I have seen a video on the web where a person is testing the galvanic isolation of several phone chargers. I am talking about this kind of phone charger.
They are plugged into the wall with no connection to earth, and are supposed to deliver 5 V between the VCC and GND pin of the USB port. I have measured the voltage between the GND pin and the earth of some of my own phone chargers. The results are disparate: 1 VAC, 8 VAC, 60 VAC and 80 VAC.
I am a bit confused with the process:
- How come the (AC) voltage between earth and GND is a means to qualify the galvanic isolation of a phone charger? Shouldn't it be between GND and neutral? The earth is not connected in the circuit.
- When the galvanic isolation is not so great, is it GND or earth that oscillates? If this is GND, does it mean that VCC and GND are oscillating but the difference is always 5 V? If this is earth, what does it have to do with the charger?