Saturday, December 21, 2013

Why public EV charging stations might not be as useful as you think

One of the first things most new or prospective electric vehicle owners research is the locations of public EV charging stations. 


We live in Los Angeles, an enormous city where many of our friends think nothing of driving 45 miles (still in Los Angeles County, mind you) to grab a bite to eat. L.A. has as large an electric vehicle fueling infrastructure as currently exists - which is to say, a lot more than most of the United States. Still, there's not enough of a network of charging facilities that you're likely to be able to plug in your vehicle where you happen to be going.

A brief online search suggests that there are around 120,000 gas stations in the United States. That averages to one station per 2,700 citizens. So California, with 38 million residents, should have around 14,000 gas stations. According to the U.S. Department of Energy, as of January 2014, there are 5,176 non-residential electric vehicle charging stations in California. However, some of these are so-called "legacy chargers," which may not have ever seen any significant use beyond promotional propaganda a decade ago. In practice, public charging stations are far more sparse than those numbers suggest. Even though a few modern companies are maintaining networks of paid public charging stations (and there are still some legacy free charging stations left over from various utility and municipal trials and promotions from the past 15 years), there are not nearly enough stations to be called ubiquitous. Their usefulness is severely limited by their scarcity.

EV charger-locating site PlugShare's map of Metro Los Angeles illustrates that even in the middle of densely-populated L.A., you could easily end up walking 3 miles - one-way - to and from the nearest charging site.
So while California might lead the way in public EV charging stations, that's not as meaningful as it sounds.


In our first weeks of EV ownership, I explored the available public charging infrastructure. We established accounts with the handful of companies maintaining for-pay charging networks. One of those companies, ECOtality, declared bankruptcy during our second week of ownership and its new owner is still struggling to reestablish a business with its network of Blink charging stations.

During our first couple of days with the Focus Electric, I drove around and located the public charging stations near our home. Several things about public EV charging became apparent:
  • EV charging stations are where they are, not where you want them. There aren't nearly enough that your destination is likely to be within reasonable walking distance of one. (And when I say "reasonable walking distance," I don't just mean a few blocks. As illustrated in the map above, that's a 3-hour walking round-trip.)
  • There are a number of websites and smartphone apps which promise to show the user the locations of charging stations. These services seem to think that users want to be able to locate a nearby charging station, as one would when running out of gasoline or diesel fuel. But because your fuel range is more precious to begin with (it's like having a fuel tank with 1/4 of typical capacity), you'd be foolish to wait until you needed to add charge before you started looking for a recharge. And because refueling takes a serious commitment in time (the public "Level 2" charging stations typically add about 20 miles of range per hour), it requires a some commitment to spontaneously decide to charge. Imagine looking down at your fuel gauge, and thinking, "Oh, I need to find a place to refuel, because I'm down to 10 miles of range. I hope we can find a refueling site within 10 miles (which could take 30 minutes to reach in Los Angeles) and we'll need to find something to do for two and a half hours while we take on enough fuel to get home." When your vehicle is constrained by these parameters, you do NOT put yourself in these situations.
  • Of those charging stations that do exist, a significant number are non-operational. Some have been vandalized or accidentally damaged; many have problems communicating with their networks (as with ATM and credit-card transactions, a real-time electronic transaction takes place in order to start and stop the charging process). One station located at a retail location I frequent has been on-again/off-again every time I've visited. 
  • A given public charging location has equipment to charge from one to four vehicles (typically one or two). The sales rate of plug-in vehicles has increased far faster than installations of charging locations, so the likelihood of finding an unoccupied charging site decreases daily.
  • Even when a municipal sign bearing a local ordinance number prohibits non-electric vehicle parking in a charging space, it's not at all unlikely that an internal combustion engine-powered (ICE) vehicle will be parked in the spot, potentially preventing EVs from proceeding to their next destination. This is known in the EV community as ICEing. Many charging stations aren't marked as EV-only at all. Perhaps worst of all, EV owners occasionally use the charging spaces as parking spaces without charging - a serious breach of etiquette and manners, since many full-electric drivers are depending upon supplementing their charge to complete their journey.
  • We established an EV charging account with the Los Angeles Metro Transit Authority, which has EVSEs (Electric Vehicle Supply Equipment, the official term for the hardware that connects your EV to a source of electricity) at some of its mass-transit parking lots. When I reconnoitered the Metro subway station near Universal Studios in Hollywood around 8am one morning, I discovered four EVs charging at the four available charging points at that locale. In all likelihood, those four drivers had gone to work for an 8-hour day, and might well expect to do the same every weekday. So the prospects of anyone else using those charging sites would be dim, or they'd have to engage in a competition for early arrival.
  • Even though it might seem logical to locate charging stations close to home, it's probably not that important, if you have your own "fast" Level 2 EVSE installed. In the event that your home charging system fails, it might be helpful to know you can walk two and a half miles home while your car charges, but if you depend upon public charging, you might just as likely end up charging 30 miles from home and having a long lunch there while waiting. 
Here's the problem with the current public EV charging infrastructure: a citizen commuting daily, using almost the entire range of their EV on the way to work, then riding public mass-transit, charging their vehicle during their workday, and finally driving their EV home at night is arguably using their EV to greatest advantage. They're generating lower emissions; lowering fuel costs; and (potentially) reducing use of fossil fuels, etc. But if there's no guarantee of recharging your vehicle before returning home, then it's an impractical or impossible plan. I'm not sure how the owners of those four cars I saw charging at the Metro station make it work - I suspect that they're not actually driving far enough to require a charge at the end of their day. Which would be a breach of etiquette and logic - taking up a charging space for 9 hours when your car only needs 30 minutes of charge (even a fully discharged average EV will be finished charging in 4 hours). Chances are, some of those EV drivers are using the EV-only parking as leverage to have a parking space in these over-capacity public transit parking lots. This is just another problem with having such a thinly populated charging infrastructure.

