I have an external garage with a 16A fuse box. I can safely charge my EV overnight using an 8A charger in the garage. My partner wants to get an EV but the garage is the only home charging option.
Is it possible to have an outdoor socket installed outside the garage to charge the Leaf and have a switch so either the existing in-garage socket or the outdoor socket takes power (not both), so only one vehicle can be charged at one time to avoid overloading the fuse box?
Yes, there is technology for this, but you'll need to evolve past the flimsy charge cords.
Tesla used to call it "Power Sharing" and now calls it "Group Power Management". Several brands support it including Wallbox Pulsar Plus. Multiple EVSEs are placed in a group, and the group is programmed for a number of amps it can share. In your case, 16 amps.
The stations coordinate - if only one car is charging, it gets 16A. When a second car plugs in, they share 8A. When one car finishes, the other car gets the full 16A. This very effectively balances charging among multiple cars, wasting no capacity.
Now you need to shop carefully. A few EVSE makers built things lazy, and have no way to reduce a car's allocation below 6 amps. Thus, every station gets assigned 6 amps whether it is using it or not. With those stations, with only one car plugged in, that car would be limited to 10 amps.
We are talking about hardwired stations here. This tech is not compatible with sockets for a variety of reasons, like no auxiliary pins in the socket to share a capacity signal.
I'm not a fan, but I know many people get hung up on sockets. In that case, you use general smart-home stuff to turn on one of the sockets, wait until either it stops drawing current or 1 hour, whichever comes first, and then switch it off and switch on the other socket. So you'd be switching every hour until 1 car is full, then switching to the other car and retrying the first car once an hour.
This is one of my favorites. On a panel with limited capacity on the standard service load calculation, and the need for multiple EV stations, you set up 2 stations.
Station #1, the "little" station, is a fixed load that uses the remaining headroom on the load calculation. E.g. 16A.
Station #2 uses EVEMS. It is taking advantage of the fact that the service load calculation must assume a probable worst case scenario of many appliances being used at once, but that's not actually true 99.99% of the time. So it has a monitor on the supply wires, and it is dynamically adjusting EV charge rate to use the capacity headroom that is in the house right now. Because of this, it can take as much as the whole service, and it is actually the more powerful of the 2 stations.
You then make competent personal choices to plug the more hungry car into station #2.
Assuming 16 amperes (A) at 240 volts AC (VAC), the maximum charge rate would be ~4 kilowatt-hours (kW-h) per hour of charging, whether for one vehicle or split among two, e.g., each vehicle getting ~2 kW-h each hour.
Would that suffice for your intended use? Consider the vehicles energy user per km, how much you'll be likely to drive, how much time they'll be given to charge, and whether charging is available at destinations.
For example, a Subaru Solterra is shown as needing 200 W-h/km (0.2 kW-h/km). If you drive an average of 50 km total each day, it would take 10 kW-h to recharge fully, which the 16 A supply could theoretically provide one vehicle in 2.5 hours, or charging two, split equally, in 5 hours. Theoretically, because supplies are not 100% efficient, and using car accessories such as air-conditioning or heating can require considerably more energy. It might take perhaps double those times to charge two cars without popping a circuit breaker.
Of course, your kilometrage might vary ;-)
As for the particulars of the chargers, that would depends on the particulars of the vehicles. You might look for vehicles with compatible charging ports, and talk with the vehicle manufactures about those chargers. Consider increasing current going to the garage -- the cost of upgrading the wiring would be minimal compared to the cost of purchasing vehicles and chargers.
My Volt and probably most EVs are able to be programmed for "time of use" charging" since some utilities charge more during the day. My utility charges about 50% more during the hours of 2-7pm during the summer. Consequently, you could have your chargers connected to the same circuit and have the cars programmed to charge and different hours of the day. You still have to have two chargers on the same circuit for this and if you ever try to charge at the same time it will trip the breaker or blow the fuse. My recommendation would be to upsize the circuit / sub-panel in your garage or add another circuit. Most EVs benefit from at least a 20 amp 240 volt circuit dedicated to just that one charger.
You can get a multi-charger or a set of chargers which do load sharing.
If they are set up properly then if only one car is plugged in (or the other car is full charged) then the entire circuit is available to the car that needs it. If both cars are plugged in and want to charge then the load gets split between them.
