5 Watt Infrared Flashlight |
Overview
This is simple project to convert a Transel-brand (or similar) adjustable zoom flashlight, which should be available at most sporting goods stores, into a very handy infrared (850 nm) flashlight. The infrared flashlight can then be used as an active illuminator for a night vision device, camera, or even for covert signaling.
The project consists of replacing the stock Cree white LED module with a 5 watt, 850 nm infrared LED module in a similar "star" package. The 5 watt infrared module used here is available on eBay for under $10. Search eBay for "1pc 5w 850nm Infrared IR LED 5 Watt" to find many distributors out of China selling these modules. The infrared LED module's overall construction quality isn't very great - I've had the lenses break off - but they'll work well for experimenting, just be careful...
The infrared LED module's specifications are listed as follows:
Emitted Color: 850 nm
Viewing Angle: 135 degrees
DC Forward Voltage: 1.4V
DC Forward Current: 1.4A
Maximum Pulse Voltage: 1.7V
Maximum Pulse Current: 2.0A
The stock flashlight ran off of three "AAA" size batteries, which were required for overcoming the white LED's approximate 3.6V forward voltage drop. Since the infrared LED module has a lower voltage requirement, with an approximately 1.4V forward voltage drop, we'll also need to modifiy the flashlight's battery holder to only require two "AAA" batteries.
Using three "AAA" batteries will work (4.5 VDC), but you'd need to increase the value of the dropping resistor accordingly, to around 2.2 ohm / 5 watt.
The stock flashlight also has an internal circuit board for switching between bright, dim, or flashing modes. The components on this board are not really required, so they'll be removed and a single 1 ohm / 2 watt dropping resistor will be added.

That's it!
Pictures & Construction Notes

Overview of the stock adjustable zoom flashlight.
It has words "TRANSEL Connecting the World" on the side.
It requires three "AAA" size batteries (+4.5 VDC).
A similar, usable flashlight appears to be the Duracell Durabeam Ultra 500 series, though I haven't tried it.

Taking the flashlight apart.
Unscrew the plastic front bezel, then unscrew the locking washer. Use a pair of needle-nose or snap-ring pliers to fit inside the little holes and unscrew the locking washer.
A metal flat washer and a plastic washer are behind the locking washer to secure the LED module against the aluminum holder, which acts as a heatsink.

Closeup of the alumimum body which holds the LED module.
This acts as a heatsink and screws into the body of the flashlight.

Removing the control circuit board for the stock LED module.
This circuit board has three settings, bright, dim, and flashing, which are selected via the half-step power switch.
The components on this board will not be used for the infrared flashlight and should be removed. Just heat the board with a hot air gun and slide them off.

Rear-view of the circuit board.
The center spring is battery positive. The exposed copper ring is battery negative

All the 5 watt infrared LED module requires for operation is a single 1 ohm / 2 watt resistor.
Solder one leg to the CS+ pad and the other leg to the OUT+ pad.

Alternate view, with the connecting wires attached.
The blue wire will go to the infrared module's + pad.
The black wire will go to the infrared module's - pad.

Modifying the battery holder to only require two "AAA" size batteries.
Remove one of the batteries and replace it by soldering a jumper wire from the spring tab to the flat tab.
This converts the 4.5 VDC battery pack into a 3.0 VDC battery pack.

You'll need to add a dab of heatsink thermal compound to the back of the infrared LED module.
The module should fit flat against the aluminum holder for proper heatsinking.
Be sure the wires are not pinched.

You may need to use a paper punch to enlarge the center hole on the plastic insulator.
You may also need to enlarge the center hole on the metal compression washer, use a Dremel tool and grinding wheel for this.
This plastic washer is REQUIRED to prevent the infrared LED module from shorting out against the locking washer.

Finished 5 watt, 850 nm infrared flashlight module ready to be screwed back into the flashlight's body.
Double-check that the center spring (battery positive) isn't shorted to ground.
Note how the shiny compression washer had its center hole enlarged to fit over the new infrared LED.

Finished operational 5 watt infrared flashlight as displayed on a TV screen via a black-and-white infrared-compatible video camera.
The final IR flashlight doesn't provide the greatest illumination, but the adjustable "zoom" lens allows you to concentrate the IR energy into a specific area, which is something most flashlights don't allow you to do.