CODICO, the Component Design-In Company, has already been dealing with this topic for quite some time and has developed among other things PLC modules for communication between charging station and vehicle. Therefore, it should be obvious to dedicate yourself to the topic display as well. This is a detail that should not be neglected, since it is all about user-friendliness.

A charging station can be designed simply and inexpensively. LED lighting modules and an app on your smartphone should be enough. Nevertheless, only a display increases the operating comfort.

Displays are primarily found at DC charging stations. These are larger and charge faster because the accumulator is charged directly in the vehicle. The display is a must-have and is used to show the charging status, charging time or remaining time and battery status. However, there is also an increased demand for displays for AC chargers. These charging stations are smaller (usually in the form of a wallbox) and charge more slowly because they use the on-board charger in the vehicles to convert from AC to DC. In accordance with EU Regulation 2014/94/EU, all publicly accessible charging stations must have a display, as is the case analogously for the traditional gas pump.

What criteria is important for displays in charging stations?

The many possibilities and options offered by the display market sometimes make it difficult to decide on the right display, or perhaps better a display that meets the requirements. Below we try to give some food for thought to help with a decision-making process. Let's go through the points in detail. 

How big should the display be?
As almost always, there is no simple answer.
The size essentially depends on what purpose must be fulfilled. Let`s stick with DC chargers. The charging columns are larger; thus, it also makes sense to use displays in a suitable format. The most common diagonals are 7 inches and 10.1 inches, although in some applications other dimensions can also be found. If you want to focus more on advertising – after all, a loading process takes a bit longer - then you'll go in the direction of 15 or 15.6 inches, perhaps even 21.5 inches. Larger displays can show more information and give the charging station an appealing look. 

For AC chargers, displays are now also becoming standard. On the one hand, the stations must comply with calibration regulations, i.e., they must display the amount of energy delivered (see above); on the other hand, a display can have a positive influence on the appearance. The displays are naturally smaller in wallboxes. OLED displays or small TFTs are usually used.

What about the optical characteristics?

Large charging stations are often located outdoors. Good readability, even in sunlight, is therefore essential.
This is achieved by very bright displays, typical values are 1000cd/m², but up to 2000cd/m² are also quite recommendable. The installation position can also contribute to this. If the display is mounted at an angle in the charging pole, it is shaded similar to the displays in a dashboard and therefore more visible.

Additionally, using optical bonding also pays off. Unwanted reflections that occur due to the air gap with air bonding are prevented. The image is significantly better in bright ambient conditions. 

A surface coating on a front glass can also help improve readability. An anti-glare (AG) coating scatters the incident light and ensures that the image content remains legible, although the contrast decreases a little. With an anti-reflective (AR) coating the incident light is reflected only at one angle, creating a bright spot, while the rest remains clear and visible. It is up to the designer´s discretion which technique is used. 

Small charging stations which are found in rows in parking lots are, by location alone, less endangered. It is therefore sufficient to use a brightness of approximately 500cd/m², and it may also be possible to dispense with other readability-enhancing measures.

Finally, the display technology used also plays a not insignificant role. The best result can be achieved with IPS (In-Plane Switching) displays. Excellent viewing angles horizontally as well as vertically, high contrast and fast response times are the main features. The MVA (Multi-Vertical Alignment) displays have similarly good properties. 

The most cost-effective variant, however, is TN (twisted nematic) technology. The viewing angles are not as wide as with the two aforementioned technologies, but can be improved with the help of a special polariser (O-film). Unfortunately, this is at the expense of the brightness. If you do not want to accept this, you should consider the viewing angle (6 o'clock vs. 12 o'clock).

The temperature behaviour

Another essential point is the operating temperature range. Is the charging station located outdoors the display can quickly get hot in summer and correspondingly cold in winter. Temperatures from +80°C or -30°C, in some regions -40°C, can certainly be achieved.
For that reason it is necessary to choose displays that also withstand these temperatures. Heat input from outside can be reduced by an IR cut filter (heat absorption filter) so that the display is not subjected to additional load. Of course, attention must also be paid to the thermal management of the charging station itself so that the display does not also heat up due to internal waste heat.    OLED displays have a clear advantage here, because their operating temperature range extends from -40°C to +70°C, 80°C and in some cases even up to 105°C. The majority of LCDs operate at -20°C to +70°C, with a smaller number of types also reaching -30°C to +80°C.

