Summary

This is a DIY spotlight / work lamp. Ultimately, this project will probably cost more than what you can buy on the market. However, here you can select the color, angle and other characteristics of the led array to fit your specific needs. You can also select how much current the spotlight uses; so if you just need some ambient light during camping, you can design the circuit for a low-intensity light that use warm (even candle-like) white leds that will last for days.

This project uses a Delwalt 20V battery pack as a power source but it is customizable and if you can change "PART-A" to fit another battery brand since "PART-A" is just glued to "PART-B". It comes with two reflectors: the first one uses 36 leds and the other 42. I have provided the source file as well so you can modify this to your heart's content and make the reflector bigger, change its shape, make leds more tightly packed, and so on... The provided parts provide a certain flexibility when using ~2V leds (such as red or amber) and ~3V leds (such as white, blue and green). Basically, you need to create a led array made of multiple series of leds in parallel [e.g. for red leds you could use 4 x 9 leds (see "IMAGE#3"), while for white leds you can use either 6 x 6 or 7 x 6 leds]. When using about 15mA per series, you can get about a whole day from a fully charged 20V 2Ah battery at high intensity setting.

IMPORTANT NOTE: For Dewalt batteries (and maybe for other brands as well), the low voltage cut-off circuit (i.e. the circuit designed to prevent the battery from being drained below a certain voltage and cut off the power to prevent the battery from being permanently damaged) is presents in the tool and not the battery itself. As such, you shouldn't use this lamp with a near dead battery or without checking the battery status from time to time (for example, every hour when the battery only has one bar left out of three). IF YOU LEAVE THE FLASHLIGHT TURNED ON AND JUST FORGET ABOUT IT, THIS COULD PERMANENTLY DAMAGE THE BATTERY ONCE THE VOLTAGE EVENTUALLY DROP BELOW 15V.

The leds intensity is controlled only by resistors and this has the benefit of using a very simple circuit but the leds will dim over time like an old incandescent flashlight. However, as the battery get drained, the leds will also use less and less power which in turn will allow you to see that the battery should be recharged well before reaching a voltage so low as to damage the battery. In other words, right off the charger (20.4V) the flashlight may use 120mA but the spotlight will drain the battery much more slowly as the the battery capacity is reduced. When the battery has only 10% capacity left, the array may use only 20mA at that point, which would not only provide much less light (a visible cue that the battery need to be recharged) but it would also greatly increase the time it takes to lower the voltage to a level where the battery can be damaged.

This lamp is also designed to allow different levels of intensity with a 3-positions switch at the base (see the circuit schematic "Dewalt_DIY_Light.png" and "IMAGE#1" provided). If the light may provide a full day on a single charge at high intensity (depending on how many leds you use and the battery state of charge), at low intensity (e.g. 20%), the light will last five times longer and with medium intensity sitting somewhere between these two.

• The battery positive pole is connected to one lead of the rocker ON-OFF switch (it doesn't matter which one). Use hot glue to secure the switch in place.
• The opposite lead of the ON-OFF switch is connected to the the "Vin" of the 3-ways switch circuit. Note that the low intensity circuit is always ON, as this prevents the led array from turning OFF then ON when changing position on the switch. Also note that the 3-ways switch is behind the top end of the circuit board in "IMAGE#1".
• The "Vout" of the 3-ways switch circuit is connected to positive side of the leds array (that is made up of many leds series, each having it's own dedicated current limiting resistor).

  IMPORTANT: DO USE electrical tape or heat shrink to prevent short circuits between the small piece of circuit board with the resistances and the exposed leads and exposed wire connections (IMAGE#2).

• The negative end of the leds array (the negative leads of each series are combined) is then connected to the negative pole of the battery using 20 - 24 gauge wire.

Q: How do I calculate the resistor value for each led series?
A: You can use 175 ohms for white, 200 ohms for amber / red / blue and 240 ohms for green and this will allow more or less ~15mA per series from a battery right off the charger (max voltage), which is quite conservative.
If you want to use another value, then you will need a multimeter, some resistors (between 300 and 100 ohms) and a breadboard. First, fully charge the battery. Then place 6 or 9 leds in series on the breadboard. Put the multimeter in current measuring mode and connect it between the battery and the breadboard. Then use different resistor values to complete the circuit. Measure the current used from a single led series until your circuit uses the desired amount of current (exceeding 25 - 30mA will reduce the lifespan of your leds). This is your base resistors that will be inside the reflector (see "IMAGE#2") and this is the maximum current each individual leds series will use.

Q: How do I calculate the resistor values of the 3-ways switch?
A: It depends on what intensities you want. Personally, I like 20%, 60% and 100%, which should be around ~250 ohm (low), ~50 ohm (medium)... and zero for high.
If you want to use different values. You will need to check with a multimeter once you have soldered all the leds in the reflector (IMAGE#3) with their current-limiting resistors. Note that the resistors used to regulate the intensity of the light are in addition to the current-limiting ones; they DO NOT replace them. Then connect all your led series together to a single positive wire and to a single negative wire (IMAGE#2). Using your multimeter and a fully charged battery, you can use different resistor values to determine the desired intensity. Note that since the low intensity is always ON, you will need to calculate the equivalent parallel resistance of the circuit [R equivalent = 1 / (1 / R1 + 1 / R2)] but only for the medium intensity.
For example, if you have determined that R1 should be 300 ohms (total) and R2 should be 50 ohms (total), then the medium intensity resistor value will actually only be equivalent to 42.9 ohms since some current will still flow through the low intensity path (thus reducing the overall resistance of the circuit). To compensate this, the resistors you will need to use should have a total of 60 ohms. It seems like it doesn't make a lot of sense to use 60 ohms when you only want 50, but believe me, if you put those values in the formula above, it all adds up correctly.

Q: Where do I get the thin copper wire you used to build the circuit?
A: Just get either 14 gauge or 12 gauge wire. You can usually buy these by the foot at most hardware stores and you may get a few feet for a dollar. Look for something that has 7 to 12 strands. Note that the individual strands of a 14 gauge 7-strands wire will be thinner than 10 gauge with the same number of strands. This light doesn't use much current so you don't need something very thick and thinner strands are usually easier to "weave". Remove the wire insulation and you now have several thin individual copper strand that you can use as "traces" for your home-made circuits.