Hands On: Working with LED Ribbons Part 1 – Creating Residential Under Cabinet Lighting
Contributed By Digi-Key's North American Editors
Editor’s note: LED lighting is an ideal DIY project: it’s fun, satisfying, and rewarding. Part 1 of this two-part series will show how to implement under cabinet lighting. Part 2 will show how to swap out the microwave oven lighting to match the color temperature.
LEDs are replacing incandescent and fluorescent lighting in a variety of existing applications, but the choices for under cabinet lighting are remarkably few. However, for the DIY enthusiast, surface mount technology (SMT) LEDs supplied pre-soldered to long strips and ribbons are ideal candidates for creating custom lighting applications because they’re small, lightweight, and they draw relatively little power.
LED strips have other advantages too. They’re easy to work with because they cut easily with a pair of sharp scissors, and they have adhesive pre-applied so they stick almost anywhere. Also, the LEDs run off a 12 volt power supply making them safe to work with.
This article chronicles a hands-on project to create under cabinet lighting in a residential kitchen using just one 5 meter length of LED ribbon, an RF remote controlled dimmer, low-voltage connectors, and a 12 volt switching power supply. The resulting compact lighting system creates a lighted counter area that is both practical (it raises the illumination level of a daily work area) and attractive.
“Honey, can you…?” The origin of many maker projects
As with many maker projects, this project started with a spousal request. Under cabinet lighting developed for a previous residence was sorely missed in the current domicile. The kitchen counter needed more light. The previous project, developed more than ten years ago, had required the use of individual one foot, encapsulated LED strips with the LEDs spaced about an inch apart in each strip.
A custom lighting controller used a pulse code modulated (PCM) motor control board based on a low-cost microcontroller with special code written by a contractor for $90, and a laptop power supply brick provided the required 12 volt power. The wiring for this earlier system was excessively overdesigned using wire and connectors capable of carrying ten times more current than needed.
What a difference ten years makes.
First, many vendors now offer off-the-shelf LED under cabinet lighting in a variety of forms. After investigating them, they fell into two categories:
- Inexpensive LED under cabinet lighting systems sold in big box home improvement stores incorporate too few LEDs to provide bright, even illumination, and they lack good dimming controls.
- Beautiful luminaires sold in specialty lighting stores that cost many hundreds of dollars.
For an engineer or maker, the lack of decently priced under cabinet lighting alternatives makes this is an ideal DIY maker project and a welcome challenge.
Start with the LEDs
The advent of SMT LEDs has greatly expanded the possibilities for lighting applications. One very interesting development is the introduction of LED strips and ribbons such as JKL Components’ ZFS-155000-CW LED flex ribbon, which is supplied as a five meter ribbon on a spool (Figure 1). The ribbon is 15 millimeters wide, and there are 1200 LEDs mounted on the ribbon.
Figure 1: SMT LED ribbons, like this dual-row ZFS-155000-CW LED flex ribbon from JKL Components, make it easy to design custom under cabinet lighting. (Image source: JKL Components)
These continuous LED ribbons incorporate a double row of SMT LEDs and SMT resistors so that a simple 12 volt power supply is all that’s needed to light them. The double row of LEDs on this particular ribbon produces twice as much light as single row LED ribbons. The ribbons are made from individual flexible LED strips soldered together to form one long ribbon. They’re also very thin, allowing for compact, nearly invisible under cabinet installations.
One terrific feature of these ribbons is that they can be cut to length with a simple pair of scissors. There are cut marks printed along the ribbon every 25 millimeters (mm), so there’s plenty of flexibility in sizing individual strips cut from the longer ribbon. The under cabinet lighting project discussed in this article used 90 centimeter (cm) strips cut from the reel, which contained enough ribbon for five such strips. The entire five meter strip has a current consumption of 4.3 amps (A), so each 90 cm strip requires approximately 774 mA. Call it 1 A, for some margin.
The LED strips are essentially flexible printed circuit boards (pc boards). The 12 volt power traces supplying current to the SMT LEDs run the full length of the strips. Cutting the strips leaves exposed copper pads at each end of the strip for attaching wires. The copper pads easily take solder but be sure to use flux to clean them before soldering.
With pads on each end, it’s easy to wire from one strip to the next using a pair of short wires. This project took advantage of that feature to simplify the wiring.
Aluminum substrate provides many advantages
The adhesive applied to the LED strip’s underside allows the strips to be attached directly to the underside of the cabinet. However, doing so has many disadvantages:
- It’s hard to replace a strip glued directly to the underside of the cabinets if the illumination drops due to LED failure.
- Wood and plastic cabinetry provide no heatsinking for the LEDs if the strip is directly attached.
- Gaps between cabinets provide places where the LED strip will have no support.
Using an aluminum bar as a substrate for the individual LED strips solves all three of these problems. Five bars measuring 36 by 1.25 inches and about an eighth of an inch thick served as the LED strip substrates for this project. Because the underside of the LED strips is insulated mostly by the adhesive, an insulating layer of inch-wide, amber polyimide tape, such as 3M’s 1205, was applied to the aluminum. This serves as extra insulation to eliminate any possibility of shorting, and to make it easier to remove the LED ribbon from the aluminum if replacement is required.
Mounting the aluminum bars also takes some thinking. The easiest approach is to drill mounting holes in the aluminum bars. However, several holes will be required to prevent sag. The approach used in this project employed drilled aluminum extrusions with a shallow “Z” cross section that act as clips for the aluminum bars. These extrusions are sold as heavy-duty picture hangers from art supply houses and they work very well in this application.
