April 23, 2016
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There are a variety of fast charging systems available for smartphones and generally each manufacturer has its own favorite system. One company which takes fast charging seriously is OPPO and rather than using an off-the-shelf fast charging system, the company has designed and developed its own, known as VOOC.

## How does fast charging work?

The basic principle of a smartphone charging system is simple. Smartphones are powered by batteries. When the battery is depleted it needs to be re-charged. To do this the smartphone is connected to a charger. The charger puts energy back into the battery. The rate at which that energy is supplied to the battery is measured in watts. The more watts, the more power. The higher the power the quicker the battery can charge. Simple!

Power is measured in watts and watts are calculated by multiplying the current (measured in amps) by the voltage (measured in volts). This means when you look at the small print on a charger you will see something like this: “5V – 2A or 9V – 2A”.

A normal USB 2.0 port works at 5V and 0.5A which is 2.5W. A charger running at 5V and 2A generates 10W, a fast charger using 9V and 1.67A creates 15W, and so on. One of the key differences between VOOC and other quick charging systems is that VOOC uses higher levels of current, whereas the others use higher voltages. So instead of 9V and 1.67A (to give 15W), VOOC uses 5V and 4A (to give 20W).

There is one other thing to know. Smartphone batteries are charged in two stages. The first stage can be performed with a high amount of power and takes the battery up to around 80%. Then the second stage kicks in where the power is reduced as the battery is topped up to full. This is why you often hear OEMs talking about how quickly one device or another can be charged to 80%, or that just 30 minutes of charge will boost the battery life by another 8 hours, etc. This is because they are talking about charging up to 80%, the charging in stage 1. The flip-side of the speedy stage 1 charging is that stage 2 is slow. Sometimes the last 20% can be as much as 50% of the total charging time!

As you can see from the graph above, VOOC is quite fast. The OPPO F1 Plus, which as a 2850mAh battery, charges from 0 to 75% in just 35 minutes, which is impressive. From 0 to 90% takes 45 minutes, but to go from empty to 100% takes 1 hour and 9 minutes. Here we can see the differences between stage 1 and stage 2. It takes 45 minutes to go from 0 to 90%, but another 24 minutes to add that last 10%. If it was possible (which it isn’t, yet) to maintain the initial charging rate from 0 right up to 100% then the battery would charge in 50 minutes, rather than 69 minutes.

## Temperature

One of the by products of charging a battery is heat. It seems that the higher the voltage used, the more heat produced. You can expect a temperature rise of around 8 degrees Celsius (or more) when charging a handset using a fast charging system running at 9V. One of the interesting aspects of VOOC is that it manages to keep the temperature rises very low. Here is a table showing the relative temperature changes for different phones (and charging systems):

DeviceTotal charge time (mins)Charge rate (mAh/minute)Temperature change
OPPO R7s
(VOOC)
81.2337.803.3
OPPO F1 Plus
(VOOC)
6941.303.7
Vivo X6D
(MediaTek PumpExpress+)
78.530.68.1
Huawei Mate 8
(Huawei SmartPower)
130.1730.728.4
Samsung Note 5
96.7830.998.5
Samsung Note 4
(QC 2.0)
8338.811.7
Moto X Force
(Motorola TurboPower)
84.7844.3519.9

As you can see VOOC is able to charge the OPPO R7s and the OPPO F1 Plus at high charge rates (mAh per minute) but yet keep the temperature change to only 3 or 4 degrees Celsius.

## Charging while watching a video

I am sure some of you have been in the situation where you wanted to watch a video or play a game on your smartphone, but the battery is running low. At which point you probably just plugged your phone into the charger while you watched the video. When you do that you will have noticed your phone doesn’t charge as quick. The reason is that when you charge a device using a quick charge system, heat is produced (as described above). However when you watch a video and/or play a game heat is also produced, this time from the CPU & GPU. That means that a phone which is simultaneously quick charging and watching a video will have two internal heat sources. This leads to the danger of over heating. As a result the phone will drop from its quick charging system to its normal charging system, to avoid any problems. But the result is that the phone will charge slower. One of the features of the VOOC system is that you can charge your handset while watching a video and your phone will actually charge up at a reasonable rate.

While writing my comparison of Qualcomm Quick Charge, Oppo VOOC, MediaTek PumpExpress+, and Motorola TurboPower I took a Galaxy Note 5 and an Oppo R7S and charged them while each device was playing a YouTube video. Normally the Oppo R7S takes around 81 minutes to recharge and the Note 5 takes about 97 minutes. While charging and playing video the R7s recharged in exactly the same time, 81 minutes. However the Note 5 took 160 minutes, which is a 65 percent increase.

As a second test I took a Note 5, a Huawei Mate 8 and an Oppo F1 Plus and drained their batteries to around 4% or 5% in preparation for a charging-while-streaming test. However before we get into that, it is worth noting the relative battery sizes of these three devices:

Charging SystemBattery Size
Huawei Mate 8Huawei SmartPower4000 mAh
OPPO F1 PlusVOOC2850 mAh
Samsung Galaxy Note 5Samsung Adaptive Fast Charging3000 mAh

So with the batteries drained, I then started streaming a YouTube video before connecting each device to its fast charger. After 30 minutes of battery charging while playing a video the Note 5 had recharged its battery to 24%. The Huawei Mate 8 did a little better reaching 31%, however the F1 Plus had charged its battery to 68%. Relative to the different battery sizes that means the Note 5 had added 600mAh, the Huawei Mate 8 added 1000mAh, and the F1 Plus added 1824mAh.

# Wrap-up

To summarize, VOOC is a fast charging system and in terms of its basic quick charging abilities it is one of the leaders. It is certainly quick, as shown by the charging times of both the OPPO R7s and the OPPO F1 Plus, two phones which use the VOOC system. However there is more to VOOC then just charging times. Rather than using 9V or 12V to achieve higher charging rates, it uses 5V but with a higher current. The result is that VOOC compatible devices don’t heat up as much during re-charge. Also VOOC is probably the only fast charging system on the market that can charge a smartphone at a reasonable rate even when the device is simultaneously being used to watch a movie.

What do you think? Do you have any experiences using VOOC? Care to share with us all?

Gary Sims
Gary has been a tech writer for over a decade and specializes in open source systems. He has a Bachelor's degree in Business Information Systems. He has many years of experience in system design and development as well as system administration, system security and networking protocols. He also knows several programming languages, as he was previously a software engineer for 10 years.