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Why DIY an EV-charging Point?

  • It’s fun to build things yourself 🎉
  • You can save some money 💰
  • You have so much freedom: how it looks, how it works, it’s almost entirely up to you 🤓

Disclaimer

Electrical safety warning sign
Adults only beyond this point!

Unless you know how to DIY some serious electrical installations on your own AND have done that before, DO NOT start building a charging point. A short list of things that could go wrong: fire, electrocution, blown mains fuses, blown built-in car charger…

Adults with electrical engineering background only!

What To Build?

Just a Charging Cable

A Type 1 charging cable
A Type 1 charging cable, image credit: Metron

It’s hard to make a reliable current limiting solution this way, so it’s probably not worth the extra effort – just buy a standard one.

But it can be a worthwhile option if you need to repair a dead charging cable. Just buy a SimpleEVSE controller, a 2-pole relay, and a power supply and put it in the old charging cable casing. Please don’t forget to put a Type A RCD on the supply side cable to keep it safe – you never know what’s behind a socket you did not install yourself.

A Full-blown Type 2 Charging Point

This is where all the options are: current limiting, automation, access control, visual design, cable v. socket, integration, automation…

Options

Current Limiting

I think it’s not an option, actually. Either:

  • You risk blowing the distribution fuses every time you forget you are charging a car and you turn on an electric oven or another large load for more than a few minutes.

Or:

  • You pay through the nose for bigger distribution fuses.

    Where I live, the standard option is 230V, 3x 20A. Most EVs now have 3x 16A or larger built-in charger. This gives you 4 amps of headroom. Any significant appliance like an oven, washing machine, vacuum, cooking plate, microwave, etc. puts you in the danger zone. So, if you want to be sure, you need at least 35A fuses. This is costly for several reasons:

    • First of all, bigger fuses directly increase your electric bill even before you use any extra power. In EU, the difference will be on the order of several hundred euros per year.

    • You will have to pay for the change and take care of the paperwork.

    • Your existing house connection likely does not have big enough cabling so you need to upgrade this as well.

    • Your local transformer station could already be loaded to the limit and you can’t even get the extra capacity even if you are willing to pay for it.

The downside to current limiting is a slightly more complicated installation and charging will sometimes take a little longer when you have big loads turned on in your house.

Cable or Socket?

My preference is clear: use a socket.

Type 2 socket
Type 2 socket, image credit: Digitehnika

Pros: It looks cleaner (no “elephant trunk” on your wall), it’s easier to weatherproof, and every EV owner owns a Type 2 charging cable.

Cons: You have to take the cable out of your car before you plug it in. But when you come home, you usually have to take groceries etc. out of the car anyway, so it’s not a big deal.

Type 2 Cable
Type 2 charger with connecting cable AKA the Elephant’s Trunk, image credit: Amazon

Access Control

RFID Reader
RFID Reader

I think most people reading this own a house and are thinking about building a charging point of their own in their own driveway or garage. If this is the case, you don’t need access control unless you live in a really rowdy neighborhood. Let’s face it, most people will not park a car in a driveway belonging to someone else, much less hook up a charging cable unless they REALLY need it. Even if they do, this will cost you a few euros at most. If you are in this situation, you can probably afford a few euros – we should look out for each other, when we can.

Nevertheless, if you need access control, it’s quite easy to arrange and you have several options:

  • The standard solution seems to be RFID. This is an easy option to implement, you just need a RFID reader:
    • Most RFID-readers have the option to simply hard wire an output to the device you want to control. In this case, any EVSE controller should have an input pin to control. Just program your reader, connect the output to the controller and you are done.
    • You could use the SimpleEVSE-Wifi solution – a simple ESP8266 board you can connect your RC522 RFID-Reader to. It takes care of access control and many other things as well.
  • You could control the charging station via your Home Assistant system. A simple switch there can turn your charging point on or off, but you can also do so much more – time control, control according to your photovoltaic plant production, the possibilities are endless.
  • Just wire a simple key-controlled switch, hooked to the enable input of your EVSE controller. Install a switch inside your home and connect it to your EVSE controller. It could even be just your RCD switch. Turn on when needed.

What Hardware To Use

Electrical Components

MCBs, RCDs, etc.
Image credit: ABB

Any charging point needs these at a minimum:

  • An RCD protection switch, type B.