Selecting the power source and the dimming method
With the LEDs selected, the next step is to select a power source. The entire reel of LEDs draws a little less than 5 amps, so a small switching supply like TDK-Lambda’s LS75-12 12 volt, 75 watt power supply is more than enough to serve this project’s requirements. The switching supply’s high efficiency means it will not generate much heat. That’s important because the power supply will be mounted and closed up inside of a cabinet above the kitchen’s microwave oven, and plugs into the same AC power outlet.
The switching power supply provides reliable 12 volt power, but has no dimming capability. Dimming required a custom design in a previous under cabinet lighting project a decade earlier. Things are no longer that complex. Inexpensive ready-made remote controlled dimming modules for 12 volt applications are now available off-the-shelf.
Case in point: The JKL Components’ ZCTR-08 wireless LED remote controller (Figure 2). This 2-piece set includes a tiny inline PWM controller that’s placed between the power supply and the LEDs, and a small handheld RF control module with on/off and dimming control buttons.
Figure 2: The ZCTR-08 is an RF-based LED remote controller designed specifically to dim 12 volt LED lighting systems. (Image source: JKL Components)
Because this controller uses RF instead of infrared communication, line of sight is not required, allowing the dimming module to be installed inside the cabinet next to the power supply.
Wiring’s not so simple
Every kitchen configuration is different, so each under cabinet lighting system requires a different wiring plan. For this project, two of the 90 cm LED strips would be mounted on one side of a central microwave oven, and three strips would be mounted on the other side. The power supply and dimming module would mount above the microwave oven.
Each strip draws a little less than 1 A, so one leg of the main power distribution tree would need to carry nearly 2 A, and the other side would carry nearly 3 A. Consequently, the wiring distribution plan called for heavier cable to supply the junction boxes, one on each side of the installation. The heavy cable would enter a junction box mounted under the cabinets on opposite ends of one kitchen wall. Smaller cables would exit the junction boxes to supply the individual LED strips on each side of the kitchen.
On one side of the installation, two LED strips would be physically mounted end-to-end, using the internal wiring feature of the LED strips mentioned above to jump from the end of one strip to the next, eliminating an extra run of cable from the junction box.
For the electrical junction boxes, two 1590B die cast aluminum enclosures from Hammond Manufacturing were used. These enclosures are ideal for this sort of application. They’re small, rugged, inexpensive, and easy to drill and machine with hand tools. A medium sized hole drilled with a step drill provides the entry point for the large cable from the power supply, and a small hole drilled at one end of the enclosure provides the exit hole for the two smaller cables supplying power to the LED strips (Figure 3). A terminal strip inside the enclosure connects the large power cable to the two smaller distribution cables.
Figure 3: A die cast Hammond Manufacturing 1590B enclosure makes a simple, easy-to-use electrical distribution box. The figure shows the aluminum enclosure bolted to the underside of the kitchen cabinet. The heavy cable connects to the wireless LED dimmer module and the two smaller cables supply power to two of the LED strips through JST connectors. (Image source: Steve Leibson)
The block diagram for the entire system shows the 12 volt power supply going to the LED strips (Figure 4).
Figure 4: The LED lighting project system block diagram shows the complete wiring diagram for the system from the 12 volt power supply to the LED strips. Note that power flows through the top, left-most LED strip to supply a second LED strip wired in series. (Image source: Steve Leibson)
The heavier power cables from the power supply to the distribution boxes were approximately 10 feet long. To prevent a voltage drop over that run, 12 gauge red/black speaker wire was used. That’s probably overkill in this application, but the wire was on hand.
Connecting from the junction boxes to the LED strips presented a more complex choice. The 90 cm LED strips were mechanically designed to be easily replaced, which meant that the electrical design should also permit easy disassembly and reassembly by using connectors.
Most of the connectors between the two junction boxes and the LED strips would carry less than 1 A, but the two LED strips wired in series called for almost 2 A through one connector. This project required reliable, inexpensive connectors and JST’s RCY Series with a 3 A current rating exceeds these requirements. This project uses cable assemblies based on JST SYR-02T RCY connector receptacles, SYM-001T-P0.6 male contacts, SYP-02T-1 RCY connector plugs, and SYF-001T-P0.6 female contacts. These compact, bright red connectors appear in Figure 3 above. JST’s RCY connectors are commonly used for low voltage battery power connections in many hobby and maker applications.
Reliable, inexpensive, prewired connector and cable assemblies with the proper current rating, like Adafruit’s 2880 cable set, are also commonly used for low voltage battery power connections in many hobby and maker applications. They would have been ideal for this project as well.
Let there be light
Drilling holes, bolting all of the components in place, and wiring everything up required a full day’s effort. However, all of the above planning paid off and there were few surprise challenges to overcome. The entire installation is compact and nearly invisible. The first press of the on/off button on the RF remote immediately lit all five LED strips, which also dimmed on command just as planned.
Figure 5: The completed lighting system provides bright, even light, and the fixtures and wire are barely visible. (Image source: Steve Leibson)
Best of all: the spouse was extremely happy with the final result.
As shown, LED ribbons are a versatile way to bring a lot of lighting to bear in a very compact, easy-to-implement manner. In particular, they are excellent when used to provide long runs of illumination.
The LED ribbon used in Part 1 of this two-part series came on a 5 m spool from which five 90 cm lengths were cut. Part 2 will show how to use the remaining LED ribbon to swap out the microwave oven lighting so it matches the under cabinet LEDs’ color temperature.
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