I faced a strange behavior of a DALI controlled LED luminaires circuit. I have 48 LED luimianires with a MeanWell ELG150-C700-DA drivers connaected according to the scheme below:
I commissioned the system and it works OK but sometimes I can't switch some luminaires OFF via the DALI commands. When I send DAPC 0 or OFF command this luminaire go OFF, but in a second the go back to 100% of their output. Besides that this problem is floating, because in a different days different luminaires start to work in a such way. Moreover sometimes ALL luminaires go ON spontaneously.
I doubt that the problem is in LED drivers because when I tested some other drivers from the same bunch, everything was OK. I think that something is wrong with the DALI bus installation quality, but I don't know from where to start the thoubleshooting.
I am a novice in a DALI theme, could you advice me what parameters I should check to find the root of the problem?
Here is a DALI signal at the beginning of the DALI bus near the 905 router
By the way why the signal amplitude for 2 DALI packets is different?
Best Answer
DALI requires less than 2V maximum difference between the highest and lowest points on the line. To achieve that you must use sufficient cable gauge and a power supply with sufficient current limit. The luminaires will go on "spontaneously" if they see a system failure condition, which is less than minimum DALI voltage for more than 500ms. For up to 150m you need to use 0.75mm squared CSA.
You may be overloading the PSU in the 905 router. Although it has a current limit at 250mA, which is the maximum allowed by DALI, you have 48 luminaires plus 3 control panels. The luminaires (assuming one DALI driver per luminaire) are restricted to 2mA each by the standard, but the control panels do not have the same restriction; they are allowed to be up to 250mA each (although not a good idea to go that high). So measure with a current meter in series at the router end what you are drawing during non transmit times, and look at the DALI signal with a scope to see if the high levels are dipping below 9.5V.