Question On Charging Via USB Cable

[George7941]

Are the connections made live? I was wondering if there is any arcing going on if a USB charging cable is plugged into a flashlight (or Lightning cable plugged into a iPhone) with the power source already on. Or power only starts flowing after internal switching, whether inside the flashlight or inside the power source? Should the power source be switched on only after the cable is plugged in?

For now I have been plugging in the Lightning cable into my iPhone with the USB power off and I turn on the power after acheiving a secure connection.

While the cable is plugged in and charging the iPhone, does using the phone cause any issues with the port contacts from the potential arcing arising from loss of connection between cable and phone?

 

[bullwinkle]

Lightning cables seem extremely prone to burning terminals, but I haven’t seen any sockets burning on any Apple devices I’ve used with them. The amperage isn’t very high, 5 amps or less.

 

[Carmudgeon]

USB is designed to be hot-swappable. As well as Lightning. Phones that use it don't draw more than 20W, if that. Don't worry about it.

The old Type-A standard had a live constant 5V across the power pins as long as the port's host device was powered on. Low wattage, and really quite "dumb" and unsophisticated, because USB was not originally designed to charge devices, only supply sufficient power to operate the peripherals it connected to, like mice and keyboards, but up to a limit. (A good example of these limits are the portable, bus-powered hard drives that come with a Y-cable to connect to more than one port; both are needed to provide sufficient power to operate the drive mechanism on compact drives that lacked any other provision to accept power.)

As portable devices became more popular, USB assumed the "charger" role by de facto practice. And because the body in charge of administering the standard lagged in updating the spec to better take on that role, each company devised their own method to get more juice out of USB ports, with the ultimate result being QuickCharge, which not only provided higher current, but increased voltage. Apple had their own "2.4" standard, as did Samsung "Fast Charge."

The USB IF finally acknowledged the deficiencies when developing Type-C, which is the antithesis of what the older standard was. It accommodates multiple protocols for data, video, and (high) power delivery, and is intelligent; each connection is negotiated between the host and the sink, though it does offer "dumb" fallback modes as well, for backward compatibility.

USB Power Delivery (PD) is the official, and only sanctioned standard for delivery over Type-C. The spec forbids deviation from that, so in the earlier days, when some tried to implement QC3 over Type-C, it was not compliant, and to be avoided. There are optional extensions to PD, like PPS, that some companies like Samsung have employed to suit their desired charging strategies.

 

[Rand]

its by communication . its not just sticking a paper clip into a wall outlet.