Why do we need Fast Charging? 

Today's smartphones have more specs than before with high performance cpu &gpu but will these smartphones will be of use without good source of power to support these high features, when batteries start to drain fast because of these high quality features, two development strategies started to emerge where one of them is to increase battery capacity and the other is to decrease charging time through what we called fast charging but the question here how these batteries will respond to the effect of fast charging process. In this article we will explain how fast charging affects the battery?

The roots of fear about the danger of fast charge lies in the technology of lithium batteries. such batteries are very sensitive to charge and discharge currents, so their work directly depends on them. An extremely fast discharge can disable lithium batteries across their time.

What harms our batteries?

If we want to know if the technology of fast charging brings harm, we need to figure out the main factors contributing in deterioration of our batteries. This includes high currents of charge and discharge, overheating, overcharging and over discharge. All modern batteries are equipped with a controller, which protects them from the last two factors. It disconnects any load as soon as the voltage drops below the permissible value. The controller also stops supplying current when it reaches its maximum.
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Controller for a lithium battery


Overheating is very harmful,as it leads to accelerated cell degradation. if the limits of the permissible heating are exceeded , the battery may melt due to boiling of electrolytes, or may even explode. The temperature monitoring function that is supported by the controller is provided to protect the battery. It does not allow the battery to overheat. This function doesn't work as reliable protection against overcharging and over discharge.


High currents during the process of charging and discharging cause harm to the battery. If you charge your battery slowly, it will work longer. There are limits, so the maximum charge current for the lithium cell directly depends on the level of its charge.
You can compare it with a cinema. if people enter one by one, everything will be fine, but the last visitors will be in their places later, but if you let the crowd come in without limiting it, the filling will take less time, but there will be a big risk for people.

If the battery is protected from its recharge, over discharge and critical overheating with a controller then fast charging forces it to increase charge currents and the electron flux density. This is what you may think happens, but that is not the case.

How does Fast Battery Charging work?

The technology of fast battery charging is difficult. It is not simply feeding a large current to a lithium cell in order to charge it as soon as possible. There are special controllers in our smartphones which  monitor the battery status, charge level, temperature, and load. knowing these parameters, the technology of fast charging selects an optimal mode of operation, will not damage the battery.
As we have already mentioned above, the maximum permissible current directly depends in the level of charge. As long as the cell is discharged, it easily endures even a 1C current value(it is equal to 4A for 4000 mAh). The technology of fast charging uses it, pouring the first percent at the maximum allowable speed. In half an hour a 4000 mAh battery can be charged up to 2000mAh of energy.
Volts/capacity vs. time when charging lithium-ion.

During the charging process, the controller gradually lowers the current to make it stay within acceptable limits. The current decreases to 0.75C, 0.5C and further on until it reaches its minimum. The last 10% are charged slowly, at the current of 0.1C. That is why our smartphones are charged up to 50% in half an hour, but it takes up to 2 hours to charge up to 100%.

If we go back to the example of the cinema, it will look like this:while the sector is empty and people can freely pass to their seats, passage is not limited as soon as the cinema seats it becomes more difficult for the following visitors to come in.





Links
https://batteryuniversity.com/learn/article/ultra_fast_chargers
https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries





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Hisham Elreedy is Digital Electronics Engineer, Graphics Designer, Blogger, Youtuber. Inspired to teach all he knows from his experience in studying undergraduate engineering by creating useful posts