MacBook Pro: CPU throttling when battery reaches 39c

[Flyview]

Hey everyone,

I discovered something on this hot July day! My late 2013 15" MacBook Pro throttles the CPU and makes the computer extremely slow (taking seconds just to register a mouse click) when the battery temperature reaches 39c.

It does this by ramping up CPU usage of kernel_task, taking away CPU from everything else. At first I didn't know what was going on because I've had the CPU and GPU much hotter (closer to 90c) than it was today without throttling. After carefully looking through the temps and going into and out of the throttling zone a few times, I noticed that the trigger seems to be the battery temperature (battery sensor 1) reaching 39c.

I was inside a hot vehicle at around 32c inside temp, running an external 4k monitor so the dedicated GPU was active. Even inside with some AC at 25c ambient temperature, no external monitor, the battery sensor is sitting at 32c without anything intensive running. That means there is only 6c wiggle room for it to go up before throttling!

Can anyone confirm? Is there a way to adjust at what temperature this happens?

P.S. I discovered TG Pro today for fan control. I had been using Macs Fan Control but TG Pro is better because you can set your own fan temperature ramps and set it based on multiple sensors as opposed to just one!

 

[Rod]

I don't think CPU activity should increase at such a moderate temperature. 39deg C is idling temp on my MBP. I would look for another cause. You say kernel task is rising above this temp, that does not make any sense to me. I frequently run at 75-80deg C while using graphically demanding apps CPU activity is near max but no loss of function or speed, kernel task activity remains proportional.


Sent from my iPad using Mac-Forums

 

[Flyview]

I don't think CPU activity should increase at such a moderate temperature. 39deg C is idling temp on my MBP. I would look for another cause. You say kernel task is rising above this temp, that does not make any sense to me. I frequently run at 75-80deg C while using graphically demanding apps CPU activity is near max but no loss of function or speed, kernel task activity remains proportional.


Sent from my iPad using Mac-Forums

I think you missed the point a little bit. I too have had the CPU and GPU up over 80c without throttling. The problem manifests when the battery temperature reaches 39c. CPU usage of kernel_task is just a method the OS uses to throttle the CPU, it's not actually the cause of the high CPU usage in itself.

 

[Flyview]

I don't think CPU activity should increase at such a moderate temperature. 39deg C is idling temp on my MBP. I would look for another cause. You say kernel task is rising above this temp, that does not make any sense to me. I frequently run at 75-80deg C while using graphically demanding apps CPU activity is near max but no loss of function or speed, kernel task activity remains proportional.


Sent from my iPad using Mac-Forums

Just wanted to update this. It turns out this had nothing to do with the battery temperature. The VRMs (voltage regulator modules) were getting too hot in the hot ambient temp. This in turn signals the CPU to throttle even if it itself is not close to throttling temperature. This was confirmed by taking off the bottom lid once it started throttling, then pointing a huge fan at the VRMs to cool them down. They are located near the center vent at the back, in between the 2 fans. It looks like Apple actually insulates these really hot components so as not to get the bottom lid too hot. I removed the black sticker insulation on the VRMs and on the bottom lid and actually connected them with 2-3 layers of Arctic 1.5mm thermal pads (6W/m2). I added the pads to any chip that got really hot to touch with my finger. Now that heat is transferred to the bottom lid instead of being trapped inside and overheating, so when placed on a laptop cooler it can actually cool itself off.