Introduction: LED Replacement Fluorescent Tube
In this instructable, I will try and outline all of the steps required to create an LED fluorescent replacement tube. This instructable is provided more as a guideline, you can change almost anything in here to suit your needs. The lamp I created contained 87 LEDs, and this guide provides instructions for that many. This instructable contains the information on how to build a lamp, but there is too much information about how it works to include here.
The approximate cost is $25.00 per lamp.
If you would like more information than this instructable can provide, check out the website for this project. http://led.hypertriangle.com
When I finished this project, I was very satisfied with the results. The light produced from 87 LEDs is very usable. You can see graphs of lux if you are interested at the website above.
The best part about this project is saving energy. The 87 LED lamp uses a mere 8.4 watts! (0.7 amps @ 12VDC)
This project was seen at the Intel International Science and Engineering Fair (IISEF) and the Bay Area Science and Engineering Fair (BASEF).
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Step 1: Materials Required
You will need an array of materials for this project.
T12 Fluorescent Tube Protector
48" x 1.5" x 0.25" Plexiglass
87 Super Bright White LEDs
29 2.7 ohm 1/4 watt Resistors
2.5m 18 AWG Bare Copper Wire
20cm 14 AWG Bare Copper Wire
1k ohm 1/4 watt Resistor
100 ohm 1/4 watt Resistor
0.2 microfarad Ceramic Capacitor
For the LEDs, if you are building your first buib, I recommend LED Shoppe. They have sweet deals on LEDs. The only problem is that they dont carry the most efficient or recent diodes.
For the bare copper wire, the 18 AWG can come from an old scrap of RG6 and the 14 AWG can come from Romex House Wiring.
The tube protector comes from most hardware stores.
Almost every other component there can be ordered from Digikey or Mouser
Step 2: Cut and Mark
A standard fluorescent tube is approximately 48 inches long and 1.5 inches wide (T12 = 12 * 1/8 inches wide). Take your sheet of plexi-glass and cut a piece that is 1.5 inches wide by 44 inches long. 4 inches is left in the tube for the current regulator and wiring in the ends. This is best done on a table saw while wearing all appropriate safety equipment. If you do not have access to a table saw, consider using a plastic laminate scoring knife.
You may need to adjust this step slightly to accomodate the tools you have available to you. To mark the surface of the glass, the strip of plexi-glass was clamped to a dry-wall "T" as shown below. Then using a utility knife and a general-purpose square, the marks were created. The dry-wall "T" used had fractional-inches marked on it, so they were used as a guideline as to where to create the marks. The first step in marking the glass is to go across the shortest side of the plastic, marking at regular intervals widthwise. Then the marks were created lengthwise. These second lengthwise marks could be omitted if extra car is taken in the next step if you want to make your plastic as mark-free as possible. The final product is shown below. This step is more of a general guideline. Your process will almost certainly differ. If you are marking holes for 87 LEDs, you will be creating 29 rows. This works out to approximately 1 3/8 inches between groups if starting 1 1/2 inches from the end.
Step 3: Drill
This process is best done with a drill press. If you are creating an 87 LED bulb like the one designed, it will take approximately 20 minutes to drill all of the holes. Grab a piece of scrap lumber and clamp it to your drill press's stage. Align it to be square to the drill press stage, and the correct distance to ensure that all of the holes drilled fall in the same plane and on the score marks. The ideal drill bit size to use is 3/16 inches. This size is slightly smaller than required but allows the LEDs to be mounted without glue. This is where you can omit the lengthwise score marks by ensuring the jig is clamped in the correct location.
Step 4: Mount LEDs
Its now time to mount the LEDs. Grab your bag of LEDs, and insert three into a row. Ensure that the polarity is kept constant. All of the positive sides (longer lead) should be on the same side of the plexi glass. Next using needle-nose pliers, bend the leads into a square as shown in the picture below. Next, solder the leads together. Repeat this process for the other touching leads. The resulting soldered connection should be enough to hold the LEDs in place. Trim off any excess lead, but leave the main (+) and (-) long as shown in the picture below.
