EV load control

mapj1:

The charger clever bit is in the car, and can modulate the load, rather like a lamp dimmer, by changing the on-to off time ratio of the switching transistors.  This is done in response to the duty cycle (pulse width modultion = PWM) of a 1KHz tone generateed  by the charging point that you have just plugged it into,

16% PWM is a 10 A maximum, a 25% PWM is a 16 A maximum, a 50% PWM is a 32 A maximum

normally the programmable current is not really just these discrete values , but can be varied continuously (you could make a charge point with a twiddly knob to set the mark to space ratio and then allow you to wind the current load the car presents up and down at will - in reality it is fixed at build time).  

As graham alludes some use CAN bus instead, but not yet many

Agreed, except:

• the car can choose to draw a lesser current than that stated as available from the charger by the pilot pulsed signal- which it may choose to do depending on the charge profile of the battery, and where it's up to in the cycle.

• To get a charging current of > 80 A [per phase] you need DC rapid charging.

• Duty cycle of the pulsed pilot signal is not directly proportional to the current over the whole range, it follows this schema (linear plus offset where charging current > 50 A):

mapj1:

The charger clever bit is in the car, and can modulate the load, rather like a lamp dimmer, by changing the on-to off time ratio of the switching transistors.  This is done in response to the duty cycle (pulse width modultion = PWM) of a 1KHz tone generateed  by the charging point that you have just plugged it into,

16% PWM is a 10 A maximum, a 25% PWM is a 16 A maximum, a 50% PWM is a 32 A maximum

normally the programmable current is not really just these discrete values , but can be varied continuously (you could make a charge point with a twiddly knob to set the mark to space ratio and then allow you to wind the current load the car presents up and down at will - in reality it is fixed at build time).  

As graham alludes some use CAN bus instead, but not yet many

Agreed, except:

• the car can choose to draw a lesser current than that stated as available from the charger by the pilot pulsed signal- which it may choose to do depending on the charge profile of the battery, and where it's up to in the cycle.

• To get a charging current of > 80 A [per phase] you need DC rapid charging.

• Duty cycle of the pulsed pilot signal is not directly proportional to the current over the whole range, it follows this schema (linear plus offset where charging current > 50 A):