Charger could be there connected to mains all the time

Main Question or Discussion Point

Hi

Suppose my phone charger is connected to the mains but the phone is not connected. The circuit is not complete because the phone should be there to make the connection complete. That means current is not flowing? That would mean the charger could be there connected to mains all the time without any energy being used. Please correct me.

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If it was as simple as putting the voltage from the wall across the battery of your phone your reasoning would be correct. However, a phone charger has components in between the wall and the phone to condition the signal so it's usable to charge the phone. None of these components are perfectly efficient and as such will dissipate some power even when the phone is not plugged in.

If you're in America the voltage from the wall is a 120Vrms sine wave at 60Hz. Your phone charger most likely outputs ~5V DC for the lithium ion battery in your phone. To do this a transformer is used to step down the voltage then a diode bridge is used to convert the AC signal to a DC one.

http://en.wikipedia.org/wiki/Diode_bridge

There are ways to lower the amount of energy used by chargers not hooked up to a phone. I'm guessing they work by sensing if the phone is hooked up then switching a relay so the circuit before the diode bridge/etc is disconnected. You can probably find out whether or not your charger is designed to do that or something similar from your phones manual.

To do this a transformer is used to step down the voltage
Thanks, Lambduh.

The quoted line captures my attention, though I'm not s science student. There are two coils in a transformer: one connected to the main and one to supply current to the phone. The coil connected to the main is continuously pushing and pulling the electrons in the other coil (that's what AC is?). That means energy is still being used all the time although it is not being harnessed. Correct? It just like the potential energy of water falling from a high place is not being utilized into generating electricity. Please guide me. Thanks.

russ_watters
Mentor
Correct.

Thanks, Russ.

But energy can neither be created nor destroyed. The energy is continuously being pumped into the second coil by the coil connected to the mains. So, when no phone is connected, where is that energy of second coil going? To heat up the wires running out the second coil? Please guide me.

Who said anything about energy being created or destroyed?

Is it not generally known that if you connect something to the mains and turn on the switch that current still flows, regardless of if the device is connected or connected and not turned on?

Just a thought.

Is it not generally known that if you connect something to the mains and turn on the switch that current still flows, regardless of if the device is connected or connected and not turned on?

Just a thought.
It is not generally known because that is not right.
There MUST be a return path. Period. End of story.
Else we are talking static electricity dynamics.

russ_watters
Mentor
Thanks, Russ.

But energy can neither be created nor destroyed. The energy is continuously being pumped into the second coil by the coil connected to the mains. So, when no phone is connected, where is that energy of second coil going? To heat up the wires running out the second coil? Please guide me.
Correct again!

You must have one of these plugged in somewhere in your house with nothing connected - touch it and see how warm it is (a lot do feel noticeably warm, but not all).