In the EV community, there are conventions that: a) if you arrive at a charging station and the car connected to the station has completed its charge, you can unplug the cord from the charged car and use the EVSE if you can get the cord to reach your own charging port; and b) if you arrive at a charging station and the adjacent vehicle is still charging, leaving your charging port door open is a message that you'd like the other EV owner to plug the EVSE into your car when they leave. However, these practices are only possible when more than one parking space is within range of the charging station's cord. Only on a few occasions have I seen more than one parking space designated for sharing a vehicle charging station.

(In the case of free chargers - mostly legacy municipal experiments and pilot EV programs from a decade or more ago - the charge will start automatically. In the case of for-pay charging, most charging networks provide smartphone apps through which users can remotely start a charging session. Our Focus Electric also has its own Internet connection, through which we can see if it's plugged in. I'd also be happy to pay to charge someone else's vehicle on our charging account in those rare occasions where I found another unattended EV indicating that it needed a charge at a for-pay EVSE.) 

As an exercise, I've experimentally plotted what it would take to drive our Focus Electric from Los Angeles to Las Vegas - a trip we make regularly for trade shows. In a conventional car, in good traffic, the 270 mile trip can be completed in a little over four hours on a single tank of fuel. To be able to make the trip in our EV, we'd want to arrive at a charging station every 60-70 miles - and that infrastructure almost exists, but for a 150-mile gap in the California desert. At each stop, if there was an available charger (some EV charging apps promise to show whether EVSEs are occupied and functional, but in only a few attempts to use this information, I've experienced very poor accuracy), and we could get our charging network account to work (I've had problems with perhaps 1/3 of the dozen attempts I've made so far), we'd then have to wait for three to four hours before driving the next hour to the next charging site. Assuming we made every charging stop, found the station vacant and charged for 3.5 hours every 60 miles or so, we'd make the "4 hour" drive in about 19 hours. But if any of those chargers were out of service - of the few excursions we've made requiring more than a single charge, one of them required four attempted locations before finding a working charger - we'd never complete the journey. So while installing just one EVSE each in Victorville and Baker, California might make the theoretical chain of required stops, it would hardly count as a kind of fueling network. In my limited experience with public EV charging stations, there's no way that I'd count on that thin an infrastructure being 100% operational, and it could only accommodate a few vehicles traveling in the same direction. 

Despite stories that there are automobile club emergency EV charging trucks which can provide Level 2 roadside charging, it sounds like these "pilot programs" provided a couple of specialized vehicles for each of a few states. I'm not planning my family's security on whether one of a few trucks in California is available at the time.

Public charging stations continue to slowly increase in number, but not at a rate which will improve this situation in the near future. It's still "pioneer days" for EVs, and those of us taking this plunge are constantly reminded of that. Even though my wife's workplace is claiming that they'll eventually be installing six EVSEs, we already know of four EVs that might use them. By the time the equipment is installed, there might be more vehicles than that. When the number of employees at one workplace which are commuting in EVs exceeds the number of charging stations, it would take some cooperative effort and scheduling serendipity to work harmoniously.


