Charging Your Tesla at Home: How Long Does It Take? How Expensive Is Home Charging Equipment?

A friend recently asked: "How long does it take to charge your Tesla at home -- and how expensive was the home charging station?"

This was my response:

I configured our Tesla Wall Connector (an “EVSE” - more about that in a moment) to report that it can provide 40A at 240VAC (9.6kW). At that rate, it adds charge at a nominal rate equaling about 37 miles of range per hour of charge. So if we’ve driven, say 70 miles on a given day, then it will take around two hours to replace that charge. If our ~75kWh battery were at 0% (something you do NOT want to subject a battery to, much less plan that close - though I’ve arrived home with <6%), it would take over 8 hours to top off (assuming you wanted to charge to 100%, which no EV owner should be doing unless it’s absolutely necessary for the next leg of a trip), with the charging system going quite gently near the 0% and 100% charge capacity of the battery (lithium-based batteries do not take on charge well at these extremes).

Our car’s on-board charger is capable of charging from AC sources at a maximum of 48A, or about 44 mi/hr. But the 240VAC service for our EV charging can’t handle that load. When we first installed an Aerovironment 30A, 240VAC “Level 2” charging station, we had an electrician run a service line from our breaker box to the breezeway of our home. The electrician told me that he installed a 50 amp line, so if I needed more current in the future, I was set. But when I removed the Aerovironment EVSE to install a Tesla Wall Connector, I found the wires disappointingly small in gauge. After no small amount of research and measurement (no visible markings on the wire), I determined that the 8 gauge wire over the 50 foot run could only safely support 40 amps. Statistics of charging sessions indicate no apparent thermally-related voltage drop, so I’m happy with that.

Regarding costs: in addition to the $700 to have an electrician run the original EV line, the Aerovironment EVSE was $1,100. However, we received a $750 rebate from LADWP for installing an EV charging station. We charged the Tesla from the Aerovironment using an included J1772 adapter for a while, until I discovered that LADWP would rebate us the entire $500 of a Tesla Wall Connector. Not only could the TWC charge at a higher rate, but I no longer have to handle the J1772 adapter daily. Best of all, the Tesla charging handle has a remote charge port button (it could be fussy to sometimes have to open the trunk to wake the car to unlatch the charge handle). We’ve also benefitted from three Federal $7,500 rebates and three California $2,500 cash incentives for adding three zero-emission cars to the state’s rolling stock.

“EVSE” stands for Electric Vehicle Supply Equipment, the “charging station” which incorporates a ground-fault system and an intelligent controller which is interrogated by an EV upon connection, reports it’s available current limit, and only while handshaking with a connected vehicle allows current to flow via big contactor relay. The charger in the car determines how much current the vehicle will attempt to draw based on the interrogation step. 

All contemporary EV’s AC charging is intimately managed in the car itself, monitoring charge and temperature and in the case of all of our EVs thus far, both heating and/or cooling the battery to optimize the charging process. Tesla cars even pre-heat or pre-cool the battery while on the road if the user sets a Tesla Supercharger as the navigation system destination, back-timing the thermal management so that the battery can immediately take on maximum charge. (Currently the highest Supercharger power is 250 kW - yes, more than most motion-picture generators, and capable of peak rates adding 1,000 miles per hour to a Model 3 or Y.

An EV owner’s commitment to upgrading home charging infrastructure should be consistent with their driving habits, lifestyle, and characteristics of the vehicle. Your Volt is the perfect example of NOT benefiting from the investment to upgrade to Level 2 (L2) charging equipment: 1)The longest possible L1 (120VAC ~12A) charge is almost achievable with a typical overnight parking period (~10-12 hrs); and 2) In an emergency, you can simply operate the Volt as a hybrid.

If a Volt owner was determined never to operate the gas engine (keeping in mind that it must periodically run a maintenance cycle), and the owner’s lifestyle benefited from charging at 22-25 miles/hour during the day at home before once again using the battery, that might be a case for investing in L2 infrastructure, but there’s hardly a financial argument.

Our choice to spend $1,100 (after rebates in installing L2 charging was clear: we would attempt to go Cold Turkey on Internal Combustion (we never used our Dodge Caravan “backup” vehicle for local driving, and we do drive a small diesel RV for long-distance road travel). I decided that we would want our EVs topped off as soon as possible, in case an unexpected journey was necessary. The economic benefits of charging off-peak were pretty comical, as our annual fuel bill was something like $500. (I calculated that it would take 7.5 years to offset the $1,100 we were quoted to install the dedicated utility meter LADWP required to offer a discounted EV off-peak rate, and both of our first two EVs were inexpensive 2-3 year leases.)

(The friend commented about this article about the development of new battery technology.)

Battery technology is economically improving, especially now. And the financial rewards of owning the Next Great Electric Battery tech represents a modern Gold Rush. The Lithium-ion batteries that power our mobile devices and most EVs have fallen in cost by an order of magnitude in a decade. The 23 kWh pack in our 2013 Focus Electric was probably worth $20K. Our 2016 BMW i3’s 22kWh battery was probably almost half that cost, and our Model 3’s 75+kWh pack was probably only around $13K in 2018.

So even this old battery tech will continue to herald much of the early EV adoption, as its cost per kilowatt-hour makes prices of electric vehicles on par with ICE-powered (understanding the operational envelopes are not the same). A battery technology with twice the energy to mass density at similar energy/cost will yield lighter, more efficient, less expensive cars, while also increasing the potential range.

(It important to recognize that replacing the internal combustion fossil-fuel paradigm for local, urban travel addresses a huge percentage of consumer transportation needs, and that long-range travel requiring short-turnaround refueling might need to be compartmentalized as something not every owner needs or wants.)