DALI lights switch on by themselves or jump to another brightness — the DALI bus is disturbed

Note which lights are affected, when it happens, at what brightness, and whether the light is really on in the room or only shows as on in the app. Note also whether it started right after a power cut, a restart of the Core or saving a configuration change in the app — that is the last cause above. A value that flashes in the app for a second and returns is a reading glitch; a light that is really on and stays on is what the next steps look for.

# Step 1I'm stuck here

On the MEAN WELL DLP-04R (the DALI power supply sold by TapHome) the LED means — for another power supply, see its manual:

1. Green: normal operation
2. Yellow: communication on the bus — normal while TapHome reads the lights
3. Red, or flashing red: a short circuit on the bus, also one that comes and goes
4. Watch it for at least a minute and record a short video — yellow and red are easy to confuse — and write the colour down

# Step 2I'm stuck here

Leave the bus power supply and the lights connected and disconnect only the DALI wires of the gateway. Watch the LED for at least 15 minutes; the lights may switch on only every few hours, so leave it longer if you can.

1. The LED stays green the whole time: the disturbance comes from the gateway side — continue with the next step
2. The LED still shows red: the problem is on the bus itself — go to Check the bus itself
3. The LED stays green but lights still switch on: the cause is not the gateway — go to Check the bus itself and check the power supply of the drivers

The power supply and the drivers are connected to mains voltage, and DALI wires often run in one cable with mains wires. Only a qualified electrician should do these steps: switch off the mains before you disconnect or tighten anything, and measure only with a suitable multimeter.

While the gateway is disconnected, TapHome cannot control the DALI lights and shows them with an error. That is expected; connect the gateway back after the test.

# Step 3I'm stuck here

Connect the gateway back to the DALI bus and disconnect A and B of its RS-485 line at the Core (for a gateway on Modbus TCP, its network cable). TapHome then sends nothing to the gateway. Watch the LED again for at least 15 minutes.

1. The power supply still shows red: the gateway or its wiring disturbs the bus by itself and is the likely cause — check its power supply and wiring against its compatibility page; replacing the gateway confirms it
2. The red disappears: the disturbance appears only while TapHome communicates with the gateway — contact TapHome support with this result
3. There was no red at any point, but the lights still switch on: go to Check the bus itself

# Step 4I'm stuck here

Come here when the steps above point to the bus itself.

1. Only one bus power supply on the bus; with several, including one built into a gateway, their total current must not exceed 250 mA
2. Enough current for all devices: a driver usually draws about 2 mA, the DLP-04R supplies 240 mA
3. DC voltage between the two DALI wires at the power supply: about 16 V
4. DC voltage at the farthest light while all lights are on: not below 9.5 V
5. With the mains switched off, disconnect the branches one at a time to find a short circuit or a bad contact, and tighten the terminals
6. The bus wires must not form a loop

# Step 5I'm stuck here

If lights come on after a power cut or after the bus power is switched back on, check in the DALI commissioning software what each driver does after power up and after a bus failure, and set it there. TapHome shows both values in Service attributes of the light as Power Up Level and System Failure Level; read them several times, because a single odd value can be a reading error. In the Resi DALI template a value of 100 % can also mean MASK: last level after power up, no change after a bus failure.

# Step 6I'm stuck here