Electronic – Electricity consumption of electrical machines – why do they consume electricity when they are not turned on


The question is, why do electrical machines consume power when they are not turned on (they are plugged into an outlet)?
Also, suppose there is a seven-port USB hub with AC power. Is the power consumed by the hub always the same regardless of how I use the hub?

Best Answer

"Turned Off", can (unfortunately) mean different things, it may refer to the device still having power available but in a low power standby mode, where consumption is minimal. Many consumer devices do this for various reasons, such as waiting for a remote signal to turn on.

If power is completely cut off (e.g. the circuit is broken) then the device cannot use any power. Switching off a device by switching the wall socket or unplugging would be an example. Also many devices have a main power switch as well as a standby switch (e.g. a mechanical switch at the rear). This is what I understand as "turned off".

The USB hub will consume less power when not loaded (ideally almost none, probably a few mA) It's efficiency under load will typically be around 80% if using a switching converter, this will vary a bit with different loads.