How USB charging works and why phones explode sometimes

Universal Serial Bus (USB), has become one of the most ubiquitous ports that we see on our PCs, laptops, smartphones, tablets, cameras, and a plethora of other devices. Apart from data transfer, it is also the standard for charging most gadgets.

Leaving proprietary ports behind (except Apple’s Lightning of course) USB has wiped the need of having different chargers and power supplies with different ports. Here is a quick crash course in how USB actually charges your devices.

Types of USB devices?

Despite its name, there are actually four standards today, USB 1.0, 2.0, 3.0 and 3.1. Then there are connectors, USB A, USB B, microUSB, miniUSB and the new USB C. More than the interface it is important to understand the standards. The older USB 1.0 and 2.0 come with four pins on the connector along with four wires inside the cable. Two of the pins carry data while the other two have the capacity to support power supply of up to 5 volts. USB 3.0 on the other hand comes with five additional pins which essentially means it has nine wires. Every USB connection includes a host and a device. Electricity can only flow from the host to the device, but data can be transferred in either direction.

When it comes to the actual current, there are three USB ports; a standard downstream port, a charging downstream port, and a dedicated charging port. The first two can be found on your on PCs and laptops and the third kind is usually on chargers. The standard downstream port on USB 1.0 and 2.0 can deliver up to 500mA or 0.5A. USB 3.0 however takes this up to 900mA or 0.9A. The charging downstream and dedicated charging ports provide up to 1,500mA or 1.5A. USB 3.1 which is the latest and the fastest, supports throughput of 10Gbps which is also called SuperSpeed+ mode. This also supports power supply capabilities of 1.5A and 3A.

USB-C is, which is slowly becoming the new standard, comes with a completely different connector. It can be plugged either way, just like Apple’s Lightning connector only with a different shape. It is capable of supporting double the capability of USB 3.0, which means it can also supply more power. Combining a USB-C connector with the USB 3.1 standard makes it one of the fastest interface around, so much so, the new Thunderbolt 3.0 is based on USB-C and is capable of 40Gbps. Note, that USB 3.1 doesn’t necessarily need the new USB-C port, it can be implemented on the older connectors as well.

USB-C is now replacing standard microUSB and traditional USB-A ports on laptops thanks to its high-speed and power supply capabilities. Smartphones like the OnePlus 3/3T and the new OnePlus 5, support up to 4A charging. Laptops like the MacBook Pro and last year’s 12-inch MacBook, booth rely on USB-C power with a 45W adapter to juice them up. USB-C has some more advantages as it can support multiple interfaces like VGA, HDMI, Display Port, high-fidelity audio and more.

Interoperability

The good thing is, all new USB standards are backwards compatible. Which means if you use a 3A charger on a device that support 1A or 1.5A, it will work just fine. One can plug any USB device into any USB cable and into any USB port. A higher rated charging will actually speed up the charging process on a low speed supported device and no it will not blow up. Of course the speed up process will only work if you have a newer device. Old devices that don’t comply to the Battery Charging Specification released by the USB Implementers Forum in 2007, will only charge at 0.5A.

With more and more adoption of USB 3.1 and the USB-C port, we can expect more fast charging devices in the future, especially smartphones.

Can your phone explode?

The answer is yes, and no. I am sure you have seen news reports of phones exploding while charging. In most cases, the culprit is not the USB connector or cable. Phones usually explode due to faulty batteries, like the infamous case of the Samsung Galaxy Note 7. However, there is a slim chance that a faulty charger or cable can damage your smartphone.

The main cause of your phone exploding is due to the lithium-ion battery inside. An external damage (when your phone drops) leading to leaks, or internal damage leading to short circuit is a potential cause for explosion. Another case is when the phone is charging. When you charge your smartphone, it often becomes hot. This is because a large amount of energy is pumped into the battery and high speeds. This again can lead to an internal short circuit in case the internal cells break down. This happens at very high temperatures or when the battery is faulty. Even overcharging, when the battery receives more current than the safety level, can lead to overheating.

Essentially, the USB cable and charger you use for charging your phone needs to comply with the safety levels of current flow. Anything above can lead to your smartphone burning to a crisp. Thus, it is advisable