DC charging is the most effective way of powering an electric vehicle battery. Scientists and engineers have made incredible progress. A new generation of DS fast chargers allow even faster recharges of up to 80% of total capacity in less than an hour.  

This guide provides a complete introduction to DC charging hardware, including information on the main charging methods, charging interfaces and communication protocols. 

 AC v DC – why DC wins for fleets 

Passenger and light commercial vehicles use an AC charger plugged into the mains. AC power is transferred to an onboard charger that transforms this to the DC charge required by the battery. 

 The solution is cost-effective, small, and lightweight, but it is slow – taking hours to fully recharge a battery. 

In contrast, DC chargers deliver power directly to the battery – ensuring a much faster charge. As a result, DC charging is an optimal solution for fleet operators who want to maximise their vehicles' operational capacity.  

DC charging technology is continuing to evolve. First-generation DC chargers were limited to 50kW, but newer vehicles can accept much larger charge rates  some, cases up to 270kW. 

Couple this with larger batteries fitted to commercial vehicles, and the benefits are clear.  

DC charging means vehicles can spend more time on the road and less time being charged. As a result, they're powering a cleaner tomorrow for us all. 

What are the main DC charging methods? 

There are several DC charging methods currently used to charge fleet vehicles, including conductive charging and wireless charging: 

• Conductive charging  Conductive charging works through a manual connection from the vehicle to the charging station. The current flows through a cable (or from a pantograph to a wire), enabling rapid recharging rates with high transfer efficiency. It's the cheapest hardware solution, but it needs manual involvement to work. The transfer of power is one-way, from the charger to the vehicle. Conductive charging can deliver up to 400kW with a CCS Type-2 connector. However, MW chargers are just around the corner and will make charging times even faster. 

• Wireless DC charging – Wireless charging uses time-varying magnetic fields to transfer power. There are two pads, one fitted to the bottom of a vehicle (which contains an induction charging station) and the other to the ground. Power is delivered to the ground transmitter to create a magnetic field. The coil on the vehicle receives this and converts it to energy to power the battery. The principle has been around for over 100 years and can deliver rapid recharging with no wires or physical interaction necessary. 

When reading about DC charging solutions, you may also read about bi-directional charging. It can also be called vehicle-to-grid technology .Bi-directional charging enables energy to flow two ways= from the grid to the battery and the battery back to the grid.  

Bi-directional charging can play a crucial role in creating a smart grid, with battery-powered vehicles acting as energy storage devices. The process is managed by cloud software and could help us tackle one of the biggest challenges we face, how to store renewable energy. 

While wireless and bi-directional charging offers enormous future potential, conductive charging is the most cost-effective short- and medium-term solution. 

Inside DC charging grid hardware 

DC charging stations combine software and hardware to deliver a speedy recharge safely. Here are the main parts of every DC charging station: 

• Grid connection – Charging stations require a solid and stable grid connection to provide the power needed for charging.
• Cabinets –The hardwearing metal cabinets must be waterproof (IP54 level protection) and suitable for outdoor installation. Heliox's cabinets, for example, are built to last 15 years or more. Inside you'll find the hardware required to deliver a charge and security features, including high-speed fuses to provide over-current protection. 
• Dispensers – Each charging station has a dispenser that plugs into the vehicle. There are several different DC charging interfaces, which we explore below. 
• Pantograph – Some larger fleet vehicles, such as buses, use a particular type of connector known as a pantograph for opportunity charging. The vehicle parks underneath a charging station, and the scissor-like arms drop down and connect to rails on the vehicle's roof to recharge the battery. The system can deliver high-power charging at up to 600kW.charging a large vehicle such as a bus in seconds. 
   

What are the main charging interfaces? 

There are several types of DC charging interfaces for fleet vehicles. Chargers must meet several international safety standards, including ISO 15118 and DIN SPEC 70121.  

Regional differences exist in the DC connectors used in Japan, America, China, and Europe (and the rest of the world). Here's what they are and how they work: 

• CCS1 & 2 Pinout – CCS stands for combined charging system. Inside both CCS1 and CCS2 interfaces are pins delivering a DC charge directly to the vehicle. CCS1 & 2 Pinout is primarily used by US and European car manufacturers, but there is a push for it to become the global standard. 
• DC GB/T – This standard is used exclusively in China. The protocol is defined by the GB/T 27930 standard. 
• CHAdeMO – This is the DC charging standard used in Japan. 
• Tesla – As you'd expect, Tesla has created its own DC charger, but things may change. For the latest European Tesla Model 3 roll-out, Tesla has chosen to use the CCS2 standard. 

DC charging communication protocols 

DC chargers must work intelligently to charge and protect the battery. There are two communication levels: high level and low level. International standards such as IEC 61851, ISO 15118, DIN 70121 and VDV 261 provide the basis for the contact between the charging station and the vehicle before and during the charging process. 

Low-level communication protocols manage the max current and the charging stage. High-level protocols manage more complex tasks, such as assessing compatibility, charging sequence, establishing physical limits, and managing tariffs and payments.  

There are three high-level communication protocols: 

1. Power Line Communication (PLC) –This is the high-level communication framework used in CCS1 and CCS2. It uses a standard TCP/IP stack (Transmission Control Protocol / Internet Protocol) for communicating. 
2. Signal Level Attenuation Characterization (SLAC) – The vehicle and charging station agree on a unique identifier based on a request-response process. SLAC is used in an environment where multiple electric vehicles and charging stations are interconnected, such as a vehicle depot. 
3. Controller Area Network (CAN) – CAN is defined by the ISO 11898 standard and is a message-oriented platform used to power quick information exchange between control units in an industrial setting. 
   

Low-level communication protocols

Smart chargers and vehicles are engaged in a constant exchange of information using pulse wave modulation (PWM). Contact is defined by several internationally agreed standards. 

The IEC 61851-1 standard, created by the International Electrotechnical Commission, is used in all electric vehicle conductive charging systems. 

 Signal voltages alternate between two levels to indicate the charging state: 

• +12 V State A No EV connected to the EVSE 
• +9 V State B EV connected to the EVSE but not ready for charging 
• +6 V State C Connected and ready for charging, ventilation is not required 
• +3 V State D Connected, ready for charging, and ventilation is required 
• +0 V State E Electrical short to earth on the controller of the EVSE, no power supply 
• -12 V State F EVSE is unavailable 

The information provided defines the maximum charge delivered to the EV: 

• Duty cycle < 3 % No charging allowed 
• 3 % ≤ duty cycle ≤ 7 % Force high-level communication protocol according to ISO 15118 or DIN 70121 
• 7 % < duty cycle< 8 % No charging allowed 
• 8 % ≤ duty cycle< 10 % Max. current consumption for AC charging is 6 A 
• 10 % ≤ duty cycle ≤ 85 % Available current = duty cycle * 0.6 A 
• 85 % < duty cycle ≤ 96 % Available current = (duty cycle - 64) * 2.5 A 
• 96 % < duty cycle ≤ 97 % Max. current consumption for AC charging is 80 A 
• Duty cycle > 97 % No charging allowed 

Charging technology continues to change, with many options and alternatives open to manufacturers. At Heliox, we can provide expert insight and advice to help you identify the charging hardware you need to power your fleet and accelerate your business. Get in touch with one of our experts.