How many watts does your phone fast charge at? How many watts does it actually charge at?

How to choose a fast charger for your phone? It's easy: look at the charger that comes with your phone. If the fast charging power marked on the charger is higher, it can charge faster, right?

Is this actually the case? Let’s look at an experiment.

Experimental plan: For a certain brand of mobile phone with a nominal 40W fast charge, use a power detector (power meter) to measure the instantaneous power during the charging process

Figure 1. (Mobile phone with fast charging function) Charging starts from 75% battery and continues to 100%.

For comparison, a mobile phone without fast charging function was also selected to test its instantaneous power during the charging process.

Figure 2. (Mobile phone without fast charging function) Charging starts from 20% battery power and continues to 100%.

Junior high school physics knowledge tells us that if we want to increase power, we have to increase current or voltage, and this is actually done.

The experimental results verify the three stages of fast charging:

(1) Trickle charging. The current is very small. Even if we intentionally cut off the power during the charging process, as shown in the experimental results Figure 1, the charging still starts with a small current.

(2) Constant current charging. The lithium ion activity of the battery is fully activated, the charger increases the current and gradually increases the voltage. This is the main stage of charging, accounting for more than 70% to 80% of the capacity.

(3) Constant voltage charging. When the battery is charged to more than 80%, the charger will slowly reduce the current input at a constant voltage until the battery is fully charged.

So, when can we reach the high power of mobile phone fast charging? As can be seen from the experimental results Figure 1, when the battery is low, the mobile phone will maintain high power charging for a period of time. After charging to a certain capacity, in order to protect the battery, the charger gradually reduces the power, and finally "slowly charges" to 100% at a very low power.

The output power of mobile phone fast charging is getting larger and larger, from 20W to 120W. In fact, the mobile phone will not maintain high power for a long time when charging. Only by scientifically understanding mobile phone fast charging can you fast charge your mobile phone correctly.