Category Archives: Product Choices

Electric Roller Blinds for More-Than-4m-Wide Sliding Doors

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One thing I didn’t pay enough attention to when planning for the electric window blinds was the width of the sliding glass doors. Some of these are more than 4m wide, which is problematic because:

  • A more-than-4m-long roller tube would need to be quite a large diameter to be stiff and strong enough
  • Very few blind fabrics are available more than 4m wide – and they’re expensive

Therefore, it’s generally better to use two narrower blinds instead of one very wide blind. The small gap between them is mostly blocked by the sliding door frame.

The issue then is that I only specified that a single 230V KNX relay be wired to each door location – and it’s not possible to simply connect two 230V blind motors ‘in parallel’ to one relay channel. The reason is nicely explained in this text from Schalk Steuerungstechnik GmbH:

Roller shutters or louver blind motors with mechanical limit-switches must as a rule not be electrically connected directly in parallel, because due to the different motor running times the limit-switches of some motors may be reached while other motors are still running. The motors that are already switched off would then receive inductive voltage at the counter-winding from the motors that are still running, which can lead to destruction of the limit-switches.

There are two main options to overcome this issue:

  • Using blind motors with ‘electronic’ (rather than ‘mechanical’) limit switches, since these don’t suffer from the same limitation
    • This was the approach adopted for the wide sliding door in one of the bedrooms and it has mostly been successful – though the limit settings on one of the motors do tend to ‘creep’ over time and periodically need re-setting
  • Multiple motors can be isolated from each other using relays, installed adjacent to the blinds, that block the induced voltage from a still-running motor from damaging an already-stopped motor

Various companies manufacture suitable relays but the products from Schalk Steuerungstechnik GmbH seem pretty good. In particular, their MGR U2 which can take the output from one KNX relay (or a pushbutton or whatever) and drive two blind motors. Variants are available for 1, 2, or 4 motors and for DIN-rail or ‘flush’ mounting (in a regular back-box, behind a blank cover plate). These do not require an additional permanent live supply and are very competitively priced.

Schalk MGR U2 flush-mounting relay for 2 roller blinds

Roof Blinds for Skylight Windows

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With work on the Outbuildings progressing, it will only be a few months until those provide a large Workshop space which will replace the current use of Bedroom 5 on the Second Floor of the House, which has been temporarily acting as a workshop and ‘shed’. It’s therefore a good time to start preparing for that being used as a bedroom; up until recently little had been done since it was first built and the walls and ceiling were still bare plaster.

Natural lighting for Bedroom 5 comes from two fixed skylight windows deeply recessed into the ceiling which slopes at 11 degrees to the horizontal. They’re tilted towards the North but with them being so nearly horizontal they do receive direct sunlight in the summer months, which can tend to make this room a bit too warm. These windows therefore want ‘blackout’ blinds which exclude enough light for sleeping in this bedroom and which can also be used to block out the summer sun.

Many of the available skylight blinds are designed to be fitted to the wooden frame of opening roof windows from VELUX and similar window manufacturers, where the blind needs to move with the window when that opens and closes. Those are a good solution where the window opens and where they are relatively accessible – such as in a loft conversion. However, they’re not suitable for this installation.

As with all the other ‘windows’ in the House, these skylight locations were wired back to KNX-managed relay controls for 230V electric blind motors, using three-core-and-earth cabling. All but one of the other windows have electric roller blinds (the exception has an electric vertical blind) which rely on gravity and a metal hem bar to operate. With these windows being so close to horizontal, roller blinds need ‘help’ to close – and to stop them sagging.

Previous research to find suitable blinds had failed to identify a good solution. The closest match is blind systems used for genuinely-horizontal ‘roof lights’ or ‘roof lanterns’. Some roof light blinds use ‘honeycomb’ fabric and low-voltage motors and radio controls, which would complicate the automation compared with a simple 230V motor and relay control. Other systems designed for (much) larger roof lanterns had minimum sizes which were slightly too large for these relatively modest skylight openings.

In the end I settled on the Helios RL Wire-guided rooflight system from Umbra Shading for which there is a good range of technical resources explaining how they work. In broad terms, these use spring-loaded wire spools to apply tension to the blind fabric and to pull it down as the motor unwinds. Local installer Butterley Barn Interiors supplied and installed Helios RL blinds with enclosed top and bottom boxes to conceal the roller tube and spring boxes.

Umbra Shading Helios RL blind in sloping ceiling of Bedroom 5

There’s a bit of a gap at each side of the blind, where the guide wires are. For an even better blackout effect that could be covered with an angle-section trim strip