Electric Vehicle Charging

I predict an electric car in my future – I had a brief test drive in a BMW i3 the other day and was very impressed. Got a longer test drive scheduled in a couple of weeks and I’ll see how the numbers stack up after that.

Electric car = electric car charging which warrants some research. While it’s perfectly possible to connect a low-current charger (as supplied with the car) to one of the external 13A sockets and leave it at that there are some other / better options to consider:

  • A dedicated EVSE (Electric Vehicle Supply Equipment) “charger”
    • The actual “battery charger” is part of the car and the various alternative solutions are just different ways of supplying electricity to the car so it can decide how to proceed
  • Some means of dynamically scheduling the charging, to either take advantage of a cheaper electricity tariff or spare solar generation capacity

Initially I found the terminology around the many options for EV charging quite confusing (Type versus Level versus Mode etc.) but I think I’ve fought my way through that now:

  • Type refers to the style of socket on the car
    • The BMW i3 models made for the European market are fitted with an IEC 62196 “Type 2” (aka Mennekes) socket
  • Level refers to the nature of the electricity supply
    • Level 1 is 120V AC (mostly of relevance in the Americas)
    • Level 2 is 240V AV (standard in Europe)
    • Level 3 is 480V DC (not relevant for domestic charging)
  • Mode refers to the nature of the communications between the car and the EVSE – basically:
    • The simple EVSEs typically supplied with EVs and fitted with a standard 13A plug are Mode 2 and operate at a maximum of 10A
    • The hard-wired EVSEs are Mode 3 and communicate with the car using a protocol defined as part of the SAE J1772 standard
      • The most interesting part of this is that the car decides what current to draw but it does that based on information advertised by the EVSE
      • Mostly this is used to protect the weakest part of the electrical circuit from overload (typically it’s the cable) but it can also be used to “ask” the car to charge at a lower rate than it might otherwise try to achieve

There are various commercial options for EVSEs – e.g. BMW offer a Wallbox (in BMW colours) – but I’m currently favouring the Open Source OpenEV which is available from the OpenEnergyMonitor folks (and integrates with their other solutions – or other Open Source solutions).

To be able to charge at 7.4 kW (32A @ 230V AC) requires a dedicated circuit with some fairly chunky wiring direct from the main consumer unit (or in my case from a new consumer unit since the two primary consumer units are already “full”). Fortunately I predicted the need for some sort of external connection and there’s already some ducting installed to take it. It will also warrant an extra sub-meter to monitor how much electricity is being used to charge the car.

CC BY-SA 4.0 Electric Vehicle Charging by Marsh Flatts Farm Self Build Diary is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

One thought on “Electric Vehicle Charging

  1. I should have also mentioned there’s a £500 grant available to offset the cost of a hard-wired charging point, funded by the UK Government Office for Low-Emission Vehicles (OLEV) – see https://www.gov.uk/government/collections/government-grants-for-low-emission-vehicles
    I’ve also just found out that Western Power Distribution are running a research project during 2017 and 2018 to investigate the benefits of ‘smart’ EV charging (mostly deferring charging until after the evening peak of electricity usage) for the electricity distribution grid. This is only available in the areas that WPD act as DNO but it offers an extra subsidy, usually resulting in completely free installation – see http://www.electricnation.org.uk/

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