Modular headrail-mounted power system for smart blinds

Customers of Automated Shading Products Demand Power Options

The option to use a power source other than mains-derived power (e.g. primary batteries, manually-recharged secondary batteries, or solar-charged secondary batteries) is essential for many potential purchasers of automated shading products. Fortunately, the hottest products in today’s automated shading market—headrail-mounted automation devices for wand-operated horizontal blinds—have a power consumption that’s low enough to enable the use of alternative power sources.

Unfortunately, conventional approaches to providing power options for such devices suffer from significant limitations.

The Problem with Conventional Battery Holders and Battery Packs

Of course, the most significant limitation of primary and secondary battery power is the need for periodic replacement or recharging.  This limitation is exacerbated if the batteries (or charging port) are difficult to access.

Another potential limitation of batteries is the size and weight necessary to provide a reasonably long run time.  This is generally not an problem for products with a long, tubular form-factor (which have plenty of space to accommodate a linear battery stack, e.g. of several AA-sized batteries), but can be an issue for other product form-factors.

The Problem with Conventional Solar Power Panels

A conventional solar power source for an automated shading product consists of a window-mounted solar panel and a cable connecting the panel to the product.  Unfortunately, such cables are unsightly, and the need to install the panel and cable is a significant drawback.

Our Solution: a Modular Power System

We’ve developed a modular power system for headrail-mounted window coverings which mitigates the above-described disadvantages.  Two of its key features are (1) bilaterally symmetrical power connectors, and (2) an outward-facing photovoltaic power module mounted on the room-side of the window covering.

Bilaterally Symmetrical Power Connectors

Our market research shows that battery power for a smart blind product is best provided by a separate optional battery module, rather than by including a battery holder inside the main product housing.  This is advantageous because it reduces the size and cost of the main product in applications where the customer will use hardwired or solar-charged power instead of battery power.

To facilitate the use of a separate battery module, our modular power approach equips the main product with bilaterally symmetrical power connectors, as shown below on our IntelliBlind™ smart miniblind actuator:

This enables a power source—which can be a battery module, hardwired cable, or other device—to be attached on either side of the main product. This configuration can power products which can be installed on only one specific side of the headrail (as is the case with virtually all headrail-motorization devices). The ability to accommodate both right-side and left-side installations is shown below with IntelliBlind™ and a battery module:

Our reference design uses magnetic spring-loaded (“pogo-pin”) power connectors, which are self-aligning and require no insertion force, for exceptionally easy coupling. The battery module is also equipped with a cup magnet to hold it to the host blind’s headrail:

This enables the battery module to be instantly and effortlessly attached and removed for battery replacement.

Advantages

In addition to avoiding the need for a battery holder inside the main product housing (reducing size and cost in applications where battery power won’t be used), the use of bilaterally symmetrical power connectors provides six key advantages:

• When hardwired power is being used, it allows the power cable to be connected on either side of the main product to accommodate different blind designs
• It eliminates the need for a cable when battery power is used.
• The magnetic mount and self-aligning magnetic connectors enable the battery module to be instantly and effortlessly attached and removed for battery replacement.
• The weight of the battery module isn’t borne by main product, eliminating the need for locking connectors that would be required if the battery module were mounted underneath the main product.
• Because the battery module is mounted to the side of the main module, instead of underneath it, there is no risk of interference between the battery module and the blind’s slats
• The battery module’s horizontal form factor harmonizes with the shape of the headrail.

Room-Side Photovoltaic Power Module

Photovoltaic power is an appealing alternative to mains or battery power for many applications, so many smart blind products include optional window-mounted solar panels.  However, mounting a solar panel to the window adds another step to the installation process, and so does the unsightly cable between the solar panel and the product.

To overcome these disadvantages, our proprietary solution uses a headrail-mounted, outward-facing photovoltaic panel located on the room side of the blind. The approach is illustrated with our IntelliBlind™ reference design:

This configuration might seem disadvantageous because the blind will typically be fully closed when daylight is the brightest, drastically reducing the panel’s average power output.  However, this reduction in power output is mitigated by a key characteristic of venetian blinds: the shading they provide is direction-dependent.  Specifically, when a blind is almost fully closed, it can still admit a substantial amount of light in the direction parallel to the slat orientation.

