Introduction
In a DALI (Digital Addressable Lighting Interface) system, the power supply is the lifeline of the communication bus. While luminaires, sensors, and controllers perform the functional tasks, the bus voltage ensures reliable signaling across all connected devices. Without proper design and management of DALI power, issues such as flickering, communication errors, or device failures can occur. This makes understanding bus voltage requirements, current limits, and power supply sizing a critical step in every DALI installation.
Unlike protocols such as DMX or 0-10V, DALI requires a dedicated power source for its communication line. According to the IEC 62386 standard, each DALI line can support up to 64 devices, and the bus must always remain within the defined voltage and current ranges to maintain interoperability and safety. This article explores the types of DALI power supplies, voltage specifications, design rules, and best practices for engineers and system integrators.
Role of Power Supply in DALI Systems
The DALI power supply provides the necessary 16V DC bus voltage that allows devices to send and receive digital signals. Unlike traditional power systems, the DALI bus is not meant to power the luminaires themselves but only to support data communication.
- Bus powering: Provides the required voltage to the communication line, ensuring that every connected device can listen and transmit signals without interruption. This guarantees reliable communication across the system.
- Isolation: Safeguards the DALI bus by separating it from mains voltage, protecting devices from overvoltage, grounding faults, or electrical interference that could damage the system.
- Compliance: Maintains the bus voltage and current strictly within IEC 62386 specifications, ensuring interoperability between devices from different manufacturers and long-term reliability.
- Stability: Keeps the communication bus steady even during heavy loads, preventing data loss, flickering, or miscommunication when multiple devices operate simultaneously.
Thus, the DALI power supply acts like a heartbeat, keeping all devices synchronized on the communication line.
DALI Bus Voltage Specifications
The DALI protocol defines strict electrical parameters to ensure device compatibility across manufacturers.
- Nominal bus voltage: 16V DC (typical operating range: 9.5V – 22.5V)
- Maximum bus current: 250 mA per line
- Polarity-free wiring: DALI bus does not require polarity matching
- Isolation: Must be separated from mains voltage for safety
If these conditions are not maintained, communication failures or even permanent damage can occur. For example, exceeding 250 mA can overload the system, while a low bus voltage may cause devices at the far end of the line to stop responding.
Types of DALI Power Supplies
1. Integrated Power Supplies
Some DALI controllers or gateways include a built-in power supply. These are common in smaller projects where only a single line of devices is needed.
- Pros: Simplifies wiring, fewer components.
- Cons: Limited expandability, may not be replaceable separately.
2. External Dedicated Power Supplies
Standalone DALI power supplies are installed when scalability and flexibility are required.
- Pros: Modular, easily replaceable, supports large installations.
- Cons: Slightly higher cost, requires extra wiring.
3. Redundant & Backup Power Supplies
In critical environments like hospitals or airports, redundancy ensures that if one supply fails, another takes over.
- Pros: High reliability, essential for mission-critical systems.
- Cons: More expensive, needs careful design.
DALI Power Supply Placement & Design Rules
1. One Power Supply Per Line
Each DALI line (max 64 devices) requires exactly one power supply. Adding multiple supplies on the same line is not allowed, as this may cause voltage conflicts and bus failure.
2. Distributed Placement
For long runs, place the power supply centrally to minimize voltage drop across the cable.
3. Line Length & Voltage Drop
- Maximum cable length: 300 meters (with 1.5 mm² cross-section)
- Longer runs require shorter device branches and optimal placement.
4. Isolation from Mains
The DALI bus must be electrically isolated from 230V AC mains to comply with IEC safety standards.
Power Calculation Example
Let’s consider a typical office project:
- Number of devices per line: 60
- Average device bus current: 2 mA
- Total bus current: 60 × 2 mA = 120 mA
- Power supply rating: Must support >120 mA (choose 200–250 mA for headroom).
Even if each device consumes only a small current, cumulative load can quickly add up, making careful calculation essential.
DALI Power Supply Current Management
The 250 mA limit is one of the most critical restrictions of the DALI bus. To manage this:
- Select devices with low bus current draw.
- Split installations across multiple DALI lines.
- Use gateways for larger networks.
Some advanced supplies also include current monitoring to prevent overload and alert facility managers.
Connection Ports & Termination
A DALI power supply typically includes:
- DC output ports: For connecting to the bus wires.
- LED indicators: Show status (power on, fault, overload).
- No termination resistor: Unlike DMX, DALI does not need line termination.
Comparison with Other Protocols
| Feature | DALI | KNX | DMX | 0-10V |
|---|---|---|---|---|
| Bus Voltage | 16V DC | 24V DC | 5V differential | Variable DC |
| Max Current | 250 mA | ~640 mA | N/A | N/A |
| Devices per line | 64 | 256 | 512 | Unlimited |
| Polarity | Free | Required | Required | Required |
| Cable Length | 300m | 1000m | 300m | Depends |
This table shows how DALI is simpler in wiring but has stricter current limitations compared to KNX or DMX.
Best Practices for DALI Power Supply Design
- Plan load distribution – Calculate bus current before installation.
- Centralize power supply – Avoid excessive voltage drops.
- Use proper cable – 2-core, 1.5 mm² twisted pair recommended.
- Avoid multiple supplies – Only one per line is allowed.
- Redundancy for critical systems – Hospitals, airports, data centers.
- Monitor bus health – Use gateways with diagnostic functions.
Real-World Applications
Offices & Commercial Buildings
- Compact external power supplies used per floor.
- Central gateways manage multiple lines.
Hospitals
- Redundant supplies ensure lighting never fails during emergencies.
- Each patient room connected to an independent line.
Retail Stores
- Cloud-connected DALI gateways with bus monitoring.
- Uniform lighting schedules controlled remotely.
Smart Cities
- Street lighting powered by industrial-grade DALI supplies.
- Predictive maintenance enabled by IoT integration.
Future of DALI Power Supplies
As lighting systems evolve, next-generation DALI power supplies are expected to include:
- Smart monitoring with real-time diagnostics ensures quick detection of faults, overloads, and voltage issues for uninterrupted system performance.
- IoT-enabled supplies connect to cloud platforms, allowing remote monitoring, energy analytics, and predictive maintenance.
- Energy harvesting designs capture ambient energy (like solar or kinetic) to power the bus, reducing dependency on external supplies and improving sustainability.
- Scalable power modules allow expansion beyond standard limits, supporting hundreds of devices seamlessly within large lighting networks.
Conclusion
The DALI power supply is often overlooked, yet it is the foundation of reliable communication in modern lighting systems. By maintaining bus voltage at 16V, respecting the 250 mA current limit, and designing with proper placement and redundancy, engineers can ensure smooth operation and long-term stability. Whether for offices, hospitals, retail, or smart cities, following IEC 62386 guidelines and best practices guarantees a future-proof installation.
A well-planned power supply strategy not only improves system reliability but also enables advanced features like energy monitoring, remote diagnostics, and predictive maintenance, making it a cornerstone of modern lighting control.