My plan for owning and operating a plug-in electric vehicle never depended upon using public stations. I still think it makes perfect sense for us to charge our vehicle at our home and use it primarily within the 35+ mile radius of operation of a single full charge. Owning an EV in a region without any public charging infrastructure could be perfectly workable. As we've owned the Focus Electric and experimented with traveling further than a single charge, we've developed strategies and familiarity with those restrictions. 

Indeed, we haven't felt restricted by having an EV. In fact, we have yet to revert to driving one of our ICE vehicles in three months. Partly, that's because we're willing to academically explore the consequences and compromises of driving trips which require more than a single charge, and because we enjoy the adventure of it. We done about six so such journeys so far. But for the day-to-day vehicular needs of our life, driving all-electric has been easy and fun.

Friday, December 20, 2013

How Do I Charge My EV?


Charging electric vehicles is a very different proposition from tanking up with liquid hydrocarbons. When we fill up on gasoline or diesel fuel, we use the product of thousands of hours of sunlight which fell on hundreds of square feet of plants, hundreds of millions of years ago. We transfer the potential energy to propel the vehicle and its occupants hundreds of miles at more than a mile a minute in a matter of seconds in a refined form of this petroleum. Through the magical process of photosynthesis (upon which pretty much all life depends), plants capture a tiny proportion of our sun's total light energy and store it in molecules they make from water, carbon dioxide and a smattering of other compounds. The natural process of plants decomposing to petroleum over vast periods of time is a battery of sorts, which takes millions of years (plus no small amount of human time and energy to extract, transport and refine) to store, but releases useful amounts of its stored molecular energy on demand when we press on the throttle pedal. Modern electric batteries can be thought of as faster than fossil fuel storage, in that they can store energy in minutes, rather than the millions of years to yield "fossil fuels." But since the Industrial Revolution, we humans have become both accustomed to the convenience and fantastic energy density of these energy sources upon which much of our civilization depends. We take for granted that the "liquid sunshine" through which we've been burning is for all practical purposes a one-time resource (for our species, anyway) and an effectively finite one. Regardless of how much crude oil there is left on the planet, when it's gone, it'll take a couple of hundred million years to make another batch - and our own molecules will be part of that batch. 

Today, we have a highly developed civil infrastructure which produces and distributes electricity to wherever humans need it. The electricity might come from any number of sources, including combustion of those plant-based fossil fuels, the releasing of the atomic bonds formed at the beginning of time in nuclear reactors, and "renewable" sources such as photovoltaic, wind, hydroelectric and wave power. When we tap into this ubiquitous electrical network and store its potential in a modern electric car battery, the process is limited by the electrochemical nature of batteries. Most contemporary EVs use lithium-ion and lithium-polymer batteries, the same technologies which are currently favored to power our mobile communication and computing devices. These battery technologies offer the most economical balance of duration and power performance to volume and weight, while offering improved charging performance (lower times) over prior technologies. However, charging batteries currently takes far more time than traditional liquid refueling.

(Find out what sources are used to produce the electricity at your location with the Environmental Protection Agency's "How clean is the energy I use?" website.)


Current EV vehicles actually incorporate the charging hardware in the vehicle, as the charging process is meticulously and intimately interactive between the charging circuitry and the battery system. This is practiced to protect the extremely valuable battery (which may represent more than half of the value of the vehicle) from range and lifespan damage due to electrical load and thermal extremes. All electrochemical batteries are affected by extremes in temperature, and electric vehicles can expect to be operated in the full range of temperature extremes, although range will be adversely affected in very cold and very hot conditions. Many vehicles, including our Focus Electric, both heat and cool the battery pack to optimal temperatures during charging and discharging to maximize both their range and their lifespan. EV manufacturers also limit the charging and discharging thresholds of the batteries during user operation to considerably less than the batteries' ultimate limits. I've read that the Chevrolet Volt pack discharges to only 30 per cent of its capacity, and I think most packs stop charging well short of 100 per cent. So while it might be possible for current EVs to have markedly longer ranges than they do (on a brand-new battery), manufacturers deliberately software-limit the stress on batteries to extend and ensure their warrantied service life.

