USB Type C cable warning

[bradly1101]

http://www.theinquirer.net/inquirer...heap-usb-type-c-cables-could-bork-your-device

The problem stems from the use of USB Type-C as a power source. The standard requires that a 3A supply be available through the cable. In order to do this, the correct resistor has to be present in the cable to control the amps being inputted. It's in the specification. It's not supposed to be optional.


In some cases, the wrong resistor is being used, or omitted entirely from connectors, and there's a risk that at best, your device won't charge, and at worst, it'll fry, explode, melt or grow sentient and turn on its master.

 

[Red Squirrel]

I heard about this, but how does it work exactly, doesn't a device only draw the amps it needs? You can plug a 7w Christmas bulb directly between the terminals of the electrical panel where 200 amps are available, it's not going to blow the bulb, the bulb will still only draw what it needs.

 

[bradly1101]

I heard about this, but how does it work exactly, doesn't a device only draw the amps it needs? You can plug a 7w Christmas bulb directly between the terminals of the electrical panel where 200 amps are available, it's not going to blow the bulb, the bulb will still only draw what it needs.

That's how I understand charging (and all) circuitry so the only thing I can think of is that they are mixing up voltage and current and that this resistor provides a voltage drop (as they all do, right?).

 

[pcgeek11]

The device will draw the current based on its resistance and charging circuit. See Ohms Law.

Current = Voltage divided by Resistance

If the device manufacturer is depending on the cable having specified resistance in place already in the design of the charging circuit, and it isn't. The current could go up enough to destroy the device. Especially if the device doesn't have its own current limiting circuit to prevent an over current situation.

So basically if the cable manufacturer cheaps out and doesn't conform to the cable specifications and the device manufacturer also cheaps out on the charging circuit design it could burn up your cheap device and cable.

 

[lehtv]

Well.. best not buy the cheapity cheap cables then. If this is a real thing then surely some manufacturers will advertise their cables as being 'charger ready' thus safe to use.

 

[bradly1101]

Of course you can throw a billion amps at a circuit that runs on only 1mA as long as the voltages match. By requiring a resistor in the cable they are essentially making it a part of the circuit, so if it's missing or has the wrong value the voltage won't match, which can easily fry your stuff and result in an over-volt/over-current situation.

The spec. seems flawed if it requires an outside party to be part of your circuit; it requires adherence where greed often roams.

My experience with cheap cables is that they usually don't fit quite right, this is something new.

 

[Mr Evil]

I heard about this, but how does it work exactly, doesn't a device only draw the amps it needs? You can plug a 7w Christmas bulb directly between the terminals of the electrical panel where 200 amps are available, it's not going to blow the bulb, the bulb will still only draw what it needs.

That's the case for passive devices, but USB peripherals are active devices. They are capable of vaying their own resistance in order to draw more or less current, depending on how much the source is capable of supplying.

...The spec. seems flawed if it requires an outside party to be part of your circuit; it requires adherence where greed often roams...

If cable manufacturers can't be relied upon to meet the spec, then devices would have to assume that they can only draw 100mA (which is the max. allowed for USB 1 without having to ask the source how much it can supply).