I have an old Dorcy Spotlight which I use all the time. Unfortunately, the Fluorescent Auxiliary light that is incorporated into this unit was failing. I wanted to keep this feature of the light. I had an old LED flashlight that the switch did not work properly, so I thought a good way to upgrade this spotlight would be to replace the old fluorescent bulb and circuitry with this LED Cluster.
This Instructable will illustrate how I accomplished that.
Step 1: Gather Parts and Tools
Spotlight with Fluorescent auxiliary light
Wire strippers / pliers
Voltmeter / Ammeter
LED Flashlight to salvage the LED's
Step 2: Disassemble the Spotlight
The first thing to do is to remove and disconnect the battery. This Spotlight has a 6 volt sealed battery.
After the battery is disconnected, remove the Fluorescent bulb
Remove all of the screws to separate the halves of the Spotlight
Step 3: Determine Existing Wiring
Study the wiring of the Spotlight. The switch for the Fluorescent circuit is fed from the Positive wire and returns to the circuit board. Two wires from the circuit board typically feed the Fluorescent bulb. The new LED's will need power directly from the battery. We need to remove any wiring to and from the Fluorescent circuit.
Step 4: Remove Fluorescent Wiring.
The diagram shows what wiring needs to be removed. All of the wiring from the circuit board to the Fluorescent bulb and the return wire from the switch to the circuit board needs to be removed. Make sure to leave the Positive wire feeding the switch intact. The last photo shows the back of the circuit board with the old wiring removed. I am leaving the circuit board in the Spotlight because it also contains the circuitry necessary to charge the battery.
Step 5: Add Wiring for LED
The diagram shows what modifications are needed to power the LED's. You will need to connect an Negative wire to the existing negative connection. For this project, I simply soldered the new negative wire on the same point the existing ones were located. I also had to add a wire from the Auxiliary switch to the location of my LED's. The last picture shows the Spotlight reassembled with the new wires. I made them extra long. They are much easier to cut than to lengthen!
Step 6: Disassemble LED Flashlight
I used a 24 LED Flashlight to obtain an LED Cluster. I simply removed all of the screws and was able to get the LED's out. Before cutting the wires off of the battery pack, mark the + and - on the LED Circuit board. It is important to have the polarity correct so the LED's will work.
Step 7: Modify LED Cluster
The modifications to the LED Cluster are pretty simple. First un-solder the two wires that went to the 3 LED cluster on the flashlight. The particular Flashlight I sourced the LED's from had a 3 LED feature for a low light located on the front of the light.
Then bypass the switch that is built into the circuit board. You may have to use the meter to test which points go to the switch. If you study the Printed circuit board closely, it is pretty easy to figure out which pins need to be jumpered. Solder a wire to jumper / bypass the switch. You could omit this step by leaving the switch on all the time. My switch went bad, so I jumpered it in order to use the switch that is built into the Spotlight.
Step 8: Determine Current Draw and Resistor
LED's will burn out if they get too much current. The LED Flashlight has a 4.5 volt battery. My Flashlight that I am modifying has a 6 volt battery. I wanted to limit the current to keep from burning out the LED's.
Step 1. Measure the Current at 4.5 volts. The schematic shows how to hook up the meter into the circuit. Note: To measure current the meter must be in series with the battery and LED's. My meter read 0.45 amps at 4.5 volts.
Step 2. Measure the current at 6 volts. I read 1.32 amps at 6 volts. The LED's were very bright, but I am sure they would not last long.
Step 3. Add resistors. I had an assortment of resistors. I found that two 10 ohm resistors in parallel (Total of 5 ohms resistance) limited the current to 0.46 amps. This was very close to the original current draw. Somebody out there may be able to explain how to calculate the correct resistance, but trail and error does also work!
NOTE: Make sure to remove the meter leads from the amp connector ports on the meter when you are finished. If you measure voltage with the meter set up for amperage, you may blow an internal fuse in the meter!
Step 9: Install LED's
Once you determined the resistor size, solder the LED Cluster to the wires you installed earlier on the Spotlight. I soldered one wire of the resistors directly to the circuit board and soldered the wire from the spotlight to the other end of the resistor. The board tucked neatly into the slot where the old Fluorescent light mounted. I took a dab of silicone glue to glue the LED reflectors to the LED Cluster circuit board.
I made some spacers out of tubing to hold the Cluster level and used some long skinny sheet metal screws to attach it to the flashlight housing. The pictures show how it is held in place. The only thing left to do is to snap the diffuser cover back on.
Step 10: Finished
The LED's are brighter and more efficient that the original Fluorescent tube. They will last 6 to 8 hours before draining the battery. The light is very useful to illuminate an area such as a tent or inside a room.
This project makes use of a few low cost materials. The Spotlight was a garage sale find ($3.00) and the LED Light was obtained with a free coupon from Harbor Freight.
Good Luck with your project!