(Click to see the 120VAC version)
|Completed 12V LED unit, powered off|
This was a fun project to do. It took all of about 2 hours, start-to-finish. It is built upon a narrow strip of 2-sided PC board material. It is ~9" long by 1/2" wide. I used a "Dremel" tool and cutting wheel to make the "traces" in the copper. (This is my favorite "etching" technique. It's far less messy than chemical etching, and it's quicker, especially for simple circuits.) The + and - markings helped me to install the LED's with the correct polarity. Trust me... it's all to easy to make a mistake in close-quarters like this! ;) The dotted lines delineated each 6-LED segment.
There are a total of six sets of 6 LED's in this design, for a total of 36. (That is the same number used in the 120V LED unit, which is shown HERE.)
|Completed 12V LED unit, powered up|
You can see how much this unit "washes out" the camera,
just reflecting sideways off the white paper!
You can build LED units like this with as many as 10 strings of 18-LED groups, per 7809 regulator. Each 18 LED group draws 70~80ma, so although you COULD wire as many as 12 groups in parallel, that gets much too close to the rated current limit of the regulator. We not only want a safety margin, we also don't want to see the voltage start dropping below 9.0! The LEDS will dim out significantly, even with a .1v drop!
With the 7809, full output is maintained with an input voltage as low as 10.5v, making these LED lights ideal for use with 12v gel cell battery systems! Once you reach 10.5v, the current draw starts to fall off rapidly, significantly reducing the risk of running the battteries down to a destructive level.
|LED light vs a 100 watt
This is obviously the BACK of the LED array, and you can see that it, too, is pretty bright!
Notes about these LED's: They were obtained by my former employer in bulk from China, so I don't have a Mfg or Part #, sorry. :( Most modern white LED's are VERY similar, though. Even at a measly 4ma, they are MUCH too bright to look at!
These LED's are rated at 20ma MAX, but you don't want to run them anywhere NEAR that! To be safe, never give them more than 15ma. They will "burn out" very quickly if they are over-driven, even by a small amount. You especially don't want them getting warm! Even at only 10ma, with 24/7 use, their output decreases to about 25% within a year. Baby them, and they last a lot longer!
If you give one of these LED's only 0.1 ma, it will be about as bright as a "standard" LED indicator! That is not a typo! 1/10'th of a milliamp makes it bright enough to use as an indicator. You can thus use them as power indicators for battery-powered 9~12v devices with a 100k resistor! Give the LED 1ma, and it's bright enough to use for a small flashlight that will last "forever" with 3 AA cells and a resistor!
These LED's have a 2.8v to 3v drop, so although it's possible to run them on just 2 AA cells, they will "dim out" VERY quickly as the battery voltage drops. Thus, you want to use 3 cells, with a current-limiting resistor to make reliable flashlights. Power the LED with just 4ma, and it is PLENTY to see by! For flashlight use, you can "get away with" running them harder, like 15 ma. You will certainly get more light, but at the expense of shorter LED life. Still, when you consider that a typical flashlight bulb draws several HUNDRED milliamps, the advantage of the LED in battery life is amazing!
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