In terms of blind control, there are two key types of blind motor, that make up the majority of the units sold in the UK and further afield:
The question is, when buying automated blinds, when should you consider using wired control by relay?
Firstly, let's rule out scenarios where relay operated blinds are not suitable:
If you wish to control wirelessly, by handset or by wireless wall switch, then relay operated motors aren't for you. You can't control a relay operated blind wirelessly.
Furthermore, if you are looking for an easy and low cost method of controlling blinds by mobile app, and by voice assistant - then the majority of the solutions on the market are low cost hubs which a user can connect to via WiFi or mobile (3G/4G) from their mobile phone, tablet or laptop using an app or web interface. Examples of these hubs include Louvolite One Touch Home Hub and Somfy TaHoma Switch.
Commands initiated from the app or web interface are translated by the hub into a radio signal which is received by the blind. These hubs can sometimes be connected to voice assitants such as Amazon Alexa and Google Assistant, allowing you to initiate a blind operation by using a voice command. Again, this command finds its way to the blind as radio signal. In short, radio motors, rather than relay motors are used with these types of low cost hubs.
That's not to say that you can't control a relay operated blind with a voice assistant. But this is more likely to be a bolt-on feature of a wider home automation system, which we'll talk about below.
If you have a smart home system, or if you are buying blinds for a commercial property to integrate with a building management system, then the method of linking the motors to the central home automation system or BMS depends on the type of blind motor that you are using.
Let's summarise the method by which both types of motor are controlled in this scenario:
Whilst a radio operated blinds can be controlled by solely by handsets and wireless wall switches, a relay operated blind can only be controlled by a wired controller. So if you are considering relay operated blinds, it is likely that you are buying them to integrated with a smart home system, or with a building management system.
The key advantage of a relay operated blind system is its reliability. The control method is wired, meaning there is a line of cable from the relay unit that is switching and controlling the blinds to the blind itself. There is very little that can go wrong between the relay unit and the blind. Some home automation technicians that I have worked with in the past will not work with wireless technology and will only work with wired devices, as they worry about wireless technologies being unreliable due to interference and range issues.
As intimated above, wireless technology does have a finite range. Typically if you are controlling radio operated blinds from smart home system, the bridge would be positioned in the same location as the home automation system hardware. Where home automation systems or BMS systems are installed, these typically have their own room or cupboard somewhere within the property - it might be in a loft, or in a "comms" room or office. In larger properties, the blinds themselves might be a considerable distance away from the bridge device. Although the range of these devices is typically extremely good, at the planning stage, some home automation technicians would rather avoid the risk of a device failing. 230vAC wired motors are often used because a cable can simply be laid from the blind controller to the blind itself providing a reliable line of control over distance.
Relay operated blinds are generally a lot lower in cost. Firstly, they do not include a radio receiver which reduces the cost per unit. Also, radio operated motors generally use the propreitory radio protocol of the manufacturer. In the case of larger brands like Somfy, this radio protocol (RTS) is used accross many different devices. This protocol and excellent connectivity is a key part of their brand. It has an associated R&D cost but also enables them to charge a premium for their brand and for their radio motors.
Relay motors are generally a simpler mechanism and standardised accross the many different providers. This simplicity and the competition between motor manufacturers also results in lower prices for this motor type.
Whilst relay motors are reliable, simple and low cost - there are additional considerations that you will need to take into account when buying blinds with this type of motor. I'll out-line these considerations below. These factors may (or may not) be considered as disadvantages depending on where exactly you are in the planning/rennovation process and what you are trying to acheive.
The motors are lower cost BUT:
Whether these additional costs outweigh the savings made by a lower cost motor will depend to a certain extent on the costs being charged by your home automation technician for the blind controls and the labour required to implement it. At the DIY end of the market, the costs of the hardware may be lower and some of the labour may be "DIY" and therefore no cost.
You'll need to plan ahead:
None of the above is necessarily a disadvantage.. unless of course you are reading this for the first time at a stage in your build where the plastering and decoration has been completed!
There is some functionality that will not be available with relay operated motors, versus radio motors which are often more inteligent:
As mentioned at the start of this post, if you are considering a relay operated motor, then it is more than likely that the reason you are doing this is because you wish for them to be controlled by a home automation system or a BMS. And the traditional and most reliable way of doing this is using relay operated motors.
Somfy Radio motors (either 230vAC, 12vDC or battery) can be integrated with smart home systems using bridge devices such as the RS485 RTS interface or the Dry Contact RTS Transmitter. The RS485 RTS transmitter has 16 channels so can control up to 16 RTS devices, or 16 groups of RTS devices. The dry contact RTS transmitter is single channel only, so is great for controlling one blind or one group of blinds. However, as mentioned above, many smart home technicians prefer to use traditional wired (relay) technology over wireless (radio) technology to eliminate the risk of interference and over-come range concerns.
Whilst we have outlined some potential cost, planning and functionality considerations relating to relay operation above - these are not necessarily disadvantages if you have the correct budget (or DIY capabilities), if you have planned early and planned correctly and if your smart home system is able to provide centrally some of the intelligence that is not incorporated in the motors themselves.
In summary, relay operated electric blinds are reliable and low cost. They use technology that is familiar to most smart home or BMS technicians and which can easily be incorporated into the vast majority of smart home systems and BMS.