Since the "charger" is actually built into the EV, it's considered incorrect to refer to the hardware used to connect the vehicle to an electrical supply as a "charger." The official term for this device is the awkward acronym "EVSE," for "Electric Vehicle Supply Equipment." However, the community seems to accept "charging station" as an expression to refer to both home and public/commercial EVSEs. 


Easier. Plug in the cable from the EVSE, and the car starts charging. When it's done, it will automatically stop. Whenever you unplug the cable, the charging automatically stops.


In our limited experience with using paid charging stations, we've used only two networks: ChargePoint and Blink. These two companies predominate in the Los Angeles area. 

Both services provide customers with methods for paying via monthly account or on a per-use basis. They have provisions for "guest" use, so any EV owner can walk up to a public EVSE, call a phone number on the EVSE, give a credit card number to a live operator, and they will remotely authorize the EVSE to begin charging your vehicle.

By establishing accounts with these charging networks, you get discounted charging rates, and the convenience of initiating a charging session by simply waving an RFID card by the EVSE. Rates vary, and are set by station owners, but range from similar to our home electrical rates to three times as much. Even at the highest rates, it's less expensive than gasoline, and we have so infrequently used pay public charging that it's not an issue for us.

UPDATE 2/16/14: I previously neglected to mention that some for-pay charging stations charge the user by the hour - even after the car completes charging. I think this is fair - they're trying to incentivize users to move on and make the station available for another EV user, and protecting their ability to generate revenue.


There are many charging stations out there there are free to use. Most of these are municipally supported - almost every town has at least one free charging station at their city hall, apparently installed as part of an "initiative" for some purpose or another. Some of these are over a decade old, and not compatible with modern mass-produced EVs. Some have been converted to the modern J1772 connector.
Most car dealerships for brands (Nissan, Chevrolet, Ford, Fiat, etc.) that sell EVs have publicly-accessible EVSEs on their lots. We've never used one, but we've been with friends using one of two parking-lot stations in a Nissan dealership for their Leaf, and our Ford dealer's EVSE is in a terrible location partially blocking a driveway through their service area. Between those two examples, I think we can extrapolate that a dealership is not going to be the best choice for charging. I've heard of people having the chutzpah to ask to charge their differently-branded EV and being begrudgingly allowed to use them. I've also seen something about "priority to (brand name)" somewhere on the Web, so some dealerships actually have established a policy to charge off-brand EVs.


If they're not doing the charging, what do EVSEs do? They provide a safe interface between the electrical supply and the charging port on the vehicle. That is, the EVSE does not energize the plug electrically until it is certain that it is connected to an electric vehicle. Users of electric vehicles would be expected to charge them in all environments (i.e., standing in the pouring rain), and EVSEs are often located where they can be accessed by small children, so their functionality must NOT be that of a 240 volt extension cord.

In addition to incorporating ground fault interrupt circuitry to help prevent electric shock to users, EVSEs only energize the conductors on their connectors when they have established communication with an EV, and interrupt power when they detect that the connection has been broken. EVSEs can even anticipate when the connection is about to be broken with switches built into plug latch mechanisms. This prevents potentially dangerous and destructive arcing from unplugging a very high current load connection at as much as twice the 120 volts with which most citizens are familiar.

EVSEs also report the amount of current which they can provide to the vehicle. The vehicle should then only begin charging at a current at or below the EVSE's advertised rate.
Our Aerovironment Level 2 EVSE


