Sub-Zero Weather: Can Your Smartphone Stand The Cold?
By Ossi Jääskeläinen
PCWorldFeb 1, 2012 6:00 pm PST
Some smartphone manufacturers don’t recommend that their devices be used in cold weather while others guarantee smooth functioning even in temperatures as low as 4 degrees below zero.
MikroPC (PCWorld Finland) decided to test if smartphone manufacturers can back up their claims.
We obtained the 15 most-sold mobile phones in Finland, as well as three others for comparison, and took them into the Technical Research Centre of Finland and their “Weather Room.” The room is a specialized research lab where the temperature can be adjusted to a fraction of a degree. Note: Many of these phones are not sold in the United States–Two notable exceptions are the Apple iPhone 4S and the Samsung Galaxy S II.
The initial temperature in the room was set to 32 degrees. From there, we kept lowering it by steps of 9 degrees until even the most persistent devices gave up and stopped working. (Note: All temperatures in this story except for the graphic below are in Farenheit.)
What Do Manufacturers Recommend?
According to Apple, its iPhones can be used only in temperatures between 32 degrees to 95 degrees Farenheit. In other words, an iPhone user taking his device outside in typical Scandinavian winter conditions will do so at his own risk. If the phone breaks down, Apple claims it will not be responsible and the damage is not covered by the phone’s warranty.
HTC and Nokia do not mention operating temperature guidelines in user manuals or on their websites. Samsung, on the other hand, guarantees its phones to function in temperatures between -4 degrees and 122 degrees.
First Fail: Apple iPhone 4S
At 32 degrees, it was business as usual for all the phones. At 23 degrees, the iPhone 4S and the Nokia N9 started showing symptoms: The iPhone reported a sim card error, and the N9 claimed its battery was nearly empty.
Lowering the temperature to 14 degrees was more than the iPhone could handle. The Apple device suddenly announced a dead battery and shut down. (All phones with LCD displays in our tests experienced difficulties when the temperature dropped below 14 degrees.) AMOLED displays proved to be able to stand cold much better and kept working at that temperature.
The Cheaper, the Better?
In our tests, the majority of smartphones couldn’t handle temperatures ranging from 5 degrees down to -4 degrees. Even if the phones managed to stay powered up, most died when put to actual use.
Feature phones, which are less complicated than smartphones, did better. Apart from slow display reaction, the feature phones we tested showed no symptoms until the temperature dropped to -13 degrees. By the time that temperature was reached, most smartphones were completely useless.
We were surprised to find that Samsung smartphones outlasted Nokia’s touch-screen devices. Only one of the smartphones we tested kept running smoothly when the temperature reached -22 degrees: The Samsung Galaxy S II.
Even if Korean engineers don’t face sub-zero temperatures as often as their Finnish colleagues, they’ve managed to design a better smartphone for such conditions. The Galaxy S II didn’t shut down until the temperature reached -31 degrees. And until that point, there wasn’t even a hint of slowness when using its display.
The Breaking Point for All Phones: -40 Degrees
The ultimate cold temperature for the smartphones we tested was -31 degrees. Even the most persistent smartphone, the Samsung Galaxy S II, shut down when we tried to use the phone at this temperature.
None of the other tested smartphones could stand such extreme conditions. But some feature phones did work at -31 degrees, even though their LCD displays showed serious slowness. But when the temperature dropped to -40, no phone in either category survived. Even the toughest ones shut down.
The two phones that survived the longest, both feature phones, were an inexpensive Nokia C1-01 and a five-year-old Nokia E65, which was one of the devices we chose for comparison purposes in the tests.
These two phones may not be equipped with high-end touchscreens, but they worked. Nokia engineers appear know what they’re doing on these phones: The coldest temperature reached in Finland almost every winter is -40 degrees.
Here is a chart showing how each phone did. Note: The temperatures in this chart are in Celsius, not Farenheit, but the relative standings of the phones in the two aspects of our testing is interesting:
Next: Blame the Battery and more
Blame the Battery
When the temperature drops low enough, a cell phone thinks that its battery is empty–even if it’s fully recharged–and shuts down. Here’s why:
A chemical reaction takes place inside the battery. The product of the reaction is electrons, and the flow of electrons creates an electric current, which the cell phone uses as its source of power. The speed of this reaction depends on the temperature: The colder it gets, the slower the reaction, and the smaller the current that the battery can provide.
The voltage of the battery isn’t stable, either. The nominal voltage of a lithium-ion battery is typically 3.7 volts but, in reality, the voltage is between 2.7 volts (for an empty battery) and 4.2 volts (for a fully charged battery).
In cold temperatures, the internal resistance of the battery grows, causing the output voltage to drop. When the voltage drops too low–below a threshold voltage–the cell phone thinks the battery is empty, even it is fully recharged, and shuts down.
Here is a chart with information on the phones we tested provided by the manufacturers:
How the Cold Affects Different Displays
An LCD display consists of layers. The actual liquid crystals are positioned between the polarizing filters and electrodes. A TFT layer (thin film transistor) is positioned behind the screen to control the pixels of the screen.
When the temperature drops, the viscosity (or thickness) of the liquid crystal material increases exponentially. Depending on the material used in the liquid crystals, the viscosity increases two-to-three times more when the temperature drops 18 degrees. This means the pixel changes its color slower in the cold.
When it’s cold enough, the pixel color change is so slow that it can’t change fully before the next frame is already drawn on the screen. This is when the display seems to work slowly and when ghosting or image blur appears on the screen.
In AMOLED displays, the colors are produced with a layer covered in organic material (OLED). This lack of liquid crystals probably explains why AMOLED displays work better in the cold.
(Translated from Finnish to English by Ossi Jääskeläinen and Sofia Williams.)