Step 5: Add Resistors and Power Rails
Next, grab your bag of 2.7 ohm 1/4 watt resistors. Trim one side of the resistor down to 1/4" and trim the (-) side of the LED triplet down to 1/4". Solder the two shortened leads together. Repeat until all of the LEDs triplets have a resistor. The reason this resistor is 2.7 ohms is due to the current regulation circuit. The LM334 (the main component in the current regulator) has a reference voltage of 64 mV. A simple ohm's law calculation can determine this resistor value. 2.7 ohms ensures that each LED gets exactly 23.5 mA.
Take some 18 AWG copper wire and being to solder it in place along the sides of the LEDs. Leave approximately 4 inches of extra wire on each end to work with at the end. Assuming you are starting with the positive rail, hold the copper wire against the LED's lead just slightly above the flattened area. This flattened area is a small "warning" that soldering below it can damage the LED, so try and stay above it. Now that the copper is held against this spot, fold the lead over the copper wire and solder. If you are bulding the 87 LED model, repeat this process 29 times until all of the LED triplets have a tie to the power rail. Then repeat this process for the resistors. The resistors do not have a "safety mark", so try and remain at least 1/4 inch away from the resistor when soldering. You will notice a 10 degree angle on the LEDs in this cross-section. This would be an ideal design that could make the lamp usable without a diffuser. However, this angle is not a requirement. It is difficult to drill accurate angles in the plexi-glass. In the bulbs that were built, the angle was omitted and the holes were simply drilled straight through.
Step 6: Create a Bi-Pin Connector
A Bi-Pin Connector is the most common type of connector used in fluorescent lamps. The bi-pins commonly used have 12.5mm between two rigid pins. To create these connectors, take a piece of scrap wood and drill two holes approximately 12.5mm apart. It helps to use a drill press and digital caliper, but it can be done with a ruler and hand drill. The depth of these holes is not important, make them at least 1/2 inches deep. The holes should be 1/16 inches in diameter. Cut two 5 cm pieces of 14 AWG bare copper wire. Insert the two pieces into the drilled holes. Slip the end cap from the tube protector over the two wires now stuck into the scrap wood. Twist the two loose ends of the wire together ensuring that the other ends remain in the scrap of wood. Prepare some low-temperature melting plastic. This is usually done by simply boiling some water and pouring the granules in. Pour the molten plastic into the end cap making sure that the plastic is at least 3/8 inches deep and distributed evenly throughout the cap. Allow the piece to cool and when the plastic is fully cooled and hard, remove it from the wood. Trim the two wires coming out of the end cap to approximately 3/8 inches. You should now have a replica bi-pin connector that can be slipped into the end of the tube protector with no effort at all. Repeat this process to create another end-cap. When you have two completed, mark one as positive and the other as negative using a marker.
Step 7: Build the Current Regulator and Bi-Pin Connectors
Build a current regulator as per the schematic shown below. You can design PCB artwork or build it on some proto-board. The LED mounting plate should now be populated with LEDs, resistors and power rails. Slide the mounting plate with all of its components into the clear tube protector. There are three terminals on the current regulator: (+), (-) and a tap. Connect the loose ends of one side of the power rails to the (+) and (-) holes on the PCB ensuring that the polarity is correct. Take a short piece of wire of any gauge and connect it to the first LED triplet between the resistor and the (-) side of the LED. Connect the other end of this wire to the tap on the PCB for the current regulator. This is the "tap" used to regulate current. The next step is to take a short piece of 18 AWG wire and connect the positive bi-pin connector to the input trace. Take the negative bi-pin connector and connect it to the negative power rail on the opposite end of the tube. This is the rail with the resistors installed. Trim all wires to be as short as possible. The final step in creating the LED lamp is to slide everything into the tube and slip the bi-pin connectors into the ends. Ensure that they are aligned with each other.
It is not a requirement to use bi-pin connectors. You could easily wire up a simple DC socket. to the + and negative of the circuit.
(A new, clearer schematic is coming soon.)
Step 8: Variation: DC Socket Instead of Bi-Pin
You can easily use a DC socket instead of a bi-pin connector. The pictures below explain it better than words can. Simply connect the positive and the negative connections in the circuit to your barrel plug.
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