Charging Two EVs on One EVSE

Two EV Nissan Leafs and one PodPoint charger near a residential property in the UK
Two EV Nissan Leafs and one PodPoint charger near a residential property in the UK

Like an increasing number of people, we have one home EV charger but have two EVs.

My 2015 Nissan Leaf has a range of about 60 miles, which is perfect for daily school runs, and trips to the office. However, this means that most nights I need to put it on charge.

My Wife’s EV on the other hand is a more modern Nissan Leaf with a range of about 200 miles, which is more than enough for 99% of all day trips out, requiring no charging from public charging networks.

While it has a range of over 200 miles, it does need to be charged about once or twice a week depending on how much it has been used, and that means that my poor old leaf with its type 1 cable needs to be disconnected from the EVSE and replaced with her type 2 cable.

Can you join two EV charging cables together?

While we could get a second EVSE fitted to the house, to allow the charging of two EVs at home concurrently, there is no reason why you can’t have two EV chargers on one domestic circuit (in the UK). Our incoming fuse fuse from the distribution network is 100 A which means that in theory, the maximum current we should pull from the grid is 60 A at any one time.

A single 7 kW (about 36 A maximum available current at 230 V AC 50 Hz) charger paired with a 32 A cable is the most it is sensible to attach to a residential supply, to avoid getting too close to the 60 A maximum draw while also powering things in the home. Our PodPoint solo 3 is fused at 40 A in the meter cupboard.

While it may be tempting to consider cutting the two cables and putting a junction box in the middle, like a weird EV extension lead, the CP and PP signals in the cables would no longer work correctly and one car may charge if the other end was not plugged in, chances are that with both cars plugged in at the same time, the EVSE would enter a fault state and refuse to supply current to either.

How to split an EVSE between two EVs?

EVSE Splitter Box, showing two EVs plugged into one EVSE.
EVSE Splitter Box, showing two EVs plugged into one EVSE.

I previously worked for a market-leading EVSE manufacturer in R&D and Test and Development… so I know my way around IEC 61851 and SAE J1772, building on the theories covered in Minimalist EVSE Charger Circuits and DIY Manual EV Emulator we can design a box that plugs into our EVSE and then allows us to plug both vehicles in at the same time.

The box will split the supply current between the two vehicles while they both demand current until one of the vehicles is full, then redirect most of the available current to the one that is still demanding current.

EVSE Splitter diagram labelled.
a. Socket-outlet
b. EVSE splitter
c. Cable
d. Vehicle connector
e. Vehicle coupler
f. Vehicle inlet
g. Charging station
h. EV socket-outlet
i. EV Plug

The OBC (On Board Charger) is responsible for converting the AC from the EVSE to the DC from the batteries, and responsible for only drawing the maximum current advertised on the CP line.

The upstream current would come into the box along with the Control and Proximity pilot signals from the EVSE and the cable, which an onboard microcontroller would use to determine the maximum available current to supply to the two downstream connections.

By reading the current carrying capacity of the cables plugged into the two outlets, and using two sets of CTs (Current Transformers) the two downstream Control Pilot signals can be adjusted in real-time to make sure that the total advertised current between the two ports never exceeded the available from the upstream supply.

When a vehicle battery SOC (State of Charge) is nearing 100 % the OBC reduces the amount of current being pulled. Since we have a CT on each port, we can monitor the real-time current draw, and then reduce the advertised capacity on that port to just above the demanded current we can adjust the current availability on the other port.


If we are using BS EN IEC 61851 Part 1 Case B we will know if a cable is plugged into each downstream socket on the box by reading back the current carrying capacity of the cable via Proximity Pilot, if we are using Case C, then we will need to hard code the maximum carrying capacity of each cable.

The GFIC and RDC safety requirements will be met by the upstream EVSE, so we don’t need to re-implement them in the splitter box. At least for version one.

Octopus and Photovoltaics

Our electricity supplier is a company called Octopus Energy, Octopus has tariffs that vary the cost of electricity depending on how much demand there is on the grid, and the availability of power. It would be nice to be able to limit the charging speed when the cost is high and charge at a higher rate when the power is cheaper. This variable charging speed would also be beneficial when we get Photovoltaic cells so that we can use the self-generated power to charge the cars for free.

Conclusion to Charging two EVs from one EVSE

I will write a post soon with more details, block diagrams as well as representative circuits shortly.

An important question is what should I call it? I wanted to go with either Hydra or Madusa however both names were vetoed by my wife… so I need a name for this project.

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