Dimming several Shelly Dimmer Gen3 in sync

You have several dimmable light points in the same room — some recessed spots, a wall light, a lamp — each with its Shelly Dimmer Gen3, and you want them to raise and lower their brightness all at once, as if they were one. It can be done, and there are three ways to do it depending on what you're after. Let's look at them with their advantages and their limits, so you choose the one that fits and not the one that sounds best.

The three routes, at a glance

There's no "best" in the abstract: it depends on whether you want convenience from your phone, instant sync with the wall switch, or simply to trigger a preset atmosphere.

• Group in the app. You put the dimmers in a group within Shelly Smart Control and move them with a single control, including by voice. It's the most convenient for everyday use.
• Local actions (device to device). One dimmer acts as master and "pushes" its brightness to the others over the local network. It's real sync: instant and without depending on the internet.
• Cloud scenes. A trigger sets several dimmers to a fixed brightness. Simple, but it needs a connection and is a bit slower.

And they're not mutually exclusive: the usual approach is to combine a group for phone control with local actions so the physical switch commands them all.

Instant sync: local actions

This is the one most people want when they say "in sync": you turn or press at one point and the rest follow instantly, even if the router is off.

It works with the Dimmer Gen3's local actions (webhooks within your Wi-Fi). You choose one dimmer as master — the one you control, from its switch or from the app — and set it up so that, every time it changes, it tells the others to copy its state.

The setup, in the app or in the dimmer's web interface:

1. On the master dimmer, go into Actions (or webhooks).
2. Create an action for the "on brightness change" event.
3. As the destination, point to the local IP address of each slave dimmer with the command to set that same brightness.
4. Repeat for the on and off events, so the group behaves the same across the board.
5. Set a static IP for each dimmer in your router. If the router changes their IP, the webhooks can no longer find them and the sync breaks without warning.

Each Dimmer Gen3 supports up to 20 actions, with up to 5 destinations per action. More than enough for a room; if you have many points, spread the notifications across several actions.

The group requirement almost nobody reads

Here's the number-one cause of "I made the group and they don't go the same", and it comes straight from Shelly's official documentation: for a group of lights to dim consistently, the dimmers must have the same model and the same connected load.

The reason is physical. Each Dimmer Gen3 calibrates its dimming range according to the load it has hooked up. If one point has three LED bulbs and another has just one, the same "40 %" translates into different brightness levels, and the start in the low zone — where LED is most temperamental — doesn't match. The result is a group that goes up and down out of step right at the start and end of the range.

Two practical consequences:

• Distribute the loads so that each dimmer in the group drives a similar consumption. If you can't, accept that the sync will be approximate, not perfect.
• Recalibrate each dimmer after any change of bulbs. Automatic calibration is mandatory on a new unit, after a factory reset and after every change of load; it's launched with a 5-second long-press of the two buttons.

A single switch for the whole room

If what you want is to keep the wall switch and have it command several light circuits at once, the piece that does it elegantly is a Shelly I4 Gen3.

The I4 doesn't dim: it reads the button presses of up to four inputs and relays the command. You place it behind the push-button and set each press — short to turn on/off, held to raise or lower — to send an action to all the Dimmer Gen3 in the room, which each dim their own load.

It's the cleanest solution when the installation has a single physical control point but several dimmable circuits behind it.

What to bear in mind before setting it up

• Without neutral and below 20 W per point, each dimmer needs its bypass. Without it you'll see flicker or glow with the light off, and that ruins the visual sync.
• The Dimmer Gen3 has no Matter. If your plan is to group via Matter in HomeKit or SmartThings, that route belongs to the Dimmer Gen4. With Gen3 the sync is done by group, local actions or scenes, as here.
• All the bulbs must be dimmable and, if possible, the same type and brand within the group. Mixing LED models is the other typical source of uneven brightness.

Frequently asked questions

Which of the three methods is best?

For everything to react instantly and without internet when you touch the physical switch, local actions. For convenient control from your phone and by voice, the group. For fixed-brightness "atmospheres", scenes. Many people use a group and local actions at the same time.

Can I sync dimmers of different models?

You can control them together with scenes or local actions, but for a group with fine dimming Shelly recommends the same model and the same load. With different models or loads, the sync will be approximate, especially at the ends of the range.

Do local actions work without internet?

Yes. They travel over your local Wi-Fi network, so they keep working even if the internet connection goes down. That's their big advantage over cloud scenes.

Why do my dimmers start at different brightness levels with the same percentage?

Almost always because of different loads or lack of calibration. Match the number and type of bulbs at each point as much as possible and recalibrate each dimmer after the change.

How many dimmers can I sync?

There's no practical limit for a home. With local actions, each master dimmer notifies a limited number of destinations per action (5), but you can chain several actions or use an I4 as a single source.

Do I need a hub or gateway for this?

No. The Dimmer Gen3 units talk to each other over local Wi-Fi. You don't need any proprietary hub or the cloud for local-action sync.

Can I mix app control and switch control?

Yes, and it's recommended. The group gives you control from your phone and local actions make the wall switch keep commanding the whole set.

Summary

• The dimmer → Shelly Dimmer Gen3
• One wall switch for several circuits → Shelly I4 Gen3
• Bypass for loads below 20 W without neutral → Bypass for Dimmer Gen3
• If you want to group via Matter → Shelly Dimmer Gen4

A specific setup in mind? Tell us how many light points you have, with what bulbs and whether there's neutral in the boxes, and we'll tell you which method fits and what you need. Technical support in English and shipping from Spain.