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15 LED Light
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Experimental LED Light Construction Project
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Build an emergency LED Light for the radio shack |
White LEDs have been improved steadily
since their invention in 1996 to the point that they are now useful for
emergency lighting situations. Several companies are selling small numbers of high power LEDs to hobbists, Hosfelt and TheLEDLight. |
| We will describe constructing an emergency light using 3 or 4 white LEDs fitted into a 1/2 or 3/4 inch PVC pipe coupling and mounted into a clamp-on miniture light housing. Since most radio shacks have a 13.8 VDC emergency supply, we will configure the light to use this power source. | LEDs may also be obtained from Radio Shack (somewhat dimmer) or from Model Train Hobby Stores. Model Train enthusiasts use them for train headlights and such. |
Parts needed:
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A little bit of theoryMost of the specifications state that white LEDs drop 3.4 volts and take about 20 ma to light. My own experiments show that a white LED can be lit with as little as 2.5 volts and 3 ma, but that the light output is substantially reduced. Interestingly, due to the intense blue-white nature of the LEDs I have used, even at low levels of light output they seem to be very bright when looking right into them. The specifications state that the LED's life will be substantially reduced if it is driven with too much current, therefore appropriate current-limiting resistors must be used. Since we are supplying a near constant 12.6 volts to the LEDs, the resistance calculation is easy using Ohm's Law: Solving for resistance Substituting We will use 470 ohm resistors since that is a common value. |
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| My old deep cycle battery puts out 12.6 volts which is normal for a fully charged battery so with the 470 ohm resistors my measured current is 19.4 ma for a single LED. Battery chargers and automobile alternator systems commonly output 13.8 volts which would yield 29 ma with the 470 ohm resistors. The specifications say that the LEDs should not be driven with more than 30 ma which which provides a small measure of safety. For a wider margin of safety, a slightly higher valued resistor could be used yielding a slight decrease in light output. For a better understanding of the workings and use of LEDs, refer to the sites mentioned above or search the Internet for 'white led'. |
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Construction |
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Step 1Because the 1/2 or 3/4 inch PVC coupling will become the housing for the 3 or 4 LED lights, it is necessary to make some spacers to hold the perfboard in place. Make these spacers by cutting a 3/8 inch section and a 1/8 section from the PVC pipe. |
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Step 2Cut a disk from the perfboard the same diameter as the PVC pipe sections cut in step 1. The disk need not be perfectly round, but must fit inside the coupler.Hint: For better LED positioning, insert the LEDs in the perfboard and cut the disk around them. |
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Step 3Experiment with the placement of the LEDs in the preferation board disk made in step 2. Test the disk by inserting the spacers and the disk into one side of the PVC coupling in order - (1) the 3/8 inch spacer, (2) the Perfboard disk, then (3) the 1/8 inch spacer. Do not cement them in place yet, but test the placement of the LEDs.You may have to enlarge the holes in the perfboard to get the LED leads to slide in easily. |
 
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Step 4You have the choice of mounting the switch in the PVC coupling or mounting it on the light assembly housing. In either case, you will need to cut 2 more spacers from the PVC pipe and another disk from the perfboard.Switch in coupling Drill a hole for the switch in the perfboard disk just large enough for the switch, slightly off to one side, then mount the switch. The switch may have a keyed washer that will require another hole to be drilled in line with the desired direction of throw. Next drill another hole on the wide side of the disk for the power wires to enter the coupling. Note that the line of throw for the switch should be perpendicular to the placement of the power cord. Switch in light assemply housing Drill a hole in the perfboard disk for the power cord then insert the power cord and install a stress relief in it so it cannot be pulled from the coupling. When you install the completed coupling in the light assembly housing, you will wire up the switch. |
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Step 5Next, solder the resisters to the LEDs. Try to orient the LED leads so that all the short leads and all the long leads can be gathered together. Now, bend the short LED leads flat and cut off all but 1/8th inch. Cut all but 1/4 inch from one of the resistor leads and bend it into an "L", then solder the resistor to the short LED leads.Gather all the long resistor leads together and solder them together, shortening them to about 1/4 inch. Now gather all the long LED leads, routing them well away from the resistor leads and solder them together. |
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Step 6Final assemblyGlue the inside spacers into the PVC coupling and insert the switch and power line disk and glue the final switch side spacer. Make sure you have enough clearance inside the coupler to keep the LED leads from contacting the switch poles. Then solder the LED leads to the wires from the switch. Ensure the negative side connects with the resistors. Check the operation of the LEDs before soldering the connections and gluing the last spacer. Now solder the LED leads and test to see if any internal parts are shorting, then glue in the last spacer. |
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The completed LED light
The completed LED light assembly has been wrapped with Velcro so it can be positioned in any direction. |
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The LED light in a lamp housing
A 3/4 inch LED assembly installed in a lamp housing. Note the switch mounted in the housing. |
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The LED light assembly with a battery pack in a TupperWare Container
A 1/2 inch LED assembly velcro'ed to the side of a TupperWare container which contains 4 D batteries. This assembly uses 100 ohm resistors due to the reduced voltage. |
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Big LED array.
This LED array uses 15 LEDs housed in a 1 inch PVC connector. Each LED has its own 100 ohm resistor to limit the current and reduce the voltage. The LEDs have a 20 degree light dispersion resulting in a beam much like a regular flashlight. Using 4 D size batteries, this assembly produces usable light for over 24 hours. This array is ideal for lighting dark work areas such as work under the car. |
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This construction project brought to you through the efforts of
Glade Powell
(KK7LW) and Robin Tuck.
We hope you enjoy this and come up with interesting and useful extensions.
