Undervolting

The effects of undervolting

- How much slower will my fan spin?

- How much cooler will my CPU run?

Here are the results from a couple experiments, aiming to answer these questions.

I ran two different tests using the maximum frequency of my MacBook (1833 MHz), meaning no performance loss. In both tests different voltages between 0.9875 V and 1.2625 V were tested.

In the first test, several processor demanding tasks were repeated. The fan was locked at the max setting (6200 RPM) using the app smcFanControl.

CoolBook was then used to set the maximum frequency, and to change the voltage. When the temperature had stabilized, it was recorded. This procedure was repeated for every voltage in the diagram.

The maximum temperature using 0.9875 V was 58 °C, compared to 73°C using the original settings. But even the modest voltage decrease to 1.1000 V showed a substantial temperature decrease, with temperatures close to 60°C.

As the MacBook gets warmer, the fan will automatically increase the rotation speed. This diagram shows the differences in RPM at the end of the Cinebench benchmark. The original driver ran more than 2000 RPM over the lowest CoolBook setting. Not showing in the diagram is the differences in temperature. At 0.9875 V the temperature reached a maximum of 63°C, while the original driver reaches 72°C!