Proposed LED/wired IoT standard can reduce energy use (part 1)

Article By : Glenn Weinreb

Using low-voltage wiring to connect LED lighting can cut energy consumption, reduce installation costs, and provide better control of lighting. Standards for communication and wiring will be needed.

In R&D initiative looks to solve energy and climate problems, I presented a strategy for reducing energy consumption on a massive scale, something called Manhattan 2. While switching to LED lighting certainly helps reduce power consumption, we can do more. You see, each conventional LED bulb has its own AC/DC power supply, which is needed for bulbs to be compatible with AC wiring and lighting fixtures with sockets designed 100 years ago. Having individual power supplies not only adds cost, it decreases efficiency and limits energy savings. A different system, one that distributes DC, would mean that each housing unit would have a shared AC/DC power supply.

In 2019, I co-founded the non-profit Manhattan 2 (Ma2), which proposes to reduce carbon emissions, and wrote a book that explains how it works. Ma2 is currently designing a 2000 square foot house-like test site to allow researchers to test devices within a system. If we start with a blank piece of paper and design all devices within a building from scratch and create standards that define how they interconnect, we can reduce energy consumption by a variety of techniques. Also, Ma2 is working on a standardized plug-and-play system for attaching solar material directly to building surfaces. A proposed standard, presented here, could further reduce energy use in new or renovated homes.

Proposed standard for LED lighting and IoT
The new wiring standard will be for interconnecting smart LED light bulbs, wall light switches (on/off/dimmer), occupancy sensors, thermostatic temperature sensors, fans, duct dampers, thermal blankets that unroll over windows, solar PV arrays, and other IoT devices. We’ll focus here on the LEDs.

The proposed wired connection provides power to devices, is 99.999% reliable, allows device electronics to sleep while not in use, and uses $1 microcontrollers. Several IC suppliers offer tiny processors that manage network communication, provide multiple A/D channels, control LEDs, and control motors. In our proposed system, the electronics move from the bulb to the socket, and we connect the socket to the network over a wired connection.

We end up with full on/off/dimmer control over each bulb. Subsequently, we can adjust lights in response to occupants entering or leaving a room, occupants watching TV (dim lights), or sunlight entering a room. This is similar to smart Bluetooth light bulbs, yet involves lower cost and better reliability.

Typical single-family home

Figure 1 shows a typical 110/220 VAC tree topology wiring diagram. In our proposed system, outlets and oven, shown on the left, stay the same. Light bulbs and light switches, shown on the right, are replaced by our new fully-automated network.

textFigure 1 A low-voltage network for LED lighting is easier to install than one for 110/220 VAC wiring.

Building requirements for low-voltage wiring (30 V limited to 750 W) are less than that for higher voltages such as 110/220 VAC. In some cases, lower voltages don’t require placing wires in metal conduits (pipes).

As for the cost, 1000 ft. (304.8 m) of 4-conductor 18 gauge wire costs about $160. The electronics that drive an LED bulb cost approximately $2. The cost of electrician installation time is, however, about $75/hr, including overhead. That’s the primary cost. If we reduce labor with easier wiring, we can provide a smarter system at lower cost.

Eliminate a bulb’s AC/DC converter

The design of today’s LED light bulb places a power supply that converts 110/220 VAC to low-voltage DC (Figure 2) in the bulb’s base (for a schematic click here and here.) These electrical components are costly, tend to fail before the LEDs, and consume energy.

textFigure 2 As this teardown shows, LED bulbs contain power-conversion electronics in the base.

If we remove the semi-transparent plastic dome atop a typical light bulb, we see an array of LEDs (Figure 3). The 15 yellow devices in this photo are the actual LED surface mount (SMT) components that emit light.

textFigure 3 A typical LED bulb contains numerous LEDs to produce enough light.

Removing the power electronics from an LED bulb opens opportunities for new shapes and sizes. A typical 120 VAC bulb has a 26 mm diameter screw base. Our new standard would need a different diameter because the two systems wouldn’t be electrically compatible. We can then shrink the bulb. Figure 4 shows a typical R19 bulb on the left and an R30 flood lamp on the right, both in old 110/220 VAC style and new proposed LED-only style. The base of the new LED bulbs is shown in the traditional form factor but would change.

textFigure 4 Removing the power-conversion electronics from an LED bulb could shrink its size.

Within a bulb, several LED SMT devices are arranged in series, in a string and then driven with a current source, such as 160 mA of current that puts anywhere between 15 V to 22 V across a string of LEDs. In some cases, there are multiple strings in parallel; two strings of 10 devices each with a total of 20 devices inside each bulb. Modulating the current dims the bulb using pulse-width modulation (PWM) turning current on and off 10,000 times a second. For 10% illumination, 10 µsec on and 90 µsec off each cycle. The current driver circuit can start with 110/220 VAC or a lower DC voltage such as 48 VDC. The current driver PCB can be in a socket, in a light fixture, or in a module several meters from the bulb, say 1 m to 10 m.

Continue reading Part 2, which looks at the system’s components.

Glenn Weinreb is founder and CEO of GW Instruments and has designed approximately 30 commercial data acquisition and control systems that connect processors to gadgets within a building.

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