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I'm currently setting up a PV island system. Electricity is stored in two parallel 12V batteries which is then fed into a 300W 230V inverter. The load connected to the inverter consists out of several industrial LED lamps which can be controlled over DALI. An additional DALI-controller is used, which dimms the lamps over a simple 0-10V interface. The inverter also has a two pin connector exposed which can be used to manually shut it off.

I'm in the process of developing a microcontroller based system which controls the inverter over the remote pins and also the LED lamps.

It is clear to me that the secondary side (230V) is galvanically isolated from the primary side (12V) through the inverter's transformer.

However, I see two options on how to connect my circuitry:

  1. Use digital isolators for communication with the DALI controller and an additional SELV 24V power supply plugged in to the 230V side. This ensures that both sides stay isolated.
  2. Directly drive the DALI controller without isolation. This connects the 12V side with the ELV side of the DALI bus. It seems that the DALI lines only have basic isolation.

With normal mains AC, I see the risk of having 230V AC on the DALI lines in case of a fault which can lead to damage and/or shock. But I'm not sure if that is a risk in my inverter system.

What isolation (if any) would you recommend in this situation?

Edit: Added Diagram System Diagram

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    \$\begingroup\$ Can you provide a diagram of your system? \$\endgroup\$
    – schnedan
    Commented Sep 19, 2020 at 22:42
  • \$\begingroup\$ Sure, I edited my post. I hope that helps. The diagram shows option 1 described in my post. Question is, if that's the way to go or if I can cut the digital isolation as well as the 24V PS and directly supply everything from my control circuitry. \$\endgroup\$
    – sqrroot
    Commented Sep 20, 2020 at 9:48
  • \$\begingroup\$ without a in depth analysis... I would connect that 8-36V in to the existing 24V and do some isolated solution for the "2 Pin Remote Con", guess you can do it with optocouplers \$\endgroup\$
    – schnedan
    Commented Sep 20, 2020 at 9:54
  • \$\begingroup\$ That sounds good but I'm missing out on galvanic isolation for the DALI bus. If I connect both grounds, the DALI controller "sees" the 12V battery side which in return poses a risk as the whole system can be exposed to 230V incase of a fault. Or am I misunderstanding something here? \$\endgroup\$
    – sqrroot
    Commented Sep 20, 2020 at 10:15
  • \$\begingroup\$ wouldn't a PELV Power supply replacing your suggested SELV supply do the trick? By the way, is there not a kind of isolation in the LED lamps? \$\endgroup\$
    – schnedan
    Commented Sep 20, 2020 at 10:24

1 Answer 1

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I would run the DALI circuit on a grounded DC supply, the grounding gives you protection in the event of a failure of the basic isolation. and makes it safe and easy to probe voltages and signals.

This may require fuses to prevent large fault currents from entering the DALI bus

Once you get the grounded system working you may want to consider changing it to an isolated system using enclosures and controls that have reinforced insulation.

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