http://www.instructables.com/id/Make-your-own-LED-bulb-replacement-for-regular-tor/

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Make your own LED bulb replacement for regular torchlightby The Corrugator on January 20, 2007

Table of Contents

intro:   Make your own LED bulb replacement for regular torchlight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 1:   Removing the glass bulb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

step 2:   Desoldering the remnant of the glass bulb from the base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

step 3:   Shaping the legs of LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

step 4:   An important final note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

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http://www.instructables.com/id/Make-your-own-LED-bulb-replacement-for-regular-tor/

intro:  Make your own LED bulb replacement for regular torchlightLED torchlight are pretty common these days, but if you happen to have an incandescent filament light bulb based on 100 years old technology, here's your chance tohave it updated with LED that last 8000 years! (if incandescent has a human lifespan)

What this instructable does:Take a regular PR 2 bulb with a P13.5s base (i.e. those most commonly in torchlight), reuse the base and insert 3 x 5mm diameter white LEDs. See image of end resultbelow.

The shortcut to this project is to go into a shop and buy one of these. But hey, what's the fun in that when you can make your own!

step 1: Removing the glass bulbThis task is pretty hazardous, so be very careful, tiny shards of broken glass cut easily and are painful to remove (from my own encounter with a broken bottle), I suggestcovering the bulb with a kitchen towel and gently grip with a plier, twist and nudge it out.

The glass bulb is fused to the metal base with a clay-like cement, and should crumble easily. Once the bulb is removed, use a mini screwdriver scrape the metal baseclean. The internal surface wall of the base has to be electrically conductive.

What's left is seen in the image below.

http://www.instructables.com/id/Make-your-own-LED-bulb-replacement-for-regular-tor/

step 2: Desoldering the remnant of the glass bulb from the baseHaving done this, you can now insert the LED legs through this hole, where it will be the positive connection to the battery.

step 3: Shaping the legs of LEDNow for some Uri Geller magic tricks!

What you need to do is bend the legs, solder the anodes together (that's the positive polarity leg, the longer one, or see http://en.wikipedia.org/wiki/LED ). A bit of tapewould help securing them together while you do the soldering.

Next, fold the cathode legs into a u-shape, about 7mm long, these have to make contact with the internal wall of the metal base.

Once you have done that, what you have is something like the image below.

Insert this into the metal base, through the hole at the end, solder and cut away the protruding excess.

step 4: An important final noteThe electrical characteristic of the LED bulb is completely different from a normal incandescent bulb, if you have chosen to use white LEDs, you would typically need atleast 3.3V to turn it on, producing optimum light output ( say, 3 x 1.2V rechargeable nickel metal hydride) , if you are using red LEDs, these may require only 2.2V, andcan be used as a direct replacement bulb for a 2 cell torchlight, no problem.

When using a white LED, the easiest method of driving these, is a connection in series, with a shunt resistor. Working on typical values for a 5mm white LED.

For 3 battery cell, between 3.6V to 4.5v, depending whether you're using alkaline or rechargeables, assuming a nominal of 4V, with the white LED operating voltage andcurrent at 3.3V, 30mA respectively, (4 - 3.3)/30e-3 , a 22 ohm resistor will do.

For 4 battery cell, between 4.8V to 6V, assuming a nominal of 5.4V, with the same typical values for a white LED, (5.4 - 3.3)/30e-3, a 68 ohm resistor will do.

A direct placement of the resistor in the metal base could save you more hassle.

http://www.instructables.com/id/Make-your-own-LED-bulb-replacement-for-regular-tor/

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Comments12 comments Add Comment

 Myself says:  Jan 22, 2007. 4:58 AM  REPLYI don't thin the resistor's function or importance is adequately explained. A lot of people are going to burn out a lot of LEDs just throwing them in there. Also,it's worth emphasizing that this will only work if the battery voltage is higher than the LED's forward voltage. No white LEDs in 2-cell lights, unless you build aboost converter! My favorite circuit for driving white LEDs from a single cell is the "Joule Thief", explained so well by Big Clive.

 _Ko0LaiD_ says:  Nov 1, 2008. 9:12 PM  REPLYi have a great circuit for a joule theif, works great also.

 laci37 says:  Aug 6, 2008. 12:52 AM  REPLYThe only thing needed to not burn out the LEDs is a resistor somewhere in the circuit in serial with the LEDs.

 The Corrugator says:  Jan 22, 2007. 2:13 PM  REPLYFound it! That's a clever little circuit indeed, cheers!

http://www.joulethief.com/kit.php

 Estwald says:  Jul 7, 2008. 2:20 AM  REPLYHow to make a Joule Thief from parts you probably have in your electronics junk box: Junk Box Joule ThiefI made mine entirely from salvaged parts and wire.

 soapshouse says:  Jun 8, 2008. 3:15 AM  REPLYGreat thinking. i just use this method and eureka i got my flash light to light up with led

http://www.instructables.com/id/Make-your-own-LED-bulb-replacement-for-regular-tor/

 benzon says:  Dec 19, 2007. 9:38 AM  REPLYHi, where will i solder the resistor

 _Ko0LaiD_ says:  Dec 9, 2007. 9:27 PM  REPLYhave any ideas on how to put LED's in a mini maglite?

  jedi pen-gui-n says:  Jul 7, 2007. 6:40 PM  REPLYl.e.d.s for my flash light? sweet!

 cf10 says:  Apr 22, 2007. 9:35 PM  REPLYHi, Great item! Will try it soon with my underpowered CatEye HL-330H.

By the way, based on your calculations you mean of course a series resistor,not a shunt (parallel) resistor. A shunt resistor would be in parallel withthe battery and would, rather uselessly, draw power from the batteryindependently of what is flowing through the LEDs while providing noprotection against overcurrents.

Whether to put the LEDs themselves in series or parallel is another issue.

Since white LEDs require higher voltages you might be tempted to putthem in parallel (cathode to cathode, anode to anode), and that maywork OK. You may get unequal currents through the LEDs, though, unlesseither the LEDs are rather well matched or you have a series resistorfor each LED - tying each anode to the positive through its own droppingresistor.

Series connection guarantees equal currents thru the LEDs and requiresonly a single current limiting resistor but requires a voltage equal to triplethe amount for a single LED, plus half a volt or so - more for long chains -across the dropping resistor.

P.S. Do not hook the LEDs (or the battery) up backwards. A careful designmight use a series diode (or a largish shunt diode with a fuse at the battery)to avoid this. Remember the anode attaches to the positive supply voltage,the negative to the other. For LEDs in series put the anode end of eachdiode closest to the positive end of the series chain.

 djmitchella says:  Feb 18, 2007. 12:47 AM  REPLYI'm running a 2D-cell flashlight with 3 LEDs; white 10000mcd ones from the seller that Dan's-Data talks about here, and it works just fine, because they havebuiltin voltage regulation: http://www.dansdata.com/gz065.htm

Next step, to make a color-changing flashlight.. The tricky part is that the plastic base of the LEDs sticks slightly over the metal lip of the bulb, so it took somefiddling to get everything to contact properly in the flashlight I used, but it works in the end.

Nice idea -- thanks!

 Nicktog says:  Jan 22, 2007. 3:29 AM  REPLYRight on! Every once in a while I see an istructable that makes me wonder how I didn't think of it myself. This is one, I can't wait to start making these--THANKS!