The Fundamentals of EV Charging

May 14, 2024

Charging an electric vehicle (EV) is a complex interaction involving sophisticated site infrastructure and advanced vehicle systems. This process requires a seamless communication exchange between the EV and the charger to optimize charging parameters such as speed and energy transfer. The charger adjusts its output in real-time based on the vehicle's capacity and battery state, supported by industry-standard connectors like the J3400 (NACS) that ensure compatibility and efficiency. As we dive further, we will explore the different levels of chargers, their functionalities, and the various connector types being used today.

How Does EV Charging Work?



Levels of EV Chargers

What’s the difference between all of the charger types? How long does it take for them to charge an EV’s battery? Well, it all depends. To fully understand the difference between charger types and their capabilities, let’s get some basic knowledge out of the way.

The Basics: 

kW: A kilowatt (kW) is a unit of power that measures the rate of energy consumption or production. It is equal to 1,000 watts, which is nearly equivalent to 1.34 horsepower.

kWh: A kilowatt-hour (kWh) is a measure of the amount of energy consumed or produced over a period of time. In the context of EVs, the kWh is used to describe the amount of energy stored in the EV’s battery and the amount of energy consumed during charging. For example, if an EV charger has a rating of 50 kW, it can deliver up to 50 kWh of energy in one hour.

Why kW?

Chargers are typically delineated by kilowatts (kW) because it is a measure of the power output of the charger. The higher the kW rating of the charger, the faster it can charge an EV battery. The power output of the charger is important because it determines how quickly the EV battery can be charged. A higher kW rating on the charger means that the charger can supply a faster charge rate if the battery can accept it, which is especially important for long-distance travel.

The Chargers

EV chargers are classified into three levels based on their power output and charging speed:



Application: Residential Garage
Kilowatts (Typical): 3.5 kW
Incoming Power: 120 Volts AC (VAC)
Time To Charge
If an EV has a battery capacity of 60 kWh and is charged using a Level 1 charger with a power output of 3.5 kW, it would take approximately 17 hours to fully charge the battery.



Application: Shopping / Restaurant
Kilowatts (Typical): 12 kW
Incoming Power: 240 Volts AC (VAC)
Time To Charge
If an EV has a battery capacity of 60 kWh and is charged using a Level 2 charger with a power output of 12 kW, it would take approximately 5 hours to fully charge the battery.



Application: Commercial / Fleet
Kilowatts (Typical): 50 kW - 350 kW
Incoming Power: 480 Volts DC (VDC)
Time To Charge
There is a wide range of Level 3 chargers available including 50 kW, 120 kW, 150 kW, and 350 kW. As an example, if an EV has a battery capacity of 60 kWh and is charged using a Level 3 charger with a power output of 350 kW, it would take approximately 10 minutes to charge the battery from 0% to 80%.

Connector Types

It’s important to note that EV charging infrastructure is still evolving, and new connector types may emerge in the future. However, understanding the differences between the most common connector types is a good starting point when learning about EV charging infrastructure.


J3400 (NACS)

The North American Charging Standard (NACS) is an EV charging connector system developed by Tesla, Inc. It has been used on all North American market Tesla vehicles since 2012 and was opened for use to other manufacturers in November 2022. The J3400 connector is based on the NACS connector and is one of several connector types that enable fast charging of EVs. NACS can also be used for AC Level 2 charging. The J3400 connector has 5 pins and can handle a maximum voltage of 277 V AC and 500 or 1,000 V DC, with a maximum current of over 650 A.



This connector was developed by the CHAdeMO Association and is used primarily by Japanese automakers. CHAdeMO-equipped EVs require an additional J1772 connector cord to achieve Level 1 or 2 charging. CHAdeMO connectors are capable of charging at power levels up to 62.5 kW.



The Combined Charging System (CCS1) connector contains a J1772 connector plus two DC terminals. It allows drivers to use the same charge port for Level 1, Level 2, or DC fast charging equipment. The only difference is that the DCFC connector has two additional bottom pins. Most EV models entering the market today charge using the CCS1 connector, and it is capable of charging at power levels up to 350 kW.

What's the Standard?

All major car makers have adopted the J3400 (NACS) connector and is now an industry standard as deemed by the Society of Automotive Engineers (SAE). SAE is a professional organization that develops and publishes technical standards for the automotive, aerospace, and commercial vehicle industries. In 2025, cars will start rolling out of the factory with the J3400 (NACS) connector, until then there will be an adapter available.  Note that the J3400 (NACS) connector uses the same two terminals in the connector for both AC and DC, whereas in the CCS1, the AC goes through the top three terminals and DC goes through the bottom two.

What's Next?

In the next part, we will recap how DC Fast Charging works alongside the different components that go into a DC Fast Charging Site.




The NexPhase™ Smart EV Switchgear is an all-in-one panel containing the entire infrastructure required between the utility service and up to four Level 3 DC fast chargers totaling 800 kW. Unlike any switchgear of its kind, the NexPhase™ features cutting-edge grid intelligence for complete EV charging station remote uptime monitoring and control.


Provides ongoing EV charger state-of-charge and utility power monitoring, enabling CPOs to accurately pinpoint charger outages, even when charger communications are down. The remote power cycle capability helps bring chargers back online faster.


The embedded monitoring system provides remote access to real-time switchgear, utility power, and charger health data with automated alarms for condition-based maintenance planning.


Eliminates the lengthy design process of traditional post-and-frame systems, which require additional costs to design, permit, and source a mixed-manufacturer panel system. NexPhase™ eliminates sourcing and supply chain delays as a single-manufacturer, turnkey solution.


Requires minimal on-site connections for the incoming power and outgoing charger connections, drastically reducing on-site installation time and electrician costs.



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We are a leader in the manufacturing and distribution of systems to support the management and monitoring of critical assets. As an expert in both vehicle refueling and utility asset monitoring, we are committed to supporting the emerging EV charging market. Our turnkey solutions enable rapid deployment with intelligent monitoring to maximize charger operational uptime.