Dimmable with 3 settings
Run times: 2-3 hours (high), 4-6 hours (medium), 20-30 hours (low)
Uses 3 AA batteries
Options for other LED colors
This hat lamp was inspired by ProdMod who designed a 3W LED video camera light
Step 1: Materials
3W Hat Lamp3W White LED
10 or 30 degree LED lens with holder
Heatsink (2cm x 2cm)
2 pin connectors
Heat shrink tubing
Clear EpoxyBattery Holder with Brightness Control
1 ohm 1/2 watt resistor
10 ohm 1/4 watt resistor
3 AA rechargeable batteries
4 AA battery holder (with cover and on-off switch)Hat Lamp Holder
Dremel with grinding disc
Hot melt glue gun
Alligator clips (to hold parts when setting the epoxy)
Step 2: Remove Extra Battery Contacts
Remove the contacts so that there is more space for the components. Use the last contact already soldered to a red wire to make this a 3 cell holder. The remaining slot will be used for the brightness control switch.
Step 3: Grind Battery Contact Holder
Step 4: Drill a Hole for the Switch and Wiring
Drill a hole for the brightness control switch. A hot soldering iron may be used to enlarge the hole. Warning: When heating the plastic, do this in a ventillated area.
Step 5: Convert 4 AA Holder to 3 AA Holder
Wire the holder as shown.
Step 6: Brightness Control Switch
Two switches will be used here. The switch included with the battery holder is used as the on/off switch. The on-off-on switch combined with the built-in switch allows three different brightness settings.
If using red/yellow/IR LEDs, a 2 ohm resistor is required. It can be soldered to the LED externally if you plan on using different colors.
Brightness settings (for 3.8V 3W LEDs)
Direct drive - 1000mA
1 ohm - 500mA
10 ohm - 100mA
Note: The recommended forward current for 3W LEDs is 700 mA but you can drive them a little higher. These LEDs usually have enough internal resistance for 3 AA batteries if you drive them directly. If using Luxeon Rebel and certain Cree emitters, you may need a minimum resistor value of 0.5 ohm for the high setting to limit the current to 1000 mA.
Step 7: Mount LED to Heatsink
Mount the LED to the heatsink. I used JB weld and clamped it with crocodile clips overnight. This keeps the LED as close to the heatsink as possible. To provide strain relief for the wires, glue part of the wire to the heat sink
Step 8: Solder 2-Pin Connector to LED
2-pin connectors allow your lamp to be detachable giving you the options to use other colors such as red for dark adaptation. You can also use it for selecting beam sizes.
Step 9: Test the Hat Lamp
Step 10: Attach Lens and Holder to LED
Grind the bottom of the lens holder to make room for the wires and solder joints. Attach the lens to holder and holder to LED using clear epoxy. Use epoxy sparingly along the rim of the lens and lens holder. Quick setting epoxy is preferred. Wipe off any excess epoxy with rubbing alcohol.
Step 11: Attach Light to Hat Using Velcro
Cut narrow openings for the velcro straps to go through. They will be used to hold the heatsink and battery holder. A small grinding disc may be used to cut the fabric. Make sure it is a hat you don't mind ruining. Hot melt glue may be used to keep the velcro from peeling.
If you prefer keeping the battery holder in your pocket, use longer wires.
Step 12: Super Bright Hat Lamp
Now you have a 3W hat lamp. To adjust the beam angle, simply bend the rim of your hat.