This instructable will show how to take an ordinary Mag-lite flashlight and modify it to hold 12--10mm high-powered LEDs. This technique can also be applied to other lights as I will show in future instructables.
Step 1: Tools Needed
12--10mm High-Powered LEDs (I bought mine from besthongkong on eBay)
Insulated wire (preferably ~20ga)
Thin plastic (preferably clear and flexible, I used PETG from a local supplier)
Step 2: The First Step Is to Modify the Light Bulb
First, take the bulb and CAREFULLY break the glass inside of a bag with a pair of pliers. Using the pliers and soldering iron, empty the bulb casing completely of its contents. Then, using 2 short strands of wire, solder one to the end of the bulb casing and one to the outside casing. When you are sure that the connections are good, fill the bulb casing with glue so as to insulate the connections from accidental shorts.
Step 3: Design and Cut Out the Array
I used AutoCAD to fit as many of the LEDs into an array that would fit inside the Mag-lite. The inside diameter of the Mag's reflector housing is slightly larger than 1.875". It turns out that 12 of these 10mm LEDs will fit. I printed out the pattern making sure to keep the scale 1:1. I printed out 2 of these identical patterns and taped them to the plastic. I drilled one of these in the small holes and the other in the center of the large holes--both with a 1/16th drill bit. I then went back and redrilled the large holes with a 13/32 drill bit. I then cut out the plastic using my scissors, keeping it just barely larger than the outer circle. I then test-fitted the plastic into the Mag-lite housing. It should fit loosely. This would be easier if you have access to a laser cutter, but with a little patience and some skill, you can do a decent enough job without such niceties.
Step 4: Soldering the Array Together
Start by placing all the LEDs through the holes in a uniform manner. I chose to place all the negative leads (flat side) on the outer ring facing outward and facing inward on the inner ring so that all the positive leads can be soldered together. Once the positives are taken care of, attach the resistors to the negative leads. In this example, the LEDs are all wired individually, since the power source is only 4.5V. For flashlights with more voltage, it may be possible to wire the LEDs in pairs, triples, etc. Cut the positive leads and one of the resistor leads to about 3/16" and solder them together. I used a wire stripper to remove pieces of insulation from the wire I had to help insulate the resistor leads from unintentional shorts. The idea here is to wire each LED with its own resistor in parallel to all the other LEDs so that they each receive the same voltage.
I've done some calculations of my own. Since batteries lose voltage over time, I decided I wanted the LEDs to be running at around 95% of their maximum when the batteries were fresh. Here are some resistor values and their corresponding voltages:
These work with the 10mm white LEDs from besthongkong:
volts LEDs ohms
4.5V 1 47
6V 1 120
9V 1 270
9V 2 91
Step 5: Connect the Modified Bulb to the Array
The next step is to solder the modified bulb to the array. Solder the outside of the bulb housing to the negative circuit and the center of the bulb to the positive circuit. Make sure the wires go through the bulb retaining ring so that the bulb housing can be screwed in correctly. Place the plastic form over the LEDs so that they are held straight. The Mag-lite reflector will not be needed, since these LEDs focus the light to a 12 degree spread.
Step 6: Fit the Array Into the Housing
Using the pliers, press the form down hard onto the LEDs. Using the electrical tape, wrap the array with electrical tape until it fits snugly in the flashlight. Press the tape down on the back of the array so that the array will fit correctly in the housing of the flashlight. Now's also a good time to test to see if the array lights up correctly.
Step 7: Make a Spacer Ring
I found that with the reflector removed, the lens no longer fit snugly, and therefore the light would no longer be waterproof. I cut out a thin ring from my plastic to fit. Place the ring on top of the plastic and trace it. Use that to cut a thin ring for a spacer.
Step 8: Put It All Together
Now all that's left to do is put it all together. Make sure the wire stub fits in the narrow, deeper part of the flashlight so that the LED array will sit down nicely. Tighten up all the parts. Now you should have a high-powered, water-resistant, high-strength flashlight for much less than most 'tactical' flashlights.
Step 9: Comparison to Standard Mag-lite
A standard D-cell Alkaline battery contains about 12000 mAh of charge.
A 3-cell Mag has 4.5V...this means the whole flashlight has...36000mAh
A 4-cell Mag has 6V--------------------------------------------------------48000mAh
A 6-cell Mag has 9V--------------------------------------------------------72000mAh total
This means that theoretically, with a 1-amp load, a 3-cell should last 45 hours, a 4-cell 48, and a 6-cell 72 hours.
I looked long and hard, and found a site that sells Mag-lite replacement bulbs.
MagLite Replacement Bulbs
Here's an excerpt: (Keep in mind my flashlight is a standard Mag about 8 years old. I'm pretty sure it doesn't have a Krypton bulb.)
MagLite Bulb Type---Base Type---Gas Fill---Batteries---Max Peak Beam---Average---Max Batt
White Star 3-cell------PR Flange---Krypton---3-C / 3-D---20,000 / 22,000------76.8------4-5 / 9-10
White Star 4-cell------PR Flange---Krypton---4-C / 4-D---24,800 / 23,000-----122.1-----4-5 / 9-10
White Star 6-cell------PR Flange---Krypton---6-C / 6-D---30,100 / 30,000-----162.6-----4-5 / 9-10
So using these Battery life ratings, we can find that:
Again, I'm not sure how accurate these numbers are, but from what I could find, these seem reasonable enough.
Using a really cool website I found, the power consumption of these LED arrays can be clearly found. LED series parallel array wizard
For the 3 cell:
3.56---diode forward voltage
20-----diode forward current (mA)
12-----number of LEDs in your array
This yields the following information:
- each 47 ohm resistor dissipates 18.8 mW
- the wizard thinks 1/4W resistors are fine for your application
- together, all resistors dissipate 225.6 mW
- together, the diodes dissipate 854.4 mW
- total power dissipated by the array is 1080 mW
- the array draws current of 240 mA from the source.
As for brightness, see for yourself. These LEDs do not require a reflector because they have a parabolic cross-section which internally focuses each LED individually.
The LEDs I used claim a 12 degree focusing pattern. Not all LEDs do. Many have a 25 degree, while others are as much as 55 degrees. I did a subjective test, and I believe that the pattern is somewhere around 12 degrees. This does mean that across a football field, much of the light would dissipate into a circle 64 feet wide, but at any 'reasonable' distance, the light works great.
As for intensity of light, candlepower is a hard thing to objectively compare, since the overall spread is figured into the equation. First of all, candlepower is no longer a recognized standard unit. It is approximately equal to 1cd or 1 candela. These LEDs advertise a brightness of 130cd apiece x 12 = 1560cd. I'm not sure where the discrepancy is, but after being blinded many times, I know that my roommates can attest to the intensity of this light!
Also, when constructed correctly, the brightness of this light should be the same whether you are using a 3, 4, or 6-cell Mag-lite. The only difference will be overall battery life, which I project to be:
Flashlight----Capacity----Current Draw----Projected Life---Life Compared to Standard 12 Hours
--3-cell-------36000mAh------240mA----------150 hours----------------12.5 times greater
--4-cell-------48000mAh------240mA----------200 hours----------------16.7 times greater
--6-cell-------72000mAh------240mA----------300 hours-----------------25 times greater