For example, a blind provides maximum shading against direct sunlight when the slats are tilted with their indoor edges upward, but this orientation directly admits solar irradiance reflected upward from the ground, as well as direct sunlight reflected diffusely from the slats. This can be seen as a bright area on the ceiling immediately above a blind that is fully closed to block direct sunlight. We mount the PV panel close enough to the slats to capture this irradiance “leakage”. There is a cosine loss because the leakage impinges the panel at an oblique angle, but the panel still generates substantial power even when the blind is almost fully closed against direct sunlight—and far more power than an inward-facing panel intended to harvest the ambient illumination in the room.

Optionally, our proprietary blind control algorithm adjusts the blind’s fully-closed tilt setting—and therefore the amount of light leakage—to maintain the required average power output over time.

Further, if the blind’s slats are automatically adjusted to maximize glare-free natural illumination (as is the case with our IntelliBlind™ smart miniblind actuator), then the slats will be be mostly open during daytime in the absence of direct sunlight, further lessening the energy loss relative to a conventional window-mounted panel.

Advantages

The room-side PV panel configuration is not well-suited to products which are too power-hungry to be powered by small primary batteries.  However, products that can be powered by AA-sized batteries (i.e., products with an average power consumption in the milliwatt class) are the hottest segment of today’s automated shading market—and our approach is the best way to solar-power such products:

• While the configuration does increase the required panel size, the panel still small enough to be visually unobtrusive and amenable to integration in a headrail-mounted motorization device like IntelliBlind™.
• Because the panel is still small in absolute terms, the additional cost over a still-smaller window-mounted panel is modest.  Further, that incremental cost is more than offset by the elimination of the need for the separate housing, mounting provisions, and wiring/connectors needed for a window-mounted panel.
• Aside from the cost advantages, the elimination of the need for a separate window-mounted panel makes for a much sleeker, easier-to-install product.

Provides Four Power Options

Our modular power system provides a headrail-mounted blind automation device with four convenient power options, as shown below with our IntelliBlind™ Smart Miniblind Actuator:

1. Pure Battery Power

Pure battery power is an appealing option for windows which receive little sunlight and where hardwired power isn’t feasible. As previously described, our modular power system enables an optional battery module which can be magnetically attached on either side of the host device, accommodating various blind designs.

2. Pure Photovoltaic Power

Pure photovoltaic power (with Li-Ion or supercapacitor energy storage) is appealing for windows which receive significant sunlight, and when hardwired power and the need for periodic battery replacement must be avoided. Our room-side photovoltaic power source can be in the form of a module integrated into the host device (either removably, as is the case with IntelliBlind™, or permanently), or it can be separately attached to the headrail via one of the bilaterally symmetrical power connectors. This eliminates the need for a window-mounted panel and the associated wiring, reducing cost, facilitating installation, and making for a sleeker appearance.

3. Hardwired Power

Hardwired power is necessary on windows which receive little sunlight and when the need for periodic battery replacement must be avoided. Our bilaterally symmetrical power connectors enable hardwired power to be fed from either the right or the left side of the host device, facilitating left-side and right-side mounting, respectively, of the host device on the headrail.

4. Battery Plus Photovoltaic Power

In some product applications, neither battery power alone nor photovoltaic power alone will provide sufficient run time. Accordingly, many power-harvesting ICs are designed to be able to use a photovoltaic source to extend a primary battery’s operating life. Our IntelliBlind™ reference design uses such a power-harvesting circuit, and our modular power system makes this kind of solar “battery extender” operation especially convenient for the user.

Applications

Our bilaterally symmetrical power connectors are advantageous for any blind-motorization device that can be battery-powered, such as our IntelliBlind™ smart miniblind actuator shown above. Our room-side PV panel is applicable to any device mounted on the headrail of a venetian blind that has an average power consumption in the milliwatt class, such as IntelliBlind™ and the headrail-mounted variant of our IntelliLux™ smart sensors.