Sizing your EVSE
Because the chargers for both Level 1 and Level 2 charging are built into the car, the maximum rate at which the battery can be refilled depends on the capacity of the charger the automaker put under the hood as well as the amount of power the EVSE can supply.
The key elements in charging speed are:
- The capacity of the car's onboard charger (kilowatts or kW)
- The voltage of the EVSE (volts)
- The amperage of the EVSE (amps)
The nominal design voltage for Level 2 charging equipment is 240 volts, but it works across a range since electrical service varies from place to place. (Sometimes it's 220 volts, sometimes 208 volts in commercial applications.) The other key element is amperage, or the capacity of the circuit supplying those 240 volts. It's probably easiest to think of volts and amps in the context of a water hose. Voltage is your water pressure, amperage is the diameter of your hose, and the water flowing through is power, in this case measured in kilowatts. All Level 2 EVSEs are built to work at 240 volts, but they are sold in a variety of amperage ratings to suit the power needs of different cars.
Common Level 2 output ratings are 16 amps and 30 amps, but there are others in between, usually spaced in increments of 8 amps and ranging all the way up to 80 amps. Which one should you buy? The short answer is you should buy an EVSE rated for the most amps your budget will allow. It may be more than your car's onboard charger is rated for, but that's no problem: The onboard charger will only draw as much as it thinks the battery can handle. Prices, though, go up in lockstep with amperage increases, both for the unit itself and the wiring necessary to support it. But when the time comes to buy a new electric vehicle, it may have a more powerful charger and you'll avoid having to buy a new EVSE to take advantage of it.
The next best thing is to size your EVSE to the maximum charging rate of the car you currently own. You can figure that out with some simple math. We'll use the Volkswagen ID.4 as an example — it has an 11-kilowatt onboard charger. Multiply that charger value by 1,000 to get watts and then divide by 240 volts to get your target amps: [11 x 1,000 = 11,000/240 = 41.6 amps]. So in order to take maximum advantage of the ID.4's onboard charger, you'd want to get a 48-amp electrical circuit.
Buying the charging station is only part of the process and cost. You'll need a qualified electrician to wire things up, and some locales require permits and inspections. An exception is if your garage already has a dedicated 240-volt plug receptacle of the proper type installed. That would allow you to buy a portable EVSE, hang it on the wall, and plug it in yourself.
For both hard-wired and plug-in Level 2 EVSEs, you'll need to install the proper-size circuit breaker in the fuse box and run wiring from the box to the EVSE's location. Then you either connect the EVSE directly or, for plug-in models, install the proper receptacle so the EVSE can be plugged in. The EVSE's specifications sheet will tell you which type of plug it has. Most are NEMA 6-50, the type used for most 240-volt garage outlets, or NEMA 10-30 or NEMA 14-30, both used for residential clothes dryers. All are pictured in this online NEMA reference chart. And in case you were wondering, NEMA is the acronym for National Electrical Manufacturers Association, which sets standards for all sorts of electrical equipment.
Costs will vary by prevailing fees for electrical work, by the amount of work that needs to be done, and the cost of any necessary permits. If the best place for your EVSE is on the interior garage wall directly behind the exterior-mounted fuse panel, there will be little wire to run and the cost could be just a few hundred dollars. If the electrician has to run wire through the wall and then 20 feet away to the EVSE location, wrapping the conduit around a corner or two along the way, it could cost hundreds more. And if your house is an older one and simply doesn't have a big enough fuse box and you have to upgrade your electrical service, you're typically talking well in excess of $2,000.