Known as "Mode 2 charging", this method of charging electric vehicles describes the use of a common household wall socket and common mains voltage (230 v) to charge the vehicle. This is usually done at 10 Amps (2,3 kW) while 16 Amp (3,6 kW) charging cables are also available on the market.

These chargeing cables have a common household plug on one end, a length of decently thick cable, a box (controller box?), some more cable and then a plug that fits the electric vehicle, such as Mennekes type 2 port. Some of these controller boxes even seem to have buttons that allow the user to select a maximum current from a few steps (8, 10, 13 and 16 Amps)

Example picture of the described charging cable.

Now, what does this "controller box" halfway along the entire cable do? Does it... change voltages and/or ampéres? Does it only interrupt the connection with a relay based on information it receives from the vehicle? Or does it send information towards the vehicle, for example the maximum charge rate/current - which can be regulated by the vehicles on-board controllers? If the box doesn't change the current or voltage, can't it simply be omitted?

  • 6
    \$\begingroup\$ No change or power conversion, just handshake between the car and outlet, oh, and significantly added cost to the end user. \$\endgroup\$
    – winny
    Commented Apr 10, 2022 at 20:42
  • \$\begingroup\$ The Toyota Prius Prime comes with something of the same category, except of course it is included in the purchase and is Toyota-branded. The main thing is to not exceed the breaker-panel amperage found in a household's panel for typical subcircuits. The technical details required by the vehicle are hidden from you and you should not need to worry about them. The box handles those details. There are other category chargers that will charge a vehicle faster (for those vehicles permitting a faster charge.) But at the expense of modifying the home and perhaps involving the energy supplier, too. \$\endgroup\$
    – jonk
    Commented Apr 10, 2022 at 21:11
  • \$\begingroup\$ Similarly, the Vauxhall Ampera is supplied with one that allows the charge rate to be switched between 6A and 10A. I have seen these devices referred to as "granny chargers" (the implication being that they would be used occasionally to charge when visiting a relative, rather than as the vehicle's regular charger). \$\endgroup\$
    – john_e
    Commented Apr 11, 2022 at 16:11
  • 1
    \$\begingroup\$ Technology connections on YouTube did a video on this \$\endgroup\$
    – eps
    Commented Apr 11, 2022 at 19:38

3 Answers 3


They are called EVSE, for Electric Vehicle Supply Equipment.

First, it's a GFCI (human safety rated RCD).

However, it's a "smart GFCI" that can self-reset at intervals - most ground faults are transient events. This means, you will come out in the morning to a charged car instead of a tripped GFCI.

You could replicate that part of its function with a real GFCI (or 6 mA sensitivity RCD)... but then, you'd awaken to a tripped GFCI and a flat car.

Second, it tells the car how much current it can draw.

This is the most important function.

When an EVSE is permanently installed, it is wired from a circuit breaker through in-wall wires to the EVSE. The wires have a current limit and the breaker protects them. The current limit might be as low as 12A** to as high as 80A**. As part of commissioning the EVSE, it's jumpered to set the ampacity of the circuit.

The EVSE sends a signal on that cable to tell the car how much it may draw. The actual battery charger is on the car, and obeys. That signal can be changed dynamically on the fly, and yes, you can do amazing stuff with that! By design and agreement with safety standards organizations. Having to upgrade your house's electric service is a sales-killer, and SAE/Tesla didn't design the standard to sell service upgrades. They designed it to sell cars.

The signal is a 1000 Hz PWM signal on the Control Pilot (CP) pin. The duty cycle in percent indicates the authorized amps, according to a table. (generally 0.6A per percent, but it gets weird above 48A).

There is no need to communicate voltage since the on-vehicle charger is a switching power supply that can accept multiple voltages.

Third, it provides a contactor to energize the terminals.

Inside the EVSE is a big clicky-clack relay. When relays are that large, they are called contactors. This physically energizes the large power and neutral pins on the J1772 or IEC 62196 connector. (the signal protocols are the same).

This contactor energizes when all the handshake protocols are agreed.

Fourth, the handshake protocols.

The EVSE monitors the CP pin to detect the presence of a car. The EV presents a 2740 ohm resistance to say it is present, but not ready to charge. When ready to charge, the vehicle changes that to 882 ohms, or 246 ohms if the car has a battery type that requires a well-ventilated space (e.g. lead-acid with hydrogen off-gassing). The EVSE will generally close the contactor at this point, energizing the power pins.

Reversely, on the PP (Proximity Pilot) pin, the EVSE (or rather, its plug) presents a 150 ohm resistance to indicate the car is plugged in. So don't drive away; do think about requesting charging. Pushing the release button on the plug changes this to 480 ohms: The car will immediately stop drawing current. The user is unplugging the car and we don't want it to arc.

Note that the PP pin doesn't even need to come down the EVSE cable. It is all handled in the connector itself. But it could; PP could carry a high-frequency communication protocol for charge balance management, or billing and payments at commercial kiosks. For that matter, there's room for that on CP. But that is not part of the J1772 or IEC 62196 standard; that's for someone else to design.

Implementation notes.

