Micro Solar Energy System: Under Cabinet LED Light

As in many kitchens, we have lights under the cabinets to light the kitchen counters. These lights are powered by 110v (the grid) and are fluorescent. They are relatively efficient, but they are all wired to the same switch, and they all come on at once. They are too bright for the gentle "ambient light" my wife and I like to have in mornings and evenings, when we are just making coffee or drifting in and out of the kitchen to visit the sink or refrigerator. We wanted a light that was solar powered, efficient, based on white LED technology, and much less bright. With a little effort, we built one! This page is for the do-it-yourself solar light enthusiast. Anyone could build one of these lights! While it does not have to be solar powered, simply recharging the batteries from a solar panel is all it takes to keep the lights "off the grid." This project is an excellent starter project for a small solar system, and it would make an excellent school science fair project as well! Here are the details:

The light has 3 white LEDs, with a pull switch used to turn it on an off. The light body is free to rotate, giving the light the ability to be directed through a 180 degree arc. Power is 4.5v DC, and the 3 LED's draw 20ma - yes, twenty milli-amps. The entire light, including switches, materials, LED's, and even the wire connecting the batteries to the light the light cost under $25 !!

It's not as bright as the 40 watt fluorescent lights next to it by any stretch, but it is impressive how much light can be produced by running only one tenth of a watt through these little solid state lamps.

The LED lamps are powered by three Ray-O-Vac D Alkaline rechargeable batteries, charged weekly using a small (140 watt) 12v to 120v inverter powered by a solar panel and battery, and a Ray-O-Vac battery charger. The system has worked flawlessly. 90% of the time my wife and I use this light source instead of turning on the five 20 watt florescent lighting fixtures. In other words, we are using 1000 times less energy to produce the light we need for many of the activities in the kitchen.

This single project enabled us to dramatically reduce the use of a number of 120v grid powered lights. While the 120v lights are still available, the solar LED lights are convenient, and they are almost always enough. They are simple, easy to build, cheap, and hundreds of times less power-hungry than their 120v counterparts.

Are you ready to build your light? Let's begin!

  1. Understanding the design, and theory of operation

    The design of the light is extremely simple. The light itself is constructed of a wooden dowel. The LED's are attached to the dowel, using electrical tape. One is attached in the middle, and the other two are attached at each end. The wire runs the length of the dowel. The dowel is then placed underneath the cabinet and suspended from the two cup hooks. That cup hooks should be fairly loose, allowing the dowel to be rotated. This will allow the light to be aimed in the most effective direction.

    The light is powered by three rechargeable D cell batteries. The LED's require 4.5 volts to operate. The three D cell batteries provide this when they are connected in series. The maximum current the LED's can tolerate on a long term basis is 20 ma. Three freshly charged D cells will drive more than that much current through the LED's, shortening the life of the LED's. To control this current, a resistor is inserted between the batteries and the light. Here is a nice page with more information. For safety, a small fuse is also installed.

  2. Choosing a location for the light

    The best place to install the light is in the work area that does not require bright light, but is frequently used. I usually set my light up close to appliances I use early in the morning, such as the coffee maker. These lights are not really bright enough for complicated cooking tasks, but they might be enough for loading a dishwasher, and they are certainly bright enough to help you find the 'fridge!

  3. Assembling the light

    After you have determined where the light will be, measure the length of the space and cut the dowel to fit, if necessary.

    Now begin to wire the light by taping the wire down the length of the dowel. Flatten it out (no twists) so the conductors do not "switch sides" as the wire travels down the dowel. Tape the wire to the dowel in three places: the middle, and both ends. Wrap the tape around the dowel an inch or so from the ends of the dowel. The wire should end at the end of the dowel on one end, and the remaining wire should continue for several feet past the other end of the dowel.

    Next prepare the wire for soldering on the LED's. Examine the wire closely. If it is "zip cord", it will have two conductors joined together by the insulation surrounding them. One of the two conductors will be identified in some manner. The wire will be a different color, or have a colored stripe on the insulation. This will be the "positive" wire. Each LED will be attached between the positive and negative wire. In the next step, you will cut through the insulation exposing the bare wire at each point that an LED will be attached, enabling the LED's to be soldered to the wire.

    Beginning at the end of the dowel with the long piece of wire extending from it, cut into the center of the wire about one inch (closer to the middle of the dowel) from the electrical tape. Carefully pull the two individual wires apart until they are far enough apart to stick your finger comfortably between them. Do this step at each location you are planning on having an LED. At the other end of the dowel, simply separate the two wire for about 1/2 in. (1 cm.).

    Take a moment to check your work before the next step. You should have a dowel that is the right length to fit easily in the space you have chosen. It should have a wire taped to it, with one end of the wire stopping right at the end of the dowel, and the other end extending past the end of the dowel by at least 1 foot (30 cm). The wire should be laying flat on the dowel, with no twists. At every place along the length of the wire where you are planning on attaching an LED, you should have cut through the insulation and separated the conductors a bit. There should be no bare wires at this point. Ready for the next step?

