Tom Konrad, Ph.D., CFA
Most plug-in vehicles (both pure electric and plug-in hybrids)
come with a "level 1" charging station which allows the vehicle to
be charged from a standard household outlet. If your vehicle
is a plug-in hybrid with limited electric range, or you don't
drive much, this is likely all you will need. Otherwise, you
will want a "level 2" charging station.
If you are a do-it-yourself-er and like to get into the
nitty-gritty, you should read the whole article. If you just
want some quick advice about the best charging station for you,
skip to the last section, "Putting It All Together."
What a Home Charging Station Does
Technically, a home charging station (also known as "Electric
Vehicle Supply Equipment" or an EVSE) does not charge your
car. You car has an on-board charger which converts
household alternating current to the direct current which is
stored in its batteries.
I personally just installed a charging station for my wife's new
Prius Prime plug-in hybrid, and concurrently applied for a grant
from New York state on behalf of the Town of Marbletown to
install a commercial charging station at my town's Community
Center. This article is based on that experience and the
responses a poll of 20 charging station owners I contacted through
Facebook groups and PlugShare, an app that allows users to find
and review charging stations, and connect with other plug-in
owners.
Before You Begin
Here is the information you'll need to make your decision.
Make/Model of the plug-in you want to charge.
Location of the closest electric panel to your parking spot.
Your vehicle's electric range (PHEVs) or the longest distance
you expect to drive between charges on a regular basis (EVs)
The make and model of the plug-in let you know the capacity of
the vehicle's on board charger, and the size of its battery
pack. You will need a charger powerful enough to fully
recharge the battery between trips, and you will need an outlet or
the charging station installed near the parking space that has the
capacity to service that rate of charging.
How Fast Of A Charger Do You Need?
If you will only need to charge your car up overnight, you have a
plug-in hybrid with limited electric range, or you will not drive
very far between charges, you probably don't need a very fast
charger. Quick charging may only be something you need on
long trips, when you can take advantage of the higher charging
speeds available at most public charging stations.
Most plug-in hybrids (with the notable exception of the Volt)
have limited electric range, meaning they can charge completely in
less than 5 hours using the included level 1 (120V) charger
plugged in to a standard household outlet. Most owners of
these vehicles will not need a level 2 charging station.
My wife's Prius Prime is a borderline example. It has 25
miles of electric range, and can be charged completely in 5-6
hours with a level 1 charger. I elected to install a level 2
charger for the convenience of being able to leave the factory
level one charger stowed in the car at all times, and because
there are times when we take the car out more than once in a
day. In this case, a quick charge between trips can make the
difference between using gasoline and staying all-electric.
Plus I like gadgets.
The table below shows approximately how much electric range a
typical EV that gets 3-4 miles per kWh can recover for charging
stations with different capacities. The number followed by
the A is the rated current in amps, the number followed by V is
the voltage. Level 1 charging stations use 120V, while level
2 charging stations use 240V.
Charging Current
1 hour
2 hours
4 hours
6 hours
10 hours
level 1 (12A 120V)
4-5 miles
9 miles
18 miles
27 miles
45 miles
level 2 (16A 240V)
10 miles
20 miles
40 miles
60 miles
100 miles
level 2 (30A 240V)
20 miles
40 miles
80 miles
120 miles
200 miles
level 2 (40A 240V)
30 miles
60 miles
120 miles
180 miles
300 miles
The rate at which a plug-in can charge is also limited by its
on-board charger. This charger's capacity is rated in
kilowatts (kW.) The vehicle's battery pack is rated in
kilowatt-hours (kWh.) A vehicle's electric range is its efficiency
(usually 3 to 4 miles/kWh times the size of its battery
pack.) So a 2016 Nissan Leaf's 30kWh battery pack and
approximate efficiency of 3.5 miles/kWh give it a range of about
105 miles. The Leaf has a 6.6 kWh on-board charger, giving
it a maximum rate of charge of about 10 miles of range per hour,
for a complete charge in 4-5 hours using a 30A 240V level 2
charging station.
Most plug-in hybrids have smaller on-board chargers to match
their smaller battery packs, as do some pure electric vehicles
with smaller battery packs/lower electric range. Much of the
information available on-line says that the Leaf has 3.3kW
on-board charger, but all 8 Leaf owners who responded to my survey
reported charging times that could only be achieved with a faster
on-board charger.
Below is the charger capacity for the most plug-ins on the
market today, along with the size of the charger needed to take
full advantage of this capacity. Additional charging
capacity is available as an option on some models.