First yes, a 12-year-old could build one of these with an Arduino, if one ignored the GFCI. Which is a bad idea.

Note that the "smart GFCI" doesn't need its own contactor to interrupt, it can use the existing contactor.

With hardwired or mounted EVSE's, the current is set during Commissioning. However, with portable EVSE's such as yours, it gets a little more interesting. Either the EVSE must make a safe assumption (such as 10A in Europe; maybe 12A in North America).

The Ford Mobile Charger has exchangeable plugs either NEMA 5-15 (120V/15A, found everywhere) or NEMA 14-50 (240V/50A, found at RV/caravan parks). The exchangeable plugs provide a signal back to the EVSE to tell which kind of plug they are, so the EVSE can set amps to 12A or 32A, respectively (80% of circuit, assuming a 50A socket may be seen on a 40A circuit).

enter image description here

Tesla goes further, and offers dongle plugs for 8 different sockets - meanwhile, a 3rd party maker also makes the "TT30" socket found at small RV park stations (120V/30A).

enter image description here

* North America and other El NEC countries require the circuit be rated for 125% of the EVSE load. So you get 12A charging on the very common 15A circuit size, at either 120V or 240V, depending on how the breaker is phased. This at 12A gives 1440 or 2880 watts of practical charging.

** Again in El NEC lands, an 80A charger just fits on a 100A circuit per the 125% rule. Since a 100A circuit is always 240V, that is 19,200 watts of practical charging. North America runs such high amps because it doesn't have 3-phase for residential.


It is for safety. It can't be omitted.

The box tells the car how much current is available at maximum so the car knows how much is the maximum current it can draw.

The box also turns on mains voltage to the charging plug when the plug is properly connected to the car, so that the plug is safe and unpowered while disconnected from car.

  • \$\begingroup\$ Thanks for your response! I expected it to be something along those lines. Do you happen to know of any standards, rules, logic or specifications? Or should I perhaps look into the specifications for the Mennekes 2 plug? I am not planning to built my own controller box, but as an electronics amateur/enthousiast and potential EV buyer I'd really like to understand all the electronics I work with! \$\endgroup\$
    – hadrox
    Commented Apr 10, 2022 at 21:22
  • 2
    \$\begingroup\$ @hadrox - J1772/IEC 62196 - en.wikipedia.org/wiki/SAE_J1772 \$\endgroup\$ Commented Apr 10, 2022 at 21:27
  • 3
    \$\begingroup\$ There is an opensource/open hardware implementation out there called "openevse". \$\endgroup\$ Commented Apr 11, 2022 at 5:06
  • 2
    \$\begingroup\$ @KevinWhite I think you meant IEC 61851, which describes what the "controller box" in question actually does. IEC 62196 is just about the plugs and sockets really. \$\endgroup\$
    – Num Lock
    Commented Apr 11, 2022 at 7:06
  • 1
    \$\begingroup\$ @hadrox youtu.be/RMxB7zA-e4Y is a very useful resource for a layman, rather than trying to decipher a technical standard! \$\endgroup\$
    – Tim
    Commented Apr 11, 2022 at 8:53

It is required. The charger for the car is built into the car itself and this is a weather-resistant lead with some smarts in it.

The dedicated wall chargers some people have installed in their homes, or fancy multiple-option chargers at the local carpark have many more amps available than a common wall socket. These things are configured to know they can draw 20A or 30A or 50A and can tell the car/s that directly.

reduced-size image from https://www.reddit.com/r/electricvehicles/comments/acahht/buyers_guide_for_ev_charging_stations/ originally, via a google image search for "EVSE"

Image source: reddit/r/electricvehicles - Buyers guide for EV charging stations

So the car and the charger have a communication, a handshake, to discuss how much power is available and how much the car can take. Sometimes that discussion can cover "this car will be here all night and can take a slow charge the whole time" or "this car is almost flat and needs to move soon so full power please"

A boring wall socket that would power an appliance has no smarts and cannot tell the car what levels are available. One of the functions of the wall socket cable is to have that conversation with the car and say "I'm just an old-school wall socket and can probably only supply 10A or 15A or whichever"

Without this handshake, the car would have to be limited to ~10A all the time A car can't "test" if there's more current available. It might try, by drawing 12A on a 10A circuit and be okay, then try for 15A and blow a breaker. Once that happens, it gets no power and that is worse than trickle-charging.

Aside: the proper name is "Electric Vehicle Supply Equipment" and is shortened to EVSE.

  • 2
    \$\begingroup\$ "... blow a breaker and getting nothing" - should that be "get nothing", or maybe "end up getting nothing"? \$\endgroup\$
    – psmears
    Commented Apr 11, 2022 at 13:41
  • 3
    \$\begingroup\$ @psmears I'm a kiwi and we probably have slightly different release-versions of English -grin- \$\endgroup\$
    – Criggie
    Commented Apr 11, 2022 at 20:54
  • 1
    \$\begingroup\$ @Criggie no, we do not. "blow a breaker and getting nothing" is a tense mismatch \$\endgroup\$ Commented Apr 12, 2022 at 14:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.