How to turn a dead flashlight into an uber LED light

I've had this dead flashlight lying around in my shop for a few months, and I decided that it was time for it to live again!

I've broken this instructable (and the flashlilght) in to a few easy steps:

Step 1: Open up the flashlight,

Step 2: Clean out the dead bulb,

Step 3: Calculate the resistance needed,

Step 4:  Solder the LEDs and the resistor together

Step 5:  Solder the LEDs to the bulbs, and

Step 6:  Reassemble the flashlight.

Epilogue

Step 1 Open up the flashlight

The rubber handle was glued in place, but since this flashlight was a few years old, the glue was brittle and the handle peeled right off. After that, it was just a case of prying the light open.

Comments

[SIRJAMES09]

I have a 2 "D Cell" flashlight that I would like to convert but you lost me with the math.

I am not an educated man so I do not understand all that math you used. I understand what a resistor does, but not how it does it...

How do I calculate what size resistor to use for my flashlight?? Things like this have always fascinated me even if I do not understand how to make it work.

[fight4gipper1]

Dude your math boggled my brain.

Could you please make it a little dumber??

[bucklipe]

With the room you have in the case, could a voltage/current regulating circuit (maybe a zener diode based unit) be installed? My understanding is that batteries are useful down to .8 volts per cell. That would allow us to put 4 cells with a start voltage of 6 volts and it would drop to 3.2 volts. That would allow keep LEDs lit from full charge down to useless. I realize you have 3 batteries in this one but the regulator would work for a variety of input voltages.

[przemek]

Remember that the regulator is essentially just wasting power: the current I through it is the same as through the LED, so the wasted power is I*(VS-VF) (battery voltage minus the output voltage of the circuit, equal to the LED forward voltage). The same goes for the resistor in the Instructables circuit---essentially it regulates the required current, and so the only way to minimize the wasted power is to select VF to be as close to VF as possible

[mccauleymon]

Perfect, I have a few dead lights kicking around, was going to replace bulbs anyway! Good project to do with my 11yr old Daughter. How much longer will batteries last over incandescent?

[darph bobo]

Hem, I can't say for sure how much longer it will last, but it will be considerably longer with the LEDs, as they have a very low current draw. I'm glad that you find that this will make a good project for you and your daughter, make sure to document it and post it here afterwards!

[Jollyrgr]

Electrical or other tape around the bulb works better than paper towel. If you heat the bulb base the epoxy/glue will melt and you can free the bulb in one piece in many cases.

[mccauleymon]

nice tip, thanks

[arkie]

Most excellent work. Good use of stuff on-hand... like cheese & bread.

[dimtick]

NICE PROJECT!!!!!!! I really like the fact that you didn't modify the flashlight itself, only the bulb. You can use this techneque to convert almost any flashlight to LED. This is a perfect project for someone with limited skills (like myself). I've got a couple expensive camping lights at home that I never use because the batteries are always dead. I woud hate to end up destroying an expensive flashlight but have no fear if the only thing i'm destroying is a bulb. Thanks

[omnibot]

Nicely done. I went the other way around when I upgraded my xenon headlamps. It just had the 2 AA batteries so I did a joule-thief as a driver circuit for it to work.

[chinese girl]

oh,cool.

[omnibot]

Thanks Best part is the batteries work for ages now :)

[janetcunningham4]

This is what recycling is all about. Instead of adding to the garbage of the world, this project gives us an idea what we might be able to revive and make it a useful thing at home. This way, we are saving the earth as well as saving some hard earned dollars when we have to buy a new one. Great idea!

[nutsandbolts_64]

Co-worker: Hmm, isn't this like, dead?
You: I dunno. It's just been sitting here for weeks. I haven't tested it out yet. *Co-worker examines flashlight* Co-worker: hmm..... *turns on flashlight* You: HOLY (lol, considering it is bright)
Co-worker: I THOUGHT THIS IS SUPPOSED TO BE DEAD!
You: Well, I may have tweaked it a little...

[shilohjim]

So timely,I was about to toss out and replace a flashlight but this is such a simple fix. Thanks.

[SimoMies]

Very good instructable indeed! I actually did this when my trusty 1$ novelty flashlight broke. Installed one 10mm superbright led inside >: D. Oh, the performance was astonishing!

[ejsilver26]

Awesome instructable. Very well explained and I prefer a 2:2 ratio for my GC..