Controlling multiple Homematic Dimmer as a group via a slider or Alexa

I have three Homematic-IP dimmer (HmIP-BDT and HmIP-PDT) in openHAB 3.01 (openHABian 1.6.3, Raspi 2) working perfectly well individually and in an “Alexa-Group” with Alexa. However, grouping them in an “openHAB-group” and controlling this one group does not work at all.

Here’s what I tried and what doesn’t work for multiple reasons:

value: oh-slider-card
unit: “%”
min: 0
scaleSteps: 10
max: 100
footer: Test
scale: true
step: 10
label: true
title: Licht Gruppe
scaleSubSteps: 5

Three problems with that:

  • Controlling the three dimmer via the Slider in WebUI works, BUT:
  • Although I can set the brightness to anything above 0% in WebUI, I cannot switch them off again by setting the slider back to 0%.
  • Whenever accessing the status of the group in WebUI, the slider is always at 0% (even though the lights are on)
  • Controlling this group with Alexa only controls the first dimmer in the group (see screenshot above), but not all three of them.

Reading in this forum I read multiple threads on the same problem (e.g. Lights - Dimmers and Groups - #4 by rlkoshak , Adding a Dimmer switch ( group? ) in a sub item in a sitemap - #7 by samverner777 , [SOLVED] Dimmer item behaviour with Group items - #3 by Nico111 , Trying to control multiple dimmers with one slider - #21 by Gufti or Hue group dimmer slider always set to zero - #2 by rlkoshak). However, since I’m fairly new with OH (and some of the solutions appear to relate to OH2) I have problems applying them to my particular situation.

Edit: The “0%-problem” appears to be covered here ([SOLVED]Struggle with Rollershutter HMIP-BROLL) as well for the rollershutter, but I’m still having problems applying this to my setting.

What is the type and the aggregation function for the group?

Dear @rlkoshak, thanks a lot for your response.

Your question guided me in finding the answer / solving the problem myself: Turned out the Type appeared to be correct already (“Group”), but it was the Members Base Type which i forgot to set (now “Dimmer”, which also sounds logical, so I could’ve found this out myself in the first place ;).

What I also found out: The aggregation function can lead to some pretty funny behavior with three dimmer, when set to “AVG” (–> leading to an endless loop of the lights powering up and down ;).

Thanks again for your help.

The UI widget is the badly-behaved part here, not your approach using Group with AVG

You could also use group feature from alexa if you don’t need them in OH. This won’t solve the grouping issues you’ve seen but it may be a solution for someone who don’t need them in OH.

Add all lights which should be controlle in that room to one group.

Group name: “living room”
“Alexa, turn of the living room lights”
“Alexa, set living room lights to 30 percent”
“Alexa, living room lights 30 percent”

You can still say something like:
“Alexa, turn off the couch light”
“Alexa, couch light 30 percent”

Thanks. I had it work that way before, and it worked perfectly well. Though I try to build things in a way to have the least amount of “logic” in Alexa, since I’m considering switching to another voice-controlled system in the near future.