Müller SC 28.23 pro4 2 Channel Astro Time Switch - Bluetooth DIN Rail

The Müller SC 28.23 pro4 is a DIN rail-mounted astro time switch with two independent 16A channels, Bluetooth app control and a built-in astronomical clock that calculates sunrise and sunset times based on GPS coordinates. Each channel switches independently on daily or weekly schedules that can reference absolute clock times or relative offsets from sunrise/sunset, making it suited to outdoor lighting, security lighting and building automation where natural light levels dictate switching times.

Designed for installation in consumer units, distribution boards and DIN rail enclosures, the SC 28.23 pro4 occupies two module widths (approximately 36mm) on standard 35mm DIN rail. The unit is programmed via iOS or Android app over Bluetooth, eliminating the need for physical buttons or complex menu navigation on a small screen. The LCD display shows current time, active channel states and next scheduled switching event, giving instant confirmation of programme status without opening the app.

The zero-crossing switching technology detects the mains waveform and switches only when voltage crosses zero, minimising inrush current and electromagnetic interference. This makes the SC 28.23 pro4 compatible with LED lighting loads up to 600W per channel, significantly higher than the typical 100-200W limit of mechanical contactors. The 10-year lithium battery reserve maintains programme memory and real-time clock through mains outages, so schedules resume correctly after power restoration without manual intervention. The unit is manufactured in Germany by Müller and carries a rated switching life of 100,000 operations per channel.

Product Specification Sheet

Product Manual

What is astro programming and how does it work?

Astro programming uses GPS coordinates to calculate local sunrise and sunset times throughout the year, updating daily to match seasonal variation. You set switching events as offsets from these calculated times (e.g. '30 minutes before sunset', '15 minutes after sunrise') rather than fixed clock times. This is useful for outdoor lighting that should activate when it gets dark, regardless of season.

Can each channel run a different programme?

Yes. Each of the two channels operates independently with its own switching schedule. Channel 1 could run garden lights on sunset-to-midnight, while channel 2 runs security lights on a weekly timer, for example.

What load can each channel switch?

Each channel is rated at 16A resistive load (approximately 3,680W at 230V). For LED loads the zero-crossing switching allows up to 600W per channel. For inductive loads like motors or transformers, refer to the datasheet in the Downloads tab for specific derating guidance.

How is the unit programmed?

Programming is done via the Müller SC pro4 app for iOS or Android, connecting to the time switch over Bluetooth. The app allows you to set daily/weekly schedules, astro offsets, random switching and holiday modes without navigating menus on the LCD screen.