Why your USB cable won’t charge your phone and how to fix it

Some users are complaining of charging issues with USB type C cables, including the Pixel 4. The reason is to be found in some internal components of the cable itself

Most of today's battery-powered electronic devices charge via a standard USB cable: some use the USB-C standard, others the micro USB, but usually you can also use adapters to connect and charge a bit of everything with a bit of all cables.

At least until today. Things, in fact, could change soon with the diffusion of devices that use the USB Power Delivery (PD) standard, that is the protocol that makes charger and device communicate in order to avoid overloads that could damage the more and more delicate devices. Because of the Power Delivery standard, so, there are cases in which the USB cable does not charge the phone, or the tablet, and there is nothing else to do but use another type of cable. That's right, because all cables look the same but in reality they are not and, as a result, there are particularly capricious devices that do not charge except when connected to the right cable.

The Google Pixel 4 does not charge

The most recent case of a USB cable that does not charge a device is that of Google's top-of-the-line smartphone, the new Pixel 4. This smartphone supports PD and is compatible with charging at a maximum power of 15 Watts. But not with all cables: of course everything is fine with the supplied one, with those of the previous Pixel and the charging also works with most of the cables with both USB-C ends.

But there are problems with many chargers that have a USB-A connector (the classic, flat one that we also find in our computers). Also many 5 Ampere cables, needed for charging at full power, seem to cause problems on the Pixel 4: despite supporting the PD standard they can't charge these smartphones. But it's not just the Pixel 4 that has problems charging with certain cables: it turns out, for example, that a MacBook Pro won't charge with the Chromebooks' USB-C power supply, while the Chromebooks charge quietly with the MacBook Pro's power supplies.

Why the USB cable won't charge the device

A possible explanation for these charging conundrums lies in the cable's built-in pull-up resistor. Resistors of this type are commonly used in USB cables, but they're not all the same: the USB-C standard calls for a 5.1 kΩ resistor, while some devices like the Pixel 4 would require a 5.6 kΩ resistor. And that's the reason why sometimes the USB cable won't charge the phone. Unfortunately, the type of resistor is almost never indicated in the cable's packaging, so we can end up buying a USB cable and then not being able to use it with a specific device, just because it doesn't have the right type of resistor.