Here is a quick walk through on how to make a variable brightness LED work light.
Required Parts1 x Portable Halogen Work light, New or second hand: $15 3x Cree XP-G R5 Mounted to a 20mm MCPCB Star (or similar) $31 1 x AX2002 IC based “highly efficient” LED driver (site is currently down, give it a few days) $3 1x Switch Rotary 3pol 2-4pos PCB Mount $3.5 1x Knob 24mm PVC Black - 1/4″ Shaft Grub Screw $1 1x Flange Mount Box ABS 87Lx67Wx32Hmm $3 1x 8 X AA Square Battery Holder $1.5 1x 70mmx25mm25mm Box section of aluminium $2 1x Length of flat aluminium (or similar) $2 7x Small self tapping Screws A 100k Resistor, a 2.8k Resistor and a 3.2k Resistor. Any combination that gives these values will do. Approx Total Cost $60USD
Also required is some cabling, heat sink paste (thermal grease), small heat shrink tube (or tape) and the usual heat shrink gun, soldering station, hack saw, drill ect. All Prices are in USD’s and does not include shipping.
Method – Preparing the light housing
Step 1 – Disassemble the halogen work light into its base components and cut off all but 10cm of the power cord from the light. Carefully discard the halogen globe and its holder as they are not required.
Step 2 – Cut the length of box aluminium so that it will fit into the housing of the helogen worklight. This is what the LED stars will be mounted too and will act to heatsink them to the housing. This may require drilling large holes in the back of the box section so that it clears any protruding parts that were used to mount the halogen globe. Once it fits snugly into the housing drill a hole from the back through the housing and box section aluminium. Then apply some thermal grease so there is a good thermal path between the two and secure with a self tapping screw.
Step 3 – Prepare the LED stars by soldering them in series and then secure them to the box aluminium with either more self tapping screws or thermal adhesive. If you use self tapping screws be sure to check that there is no continuity between any of the LED star pad’s and the light housing.
Step 4 – Cut the original reflective shroud down the middle and fold the resulting sections so that they fit between the box aluminium tubing and the light housing. When the glass window is added later this is enough to hold it in place. The LED driver will sit under low reflective shroud.
Method – Preparing the LED driver
Step 1 – Modify the driver as described here by cutting a track and adding a 100k resistor so that the current to the LED’s can be controlled remotely by changing resistor values. Now connect the three LED’s in series to the drivers output with about 5cm length of wire. This connection is not shown in the image below. What is shown in the image below is a10cm length of wire to the drive input and another pair to the driver (green wires) that will control drive current (and thus brightness) depending on the resistor value selected.
Step 2 - Once the drive is all wired up and tested (test at 12v DC and the green wires shorted), heat shrink the entire drive to prevent it from shorting to anything and feed the green wires and the supply (red+black wire above) through from the front to the back of the light housing. Then tuck the LED drive under the reflective shroud so its out of sight.
Step 3 – Now its time to wire it up. Install the 4pole rotary switch into the back plastic compartment of the original light housing. Next spend some time with a multimeter and identify which pole is switched when you turn the switch. It should look like the image below on the left. Label each pole position. Then wire the positive in for the drive onto one of the centre poles (pole B below) of the switch. Then join the other three outer poles together and then to the original positive wire coming into the housing that was the mains wire for the halogen light. When the switch is at the ‘off position’ there should be no connection between the power wire in and the red positive wire for the driver. Join the other original negative wire straight to the negative of the driver. If your halogen light had an earth wire, remove it as its not needed.
Method – Preparing the battery box
Step 1 – Take a length of flat aluminium thats around 30cm in length and bend it into a ‘U” shape so that it fits around the base of the work light in the same way as the image below.
Mount the flat section of the batter box to this ‘U’ section with self tapping screws. Cover the screw heads with a short length of tape to prevent any accidental short circuits to the frame. Solder (or install plugs onto) the original power leads to the 8x square batter holder with about 5 cm of length. Then place the battery holder into the battery box and mount to the light. Then reassemble the light frame (in yellow above) and you should be done.
If I was going to start from scratch again I most likely would have gone with a slightly different design to make it similar to construct and cost less. Instead of the tripple XP-G’s I would used a single MC-E, which is about a third of the cost but not as efficient. To drive this MC-E you could then use one of the many different constant current drivers found on DX which also have different modes selected by a momentary switch. This would do away with the fiddly rotary switch.