The term fast charging these days has been largely screwed up, and this stems from a place where smartphone manufacturers have made bogus claims about how fast they users will be capable of recharging phone batteries without discussing all the dynamics. This has played negatively in the minds of users who expect phones to fully recharge in less than an hour or a little more. I will look to discuss this topic as simply as I could so it could be easily understood.
There are a couple of things that affect how fast your phone is likely to charge, these include power output, the quality of charger and charge technology. But from our title am sure we already know today’s discussion is about power output (usually calculated in watts), this describes how much electricity is delivered to your phone and power is determined by the product of Voltage(V) and current(A) which is usually indicated somewhere on your charger as output. This means if your charger is rated for 5V and 1A your power output will be 5watts, increase that current to 2A and your power output becomes 10watts.
Now the problem is, at what point will a power output be classified as fast? To understand this we have to determine how much power a regular USB charger produces, for USB 2.0 the power output is 2.5W and for USB 3.0 its 5W. This means a typical fast charger has a minimum power output of 10watts and other common fast chargers have an output of 15watts or 18watts. At this rate, it’s easier to juice up your battery quicker without risk of damaging the battery. Some chargers are rated as high as 50watts but these are usually proprietary, and the circuitry is designed for specific batteries to prevent damage of the battery as a result of overheating. Using these extremely high power chargers on your phone could either turn your phone to a time bomb or just charge your phone at its normal rated speed if the charger is dynamic/safe to only deliver the power output rated for your phone.
My fast charger feels slow, it takes almost 2hours to fully charge my phone, is my charger broken? There are a couple of explanations to this and some of them I will discuss when talking about the other factors of fast charging, but from a power output perspective, one of the reasons for that could be the capacity of your battery. It’s going to take a much shorter time for a 10Watts charger to fully recharge a 2500mah battery than it will take to fully recharge a 4000mah battery if you intend to charge a 4000mah battery as fast as a 2500mah battery would then you would need more power.