This application note describes the correct cooperation of digitalSTROM products with various LED lights and power supply units available on the market.
Types of LED bulbs
LED bulbs can generally be divided into three product groups:
- LED operated via power sources (usually constant current or constant voltage sources). This is power source has got a 230V input and is also known as converter.
- 12V illuminants to be used with conventional or electronic transformers.
- 230V illuminants with GU10, E27 or E14 socket.
- Dimmable converter/ballast with 1-10V or DALI.
Bulbs that fit into existing sockets, are also known as retro-fit illuminants and the necessary electronics for the operation of the LED is already integrated.
Basics on dimming methods
Basically, there are two types of dimming processes that are used depending on the load type of the illuminant.
A) Leading edge method
The front part of each sine half-wave is being cut off.
Permitted lamp loads for this method:
- All resistive loads (e.g. bulbs, high voltage halogen lamps etc.) marked with the following symbol:
- All inductive loads (e.g. iron core transformers for example for 12V halogen spots etc.) marked with the following symbol:
B) Trailing edge method
The back part of the sine half-wave is being cut off.
Permitted lamp loads for this method:
- All loads, including electronic transformers and power supplies, except inductive loads (these usually lead to immediate destruction of a trailing edge dimmer), marked with the symbol:
Resistive loads are therefore permissible for both dimming methods. However, the trailing edge dimmer offers a gentler operation for the bulb thanks to the smooth switching and thus has a positive effect on the lifespan of the bulb. The digitalSTROM products with dimmer output use the trailing edge method.
Basics on protective measures of digitalSTROM products
Overload shutdown of the output
All digitalSTROM products with load output are equipped with an overload shutdown. The output current is constantly monitored in the terminal blocks. If the output current exceeds the terminal block's rated current, the output is switched off. Shutdown happens faster, the greater the overload compared to the rated load. This must be considered especially with loads with increased inrush currents:
Example 1: A 150W high voltage (0.65A rated current) halogen spotlight has an inrush current of over 2A. After approx. 100 ms, the current has decayed to the rated current of 0.65A. The overload cut-off is set so that this short-term overload of the terminal block will not trigger the shutdown.
Example 2: Fluorescent lamps with conventional ballasts have a very strong shift between the voltage curve and the absorbent current (phase shift). This displacement causes much more current to flow out of the terminal block. Due to the actual considerably higher current, this current shift may cause the shutdown to respond. In case of a minor overload, the shutdown may happen only after several seconds.
When the overload switch-off has responded, the status LED of the terminal block flushes 4 times as an indicator. An automatic restoration of the initial value does not take place. The output is only switched on again by pressing a push-button (at the push-button input of the terminal block) or a mood scene call from the digitalSTROM system. If the overload continues, the output is switched off again.
Overtemperature shutdown of the terminal block
All digitalSTROM products with load output are equipped with an overtemperature shutdown. It responds and disables the output if the terminal block becomes too hot due to excessive ambient temperatures. When the overtemperature shutdown has responded, the status LED of the terminal block will flash once as an indicator. A recovery of the initial value takes place automatically after cooling, e.g. the terminal block continues to operate normally after cooling down.
Short circuit protection at the output
The digitalSTROM products with load output also have a short circuit cut-off. It responds and switches off the output if the output current suddenly exceeds a threshold > 8A. The output of the terminal block is then shut down very quickly to avoid damaging the terminal block. High inrush currents can also occur if it is a capacitive load (electronic power supply unit with large input capacity). This may also be the case with small LED bulbs / converters if the inrush current is large enough to cause the short circuit protection of the terminal block to respond. To ensure that the terminal block is protected against short circuits at the output and capacitive loads can still be switched with increased inrush currents, a renewed switch-on attempt is made automatically after approx. 100 ms to switch on a capacitive load after a response of the short circuit detection.
The switch-on attempts of the output are repeated up to a total of 32 times. In general, this number is sufficient to safely turn on this kind of power supplies. If the current causing the short circuit is still too high after 32 switching attempts, the terminal block terminates the restart procedure and displays the error code short circuit by flashing twice. An automatic restoration of the initial value does not take place. The output can only be switched on by pressing a key (at the push-button input of the terminal block) or via a digitalSTROM command.
