Posted: 2/19/2007 9:21:27 PM EDT
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I have a huge supply of 9v and AA batteries and I want to learn how to build lights I can run off of them. What do I need to know? I'm going to state that I do not want to buy pre made stuff, I want to buy the LEDs and solder my own set ups. Tell me about LEDs.  |
| From what little I can glean about LED's, they take less power, and can run 10 or 11 years without replacing the bulb. Luxeon bulbs are considerably brighter than standard LED's, but also drain more power. I'm not sure if there is anything brighter than Luxeon or not. A 3 watt , 2 cell AA flashlight is about as bright as a one watt, 3 AAA Dorcy light. Also, even bright luxeon LED's don't put off much heat, compared to a comparable Xenon bulb. gk |
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One thing you should be aware of is that you should put a current-limiting resistor in line with them. They WILL consume a lot of current (read: shortened battery life) if you don't do this. I played with them many years ago. I suggest you get a variable resistor from Radio Shack and experiment with the proper resistance values. |
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Basically, LEDs are diodes. Diodes (theoretically) only conduct electric in one direction. That is, if you hook a battery up one way to a diode, it will conduct electric, and reversing the connection will cause to current to flow. Diodes have an anode and a cathode. One has penty of lose electrons and the other a depletion of electrons which causes current to flow easily fron the side with ample electrons to the side with an electron depletion. All diodes produce light (believe it or not). Light emmitting diodes (LED) are made with a clear or tinted casing with a large surface area. The doping of the diode material causes the light to be different colors. The color of the casing has little to do with the color of light (its usually just a color enhancer or difuser). Typical normal diodes begin conducting at around 0.7v while leds need a higher voltage, typically 1.5-5v depending on several factors such as size and even color. Blue and white LEDs are the newest colors and also consume the most power. Typical power consumption is around 20mA for most colors (1A is 1000mA). White LEDs can take much more and usually require a higher voltage around 3-5v. Diodes and LEDs require resistance in series with the diode. Otherwise, the diode will attempt to conduct infinite current and make itself a resistor. The value of resistance is proportional to the amount of voltage needed to acheive the currect amount of current for the LED for the supply voltage. Simply put, a specific LED, you will need a higher value of resistance for a higher supply voltage to keep the current to the LED at an acceptable level. I would go thru the steps of calculating the required sistance for a particular LED, but its late and I'm tired. -Foxxz ETA-LEDs en.wikipedia.org/wiki/Led |
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One of the easiest ways to home-brew your own LED lights is by buying an incandescent flashlight, removing the existing incandescent bulb, and replacing it with your own LED counterpart. This solves the problem of coming up with a compact, relatively inexpensive battery holder, switch and reflector. For 2-cell (3 volt) flashlights, you can simply crush the existing glass bulb with a pair of pliers, clean out the innerds with a dremel tool, and solder in a white LED (longer lead to the center positive pin; shorter lead to the negative outside bulb base). Lumex makes an excellent low-voltage 5 MM LED for this purpose (available from Digi-Key under part no. 67-1691-ND for about 80 cents). This LED isn't quite as bright as the original incandescent bulb, but will run on two alkaline AA cells for several hundred hours - VERY handy as a hurricane lamp. Note that only a few white LEDs will produce significant light from only 3 volts - Thus,substitution of some other non-Lumex LED is NOT recommended. For flashlights with more than 2 cells (i.e., more than 3 volts), you usually have to install a current-limiting resistor in series with the LED, in order to limit the maximum current to a safe value (typically 0.02 amps for 5 MM LEDs). For brighter LEDs, the home-brewing task gets a little more complicated: Not only must you provide proper voltage and current to the LED, but you must also provide some means for carrying away the heat produced by the LED. Usually, this involves "heat-sinking" the LED, in which the LED is mounted in such a way as to conduct its heat to the flashlight's metal enclosure (often augmented with the use of thermal epoxy or grease). By far, the slickest high-power LED flashlight modifications involve the installation of Cree Semiconductor's new XR-E LED. This LED is roughly twice as bright as LumiLED's 3 watt Luxeon LEDs (which were the state-of-the-art LEDs just 12 months ago), without consuming any extra current. Cree XR-E LEDs are available in the standard Luxeon "star" package (here is one source), which makes it pretty easy to hot-rod Luxeon flashlights to produce a twofold increase in light output - just remove the existing Luxeon LED, replace it with a Cree XR-E (including a liberal quantity of thermal grease), and you instantly gain twice the lumens. Done right, you can end up with roughly 135 lumens- much brighter than just about any incandescent flashlight on the market. ETA: If you'd like to add extra features to your LED lights (i.e., dimming, strobe mode, operating a 4 volt LED from a much higher or lower-voltage battery, etc.), several companies sell handy LED converter boards and other LED parts: The Sandwich Shoppe TaskLED Lighthound SuperBright LEDs AutoLumination |
| If you try to run an LED directly off a battery or other power source, more than likely the LED will literally burn up in a few seconds. It might survive, but will be damaged. All you need is a resistor to limit current. When I used to build circuits about ten years ago, I'd buy LEDs in a package and on the back it would list its power consumption and the resistor needed could be calculated fairly easily (I forget if the resistor needed was listed on any of them). The higher the voltage, the more resistance you'll need. If you want to put, say ten LEDs in series, you should user a higher wattage resistor otherwise you might shorten the life of the resistor and or burn it up. A one watt resistor should work for ten LEDs just fine. There must be sources on the net to figure out how to calculate everything, or I am certain other members will come along and post the information shortly. Just make sure to be quick with the soldering so you don't damage the LED or resistor. Ger a breadboard and practice on that first, then you can buy blank circuit boards and etch your own pattern on it if you really want to get serious (I used to do just this). |
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This site probably has all your answers: www.candlepowerforums.com Check out the LED section, and also the Custom and Modified section. |