Lost in Translation: Where People Get DALI Wrong (1)

The DALI (Digital Addressable Lighting Interface) standard has had a very uphill battle in the USA. Lots of resistance, mostly quoted to it being problematic and expensive. On the other hand DALI has almost 100% market share in Europe and similarly in Asia and Middle East.

DALI Alliance has been trying to change this, addressing the North American market with several campaigns, but they have not been too successful so far. And the reason is, despite DALI being a very good technology, there are many misconceptions, false myths, contradictory statements (even by the DALI people themselves). Here I'll address some key concepts that people often get wrong or are falsely propagated even by those who should know in the first place.

DALI is polarity free. I have heard this so many times. Even from the founding fathers of DALI. So yes, in principle it is, but in practice it is not. DALI bus signaling works by shorting the bus. There are two wires and there is small DC (around 18V) current flowing in them (that is why the bus needs to be powered). The bus goes to active state when it is shorted by any attached device and the bus voltage drops below 4.5V. DALI products are designed with internal rectifier bridges so it really does not matter which way the two bus lines are connected - the device will always be able to short / pull the bus down. BUT - and this is a big BUT - bus polarity starts to matter when there are more than one devices powering the bus (bus power supplies). And this situation is very common today, as bus power supplies are integrated into LED drivers. So whenever there are two or more drivers with active bus power supply function enabled (D4i drivers must have that in the factory default state), the polarity of course matters - you MUST connect DA+ to DA+ and DA- to DA-. So my suggestion to DALI Alliance is: stop spreading the "polarity free" myth. It is unnecessary, outdated (was true before D4i) and totally misleading.

At this time it is worth explaining the D4i piece: D4i is a set of  additional extra mandatory requirements on top of DALI. DALI is a set of specifications (they are called "Parts"). And D4i is only applicable to LED drivers (DALI calls them "control gear"). One notable aspect of D4i is that it makes the Parts 251, 252, 253 mandatory, meaning a D4i driver exposes the rich set of asset (251), energy/power (252) and maintenance (253) data points. They are BTW fully mapped to the wireless Bluetooth NLC standard - this mapping is defined in DALI Part 341.

Now: D4i also makes it mandatory for drivers to include bus power supply function AND have it enabled by default. This itself is one of the greatest features of DALI, as it effectively enables connecting a compatible DALI device (such as a wireless Bluetooth NLC sensor controller with DALI interface) directly to the driver (using just two wires) and the device is then bus-powered (draws its own power from the bus and talks bi-directionally to the driver over the same 2-wire bus).

The problems with D4i drivers (which are the majority of drivers on the market today) start when you want to either "stack" a couple of them together or use in a legacy DALI system with central system/application controller. In that case (D4i drivers with active bus power supplies) the polarity absolutely matters AND you cannot stack more than 4 units. That is why some people have been calling for "D4i-" (minus) meaning "give me the Parts 251/252/253 data points but not the active bus power supply". Unfortunately these voices have been quite loud, adding the "minus" part to the confusion introduced by DALI with the "DALI+" (plus) sub-brand that identifies the home-brewed (and doomed) wireless variant of DALI.

So remember this:

• A single DALI driver connected to a Bluetooth NLC sensor-controller: polarity does not matter, make sure it is a D4i driver (will power the sensor-controller and offer the wealth of data points).
• Multiple DALI / D4i drivers in a luminaire - up to 4 can be "stacked" together, but polarity matters (DA+ to DA+ and DA- to DA-).
• Non-D4i drivers: an external bus power supply must be used
• A legacy DALI system with a central controller: typically the central controller provides the bus power, so make sure you use non-D4i drivers or you disable the bus power supplies in D4i drivers (they are enabled by default).

I hope this makes things clearer.