Here are some basic electrical concepts that the EV owner may encounter regarding charging equipment:
  • The unit of measure of electrical difference of potential is a volt, abbreviated with the letter "V," as in "240V." The higher the voltage, the easier it is for electrons to flow past conductive impediments, or resistance.
    • Typical household outlets are 120 volts. Some appliances, such as all-electric clothes dryers, stovetop ranges, ovens and air conditioners are designed to run on 240 volts, and will use plugs and outlets that are incompatible with 120V outlets. 
  • The unit of measure of electrical current is the ampere, also called the amp for short, and abbreviated with the letter "A," as in "30A," meaning "30 amperes." The higher the amperage, the more work can be done by that electrical source. 
    • Typical household outlets and the wires to them are designed to safely convey about 15 amps of current. If that current is exceeded by more than the safe level (like plugging the waffle iron and toaster into the same circuit), then a fuse or circuit breaker designed to limit the current to 15A will interrupt the circuit before the wires inside the walls get dangerously hot from exceeding their designed maximum load of (in this case) 15 or more amps. 
    • Some appliances may require higher currents of 20 to 50 or more amps of current. These will utilize special plugs, preventing the higher-current device from being plugged into an outlet with inadequate supply. Some outlets and plugs are designed so that lower-current devices can also be utilized in outlets designed for higher-current devices of the same voltage.
    • Circuit breakers are a protection mechanism to prevent wiring and connectors inside the structure from dangerously overheating due to overload. The current rating (in amps) of the circuit breakers is chosen to suit the expected load from connected electrical devices, and the total load of all the circuit breakers is chosen not to exceed the available current from the wiring supplied by the utility company to the circuit breaker panel. From the circuit breakers, wires designed to conduct a specific maximum current are routed to one or more locations, where they are terminated by either an electrical outlet, or a permanently-wired device.
  • Supply refers to the electricity which flows from utility company infrastructure to the customer's site, through a circuit overload protection mechanism (fuses or circuit breakers), and to the outlets and devices which require electrical power.
    • A device's rated operating current should never exceed the current rating of its electrical supply. So a 12A appliance is fine in a 15A circuit. So are three 4A devices. A 10A toaster and an 11A microwave oven in one outlet, totaling 21 amps, is NOT appropriate and should cause a 15A circuit breaker to "trip" in order to protect the 15-amp rated wiring and connectors.
    • An electrical supply's current rating can and should exceed the loads placed on that circuit by the total current draw of all devices on that circuit. For example: It is OK to plug either a 1A, 10A, or 25A device into a circuit properly wired to supply 40 amps. It is also OK to plug all three, totaling 36 amps. Having a higher-rated supply circuit (that has been properly installed for its advertised amperage) than the expected device's rated load is typical and desirable: when you turn a single 60 watt porch light on, that represents a 0.5A load on what is likely a 15A circuit.


There are currently a handful of EV charging standards. These are characterized by: 1) the voltage and current requirements of the charging equipment; 2) the rate at which the given charging system adds charge to the vehicle's battery; and 3) the kinds of physical connectors used to connect the charging equipment to the vehicle. Most contemporary EVs have flexible charging systems that can electrical supply from a range of available supplies. These systems often automatically adapt to the available power supply.

The charging standards most commonly encountered by EV users today include:

  • Level 1 - Uses the SAE J1772 connector on both the vehicle and the charging equipment. Plugs into common household 120 volt AC outlets, and draws less than 16 amps. While this allows users to plug their cars into existing outlets found anywhere, charging is extremely slow. In the case of our Ford Focus Electric, Level 1 charging adds about 4 miles of range per hour, so a fully depleted battery pack might take as more than 20 hours to replenish at this rate. Most vehicles are sold with Level 1 chargers included. Despite the apparently slow charging, it's a good thing to have with you at all times. We visited friends recently who live far enough away that we required an additional 30 miles of charge to return home. But because we were parked at their house for more than 7.5 hours, an extension cord across their yard was adequate.
  • Level 2 - Uses the SAE J1772 connector. Using 240 volt AC sources up to 200 amps (typical home Level 2 EVSEs range from 20 to 60 amps), this is also sometimes referred to as a "fast charger." Charging rates/times vary. In the case of our Focus Electric, our home L2 EVSE and commercial L2 stations add about 20 miles per hour of charging. All of the for-pay charging stations we've encountered so far were Level 2.
  • DC Fast Charging - Uses the CHAdeMO connector. This infrastructure promises charging rates which close the gap to traditional liquid hydrocarbon fueling. The Chevrolet Spark EV, Mitsubishi i-MiEV and some models of Nissan Leaf are equipped with connectors for this very fast charging standard. (Tesla Motors is currently taking pre-orders for a $1,000 CHAdeMO adapter for their Supercharger-equipped Model S. Non-Supercharger Model Ses will require an additional $1,900 upgrade.) Most CHAdeMO-equipped EVs claim that the 480 volt DC charging system can charge a fully depleted battery pack to 80 per cent capacity in about 30 minutes, providing 60 to 70 miles of range (Tesla claims 150 miles in an hour). This is still far less than the 300-600 miles of range a gasoline or diesel vehicle can add during a 5-minute refueling stop, but makes far more practical the notion of a trip which requires multiple full charges, where each 1 hour/60 mile drive would be followed by a 30 minute charge (our Focus Electric requires a 3.5 hour charge to replenish each 1hr/60mi driving stint). Nissan warns that DC Fast Charging may significantly affect the long-term range performance of the battery pack, indicating a deleterious effect of this charging system upon batteries. For 36-month leasees, this isn't as much of a concern, but for purchasers of EVs, this might give pause. In any case, CHAdeMO charging stations are very rare, even in the Pacific Northwest where the standard has had the highest distribution. I considered this as attribute while we were shopping, and when I realized how unlikely it was that we'd actually encounter a CHAdeMO station, I excluded that consideration.
  • Tesla Motors - EV manufacturer Tesla Motors chose to establish their own proprietary connector standard, rather than adopt the widely-used SAE J1772 connector (they make adapters to most of the other connector standards available for purchase). But since 2012, Tesla has sold over 20,000 Model S in the United States, and projects 30,000 more sales in 2014, so they may not have needed to conform to the widespread standards. Because the Model S' optional 85kWh battery pack is far larger than every other EV (giving the Model S three to four times the range of other EVs), but it uses a similar amount of power during operation, the rate of miles of charge over time is similar (effectively depending upon driving style), but replenishing the full pack on slower systems can take a long time. Tesla maintains and is expanding its own network of Supercharger DC fast charge stations, which can add 120 miles of range to their 85 kWh Model S in 20 minutes, or 200 miles in 30 minutes. Tesla's intentions are to provide owners of their premium EV an infrastructure for traveling longer distances with similar ease to traditional internal-combustion refueling. As of 2013, Tesla announced their intention to make each of their Supercharger Stations into a "battery swapping" station, where owners could pay to borrow a charged battery pack, which could be changed in as little as 90 seconds. Tesla also claims that by Winter 2013, they will have established a "coast to coast travel" network - but I suspect that this reaching one point on each coast, so you might still end up 1,000 miles short of your destination. 


