What does a EV charging point actually do?

I have bought a 2nd hand Nissan leaf and have been happily charging it slowly from a 13A socket (fed by solar panels) for 6 months using the "granny lead" that comes with the car.

Yesterday, when I turned it on, the READY and CHARGE light flashed about once per second, as did the lights on the dashboard, and there was a click each time from the unit. The manual does not list this combination as indicative of anything.

This lead me to wonder what the "charging unit" actually does, It lists its input and output as 250V ac so it clearly is not a transformer/ rectifier. If it is a protective relay measuring neutral earth voltage, then maybe the ON / OFF is caused by something happening to the voltage in the house?

I have not found any information on the internet as to what is inside these units.

  • I always thought that they were an extension lead with a suitable plug at either end. The lights may simply indicate that the lead is receiving power from the mains and is connected to the car.

    AFAIK, there are no safety features as such.

    However, what isn't clear to me is what you mean by "charging unit".

  • Apparently they have a temperature sensor on the live pin of the 3-pin plug


    Might also have an rcd in the box

  • It clearly does more than that as it claims: "

    • Recognition of Dangerous Voltage on the Protective Conductor"

    though how it manages that when there is only a standard 3 pin plug, I don't know.

    It looks similar to this:


  • 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.


  • This depends on whether it's an AC or DC charging point. and, if "AC", which Charging Mode.

    WIth AC charging, Modes 1, 2 and 3, the actual battery charger is in the vehicle. However, with the exception of Mode 1, it doesn't mean there's nothing in the charging lead (Mode 2) or charging point (Mode 3).

    Mode 1 charging describes simple plugging in an electric vehicle to a standard socket-outlet. This Mode hasn't been used for a number of years.

    Mode 2 charging permits charging through a special charging lead, that has the additional feature of residual current protection in a lead, as well as permitting the vehicle to monitor the protective conductor within the vehicle, and know the current delivery limit of the charging lead. Power is applied by the lead to the vehicle only after successful "handshake" with the vehicle.

    A Mode 3 (AC) charging point has a number of features:

    • Monitoring of the protective earth connection by the vehicle.
    • Lets vehicle know how much charging current is available (some charging points permit this to be set by the installer, or varied dynamically dependent on either installation maximum demand, or SMART charging instructions).
    • RCD and protection against DC currents must be provided in the supply to the charging equipment, or in the charging equipment itself (hence, failure to install Mode 3 EVSE properly in accordance with BS 7671, taking into account manufacturer's instructions, may mean the charging point is not safe).
    • Handshake to be completed before power is connected to vehicle (and checked during charge, and if it fails, power is disconnected from vehicle).

    Mode 4 (DC charging) moves the actual charger from the vehicle into the charging point, as well as having a number of the other features of Mode 3 charging. The charging point and vehicle battery communicate to determine the most appropriate charging current to deliver, based on the amounts available if there is a limit from the charging point.

    Recent legislation has minimum requirements for functionality of newly installed charging equipment - i.e. at least Mode 3, with certain features that are 'optional' in the standard becoming mandatory (including SMART charging).

  • Being automotive there are far too many standards and it is getting more complex not less.

    In US literature, the mode numbers may mean something different, so be careful when browsing the web as 'mode 3 charger' is not universally defined the same if you are not reading 230V land literature -some folk mean DC charging.

    DC charging "standard" is also a bit variable -  DC charging voltages from as low as 300 up to 1000 (now and later maybe higher for lorries) and currents up to 100A (now and later maybe higher for lorries) are required.  So perhaps the DC charger is better visualized as  a large programmable DC power supply, and the negotiation between car and charger is far more complicated, as the voltages and current limits etc are car model and battery specific, and also far more safety critical  as a result.

    Personally I think private driveway charging will probably be 'just give me the mains, I have a charger in the car matched to these batteries' for many years to come.

    However a DC tap to the batteries does raise the interesting prospect of  using the car as a mobile storage battery, and inverting high powers  back to the house in times of loss of supply, or to base-load solar or similar generation, and indeed this sort of thing has been done, although it is a bit experimental, and not very common at the moment.

    For more modest powers some cars have charger designs can support inversion, and generate 'mains' themselves, sadly not yet as self generating islands - that would be really useful for getting power to remote sites  etc.


  • For more modest powers some cars have charger designs can support inversion, and generate 'mains' themselves, sadly not yet as self generating islands - that would be really useful for getting power to remote sites  etc.

    Not cars, but ... www.ford.co.uk/.../e-transit

    At least for portable tools.

    There are also products such as this, providing similar options for many vehicle types: www.claytonpower.com/.../

  • Thank you for all the helpful replies.

    Yesterday my "granny lead" was cycling on and off at about one cycle per second, with the Power and Supply lights going on and off and the Fault light staying off. Today, it is behaving itself.

    I was wondering if it could be detecting a high neutral - earth voltage at my house and turning off, which reduced the load and the voltage and turned back on again?

    I can't think of anything else that would cause it to cycle in this way, but I am not convinced by my own idea either.

  • Interesting, the transit is very sensible,  and either of those is probably good enough for the average household with ADMD of a few kW.

    It occurs to me that access to the batteries direct would allow a significant step up in peak current, as it would  allow you to add the electronics for the car to double up as something like this.

    https://bynder.aggreko.com/m/6b7864c6764fb3f7/original/45-kVA-Battery-Storage-Datasheet.pdf Which would probably have some applications too - it then allows you you have a self propelled  generator truck, and you could have a few parked up & humming gently behind the stage at pop festivals etc instead of the current method using  tanks of diesel and the equivalent of a bus engine throbbing away inside half a  shipping container.


  • well if you suspect a fault, you could monitor the earth neutral voltage. and then plug in a kettle or something. Don't overlook simple under voltage drop out either.