In this context, exposure to UV radiation should not go unmentioned. If prolonged exposure to UV light is expected, countermeasures, for example UV filters, must be taken. A possible imprint on a front glass should then also be made with ceramic inks, as organic inks can peel off.

The operation

Of course, a charging station can be operated via buttons and keys, but nowadays a touch screen is state-of-the-art. However, resistive touches are not recommended for such an application. They are inexpensive, but can easily be damaged. That leaves the projected capacitive touch. The handling is intuitive, whether as single or multi-touch. It is important that the touch can be adapted to certain circumstances or adjusts to them automatically. For outdoor charging stations, water (think rain or snow) must not trigger any function. A function in contact with gloves (at least with thin ones) should be ensured if possible. Both together is not easy to realise. It depends on the choice of the right touch controller.

The mechanics

Equipment in public places must also survive damage and vandalism. In terms of the display, this means that safety precautions have to be taken to prevent them. A thick front glass behind which the touch and display are then located is the most common method. Depending on the specific requirement, the thickness can range from 3mm to 10mm. In addition, optical bonding helps to make the entire display unit more stable. The glass can therefore be chosen a bit thinner without sacrificing resistance. Chemically or thermally tempered glass is an additional safety factor.

PMMA, commonly known as Plexiglas, as a front protector is flexible and breaks with difficulty, but it has the disadvantage of being easily scratched. Who wants to charge their vehicle at a charging station with an unsightly display? Glass is much more robust.

The installation in a housing also needs to be considered. The unit can be mounted from the front or the back. It is essential to ensure that this is waterproof and that the electronics in the charging pole are protected. IP65 is usually specified for this. The use of industrial adhesive tapes or special industrial adhesives is mandatory.

For wallboxes and smaller AC chargers, the focus is primarily on the design. Due to the special shape, it can happen that a completely customized display including touch and front glass is developed.

The electrical connection

If we consider the display as such, the communication for the mainly used sizes (7" to 21.5") is done via LVDS interface. The advantages are obvious: differential signals - therefore less susceptible to interference; long lines, several meters are possible - display and computer can therefore be distant from each other; low power consumption; low number of lines.

Naturally, other interfaces, such as RGB or MIPI are also used, but are not as common at the moment.

HDMI represents its own variant, so to speak. The interface is standardised and offers a direct connection possibility, for example to a BOX PC, which fulfills control tasks. On the display side, a corresponding adapter board is required to convert HDMI to the respective display interface.

If additional electronics are already available on the display side, the way to higher integration is not far. Available are displays that allow a direct connection of a Raspberry module. The display gets additional intelligence, e.g. the GUI (Graphical User Interface) can be stored there and does not burden the computer responsible for the charging electronics. This can therefore be realised more cost-effective. 

If you go further in this direction, you'll end up with the smart display. Intelligence is shifted to the display, and the computing power required for the entire system is distributed. This allows the modular design of a charging system. The connection to other modules is made via CANbus or RS485.

Conclusion

There are many points to deal with when selecting a display for charging stations. With the above overview, we would like to point out what we consider to be the important points. 

If you go into detail, there are other aspects that are worth examining. In general, the points apply not only to charging stations, but actually to many similar applications, such as info terminals, vending machines and similar.

Take advantage of our expertise! Discuss your project with us! Whether it is the choice of a suitable display or a desired customisation, we are at your disposal.

For further questions:

Christian Forthuber

Christian.forthuber@codico.com

+43 1 86305 158

About CODICO

CODICO stands for the design-in-distribution of high quality electronic components. The widespread product portfolio includes active and passive elements as well as products from the field of connection technology. The company operates from the Austrian headquarters in Perchtoldsdorf on the southern outskirts of Vienna as an independent privately owned company, and maintains a large number of sales offices in Germany, Denmark, Italy, France, the Czech Republic, Slovenia, Sweden, the UK, and has other partner companies in Central and Eastern Europe on its team. Backed by a high level of technical expertise, CODICO puts its focus on the Design-In sector. What makes CODICO particularly special is the providing of technical support from the development phase through to the end product, as well as the marketing and sale of exclusively top quality products.