phone charger residual electric flow

Question

Not actually sure if this is too simple a question for this exchange.

Just now I picked up my phone charger and unplugged it to move somewhere and plugged my phone in to the recently unplugged (from the wall) charger, and my phone registered that it was plugged in and charging. even though it was plugged into a charger not connected to a power source.

I can understand in theory that there was some residual electric current in the charger, just enough to trigger my phone. However, I fail to understand the scale. How much residual electric charge could be left in a 1m phone cable, and how long before it dissipated?

How does this play into the whole completing the circuit, as there was no real ground connection.

Answer 1

I can understand in theory that there was some residual electric current in the charger, just enough to trigger my phone.

Not quite right. There was electrical charge left in the device. Once you plugged in your phone the charge was able to move and moving charge is called current.

However, I fail to understand the scale. How much residual electric charge could be left in a 1m phone cable, and how long before it dissipated?

No charge is stored in the cable. It's stored in the capacitors in the charger. The charge is given by \$ Q = CV \$ where Q is charge (coulombs, C), C is capacitance (farads, F) and V is voltage (volts, V).

How does this play into the whole completing the circuit, as there was no real ground connection.

Circuits don't need a connection to ground (as in the Earth). If they did electrical circuits would not work in aircraft (insulated by air), cars (insulated tires) or your phone. What happend is that your phone completed the circuit between the charger positive and negative terminals and allowed current to flow around the circuit of the charger, cable and phone.

Answer 2

There is residual charge, but it is not in the cable.

It is in the charger and is due to the conponents discharging down to the lower charging limit - capacitors most likely.

This is the reason that one is careful when opening any device - using a finger to discharge even a small cap is painful or at minimum annoying - usually causes the use of words Mum told you not to use...

Answer 3

How much residual electric charge could be left in a 1m phone cable, and how long before it dissipated?

This is not about how much charge is left in a 1m cable. There is not much, but the charger does have an output capacitor that might have quite a lot of charge, 1000 ++ uF times voltage. And it will hold this charge for several seconds, until the self-discharge or light load will discharge it. So if your phone software is sloppy (as it usually is), it will report the condition as being charged. Just forget all this stuff and don't confuse yourself.