KNX: Integrating LED Switching Power Supplies Into Building Automation

There is a vast number of LED power supplies on the market, but most do not have the prerequisites to integrate them directly into a KNX building automation system. Instead, for LED lighting, switch actuators and other devices are used.

A KNX switch actuator forms an interface between a digital KNX system and analogue electrical devices. The actuator converts the commands received from sensors, automatic switches and timers into actions. The usual economical solution currently includes equipping a switch actuator with electromechanical relays, thus allowing any type of connected load to be switched.

What do I need to know about this?
• To ensure the high reliability of switch actuators in a demanding KNX building automation system, a high-quality relay is needed. The performance and service life of relays is sometimes defined by the EN60669-1 standard.
• If a larger number of LED power supplies are installed, the maximum inrush currents and technical parameters of the relays being used have to be taken into account when using switch actuators.
• Inrush currents also influence the selection of a suitable circuit breaker and the use of an additional inrush current limiter. This can significantly reduce installation costs by using smaller circuit breakers and cross-sections and fewer fuse circuits.

► Tip: With their ICL-16 and ICL-28 series, MEAN WELL offers inrush current limiters for capacitive loads from 2500 to 6000µF.

Another possibility is to integrate LED power supplies with an analogue 1-to-10V dimming interface by using a dimming actuator such as the KAA-4R4V-10 from MEAN WELL, or to integrate LED power supplies with a Dali interface into the KNX installation via a KNX-Dali gateway.

What disadvantages are there?
• With dimming actuators installed at the sub-distribution level, the cable routes to the lamps can sometimes be very long, which can negatively affect the analogue 1-to-10V system.
• Also, identifying and addressing individual luminaires via a KNX-Dali gateway can become very time-consuming.
• A central KNX-Dali gateway can also be a potential source of malfunction for the entire lighting system and makes it difficult to collect data such as the power consumption of the lighting equipment.

In applications where power requirements and dimensions allow, therefore, an LED power supply with a KNX interface should, if possible, be used directly, to avoid additional dimming actuators or gateways.

► Tip: MEAN WELL offers LED power supplies of this kind for constant voltage applications with 60W and 120W output power (PWM-120KN and PWM-60KN series)as well as for constant current applications with 25, 40 and 60W output power (LCM-25KN, LCM-40KN and LCM-60KN). Additional solutions, like the PWM-180KN, are currently in development.

Generally speaking, the installation of KNX devices, including the KNX power supply and switch actuators, often takes place in a switching cabinet inside a building. To ensure an integrated installation, the mechanical dimensioning of these devices should be done according to the DIN 43880 standard.

The width of KNX devices for top-hat rail mounting is defined by "division units" (TE), where one division unit should be no wider than 18mm. The space available in sub-distribution switching cabinets is usually very limited.

► Tip: Devices designed to be as narrow as possible are called for here. Suitable devices include, for example, the 8-channel switch actuators (KAA-8R and KAA-8R-10), 4-channel dimming actuators (KAA-4R4V and KAA-4R4V-10) and 1280mA KNX power supplies, with or without diagnostic function (KNX-40E-1280 and KNX-40E-1280D), at only 4 TE wide, as well as the 640mA KNX power supply (KNX-20E-640), just 3 TE wide, from MEAN WELL.