Range Confidence: Charge Fast, Drive Far, with your Electric Car

By David Herron

How should you plan wiring for your garage intention to charge an electric vehicle?

Perhaps you own your home, and are thinking to buy one or more electric cars in the future. Or maybe you already own an electric car, and want to plan for future electric car charging at home. How do you plan for future-proof electric car home charging support?

At the time of this writing in mid-2017 it's obvious we're at a juncture point for electric vehicles. The 200+ mile range affordable electric car is upon us, the Chevy Bolt went on sale in January 2017 and the Tesla Model 3 is on the cusp of deliveries to paying customers. It means the needs of a typical electric car driver will change from the 80-100 mile range vehicle to ones with over 200 miles range, and that may influence the required charging rate.

Except that our real driving distance need will not change just because we have longer range electric cars. We'll still have the same typical daily commute, and the average drivers will drive on average less than 40 miles a day.

J1772 is here to stay

Single-phase AC charging through a J1772 connector will almost certainly remain as the primary charging method. Single-phase AC is ubiquitous in homes, and easy to provision.

Therefore the charging stations will continue being connected to a circuit on a service panel. The question is the charging rate.

Charging rate sufficient for the needs of two cars

As we've gone over in so many ways in this guide, the charging rate is the big question. See What charging rate do we need? “As fast as possible” isn’t always what’s needed

The charging rate you install affects whether the service panel in your house, or even the nearby electrical grid, requires upgrading. The higher rate charging stations are convenient because the car recharges more quickly, but they're more likely to require a service panel upgrade.

Typical driving distance, typical charging needs

In other words, it's necessary to evaluate your real needs. As we've suggested elsewhere, keeping a diary for a couple months of where you drive is a great way to evaluate your real driving needs.

Most of us drive 40 miles or less per day. Recharging 40 miles of range overnight can be done with a simple 120 volt outlet supplying 4-5 miles range per hour of charging. A 240 volt 16 amp charging station supplies 11-12 miles range per hour of charging, meaning it can supply over 100 miles range in an overnight charging session.

Will having a 200+ mile range electric car mean your driving habits change? It may because you'll be tempted to take it on longer trips, as you should. But would your daily commute change? That's very unlikely.

In other words, your real charging needs for your daily commute is the same as today. Charging 240 volts at 16 amps requires a 20 amp circuit, and is quite sufficient for home charging. With two electric cars at home, that means 2 such circuits.

See Installing cheap/inexpensive electric car charging at home

Handling a recharge-from-empty event in 200+ mile range cars

Maybe the temptation of a longer range electric car means you'll more frequently arrive home with an empty battery pack after a long drive. Those weekend jaunts to the mountains could more commonly be handled with the electric car. Come Sunday evening, after a long drive back on roads jammed with others returning from their own weekend adventure, you're likely to arrive home with an empty battery pack, crash for the night, and need to drive to work the next day.

In other words it'll be tempting to have a higher power charging station at home. After all a 60 kiloWatt-hour battery pack will require close to 20 hours for a full recharge at 240 volt 16 amps.

How often will you face a recharge-from-empty event? That's for you to determine. For those who'll rarely need a full recharge, it's probably best to rely on a neighborhood DC fast charging station and at home go with a less expensive lower power charging station.

On the other hand a 240 volt 40 amp circuit (for a 32 amp charging rate) would fully recharge a 200+ mile range car in about 10 hours. A fairly modest bump upwards in the charging rate is sufficient for for this scenario. Surely adding 200 miles range in an overnight charging session is enough?

With the longer range EV's, the automakers may decide to finally increase the power of the on-board charging unit. It's anybody's guess what that increase might be. Again the higher the power you plan for, the more likely you'll need a service panel upgrade.

Smart-grid-connected charging

The automakers and charging station companies are working on integrating smart grid services into electric cars. Their large battery packs are extremely tempting for utility industry regulators.

It is unlikely this will mean a change at the service panel. You will almost certainly require a different charging station, one that can handle two-way power.

Wireless charging

Wireless charging stations are also on the horizon, and can be purchased today as an aftermarket add-on. They still connect to a regular circuit in the service panel, and therefore do not require any changes to the house wiring. Current wireless charging systems have power limitations and won't impose much demand on the power capacity of the house.


Range Confidence is Copyright © 2016-17 by David Herron

How should you plan wiring for your garage intention to charge an electric vehicle?

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