Effects and results from undervolting
Below is a graph from the program Mobile Meter where I have measured the temperature of the CPU in our laptop.
(1) Green: The CPU is run at 1.175V 1600 MHz without load. Temp: ~60 °C (140°F) and the fan is still (noiseless).
(2) Blue: We start Prime 95 and maximize the CPUs load. Temp: 64 °C (147°F) . The fan starts spinning precisely when the long line begins and it keeps the computer stable at 64 °C (147°F).
(3) Yellow: Prime 95 is shut down and we increase the voltage to 1.450V (original). Idle temp: ~64 °C (147°F).
(4) Red: Now we start Prime 95 again. The temperature leaps from 64 °C (147°F) to 71 °C (160°F) degrees in a matter of seconds. Later on we reach a max temperature of ~78 °C (172°F) degrees.
All tests were performed in four Prime 95 steps.
The result speaks for itself. At full load with the original voltage, the CPU temperature rose to ~~78 °C (172°F) in a couple of minutes. When we ran the CPU undervolted, the temperature was stable at 64 °C (147°F). With the help of undervolting we have managed to lower the temperature at full load with 14 °C (25°F)! This is an 18% reduction counting Celsius. About the same as we managed to lower the voltages which gives us an indication of the relationship between the voltage and the heat development.
The only way to show you how much battery time there is to be gained is by measuring how many Watts we have saved. We will again use Mobile Meter and remove the PSU to see how much effect the computer uses from the battery when it’s not under load.
Here you see the direct difference. We have saved 2 Watt, or about 19% which suits our previous pattern. We move on to see how much effect it uses with full load, running Prime 95.
Strangely enough the differences between the readings in the load tests are relatively small compared to the ones when not under load. Exactly how Mobile Meter works regarding this we’re not sure, but there is still the same differences between the original and the undervolted system, but now the difference is 21%.
No matter how we approach it, it is clear that there is much to be gained by undervolting your laptop, especially when it comes to heat development and power usage. Both are important to a laptop computer.