The Daily Use of EV Chargers: Human Interface Technology

­Automotive manufacturers are increasingly offering a wider selection of EVs to their fleet, which requires a larger quantity of easy-to-use chargers for customers. There are several types of chargers that are currently in use including Level 1, Level 2 and DC fast chargers depending upon their size and capacity. However, despite the expansion of charging infrastructure, the charging process is not that intuitive to the users, so the use of HMI displays has made a difference when it comes to accessibility and adoption.

Charger Levels

Level 1 equipment charges vehicles by using 120V or 240V, while drawing currents up to 15A. Due to the voltage and lower current consumption level 1 chargers take the longest to charge an EV battery. Users can expect about 40 miles of charge from an 8-hour charge time. Although the charge-time is slow, the advantage they offer is that they are small and can easily plug into home electrical outlets and most EV manufacturers provide a portable level 1 charger with the car.

On the other hand, Level 2 chargers allow charging through 240V and operate at much higher current draw levels of 32A up to 80A. Level 2 chargers offer enough output power for an EV battery to reach 100% capacity from an overnight charge. They are relatively bigger in size and are used mostly in indoor/office parking spaces. DC Fast chargers or level 3 charge the battery directly by bypassing the onboard charger (OBC) in an EV. This allows for output voltages in the range of 400V to 800V which dramatically increases the charge rate and significantly reduces the charge time.

Regardless the capacity and size, all of these chargers can benefit from adding HMI to their design.

Chargers and HMI use cases

EV chargers are installed in a variety of places ranging from home garages (level 1/level 2) to commercial and public charging stations (level 2/level 3) that support higher charging currents. The charging experience, however, has been reported with declining satisfaction around the world. Next to charger availability, ease-of-use and reliability has become increasingly a public concern with reports of of many unsuccessful charging attempts worldwide. HMI touch displays have been seen as a promising solution to remedy some of the issues.

Main Benefits of HMI technology

·       Quick and easy access:The typical charge point provider expects users to use propriety apps on the phone to use their charger. As an alternative, radio frequency identification (RFID) membership cards are issued to the users to access the charger. It has been reported that if there is a touch display available, a user will prefer it than downloading an app. Average user needs to carry five RFID cards or install up to 10 apps on their phone. Touch display availability to gain access (especially in remote areas with bad phone connection), gives users more confidence and a quicker way to initiate the charging process.  

·       User interaction: Using an HMI display, charge point providers can do bi-directional communication with the user. They can show instructional videos on how to use the charger. They can guide the user on how to select the right cable/adapter, follow the right sequence of steps as well as how to start charging and stop charging. This is helpful for newcomers and elderly users. Additionally, unsuccessful charging attempts or malfunctioned charging process can be reported to the user via HMI with specific causes such as loose/incorrect cable, incorrect charging sequence, not enough credit on the account or fault inside the charger.

·       Payment method: HMIs allow users to initiate payment through familiar touch interface with credit card or even bar codes. After the charge is complete, the user is notified to press stop charging button and tap initiate payment. On credit card payments, users can provide PIN on the screen to complete the payment.  

·       Electricity price transparency: Using HMIs, charger network operators can display the usage price depending on various factors such as charging as a guest, member or elite member. Many countries demand the transparency of how much a user is getting charged on a particular network of a particular company.

·       Language selection: Users from different language backgrounds can use the same charger by selecting their preferred language using a touch display. It allows charge point operators to easily capture a wider user base.

·       Info portal: Charging status and various vehicle stats can be displayed on screen. Chargers can guide user to start/stop charging and inform about the battery and vehicle health.

·       Revenue stream: One can show ads on the screens to receive revenue through them.

Charger Displays

The displays for EV charging stations can vary widely, some have no display, while others have a small or large touchscreen display. The inconsistency of the displays can adversely impact the user experience.

Some of the newer chargers offer larger displays to provide clear information to customers charging their vehicles and to offer advertising space as many are accustomed to seeing at gas stations.

Since most EV chargers are located outdoors, the displays must be capable of operating in extreme weather conditions including high winds, dust storms, rain and snow. In addition to being exposed to harsh environments, EV chargers must also be sensitive enough to detect user input. For example, a touchscreen display must be able to detect user input in cold temperatures, in wet conditions, or possibly with the user wearing gloves.

Click image to enlarge

Figure 2: Public EV Chargers

Display Characteristics

Thin-Film-Transistor Technology or TFT LCDs are used with many EV charging stations. When choosing a display for a charging station, engineers should look for enclosures qualified for UL-F1 and displays designed for outdoor use per UL 746C. Products designed for UL 746C have been tested to withstand UV light exposure and are tested by using either a twin-enclosed carbon weatherometer for 720 hours, or a xenon-arc weatherometer for 1000 hours.