While charging an EV battery is many times slower than replenishing gasoline or diesel fuel, it provides practical fueling times for many situations. At the typical Level 2 charging rate of 20 miles per hour, a typical 8-hour workday or sleeping period is enough to recharge the batteries of those EVs whose ranges are 100 miles and under (8 hours x 20 miles of charge/hour = 160 miles). 

But it's important to consider available charging rates together with expected driving habits.

For some EV owners, there may be little incentive for spending potentially thousands of dollars to install a Level 2 EVSE. Though a Level 1 EVSE may charge slowly at 4 miles/hour, if your commute is 20 miles round-trip, you only need 5 hours of L1 charging to compensate for that. It could be perfectly economical and acceptable to charge only with the L1 EVSE.

At the other end of the spectrum, the fastest available charging might seem like a way to travel beyond the range of a single battery charge. However, even 20 mile/hour charging rates of typical L2 public charging stations create awkward delays in travel. Pausing at a charging station for 90 minutes to gather 30 miles of additional range to complete the day's travel may not coincide with a productive or safe location for spending 90 minutes. It's possible to do - we've been scheduling meal stops within walking distance of charging locations before we set out on trips which exceed a single battery charge. But it's an awkward process, and finding an occupied, faulty or even missing EVSE at your planned stop can sabotage the plan and the trip. Many owners won't be exploring the world past the range of their EV's battery, but we've been deliberately making that part of our ownership experience. While it feels like Pioneer Days for EV owners, you can make it work with some preplanning and a willingness to take longer trips at a, uh, leisurely pace.

The Tesla Model S and those few vehicles with DC Fast Charging can charge much more quickly, but the networks of public charging stations supporting them is even smaller than the thinly-distributed Level 2 stations that predominate. The difference with these fastest charging technologies is that an EV owner might be willing to wait 30 minutes to collect 60 miles of charge, while 3 hours (at L2) would be intolerable. But one might have to drive 30 miles out of the way to find stations that support these fastest standards. (Some members of the EV community - including Tesla Model S owners - make their home EVSEs available for use by sharing their location on sites like PlugShare.)


