What Is Qualcomm Quick Charge + How It (Really) Works

A small sample of Q.C enabled devices

With very slow (but somewhat steady) battery capacity growth in an ever-connected world, it is clear that users are more battery-life conscious than ever before. The next best thing to “more battery capacity” is “faster charging” – ideally you would want both.

To that end, several technologies have been created to charge electronic devices faster, and Qualcomm’s quick charge is one of them. Yet, with a multitude of phone makers, accessories maker and competing technologies, the fast charging landscape can be very confusing. Let’s try to put Qualcomm’s Quick Charge (QC) on the map to see what it can, and cannot do.

What is it?

From 10,000 feet, Qualcomm’s quick charge is designed to safely draw as much power as possible from the power supply, in order to charge the battery as fast as its chemical components can support it.

Unlike what is often shown in movies, charging faster isn’t only a matter of providing “more power”. You have to make sure that it can be done safely, since batteries are known to explode or catch on fire under specific conditions.

Also, since charging and discharging a battery is based on chemical reactions, there are no commercial applications that can miraculously charge batteries in seconds. Finally, increasing the density and voltage also comes with trade-offs concerning the longevity of the battery, so this is a delicate trade-off.

Qualcomm says that Quick Charge can charge about 75% faster than conventional chargers. Our tests show that the claim is true, and to add some context, Qualcomm is about 75% faster than regular chargers with a 5V 1A electrical output, which is already much more powerful than the plain 5V 0.5A USB.

Quick Charge 3.0 was launched in 2015 and is mostly a power-efficiency optimization that charges at the same speed as QC 2.0 but generates much less heat while doing so. It charges 2X faster than QC 1.0, and is 38% more “efficient” as QC 2.0.

Quick Charge 2.0 (QC2.0) chargers can support 5V, 9V or 12V (volts) and up to 3A (Ampere) and 60W (see the QC2.0 video demo).

Quick charge 1.0 could support 5V and 2A (10W). Many chargers on the market support 5V 1A, and standard computer USB ports output a minimum of 5V, 0.5A. There are many more variations that land somewhere in between.

How it works, in practice

Most fast-charging technologies work in the same way: draw more power, safely. To achieve that, QC is relying on two mechanisms:

A quick-charge enabled phone will always try to draw as much power as it can, whether the power source is QC-certified or not
1. But it won’t ever draw more than 2A, for safety reasons
A QC power supply can be identified by a QC-enabled phone, which ensures that drawing up to 3A is safe.

For this reason, QC-enabled phones will still charge faster on random 2A (non QC) chargers, but not as fast as with a certified QC power supply.

The higher voltage is there to compensate for possible power loss and power inefficiencies in different points of the system (cable length, etc…).

I have actually verified this with the new LG G4, and observed that with a proper QC-enabled adapter, it charges about 23% faster than with a non-QC 2.1A power supply. Depending on the phone, your luck may vary.

Incidentally, small details such as cable quality (I’m serious), cable length and other factors that could create power-loss from the power supply to the phone could affect charging speed. Here’s what you need to get quick charge working:

A Q.C certified adapter
A decent cable (copper/metal diameter). I have seen flimsy cables that would not allow fast-charge
A C compatible phone. Check the specifications or the Qualcomm Q.C list

Common questions:

Are Q.C adapters from different manufacturers compatible? Yes
How do I know if my charger is Q.C: check for a Q.C logo

How to measure it?

It is common to read things like QC should charge a phone by 60% in 30mn or something of that kind. This is a good way to show the faster charging on any given phone, but this is not great to compare phones with different battery capacities.

We prefer to use “mAh per minute”, which better describes how many units of energy are being stored for every minute of charge. While it is not a strict energy storage unit, it’s clear enough to compare charge speed between devices of a similar category, like phones. See what is mAh.

Also, note that while charging speed is relatively stable from 0% to 70%, it gets progressively slower. For instance, it takes considerably more time to go from 90% to 100% than from 0% to 10%.

mAh/mn is simple: if your phone has a 3000 mAh battery, and it charges by 50% in 30mn, it means that 1500 mAh worth of energy has been accumulated in 30mn, which is 50 mAh per minute.

The chart above shows a small sample of charge speed from popular smartphones. The top speed that we have seen so far is 50 mAh/mn of charge. That’s true for some Q.C phones, but not all. Phones using other sort of fast-charging technology also top at 50 mAh/mn, like the Galaxy S6.

Are we looking at another Standards battle?

Not really – at least, not in the “winner takes all” sense. Although there are relatively few Q.C-certified chargers today (relative to the overall market), it is not very difficult for power supply makers to build a compatible charger and pass the certification.

Also, a Q.C charger can also be certified for other fast charging protocols such as Samsung’s and others. More likely, Q.C will become one of many fast-charging protocols which will hopefully be supported by most chargers in the future – that remains to be seen of course.

Conclusion

Quick Charge addresses an essential need to extend or improve the battery life as conveniently as possible. Being able to gain a significant charge in a relatively short time can make all the difference in the world.

However, until OEMs make it easy for users to see (on the screen) if a fast-charging is underway or not, some confusion will remain. Some communications efforts are underway, and this protocol is bound to expand, so in the near future the odds to have a happy match between phone and charger should be much higher. In the meantime, you need to pay a bit more attention. Happy charging!

Qualcomm’s pitch for Quick Charge:

Filed in General. Read more about Battery and Qualcomm.