Well, there is just enough in the bump of the granny lead to fool the car into thinking it is connected to a fully functional charge point. So, what's in a  'real' charge point you may ask.

Well the charger itself, the bit that rectifies and regulates  the supply to the battery is inside the car - it has to be really as there are so many variants of car battery voltage, amp hour capacity and charging regime. But the car needs to know how much current it is allowed to take from the mains, and when it is fully plugged in and it must not allow making or breaking of the plug- and socket connection under load. And the charger should not put mains onto the cable, until a car has been connected and requires charging.

So, in the simple version the charge point has a relay that only livens up the socket when a car is detected and requests current, and this is done using a current sent earth and a pilot wire, the loop is only closed and current flows when the plug is fully seated. Further, that 'car detection' signal is modulated by the charge point to indicate to the car that it is a 16 A or a 32A charger or whatever, or in the case of the granny lead, the very minimal level of current is permitted.

Newer cars support additional fast charging methods, and 3 phase supplies but the 'granny lead' is the simplest permitted.

All the granny lead has to do is to emulate enough of this to fool the charger built into the car into coming on and drawing no more than 10-13A from the single phase mains.

Mike

Well, there is just enough in the bump of the granny lead to fool the car into thinking it is connected to a fully functional charge point. So, what's in a  'real' charge point you may ask.

Well the charger itself, the bit that rectifies and regulates  the supply to the battery is inside the car - it has to be really as there are so many variants of car battery voltage, amp hour capacity and charging regime. But the car needs to know how much current it is allowed to take from the mains, and when it is fully plugged in and it must not allow making or breaking of the plug- and socket connection under load. And the charger should not put mains onto the cable, until a car has been connected and requires charging.

So, in the simple version the charge point has a relay that only livens up the socket when a car is detected and requests current, and this is done using a current sent earth and a pilot wire, the loop is only closed and current flows when the plug is fully seated. Further, that 'car detection' signal is modulated by the charge point to indicate to the car that it is a 16 A or a 32A charger or whatever, or in the case of the granny lead, the very minimal level of current is permitted.

Newer cars support additional fast charging methods, and 3 phase supplies but the 'granny lead' is the simplest permitted.

All the granny lead has to do is to emulate enough of this to fool the charger built into the car into coming on and drawing no more than 10-13A from the single phase mains.

Mike