Looking to install electric car charging infrastructure at your next project? Several considerations need to be made to land on the right path for each new site. Below are some insights from VCA Green’s energy team.

Charging Basics

Electric cars have an onboard charger built into them that allows the car to take standard AC energy and convert it to the DC energy that the battery needs. Electric cars and plug-in hybrids with smaller batteries tend to have smaller, or lower power onboard chargers, usually in the range of 3.3 to 7.7kw. Battery Electric Vehicles or BEVs with larger batteries may have up to 19kW, but below 8 kW is most common across the different brands.

The speed at which an electric car can charge is limited either by the acceptance rate of the onboard charger or the power coming from the wall outlet—whichever is lower. Your car will never charge faster than the size of your onboard charger. The diagram below shows how energy flows to the battery during charging.

electric car charging current diagram

Electric Vehicle Supply Equipment (EVSE) is just a fancy term for charging stations. For Level I and Level II charging, the onboard charger determines the fastest rate that a car can charge. In the diagram, it’s clear that all energy must go through the onboard charger before it can be stored in the battery.


When most people refer to “chargers,” they are referring to the electrical cord that connects their car to the wall. This is technically “EVSE” or Electric Vehicle Supply Equipment and not a charger. However, “chargers” is easier to say, so everyone just sticks with that terminology out of convenience.

Three levels of charging are available for electric cars today: Level I, Level II, and DC fast charging.

• Level I charging refers to a standard 120-volt outlet. All electric vehicles come equipped with a cord that you can plug into a common outlet. It’s exactly like charging a smartphone or laptop. This sends 120V power to your onboard charger enabling it to slowly charge your car.

• Level II charging refers to the more powerful systems typically connected to a 240-volt split phase or 208-volt single phase electrical supply and an EVSE unit. You can purchase a Level II EVSE unit and install it in your home or business usually with the help of a licensed electrician. It sends this higher voltage electricity to your onboard charger enabling it to output more power up to its maximum rating.

• DC fast charging (not called “Level III”) is the fastest type of charging available. These require a substantial amount of power that goes beyond the services that feed the typical home, so you cannot install DC fast charging at home. These are large devices used for public charging on the go. The DC fast charger is an actual “charger” because it bypasses the car’s onboard charger completely and charges the battery directly and intelligently with DC energy. This enables the battery to charge as quickly as the battery chemistry and heat dissipation will allow because it is not hamstrung by the limits of your tiny onboard charger. A few cars are touting up to 350kW DC fast charging speed.

Most EV drivers charge at home as a matter of convenience. However, public charging makes it easier for drivers to charge on-the-go, pressed for time, or when they need a little extra juice they can’t get at home.

How Long Will It Take to Charge?

Charging is totally different from refilling gasoline. Most gas-powered cars are refueled when they are nearly empty. On the other hand, EVs are charged opportunistically; when there’s a plug available, drivers will use it.

EV charging takes advantage of all the time cars spend parked, which is estimated to be between 90% and 95% of the time. Even though charging a car takes longer than pumping gas, you don’t stand around attending to your car while it is charging. You park your car and plug it in like a cell phone and then go about your day as usual. When you come back, your car has been charged, you unplug it, and drive off with a “full tank” or battery in this case. In fact, since it takes less time to plug in your car and walk away than it takes to stand there watching the fuel pump meter, EVs save you time that you would otherwise spend driving to and from the gas station to pump gas. Here’s a chart showing average charging rates for each of the three levels of charging:

Different models have different sized batteries, different on-board chargers, and therefore have different rates at which they can charge, but the above table gives the general idea.

What To Look for In a Charging Station

Understanding how charging works is helpful for understanding your EV, or the EVs of your clientele, and for picking out a charging station system that will suit your needs.
The maximum power output of a typical 32-amp EVSE at 240-volts is 7.7 kW, which translates to a rate of about 25 miles of range per hour of charging. With the average commute of 40 miles daily, it only takes 2 hours to cover one’s commute. Even if someone had a 100-mile commute to work, they might see their car fully charged by lunch.

It is generally accepted that battery degradation happens faster when you charge faster due to the heat in the battery. Therefore, charging up gently at a low kW should improve battery life over high kW charging. If you have multiple tenants or clients, should you install fewer and faster chargers and have them move their cars to allow someone else to use the charger when their car is finished, or would several more affordable and lower power chargers make more sense to allow people to park and forget? How are you going to recover the cost of your charging system? Is it an amenity or are your customers going to pay for the power their cars consume?

An at-home Level II charging station’s power output should roughly match the EV’s acceptance rate for convenience of faster charging, but for life cycle costs, low power and longer charging times is more affordable. More powerful stations are more expensive to purchase AND install as the breakers and wires must be larger to handle the power. Do not underestimate the cost of the electrical gear required to supply the power to your EVSEs – it’s very easy to kill your budget here. Here are a few factors to consider when comparison shopping for your EVSE.

Current: 32 amp or less chargers are most common, provide about 7.7kW/25MPH speed of charging and many come with extra features including load management and billing software. Spending more money for high-current EVSE stations won’t make all cars charge faster, only some of them that have high power onboard charger.
Cord length: The cord should easily reach your plug port from the EVSE station. Since not all cars have the charge port in the same location a 25-foot cord is generally recommended for most installations (make sure it’s enough). You cannot use an extension cord to give yourself extra length!
Physical size: Some charging stations are bulkier than others. Consider the space you must install the station and the dimensions of the unit.
WiFi or Internet connections – monitor your charging, schedule charging sessions, get notified when charging is complete, etc.
OCPP software – This is an open protocol so you can select the management software amongst bidders (opposite from proprietary software).
Intelligent load management – allows you to connect multiple EVSE to fewer circuits. i.e., connect 400A or charging stations to a single 250A service. The charging units automatically drop their power         output to not overload the electrical circuits.
Billing software – Many providers have software that can automatically take payment from credit cards or can allocate the energy used by tenants from activating charging session from key fobs, card access, QR codes, or even physical keys.

Check out InsideEVs for great information on available EVSE chargers.

How fast do we NEED to charge?

Overnight charging at home can typically be accomplished with a Level I station. Even the 32A Level II stations can deliver full driving range in the 6-to-8-hour window in which most people are working. Most homes only have a 125A service so asking your home to provide 80A only to your car seems a bit unreasonable. For that reason, it’s quite possible that 11 to 12 kW will be the max onboard charger size in popular privately owned vehicles for years to come. Commercial vehicles, however, are tough to guess. This means that a 50A EVSE is likely to be a common large size with the 32A being the most common average size.

If your development needs dozens of chargers, maybe having a couple faster EVSEs for shared or common spaces and slower EVSEs for assigned parking stalls makes sense.

No matter how you look at the trends and the regulations, EVs are coming. That means charging infrastructure is going to be required. Growing your charging infrastructure without installing massive electrical systems will require comprehensive consideration of the variables and careful planning to keep costs in control while providing exceptional service and convenience.