2005
17,178
3,134
Your explanation is close, but not quite correct.

A MacBook can pull more power than the charger supplies. That's especially true if you use a Retina MBP with the wrong (weaker) charger. When that happens, the MacBook pulls the addiditonal power needed from the battery. So the battery empties, very slowly. When your power usage goes down, the battery can be charged again.

Worst case, you can manage to empty the battery. At that point, the MacBook will reduce its clock speed to reduce power usage, and charge up the battery a bit.
 

Spikeywan

macrumors 6502
Dec 11, 2012
252
0
Yeah, I was playing F1 2013, and the charger fell out. Suddenly everything went very choppy. I couldn't work out what was wrong, then the low battery warning came up. Stuck the charger cable back on, and the frame rate recovered.
 

malman89

macrumors 68000
May 29, 2011
1,651
6
Michigan
Yeah, I was playing F1 2013, and the charger fell out. Suddenly everything went very choppy. I couldn't work out what was wrong, then the low battery warning came up. Stuck the charger cable back on, and the frame rate recovered.
That's due to different power profiles between being on the charger and battery power, not due to the battery charge. There's probably some default Energy Saver options that throttle the CPU/GPU when only on battery power.
 

JoeG4

macrumors 68030
Jan 11, 2002
2,671
169
Bay Area, Ca.
It's because at full tilt those little 65w (or 85w) chargers aren't enough to charge the computer and power it. You're probably pulling down 100-120w combined, and it goes off the battery too as a bit of a reserve.
 

matthewadams

macrumors regular
Dec 6, 2012
214
34
A potential solution (and also an improvement to graphics) may be to use "ThrottleStop" to limit your CPU power to 1.8ghz.
First of, it takes in less power that way and second (and more important) less heat from the CPU which means more thermal-space for the GPU (which potentially results in improved framerates).
 

gnasher729

macrumors P6
Nov 25, 2005
17,178
3,134
A potential solution (and also an improvement to graphics) may be to use "ThrottleStop" to limit your CPU power to 1.8ghz.
First of, it takes in less power that way and second (and more important) less heat from the CPU which means more thermal-space for the GPU (which potentially results in improved framerates).
The MacBook does that all by itself (from experience, running Handbrake for 48 hours with the wrong charger). Once battery goes too low, the clock speed goes down until the battery recovers back to 10% or so.

It's because at full tilt those little 65w (or 85w) chargers aren't enough to charge the computer and power it. You're probably pulling down 100-120w combined, and it goes off the battery too as a bit of a reserve.
When MacBooks had removable batteries, some people ran them with battery removed and were wondering why their Macs were so slow. The reason: The Mac reduced the clock speed so that it could guarantee not to exceed what the charger could supply under any circumstances whatsoever, because without the battery, getting not enough power from the charger would crash your computer.