Table 2: Charging
Capacity of Various Plug-in Vehicle Models
Charging station required
for fastest possible charge
Minimum Recommended Circuit
On board charger capacity
Vehicle Models
40A -level 2
50A 240V
10kW
Tesla Model S. Tesla Model X. Mercedes
B-Class Electric
32A -level 2
40A 240V
7.4kW
BMW i3
30A - level 2
40A 240V
6.6kW to 7.2kW
Nissan Leaf, Chevrolet Bolt, Ford Focus
Electric, VW e-Golf, Fiat 500e, Kia Soul EV, Hyundai Ioniq,
Chrysler Pacifica Plug-in Hybrid
16A - level 2
20A 240V
3kW to 3.7kW
Chevy Volt, Audi A3 eTron, BMW X5 xdrive40e,
Chevrolet Spark EV, Ford C-Max/Fusion Energi, Hyundai Sonata
Plug-in Hybrid, Mercedes C350, S550, GLE550e Plug-in
Hybrids, Mitsubishi i-MiEV, Porsche Cayenne/Panamera S
E-Hybrid, Prius Prime, Smart Electic, Volvo XC90 T8, Porsche
918 Spyder, Nissan Leaf (some early models).
10A- level 2
15A 240V
2 kW
Prius Plugin
Circuit Size
The final factor which may limit the size of the charging station
you need is the capacity of the electrical circuit you will be
using. If you try to charge a car at a rate equal to or
greater than the capacity of your wiring, you will flip the circuit
breaker. Unless the circuit is rated for continuous use, you
should limit the charging rate to 80% of the circuit's
capacity.
A second reason for charging at slower rates is efficiency.
The electricity lost (called line loss) is proportional to the
square of the current (the A or amps number in the charging rate)
and inversely proportional to the capacity of the
wiring. Line losses also increase with temperature, and the
lost energy becomes heat in the wiring, further reducing
efficiency. Line losses become more significant the longer the
wiring between your main electrical panel and your charging
station. With properly sized wiring, these losses will usually
be less than 2 percent of the electricity used. But 2% can add
up given the large electricity consumption of EVs. 35 miles of
driving a day in a typical EV uses 3650 kWh over a year. Two
percent of that is 73kWh, or two to three days worth of a typical
household's electricity usage.
Most charging stations can be set to limit charging speed to less
than their maximum capacity. Many plug-in vehicles also have
the capacity to limit their charging rates and charging times.
This feature can be used both to keep actual charging rates within
the capacity of the circuit, as well as to reduce charging rates
further in order to reduce line losses. Choosing specific
charging times (either with your vehicle or some charging stations)
can also save you money because of preferential rates from your
utility.
If you have to install a new 240V circuit to service your charging
station, I recommend installing at least a 50A, 240V circuit, or
even a 100A, 240V subpanel for your garage if you can.
Reasonably affordable EVs with large battery packs and powerful
on-board chargers such as Tesla Model 3 are likely to be widely
available in the next few years. You'll want the charging
capacity to accommodate your new, long range EV. If you have a
two car household, you may also want the ability to charge two cars
at the same time.
Higher capacity wiring will cost you more today, but the extra cost
will be a fraction of the cost of the electrical work.
Upgrading your wiring at a later date later would involve doing
everything over again. Even if you never need a more powerful
charging station, the reduced line losses will help defray the extra
cost over time.
Should You Oversize Your Charging Station?
You may find a charging station with the features you want but a
higher capacity than you need. If the rated power of your
charging station exceeds 80% of the capacity of your circuit, make
sure that you are buying one that has the ability to limit the
charging current.
One good reason to oversize your charging station is durability,
which my poll respondents felt was the single most important
feature. Since no brands have a long history, it's hard to judge
which brands are likely to be the most durable. However, it
is a good bet that a charging station rated to supply 40 amps of
current is likely to last a long time if it is only used to charge
cars at 15 amps.
Features
I included a question about features in my poll. Here are
the ones my respondents found most important:
Durability, a long charging cord, charging speed, cost, and being
outdoor rated were among the most valued features. One I
neglected to ask about was the charging station having a plug as
opposed to being hardwired. Charging stations with plugs
don't cost much more than those without, but even if they are too
large to be truly portable, it makes them easier to take with you
if you move.
Some features may have gotten lower ratings in my poll because
they are only useful to some users, even if they are essential to
the users who want them.
An outdoor rating will be essential if your parking space is
outdoors, but it will be irrelevant if you park in a
garage.
The ability to control charging times will be important if
your car does not have this feature itself- but only if your
electrical utility gives rewards or preferential rates for
avoiding charging during peak demand. That said, utility
rates for plug-ins are changing, and you may need this feature
tomorrow even if it is superfluous today.
Safety Certification
Intertek and Underwriter's Laboratories are Nationally Recognized
Testing Laboratories provide safety certification for EV charging
stations. If your charging station has one or both of these
safety certifications (the ETL or UL logos, respectively), you can
be assured that the product line has undergone rigorous (and
expensive) safety testing. One of these certifications will
be required for a direct-wired EV Charging station to pass an
electrical inspection. However, and EV charging station with
a plug will only require an electrical inspection for the wiring
to the outlet. Safety certification is also required by most
government rebate programs for electric vehicle chargers.
Buying a charging station without such a safety certification
does not mean it is unsafe. In fact, charging stations are
primarily safety devices to ensure that the vehicle's on-board
charger can access household current safely. I did an
internet search, and only found two reports of fires that could
possibly be linked to electric vehicle charging after trying
several variations on my search terms. In contrast, a search
for "hoverboard fire" quickly produces reports of "half a million"
fires and many videos.
