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Salvaged Circuitry

Adventures in Tinkering

LED Flashlight Project

I decided to make a high power LED flashlight after realizing that both of my personal flashlights were inadequate for finding just about anything at night - including the screw drivers directly in front of my workspace. Even after recharging the batteries in both of them and replacing the bulb in one, the light output simply was not enough. Sorry maglight, 12 lumens is just not acceptable anymore. I went ahead and began my search for a decent LED bulb which didnt cost an arm and a legin the nearest hardware store

In this case, I biked to the nearest Home depot to look for a bulb. I noticed they had 2 major brands for LED bulbs: ecosmart and phillips. The more modest Ecosmart bulbs were partially subsidized by homedepot and some entreprenuer, while the higher power philips bulbs were significantly more expensive. After realizing the current market prices, I went back home and looked them up online to see if I can get any better deals. Well, It turned out that online and instore prices were about the same per lumen bulb. Thus, I went back to the store to purchase a bulb. However, this time I noticed that there was a stray LED bulb on the shelf: a 65watt LED Philips bulb. What made this even sweeter was that there was no other similar phillups bulb there. All the other 65 watt bulbs in stock were of a different design. I tested the bulb in one of their incandescent bulb displays and sure enough, it worked. Taking into account Home depot's policies on in stock items with damaged packaging, I went to customer service and asked how much it would cost to purchase their unpackaged LED bulb. I was expecting $20 at least, since this was a $45 light bulb before tax. I walked away paying only $5 for the bulb. Pretty amazing.

The first thing I did was to make sure the bulb still worked when I got home. I tested it in my basement without any lights on. Sure enough, it worked perfectly. I actually purchased a 25watt ecosmart bulb a few weeks prior because I had no other options for a cheaper LED bulb at the time. I ended up dropping it and in the long run it broke, but thats another story entirely.

Now that I knew there was nothing wrong with the bulb, my first instincts were to access the LED circuit board. The lightbulb runs off 120V AC, but LED's natively are DC components, so If I can bypass the AC componenets, I can make a worthwhile flashlight without damaging the lightbumb itself.

I noticed that the front of the lightbulb was held together by little plastic clips. Be very careful not to break these these clips and dont put too much pressure on them. From my experiences with taking apart laptops and LCD monitors, plastic clips can range from the two extremes: quite robust or very flimsy. Most of the time they are very flimsy and snap off easily.

After gently prying loose the plastic tabs, there was a second layer of plastic underneath the plastic ring: the plastic micro lenses for the LED's

After removing the 3 short screws you get a LED bulb that looks something like this:

With the front mostly disassembled, the SMD LED board is easily visable.

If you look close enough, there are 2 through hole leads labeled "+" and "-" This is where the DC LED's are receiving power from the AC to DC converter in the base of the bulb. Of course, there is a certain voltage DC going to this circuit board, and the only way to test this is to use a good old voltimeter while the bulb is screwed into a scoket and turned on. Be very careful not to cross the leads while you are testing the bulb, as this will probably short the LED bulb and you will be back a few dollers (well a lot more if you didnt get this bulb for $5). After testing, you will probably obtain a vaue of about 23.33 volts DC. Of course, it would be really nice if Philips mentioned the DC voltage in their manual for the bulb, but the only thing remotely available for this bulb is a table for how much more efficient the LED bulb is than incandescent and CFL light bulbs:

I will not be needing the AC to DC electronics, so I am going to solder directly to these leads. In this way, I can keep the flashlight entirely DC, yet still be able to use the bulb in an AC socket If I so wanted to (I would have to desolder these wires of course, by they only takes a sec).

You want to make sure you inflict no damage to the SMD LED board at all costs. In this case, I routed the wires through the bulb design, which has holes around the parimeter of the bulb. I looped the wires around the aluminum shell so I would not accitentally pull on the leads of the circuit board too much to cause damage. Yes, the lightbulb remains stationary quite well in a connon solder spool.

The next step was to make a battery source for testing. This is not the final battery pack, it is just going to be used to test the bulb out in different locations: mainly outside. In this case I used (8) 3.4V 1.1 ah 18650 A123 battery cells to get close to 23v DC the LED bulb required. I did not charge the batteries to their full capacity, as 27,2v will exceed 23volts significantly.

When making the battery pack, I found it best to hot glue the batteries together and use metal clips to join the cells. Make sure you label the first battery in the pack as "+" and the adjacent one as "-" and work you way down the pack. Solder metal clips from + to -, leaving one set open. these two open ends of the battery will he the + and - of the whole battery pack.

Once all the wiring of the battery pack is done, your best bet is to isolate the pack from it's surroundings. The easiest way I know of doing this is using heatshrink. Luckily, I was able to come across a bit of large diameter heatshrink. I put my battery pack inside the heatshrink and cut off a moderately sized piece and placed it below the nozzle of my heatgun.

It is really neat how easily heatshrik conforms to it's inner contents with just a little heat.

The next step would be to connect the battery to the bulb. However, I wanted to make sure that I did not blow out the LED's, so I wired a potentiometer, a fuse, and an on/off switch in the circuit. The potentiometer varies the voltage going to the LED's, which would prevent the LED's from receving too much voltage, the fuse is wired up to protect the components of the circuit and the switch is there for obvesious reasons.

Here's a picture of the Potentiometer I used. I will try to get a picture of the whole circuit.

Here's a picture of the overall circuit working on the lowest setting of the potentiometer.

Here's a picture of the overall circuit working on the highest setting of the potentiometer. As you can see, this is one powerful light bulb. Now, the first question you might ask would be how hot does this lightbulb get? Well, lets say it becomes noticably hot after 10 munites of continous use. not enough to burn you, but enough to warm your hand fairly well in the winter time.

After wiring everything up, I went outside and tested the setup. I simply could not believe the results..

Here's a before picture

Here's an after picture. As you can see, my neighbor must be happy lifving across the way.

Another before picture

After picture. That is absolutly amazing.

Wanting a way to control the light, I sorted through my stash of lenses salvaged from random discarded items. I stumbled upon a lens used to disperse the light in an overhead projector.

What is really neat about this lens, is that the center has a very large width, making the bulb look like a fish-eye lens. What is even more amazing is how the lens exactly fits inside the bulb's circular mounting region, where the plastic lens was screwed on. Essentially, I could make a simple bracket that would hold the lens in place which wouldnt be too hard to fabricate. However, I realized this lens would do the opposite of what I wanted: a crisp spot-light like beam.

Regardless, that is one sweet lens. Up next, I am going to go through the steps of making this a finished package. More to come.