    The conductors in the wire must be exposed so the LED's can be soldered onto them. The insulation must be cut away from the wire to allow this. There are two possible ways to accomplish this:

    1. Cut the wire completely at each LED position, and strip the insulation off the cut ends.
    2. Carefully "carve" the insulation away from one side of the wire, leaving the conductors intact. If you have patience, carve all the insulation away from 1/4 in (1 cm.) of the wire - both conductors.

    If you choose option 1, your soldering job will be cleaner, but you may need three hands to hold everything while soldering. You will need to hold both ends of the wire, the LED, the soldering iron, and possibly the solder! If you have a helper, this is probably the better technique.

    If you choose option 2, the wire itself will not be cut, so you will be able to hold the LED onto it with one hand and hold the soldering iron with the other hand. You can probably assemble the light without a helper if you choose option 2. One possible problem with this technique is that any remaining insulation on the back side of the wire (if you could not cut it completely away) will probably melt during the soldering, so the finished work may look a little messy.

    At the end of the dowel where the wire stops, simply trim the insulation back 1/4 in. (1/2 cm.) so the bare wire is exposed.

    It is time to prepare the LED's for soldering. Handle the LED's with care. If you happen to develop a charge of static electricity, and touch a LED, it could be "zapped!" That means no petting the cat during this next activity!

    LED's have two wires (also called "leads") coming out of the bottom, and lens on the top that focuses the light. Look closely at the leads - one is longer than the other! Not by much, but there definitely is a difference. The longer lead will be attached to the positive wire on the light, and the shorter lead will be attached to the negative wire. It's a good idea to mark the LED with a black felt tip marker (just a tiny, tiny dot on the bottom!) so you know which lead is which. Remember whether you marked positive or negative!

    Before soldering the LED's onto the wires, bend the leads on each LED to make the job easier. Bend the leads about 1/4 inch (.5 cm.) from the bottom of the led. Bend them in opposite directions, until they are at 90 degrees from their original position. You should be able to gently set the LED on to the wires you stripped, with each lead going to its respective wire. It won't say there, of course - that is what the solder is for. Don't bend the leads on all your LED's yet, or you will loose track of which lead is positive! Bend them one at a time, right before you are ready to solder them, and keep track of which lead is which.

  4. Assembling the power source

    I used a battery holder designed for 6 D cells like this one available through this page, but you could also use a holder like this which looks like it will be a bit more manageable.

    While both of the holders listed above are designed to hold six D cells and provide approximately 9 volts, I added an new connection to enable three D cells to be used resulting in the 4.5 volts the LED's work with most efficiently. My original intention was to have two parallel sets of 3 D cells in the holder, enabling twice the run time of three cells, but the three cells ran so long I never found the need to install all six. If you wish, you may simply purchase a holder for 3 D cells. There is nothing magical about D cells, either. I wanted the longest possible time between charges, so I chose the largest readily available rechargeable alkaline battery i would find. C cells and even AA cells would work with more frequent charges or less frequent use.

    Let me add here that I strongly recommend rechargeable alkaline batteries for this project, and in fact, none of the resistor calculations will work for other types of batteries. Be especially wary of NiMH (Nickel Metal Hydride) batteries, as they "self discharge" quite rapidly, and you will be charging them more frequently than you would like.

    The Ray-o-Vac "Renewal" rechargeable Alkaline batteries I used are available in hundreds of location and cost approximately $3 (or less) each. You need a RayoVac Renewal 8 position battery charger as well. There are always deals available on batteries. Shop around. This site advertises a free charger with every 12 Renewal C size batteries. As I said above, C batteries would be fine for this application. They have roughly 1/3-1/2 the capacity of D cells, so you would need to charge them more often, but would otherwise work perfectly.

    Finally, if you just feel the hassle of monitoring and charging batteries is too much, consider using standard D alkaline cells and simply replacing them when the lights get too dim. You may find that the batteries will last for months and the convenience will be worth the long-term cost of using non-rechargeable batteries.

    It's a good idea to build the lights and test with regular, disposable alkaline batteries. Make the decision to purchase rechargeable batteries and a charger after you have used the lights for a full battery cycle, and have some idea what your needs area.

  5. Testing
  6. Installing the switch
  7. Installing the light and power source
  8. Testing and troubleshooting
  9. Maintenance

I am considering building a kit of parts for this light. I would offer the kit for sale to do-it-yourselfers so they could build the lights without having to locate all the correct parts. If you would be interested in such a kit, please let me know by clicking on the button below. Don't worry, there is no tracking of who you are, I am just counting how many people would be interested.

David "Photons, not Neutrons" Butcher


Disclaimer

This information is provided in good faith but no warranty can be made for its accuracy. Follow these suggestions at your own risk! If you notice something incorrect or have any comments, or information to add to these pages, feel free to mail me.
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David Butcher
davidbu"at"www.los-gatos.ca.us
Tel (408) 978-5495
Los Gatos, California 95030

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