Why does atmospheric temperature affect the operability of circuits and other components in modern electronic devices?
In: Engineering
The biggest problem is that heat is a runaway thing when it comes to electronic components.
Copper, the most common element for transmitting power and signals in your phone, for instance has a temperature coefficient of +0.393 percent resistance per degree C. So when your phone goes from 20 to 45 degrees C (70 to 115F) it means just the parts that are 45C experience an extra 7% resistance which means an extra 7% power usage.
What happens from that extra power usage? It comes out as more heat. Which then increases the temperature inside the case, which then increases the resistance and you see what happens.
Now while your phone may be at 45C, other internal components are going to be worse for wear. The temperature of your CPU is going to be going up at a much higher rate and while it is lowering performance if it heats up past a certain temperature, eventually it reaches a point where it can’t keep it cool even at relatively low frequencies. At this point, your phone is probably going to be looking to shut down ASAP.
The other major component that is going to struggle with heat is the battery. The battery’s internal resistance goes up, the current goes up, the more wear and tear that current does to the battery. It also starts to heat up more, which can be a problem since the harder a lithium ion battery is driven, the more hydrogen and ethylene the battery will generate. If the battery is hot, and has too much flammable material inside it, what then?
Short answer is you get the Note 7.
So your phone carefully monitors battery temperature, voltage, current, internal resistance. If any of these get the danger zone, your phone is either going to reboot or go into shutdown mode in order to basically stop the battery from going any further down that road.
The atmospheric temperature is important because it lets the phone transfer heat to the atmosphere quicker. The rate of transfer of heat through a system is affected by the difference in temperatures of the two systems. If one system is 95C into 20C atmosphere it will transfer heat away from the 95C source faster than a system with a 95C part in an atmosphere that’s 45C because the different is 75C instead of just 50C.
Cold is another thing altogether. Cold is usually battery related. When the phone is too cold the reactions that make the battery power itself proceed to slowly or not at all. This means for all intents and purposes the battery looks dead.
Also, you can get condensation around parts that are warmer (like the CPU) if there’s a large difference in temperature between cold outside air and the warm CPU. This would typically be pretty bad as well. It can short out the components but also corrode the copper traces.
So manufacturers will often try to limit operation of the device to minimize the problems. Others (like Tesla) carefully control the temperature of the battery using external sources (heaters and cooling systems) to maintain the optimal temperature inside the cells. When a Tesla is operating under full acceleration it can be as high as 600kW pulling 1500 amps. The cells get incredibly hot so there’s a liquid cooler in the battery pack to get heat away from them.
When it’s getting warm, a few things can happen. A lot of conductors and semiconductors become more resistant to electricity at high temperatures, so circuits which are sensitive to resistance can get thrown out of whack when they overheat – this is one reason why old synthesizers can go out of tune. At higher temperatures, you’ll start to burn plastic and warp the semiconductor die in an integrated circuit, potentially breaking or crossing/shorting its electrical connections, or soften and break solder joints.
At low temperatures, semiconductors can be more conductive than the engineer expected/intended, and that can cause unexpected voltages to hit unexpected parts of the circuit. (But sometimes, the lower resistance is desired; certain electronic devices can perform much better when cold!) Besides that, when electronics are colder than the surrounding air and are warming up slowly, they will attract moisture out of the air and become covered with condensation. Water in the device can cause corrosion and short circuits.
eta: In extreme cases, condensation can get into tight spaces, and then freeze, and the expansion of the water can loosen or break connections. The same thing happens to the roads in cold cities in the winter, and that’s why there are so many asphalt trucks out in the springtime.
Latest Answers