Of the two possible EV charging station fire reports I found, one
could
not be directly linked to the charging station in question
(a UL listed Siemens model.) The other fire started near a
home charging station of unknown brand which had been
installed by the owner. Since we don't know the brand
of the charging station, we can't know if it had a safety
certification, but improper installation could easily have caused
the fire.
Brands
While few people have more than a couple years experience using
charging stations, my poll respondents had this to say about the
following brands:
Top Recommended Brands:
ClipperCreek: Recommended by more respondents than any other
brand.
JuiceBox: Probably the best options in terms of power
and features for the price.
ChargePoint Home
Bosch
Tesla
Siemens/Versicharge
GE Durastation
Mixed Reviews:
Aerovironment (some re-branded by Nissan): Expensive, but a
good warranty. One (of four) had it break right before the
warranty expired. He was unimpressed with their customer
service, but said he thought service had gotten better in recent
years.
Audi: Expensive to install, but easy to use.
My Top Picks
Duosida 16A: $289 on
Amazon
A basic portable charging station with a long cord and a
great price. Not designed for wall mounting. Not
safety certified.
ClipperCreek 16A, 24A, 32A, and 40A: $402, $538, $601, and $895 on Amazon.
A well-rated charging station with a long cord and a
reputable brand.
GE DuraStation 30A: $397
on HomeDepot.com
A powerful, no-frills charging station from a recognized brand.
Maximum current can be adjusted to 30A, 24A, 16A, or 12A using a
jumper.
JuiceBox 40A: $499 at
eMotorWerks
The least expensive 40A charging station available.
Maximum current can be set by
adjusting trim-pots inside the enclosure. Not safety
certified, the company says they expect UL certification in
March 2017.
JuiceBox Pro 40A and Pro 75A: $599 and
$899 at eMotorWerks
Full-featured, high-power charging stations at a low
price. Wi-fi enabled. Can be adjusted with a smartphone
app to charge at any lower current required. Not safety
certified, the company says they expect UL certification in
March 2017.
(prices include shipping)
I had personal experience with eMotorWerks (JuiceBox) support
through eBay, where I bought a refurbished JuiceBox Pro 40.
I found them very slow to respond, and had not reached a
resolution after a week. But given that mine was a cut-price
refurbished unit (and their prices are amazing to begin with) I
still give the brand my highest recommendation.
I contacted eMotorWerks and asked them to respond to the previous
paragraph. Here is their response:
"We appreciate the endorsement of our products, and are working
diligently to fully staff and train our support team. Our sales
have nearly doubled at the end of 2016 due to accelerated growth
in EV sales (record 25,000 EVs sold in December, nearly twice
the previous year) and successful programs we recently launched
with our utility and Community Choice Aggregation partners.
We're working to further grow our support team and deliver
top-notch service to all our customers."
After the first version of this article was published,
eMotorWerks solved my problem to my complete satisfaction.
If you want top-notch service, ClipperCreek
and ChargePoint
Home have good reputations according to my poll
respondents. I do not know if growth is straining their
customer service departments. You will pay $100-$400 extra
for similar models from these vendors compared to eMotorWerks, but
you may consider the extra expense worth it, especially if
JuiceBox has not yet received its UL safety certification when you
care buying your charging station and this concerns you.
Putting It All Together
Although this is a rather technical article, choosing a home
charging station does not have to be complex. Here are the
essential steps:
If you do not drive much or your vehicle's electric range is
less than 20 miles, a level 2 charging station is probably not
worth the cost. Try using just the factory level one
charger for a while. Otherwise:
Use Table 2 to determine the charging station capacity your
vehicle can use.
If you are doing your own electrical work, go back and read
the whole article. Otherwise:
Purchase a charging station from my top picks (above) with a
rated capacity at least as high as given in Table 2. If you are
relying on a government rebate program to pay for part of the
cost, make sure that the model you choose qualifies for the
program.
Have an electrician or three give you quotes to install a "240
volt(V) 50 amp(A)" circuit to your parking space and install
your charging station. You can also ask them for a quote
to install the minimum recommended circuit for your vehicle from
Table 2, but the savings are not likely to be significant.
You will probably be better off with a 240V 50A circuit in the
long run.
Have your electrician install the charging station, and adjust
the charging station's maximum current to not overload the
circuit. The adjustment should not be needed unless you opted
for the cheaper electrical circuit.
Charge your car quickly at home.
The prices and specific models mentioned in this article are
based on what was available at the start of 2017, and will
change. The advice about charging station and circuit sizing
should be more durable.
Giving Back
After you install your charger, I encourage you to let the
occasional plug-in driver charge at your home. You can do
this with PlugShare.com
and the PlugShare app (Android,
iTunes)
which is a great resource for finding both public charging
stations and plug-in owners like yourself who want to may electric
driving as worry-free as possible by extending the network of
public stations.
My own charger is available on the PlugShare, and I'm looking
forward to meeting the first plug-in driver I can help with a
charge.