Maybe not. The answer for you is based upon several factors:
  • How much power you will use for your commute.
  • How fast your vehicle can charge (which is a combination of your vehicle's charging system and the current that a given location's EVSE provides).
  • How long your vehicle will be stationary at an charging source. 
  • Whether you want your vehicle to be charged as soon as possible, for unexpected transportation needs, or are prepared to potentially leave the vehicle charging until shortly before the next schedule departure time.
Here are simple formulas for visualizing what kind of charging schedule you can expect from a given set of these parameters:

[Miles depleted from battery] / [EVSE miles of charge per hour] = [hours to complete charge]

[hours to complete charge] + [arrival time @ EVSE] = [charge completion time]

So for example, if your drive to work is 22 miles one-way, then a round-trip would cover 44 miles. If the Level 1, 120 volt, 15 amp EVSE which came with your car charges at a rate of roughly 4 miles per hour, and you arrive home at 6:30pm (18:30), then:

44 miles / 4 miles chg per hr = 11.0 hrs (11 hrs, 0 mins)

11:00 + 18:30 = 5:30am charge complete

While the same trip with a 20 mile per hour Level 2 EVSE results in these figures:

44 miles / 20 miles chg per hr = 2.2 hrs (2 hrs, 12 mins)

2:12 + 18:30 = 8:42pm charge complete

In the real world of EV driving, the actual impact of driving even the exact same route can affect battery depletion and thus charging times by more than 30 per cent, so some actual driving tests would be necessary before committing to a charging solution.


Perhaps some day, every parking spot will automatically charge our cars inductively. But for now, for-pay commercial and free public EVSEs are somewhat sparsely distributed, even here in Southern California.

The most significant function of public charging stations is that they provide the only practical way to travel to destinations beyond the range of your EV's battery. But because public charging infrastructure is rather thinly distributed, one must be careful to plan alternate charging locations in case EVSEs at proposed stops are either occupied or non-functioning. We've made several trips beyond single-charge range in our first months of EV ownership, and we've had to make use of contingency plans a number of times when public charging stations turned out to be broken or already engaged with another EV.

For more, see my post, Why public EV charging stations might not be as useful as you think.


In the days before automobile manufacturers began producing EVs, hobbyists charged their home-built electrics from household circuits, including not only typical 15A, 120V services, but the higher-powered service sometimes installed in homes to supply power to appliances like electric clothes dryers and ovens. 

So can these circuits - which sometimes have the 240 volt, 30+ amp service required for Level 2 charging - be used for fast charging an EV? Can you take your L2 EVSE along with you and plug it into the dryer outlet in your grandma's house? Maybe. 

While modern EVs typically come with a Level 1 EVSE which can plug into any household outlet, it's almost never going to be convenient to charge for the 20+ hours it might take to recharge your fully-depleted battery pack after 75 miles of driving (in the case of the largest battery pack in a Tesla Model S, you could spend 90+ hours after driving 300+ miles).

It's possible to plug a Level 2 EVSE into some of these existing outlets, but it's a non-trivial pursuit. There are many standards of outlets and plugs, some having bearing subtle differences which both identify them and prevent inappropriate connections between devices and electrical service. If you happen to be the adventurous sort who has a reason to periodically travel well beyond the range of your battery and know that a home or business owner somewhere along the route won't mind you using their electricity (and possibly unplugging their oven, and parking on their grass so the cable will reach through the kitchen window), it's possible to take along your L2 EVSE (provided it has a plug for 240 volt power - some are designed to be wired permanently) and the appropriate adapters (no home or business is likely to have the outlet type which is physically compatible with your EVSE's plug), and charge fast enough that you don't have spend the night (or more) before returning home.

Me, I'm enough of a geek that I've been scheming about making trips requiring several full charges. This involves almost 80 per cent of the trip time spent charging, and 20 per cent in motion. So traveling 300 miles could take more than 20 hours - IF you make it to the charging stations, AND they are available and operational. If we do this, one of the options for fast charging is plugging our L2 EVSE into a 50 amp, 240 volt service in a campground. So that's one of the adapters I'll have in our kit.


Most owners of EVs with 80 miles of range probably rarely use charging infrastructure away from home. Indeed, the point is that most automobile owners drive far less than 80 miles per day. If you fit in this profile, you may not need to concern yourself with charging away from home.

If you're lucky enough to have a charging stations at your destination, you might be one of the very few who can travel nearly the full range of your EV's battery in both directions. But if you drive more than half of your range, the charging system at your destination must be available and functional, or you'll either be stranded or looking for a public charging station that's within whatever remaining range your EV's battery has.

If you live in a region with public charging stations, that provides some flexibility to the kinds of travel you might undertake. But the availability and operational status of public stations is unpredictable at this point in time, so you must be prepared with contingency charging locations which are within range, and the effect that this will have on your schedule.