Dim Up Failure

[Peter-Marc]

I've recently updated my C-BUS system from 5508D1A to 5508D1D dimmers.

All good except on a couple of channels the on light in a scene fails to dim up when a scene is triggered. If I turn off and on again all is good. Also if I set a min level of 4% the lights go off and always trigger next time the scene is turned on.

Any thoughts as to why this might be?

[Mr_C]

Hi Peter,

What you’re describing is typically seen when the new digital dimmers haven’t had their load type confirmed on each channel after installation.

Unlike the older 5508D1A units, the 5508D1D dimmers require per‑channel load detection and confirmation before they settle into normal operation. If a channel is left unconfirmed, you can see symptoms like:

• Lights not ramping up correctly when triggered from a scene or dimming function with no or fast ramp times of 0 to 8 seconds
• Slow or inconsistent ramp behaviour
• Needing an off/on cycle before the level behaves as expected
• Unusual behavior around low levels 

This is covered in the documentation:

• First Power Up / Load Detection Mode (TE/LE) in the user guide
• First Power Up Settings in the installation sheet

Before looking at anything else, I’d suggest confirming that all channels on the dimmer have been properly detected and confirmed.

You can do this either:

• At the unit using the front buttons, or
• Via SpaceLogic C‑Bus Commissioning Software (SLCC)
  • Perform a live scan
  • Right‑click the dimmer (from the live network, not the database)
  • Select the channel confirmation option

This step is important—even if only a couple of channels are affected.

Regarding the 4% minimum level

The behaviour you’re seeing (lights turning off at 4%) can also be related to the load profile.

Once channel confirmation is done, if the issue remains:

• Create a custom load profile in SLCC
• Use the built‑in wizard to tune:
  • Minimum conduction time
  • Maximum conduction time

If lights are dropping out at low levels, you’ll typically need to increase the minimum conduction time slightly. The wizard makes this quick to test and optimize.

Suggested approach

1. Confirm all channels (critical first step)
2. Re-test scenes
3. Only if needed, tune the load profile using SLCC
   
   
   If you confirm the channels and still see the issue, happy to dig further—but in most cases this resolves exactly the behavior you’re describing.

[Peter-Marc]

Thanks for your advice. I followed the commissioning to the letter. but haven't touched on the load profile.

That said, whilst I use Varilight transformers throughout the house, without other issues, I swapped out the transformer and the problem resolved. 

Thanks

[Mr_C · Accepted solution]

Hi Peter,

Thank you for the update.

It sounds as though a custom load profile could have been an effective solution for the Varilight transformers.

Assuming that the mode detection and configuration were correctly set for transformer operation, it is worth noting that the 5508D1A is a leading-edge, 2-wire dimmer, whereas the 5508D1D supports both leading and trailing edge modes. The 5508D1D, however, can exhibit intermittent startup issues if the selected mode does not align with the characteristics of the connected load.

Varilight transformers are often electronic in nature, and these typically favor trailing edge operation. Without specific model details it is difficult to be definitive, but this is the most common behavior observed in the field.

It is also worth noting that many electronic transformers include internal protection and control features such as soft-start (gradual ramp to full brightness), auto-resetting overload protection, thermal protection, and short-circuit protection. The selected dimming mode can influence how these internal mechanisms behave. For example, operating a transformer in leading-edge mode when it is designed for trailing-edge dimming can increase electrical stress and potentially lead to overheating, which may in turn trigger thermal or overload protection and manifest as startup or stability issues.

While I cannot confirm whether the specific Varilight model in your installation includes these features, the behavior described would be consistent with this type of interaction.

If the operating mode had already been confirmed as correct, a custom load profile would likely have provided a straightforward resolution. Adjusting parameters such as minimum startup level, or applying a small kick-start, typically resolves startup instability and helps maintain stable operation at very low dim levels (e.g. level 1).

The configuration wizard for custom profiles is generally quick and easy to use—often significantly faster than replacing the hardware.

While it may be too late to trial this approach in this instance, it may be useful to keep in mind for similar scenarios in the future.

[Peter-Marc]

Out of curiosity I swapped the new Varilight YT105Z back to the original YT105 and adjusted the kick-start time and all was resolved. Thanks for the lesson for the future. Thanks for the lesson for the future.

In the interim the LED lighting on another channel has stopped turning off. I have started a new thread, which I would be grateful for you looking "Transformer LED Channel Will not turn off"