Notes on the operation of LED lamps with digitalSTROM dimmer products
12V bulbs with conventional transformers
Conventional transformers (e.g. wound toroidal transformers) are an inductive load and can only be switched with the relay terminal block GE-KL200 or SW-KL200. Operation with the GE-KM200/GE-TKM210/GE-SDX200 terminal blocks is not possible.
12V bulbs with electronic transformers
Electronic transformers usually have a minimum load of 20-105VA or 50-150W for example. This minimum load must also be observed when operating with LED lamps (see also below "problems with low-load electronic transformers").
Not all electronic transformers can be dimmed on the primary side by means of a phase dimmer. Here the instructions of the respective manufacturer are to be considered.
Even the majority of available 12V LED bulbs can only be switched according to the manufacturer and are not dimmable. Here the instructions of the manufacturer are to be considered, too. With only switchable LED lamps, make sure that the digitalSTROM terminal block used is configured to switching mode (factory setting).
Some electronic transformers have a very high inrush current. The specification can be found in the data sheet of the transformer (power supply), e.g. "INRUSH CURRENT (max.) 70A/230V" or "INRUSH CURRENT (< 2 ms) 230VAC 10A max.".
It should be noted that there is a possibility that the short circuit detection at terminal block M may respond temporarily and that the terminal block switches on the load with a delay (see previous paragraph "short circuit protection at the output". If there are permanent problems with the control of the transformer, the terminal block must be switched to switching mode or use a corresponding relay terminal block L with increased switching capacity.
LEDs operated via power sources
For "High Power LEDs" there are special ballasts that provide a constant current. Most of these ballasts have a wide range voltage input of 90 - 264 VAC / 127 - 370 VDC. They are usually not dimmable by means of commercially available leading edge or trailing edge dimmers. As an alternative there are special ballasts with 0(1)-10V control inputs, which regulate the LED current. Again, some ballasts have a very high inrush current. The specification can be found in the ballast's data sheet, for example "INRUSH CURRENT (max.) 70A/230V" or INRUSH CURRENT (< 2 ms) 230VAC 10A max.". Again, attention should be paid to the occasional response of the short circuit detection. Ballasts or converters with 0/1-10V control inputs can be operated with the GE-UMV200.
It is important to distinguish between three different types:
- Non-dimmable bulbs.
- Bulbs that can be dimmed in gradual phases by briefly switching off and on.
- Dimmable bulbs (suitable for leading edge dimmers or trailing edge dimmers, depending on the design).
When using type 1 bulbs, the digitalSTROM dimmer products (terminal block M,
cord dimmer M) must be set to switching mode (factory setting).
The use of type 2 bulbs in connection with digitalSTROM should be avoided, as the flashing command via digitalSTROM activates the bulb's dimming function.
When using type 3 bulbs, make sure that the bulb can be dimmed by means of a trailing edge dimmer. Dimmable bulbs, which must be operated with a leading-edge dimmer, can only be switched with digitalSTROM products. For this the configuration of the terminal block must be considered.
Dimming with digitalSTROM products
At the time of delivery, the stored dimming curve in digitalSTROM products with dimmer output is matched to the curve of the brightness change of high-voltage halogen lamps. The dimming curve describes which percentage of the output value corresponds to which switch-off time (see fundamentals of dimming procedures). The dimming curve is set in such a way that the eye perceives a brightness change as uniform as possible.
Changes of the dimming curve
LED bulbs usually have a slightly different brightness curve when dimming than halogen bulbs. Especially in the lower range (dark area) they require an adjustment of the curve in the dimmer. Via a corresponding app "Dim Wizard" in the digitalSTROM server, the curve can be adapted to the light source.
Problems with low loaded electronic transformers
When the electronic power supply units are under-charged, a residual voltage at their input can be maintained when switching off, if the 230 V AC voltage has not yet passed the zero point (polarity change). This residual voltage is caused by the input capacity of the power supply. The subsequent principle-dependent reloading process in the power supply unit at AC voltage leads to increased compensation currents, which in turn causes the internal short circuit detection at the output of terminal block M to respond. If the load on the power supply is correctly dimensioned (high enough), these compensation currents are avoided or significantly reduced, and dimmer operation with the digitalSTROM products is possible without any problem.
Selection of illuminants / digitalSTROM product