Products are subjected to water immersion testing in which the device under test is immersed in water for seven days at 70°C. Device readability is another important consideration as displays can be hard to read in sunny conditions. Therefore, the display should be bright enough to be easily readable under all lighting conditions.

Additional considerations with displays are the IP and IK ratings. The IP rating will designate how resistant a device is to water and dust ingress while the IK rating will convey how durable the product is to impact.

HMI (Human-Machine Interface) Requirements for EV Chargers

The HMI of an EV charger is not just a hardware panel; it’s the critical interaction layer between the user and the charging system. An intuitive, resilient HMI helps users complete charging sessions quickly, confidently and accurately. Additionally, public chargers must exhibit exceptional durability and impact resistance. These units often endure rough handling due to vandalism, accidental bumps, or deliberate tampering. Below are key design considerations.

Public EV chargers must be durable with features like reinforced gorilla glass for withstanding severe impacts and minimize maintenance needs. Reinforced front panel designs with secure mounting points prevent internal damage under stress, ensuring long-term reliability.

Touchscreen performance in outdoor chargers is also crucial, especially under harsh conditions. Displays must handle moisture from rain, high humidity, or frequent cleaning with water and various solutions. Anti-false-trigger algorithms and specialized sensors help maintain functionality even with wet surfaces. Components must resist extreme heat or freezing temperatures to prevent issues like cracking or warping. Properly sealed enclosures are essential to combat condensation in foggy or coastal areas.

Both thick cover glass and moisture on the screen place unique requirements on touch controller semiconductors. Extreme sun/UV exposure can degrade the screen performance and touch sensor. Therefore, UV filter coatings are often very helpful on the screen. Anti reflective coating for better readability and anti-fingerprint coating for screen cleanliness are also some of the treatments frequently done in the industry. Additionally, users wearing gloves need seamless touchscreen interaction. In capacitive touch technology, each of these is considered as a layer between human finger and touch sensor. A good IC controller must be able to detect a minute signal from the finger in the presence of these layers.

Maintenance and cleaning are inevitable for public chargers exposed to dirt, pollution, and graffiti. Surfaces must withstand frequent cleaning with various conductive chemicals without etching or discoloration. A touch controller must be able to distinguish conductive chemical liquids influence on the screen. Carefully designed panels or modular screens with air gap between glass and LCD can reduce downtime by allowing quick replacements when needed. A touch controller must be sensitive enough to allow insulating layer of airgap in the display stack.

Finally, software and firmware play a vital role. Over-the-air (OTA) updates enable remote changes to HMI features, security patches, or payment methods, eliminating the need for on-site intervention. Clear error messaging helps users navigate issues and supports remote troubleshooting, while advanced systems offering user personalization or loyalty programs must prioritize secure, intuitive design.

EMC and EMI considerations

EMC and EMI standards and performance must always be considered when working with electrical equipment. EV charging stations consist of high voltages and lots of switching power circuitry, emitting high noise and strong magnetic fields, which can disturb nearby circuits and create unintentional and unexpected behavior.

EV charging stations with EMI/EMC compliance means the chargers include immunity to electrostatic discharge (ESD), electrical fast transient (EFT)/burst immunity, and radio frequency/electromagnetic field immunity. 

Connectivity

Connectivity options are an important feature of EV charging stations. To process payment or find availability information for charging stations they must be able to communicate that information. Wireless connectivity is the preferred option for scalability reasons.

As more charging stations are available, running cables to tens or hundreds of stations becomes expensive. Wireless connectivity allows new sites to be able to rapidly be deployed and eliminates the hassle of running and maintaining cables.

IoT modules are becoming a viable option. Current IoT modules are readily available and can operate over large distances. These will allow the charging station to communicate the metering usage, user, and billing information to the cloud. They also have working security and encryption readily available.

Overall, important considerations must go into the components selected for EV charging infrastructure. The EV chargers must be simple and intuitive to use, provide users with informative information and feedback, and communicate information reliably and securely. Addition of HMI touch displays have proven to simplify the charger usage and adoption. Furthermore, these human machine interfaces must be durable, reliable in extreme weather conditions, and be designed to meet and comply with various EMC and EMI standards.

Microchip offers advanced HMI solutions for electric vehicle chargers, including maXTouch® controllers for seamless touch experience on rugged screens in harsh environments and a family of SAMA7D65 MPUs with advanced graphics and connectivity features that enables developers to easily design graphics into their system. These solutions integrate seamlessly with charging systems, providing robust and intuitive controls that are essential for modern EV infrastructure.

Microchip