The most common 12 volt LED lights are designed to replace incandescent light on cars. These are well suited for 12 volt micro solar systems but lower power automotive lights are hard to find (1/4 watt and lower). So I decided to make some of my own for my 20 watt setup. I bought the piranha LEDS from lighthouseleds.com (less than 25 cents each). The rest of the LEDS in this Instructable are from auctions I won on ebay. The 3 wire connectors are industrial waste from a company I used to work for (cut off of servo motors) as were the header pin strips. I could have skipped the pin strips and soldered wires on but I wanted these to be modular. The clothes pins make the lights versatile and easy to move from place to place.
Step 1: Several Types
The Some circuits also have an on/off switch. I used 4 LEDS with 12 volts so that light will dim and shut off before the lead acid battery drains too low. Discharging a lead acid battery too low will shorten it's useful life. Here the resistor values I used
4 piranha LEDS: 50 ohms, 12 milliamps
4 straw hat 8mm: 50 ohms, 11.3 milliamps
4 one watt: 2 ohms, 40 milliamps.
You may be wondering why I decided to run the piranha and straw hat LEDS so far below the rated 20 milliamps. The smaller component LEDS are at peak efficiency at about 8 milliamps. Also the lower power circuits are intended to be bright enough to read by if held about 1 to 2 feet above a book. These were quite acceptable for reading, The one with 1 watt LEDS will make a nice area light in a blackout. The clip with the square LED assembly (the 5th one pictured above) was an automotive light and will be used as an area light as well.
These were quick and easy to make with no circuit board required. Below are some links to related Instructables I have done:
This first one shows how I put together a couple of my micro solar setups. I used "dead" car batteries instead of new batteries to cut the cost of the system in half. They work great. The largest one is a 20 watt system and can run a 10" camping fan 24/7.
Here is one for modifying an inexpensive LED lantern flashlight to run for over 300 hours on the same battery:
Step 2: Lighting Up the Off Grid Third World
Below is the text from an article I wrote recently. This simple application of modern technology can have far reaching benefits:
"Rather than keep you in suspense or have you read pages of philosophical ramblings before getting to the solutions (I will ramble soon enough), I will first post a link to a short two page summary of a study that clearly explains the magnitude of the problem of lighting in off grid regions. It includes among other things the financial burden and health related issues. It is worth the couple of minutes to read.
(Update 5/22/2018: The link to the study no longer works so it has been deleted).
Here are two solutions. One is a daylight only solution. In other words you are electrically bringing in a minimal amount of sunlight indoors during the day. It is like a small skylight but electric rather than physical and can be moved where needed (the cost can be less than a dollar). In my opinion it is better than the two liter bottle installed in a hole in the roof solution. No, I did not make that up.
This electric skylight project used two solar cells but can be made with one. A manufacturer of the original solar lights can be contracted to make the unfinished assembly with the housing, solar cell and connecting wires for in large quantities for a huge reduction in cost.
Here are two 24/7 (day and night solution) micro solar set ups that utilize a discarded used “dead” car battery to store solar generated electricity for use 24 hours a day. The use of a throw away battery can reduce the cost of a micro solar set up by as much as 50 percent while not sacrificing performance. If you have any interest in making your own micro solar set up you will want to read this. It includes information for actual 5 and 20 watt systems still in use today.
You may be asking “What can you do with 20 watts?” It does not seem like much. Well first lets come up with a baseline called zero or nothing. Try this. On a Friday night, if you don’t have to go to work the next day, at about midnight. Shut off all the lights. Cover up the windows with heavy blankets if any light comes in from outside. Cover up or unplug any electronic devices that emits any light whatsoever. Now that you are in total darkness what would you like to do? Read? How about the common off grid activity called playing card games. Lets draw pictures on a little chalk board. You can’t do much for 12 hours a day under these conditions. Now light up one candle. Take a look around. In comparison to nothing it is a huge and useful amount of light. The 4 LED desk lamp in the article puts out over 4 times this amount of light and it is concentrates it in a small area. It works quite well for reading and many other things. I choose the “Piranha” type LEDS for this design because they are very efficient. The lamp runs on less than ¼ watt of power and can be connected directly to a car battery. A quarter of one watt? For the same amount of power used to light up an old school 75 watt incandescent light bulb you can power 300 of these desk lamps or 1200 individual piranha LEDS. 20 watts could have some potential. So could 5 watts. It should be noted that the power used in the circuit is determined by a component called a resistor. A variable resistor can be added to the circuit such as the type with a knob to be used as a control. This would provide the means to adjust down the power even lower if all you need is the equivalent of one candle of light. The circuit board with the components function just fine as is. It is not necessary to install it in a light fixture.
So, we can collect sunlight for about 12 hours a day during the summer. The two set ups do not track the sun. The 20 watt set up generates about 120 watt hours (not kilowatt hours) of power a day. The charge controller and battery are not 100 percent efficient so there is some loss of useable power there. So how many quarter watt LED circuits can we power up and for how long? In theory, about 16 if they are to be run at full power 24 hours a day. In practice, if the LEDS are getting a little too dim before sunrise the following could be done:
1. Add an additional resistor to each circuits or change the resistor in the circuit so they run at a slightly lower power. My testing shows that the difference between running LEDS of this type at 75 percent of full power rather than full power (15 milliamps vs. 20 milliamps) produces a negligible change in brightness. This is due primarily to the fact that LEDS are at peak efficiency at just below half power.
2. Don’t run the circuits 24 hours a day.
3. Run a few less circuits.
4. Use a larger solar panel.
5. Try a different “dead” car battery. My limited testing indicates that only about 75% of dead car batteries will work in a micro solar system.
How can this best be used to benefit the most people in an off grid third world neighborhood? The solar panel and battery would be on one roof top. About 12 to16 houses would be connected to the system with any of the following types of cable: 4 wire telephone cable, bulk CAT5 network cable, twin lead antenna cable, low voltage control cable used to wire home alarms systems, sprinkler control cable or any other two or more conductor cable that’s cheap. The cable is run into the homes through a small hole (¼ inch or less, simple). All the circuits combined draw about one half amp of current total so a 2 – 5 amp in line fuse back at the battery should work fine to protect the battery in case of a short circuit at one of the houses.
There you have it. 16 families reading and playing and having fun at all hours of the day or night without spending money on kerosene.
How can we reduce the cost:
1. Make the system larger. How about a 60 or 80 watt system? Larger panels usually cost less per watt.
2. Buy in bulk (quantity discounts).
3. Buy used panels (my 80 watt, slightly used panel cost only $100.00).
Ultimately after a few pilot systems prove the concept works and any bugs are worked out, large corporations could donate the funds to Christian missionary organizations who would transport (they are going there any way) and then install the systems in neighborhoods of interested families. The corporations get bragging rights (three corporations come to mind) and tax write offs. Lots of families get what they need (what we have and take for granted). Missionaries get to be bearers of light yet again.