Solar powered lights are a great idea. They store energy by day then use that energy to light the night. No wiring is needed, they are portable and light weight. Sadly, most are benign “glow lights” and lack the ability to provide real illumination. Also they use very white colored LED's which are good on efficiency but harsh and unappealing. Many use the older Nickel Metal Hydride batteries and have ugly exposed solar panels.
In this instructable we build a self contained, solar powered, real “security light” that is attractive, has hidden solar panels, has a bright, warm color light, uses modern lithium batteries and comes in under $80.
Being a “jack of all trades but a master of none” and fairly new to Instructables, this was an experiment in learning as well as teaching. As I write this, my security solar light has been successfully functioning for days.
The main components are: 1) Light Fixture, 2) Solar Panels, 3) Batteries and 4) Solar Charge Controller.
Step 1: The Light Fixture
The light fixture consists of the housing, the bulb and the socket.
The fixture housing is free with your own 3D printer! Otherwise 3D Hub will make copy for a charge (if using them don't forget there are two files that need to be printed - the house and the support ring). For the fixture housing i've included the Autocad dwg and dxf files. These files were used to create the 3D model in another Autodesk product called 123D Design. This great little program is very versatile yet powerful, and best of all its free! From there an .stl file was created which is the model file used by 3D printer software to generate Gcode for the 3D print.
The bulb is a 3 Watt, 12 Volt, LED, MR16 type. MR16 means “multifaceted reflector” , 16 x 1/8” = 2” Diameter or about 51mm. These bulbs come in a variety of wattages, color temperatures, lumens, beam spreads and dimming capabilities. The lamp used here is a “warm white” (3200 Kelvin temperature) , has a beam spread of about 35 degrees (35-40 is medium flood) and is dimmable. Dimming is important since the Solar Charge Controller is programmable and can be used at various preset dimming levels. This may become important in your region of the country if you have fewer annual hours of sunlight. If there is less solar energy, you could trade off the amount of light for the number of hours of nighttime operation.
Light output is rated in lumens. Lumens is a measure of light just as inches is a measure of length. This bulb puts out around 400 lumens at full power. To gain perspective, a standard old 100 Watt incandescent bulb had a lumen rating of 750 lumens so at 400 lumens, this bulb is roughly equal to a 50 Watt incandescent bulb. Footcandles (fc) is a measure of the amount of light on a surface. This fixture delivers 3fc on the ground with the light up at about 8'. For perspective, most cities require just 1fc minimum of light for commercial parking lots.
Here is a link to the Light Bulb -- $5.99 : http://www.ebay.com/itm/142045890797?_trksid=p205...
The socket ends up free floating in the housing and is only attached to the bulb. Here is a link to the Lamp Socket – $.88 : http://www.ebay.com/itm/MR16-GU5-3-Ceramic-Wire-B...
Also here is a link to a free Android smartphone app that measures footcandles called Light Light Meter Pro: http://www.ebay.com/itm/MR16-GU5-3-Ceramic-Wire-B...
Step 2: The Solar Panels
During the summer in Southern California roughly 10 hours of every 24 hour are night hours and 14 are daylight. Of course this gradually reverses to mid winter when there is 14 hours of darkness which is our worse case condition. We need to divide 14 by 10 to find the ratio of power in to power out for the winter. Given the fact that I intended to use a 3 watt bulb, we will need 1.4 times that input for 10 hours. Since the system really only has full charge on the sunniest days of about 6 to 8 hours the light will probably only work at full capacity about half the night. As I have tested this system for about a week the solar is barely able to keep up for all night and the lights were pretty dim after 9 or 10 hours. Another set of solar panels in parallel would boost the system for any occasion, long days or short , winter or summer.
Solar Panels – $23
The mounting platform is a cutdown piece of pressure treated lumber. Pressure treated lumber is essential for wood exposed to the elements. All holes, screws and cut sides should be sealed water tight to prevent dry rot and termite damage.
Pressure Treated 2x4 – $8
Step 3: The Batteries
The system uses (6) Lithium Ion 18650 Batteries. Each of three are wired in series and the two sets wired in parallel. This setup gives us 12 Volts and about 4 Amps of capacity. You can house the batteries in two holders as pictured or use a single laptop battery and find the positive and negative leads to connect to the system.
Buying one of these , even if you take it apart will come with a battery management system to keep the batteries from over charging or under discharging.
6 Cell Laptop Battery - $20
Battery Holders - $2.20
Using the battery holder method is fine but either way they will need to be made waterproof by spraying some clear sealer on them.
Step 4: The Solar Charge Controller
The solar charge controller is the brains of the operation.
The unit opens the way for the solar panels to charge the batteries, senses when the solar panels are finished for the day which turns the on light and starts the timing and dimming program based on user input. The unit isolates the solar panels which can draw off the batteries when not producing power. Also the battery charging paradigm for your particular battery type can be custom programmed.
Charge Controller – $15