EV load control

Do you have access to BS EN 61851-1?


This standard specifies the protocol used by Mode 3 and Mode 4 chargers to communicate with the vehicle - although for Mode 4 chargers, the basic functions are extended as discussed in BS EN 61851-23 and BS EN 61851-24. Some functions are optional for both vehicle and charging point. Some charge points are indeed set up to deliver only one or more fixed power levels, others have more fine control available. Because the control is digital, even in the most advanced chargers, the steps are discrete.


In the most basic systems (where there is no CAN bus or similar comms) the pilot's pulse width communicates the amount of power available for charging.


The vehicle will determine whether or not it draws current if the charging point (EVSE) can't deliver enough power - with many vehicles on the market, the threshold of temporarily curtailing charging is often around 10 A.

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

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):

Duty cycle of pulsed signal received from EVSE

Max current the vehicle may draw

< 3 %

Charging not permitted

3 % ≤ duty cycle ≤ 7 %

Digital comms will be used to control off-board DC charger or communicate line current for on-board charger. Digital comms may also be used with other duty cycles, but current draw must not exceed that indicated by a duty cycle between 8 % and 97 % even if the digital comms indicates a higher current. Charging is not allowed without digital communication. 5 % duty cycle shall be used if the pilot function wire is used for digital communication

7 % < duty cycle < 8 %

Charging not permitted

8 % ≤ duty cycle < 10 %

6 A

10 % ≤ duty cycle ≤ 85 %

Available current = (% duty cycle) × 0.6 A

85 % < duty cycle ≤ 96 %

Available current = (% duty cycle - 64) × 2.5 A

Duty cycle > 97 %

Charging not permitted

If the threshold is normally set at 10amps does that mean you can’t trickle charge say from a separate solar supply?

You need a solar supply capable of a good few KW, certainly, it rather depends on the car in question.

Basically at the currents thrown around in the motor control,  10A is a trickle....