    This is expensive, but important! A regular RCD (type AC) could fail to protect you in case your car charger fails in a way that makes the fault current non-sinusoidal (e.g. leakage on only one leg of the rectifier). A type B RCD is a more expensive, but it will reliably trip for DC fault currents as well, which are unlikely, but possible in case of catastrophic damage of the built-in charger in the EV. It is also required by the relevant standard (IEC 60364-7-722:2018). Current capacity should be equal to or larger to your fuse rating. Trigger current should be according to your country standard (30mA for me).

  • A fuse.

    A regular installation fuse with the same nominal current you want the charging point to have, type A or B (no need for starting current protection).

  • A relay.

    A relay (or a contactor) that breaks all the phases AND the neutral. E.g. for a 3-phase charging point you need a 4-pole relay. Nominal relay current should be at least 120% of the nominal fuse current. (E.g. for a 16A charging point, use at least a 20A relay.)

  • A surge protection device.

    An over-voltage protection device, type 2, 2-pole for 1-phase and 4-pole for 3-phase charging points. If your car is not protected from lightning (e.g. away from the building, no roof, etc.), use T1+T2.

  • An enclosure.

    It’s best to put all of these in an enclosure with a DIN rail. If the enclosure is exposed to the elements, it needs at least an IP55 rating. Some people prefer to put their RCD switch inside the house, so they have an easy way to turn off the entire charging point there as a kind of access control.

  • Cable or socket.

    Also expensive, but you don’t want to skimp here, since it is subject to wear. I usually put it next to the enclosure and build an extra sturdy bracket for it – it takes some force to plug and unplug the Type 2 cable.

The EVSE Controller

The SimpleEVSE controller
The SimpleEVSE controller, image credit: GWL

You could implement everything using a simple ESP8266 board and some peripherals. But unless this is something you dream about doing, I would very much recommend you go modular: Buy a proven EVSE controller to do all the SAE J1772 standard signalling and control (pilot signal, current control, relay control, enable/disable).

A good option is the Simple EVSE open source project. You can build it yourself or buy a built module at GWL. I built three chargers using their kit already and can recommend them (they have sockets, cables, relays, etc. too). But there are other options too: OpenEVSE, DehneEVSE, smartWB, and others.

You could also buy a ready-made charging point – you can now buy them at hardware stores. But you will a) overpay for the components you get and b) lose a lot of flexibility. Always go open-source when you can, it will save you trouble in the long run (when the supplier decides to stop supporting it).

The Charging Point Controller

The EVSE controller will take care of the signalling and turning the relay on or off. But what about current control, access control, automation, supervision, energy metering, cost counting etc.? This is where it gets interesting. You have many options:

No Extra Controller

If you don’t want any of the above options, just build a dumb charging point. You need a RCD, fuse, EVSE controller, relay and a socket/cable. It will work, but read about the options to understand why this may not be a good idea.

Ready Made Integrated Solution

Some solutions, like OpenEVSE and smartWB, already take care of some of these options. In essence, they contain both the EVSE controller and the charging point controller. But in my opinion the extra cost is not worth it now that we have ESPHome to play with. Just read their githubs and send these awesome guys some beer money via the donation link, they deserve it.

Simple EVSE-WiFi

A simple ESP8266-based solution with an in-built web server for the Simple EVSE charging controller that will take care of:

  • Default functions:
    • Turning the charging point on or off
    • Setting the charging current
    • Charge logging
    • Control of the SimpleEVSE charging controller registers
    • HTTP API for automation
  • Optional functions:
    • With added RC522 RFID-Reader:
      • Authentication
      • User management
    • With an added S0 or ModBus energy meter:
      • Measuring charging power
      • Metering charged energy (included in log)

You will need to control the current via the API if you want current limiting. This is easily achievable e.g. in Home Assistant, where you probably already have a smart energy meter integrated. Use the REST service integration.

ESPHome

A truly versatile solution that works with an ESP8266 or ESP32 board. It is extremely convenient, you simply program your ESP board via USB once and then you can change the configuration any time using OTA via WiFi. You simply change the YAML file and run the upload program.

The magic of ESPHome is it can work standalone very well, but it is also EXTREMELY easy to integrate into Home Assistant. Whatever hardware you choose to integrate into your charging point (energy meter, sensors, RFID, display, buzzers, LEDs, etc.), you simply add to the YAML configuration file using provided integrations. You can then link these directly using automations within ESPHome or indirectly in Home Assistant.

Conclusion

These are some of the options and things you need to know if you want to build a homebrew EV charging point. In the next post, I present an example solution using ESPHome that includes current limiting and works standalone.

If you found this article useful, you can buy me a beer here.