Low-Cost Single Battery Torch

Many of you have seen torches in gas lighters. These torches run on 3 button cells (3 x 1.5) at 4.5 volts. The reason is, their bulb uses an LED (Light Emitting Diode), which operates at 2.5 to 4.5 volts depending on the color, and consumes 20-35 milliamps (ma) of current. Meanwhile, conventional 2-battery torches use 2.5V and draw 2.5 watts or more, so if you keep such a torch on continuously, two batteries will last for about 2-3 hours (on average). But LED torches, even if you run them non-stop on button cells, will last 5-6 hours because their power consumption averages just 30 ma. However, not many people bother to replace the batteries in these torches—once the battery or the gas runs out, they just throw them away, as the cost of the 3 batteries is 10-20 Taka.

Here I am sharing a small circuit that lets you power this LED with just one battery and a pencil, instead of three batteries, and its lifespan will be approximately 10-15 hours if kept on continuously. I collected this from the internet and modified it using items available locally.

Coil

The coil is very simple: from any old electronic tube set—these often break—you can find transformer wire and its iron core, which you can cut down to size and use, or any ferrite core will work. Using insulated wire from a transformer, get enough for 25×2 = 50 turns, then fold the wire exactly in half. Wind 25 turns onto the ferrite core, and after cutting the two ends of the wire, your coil is ready. That’s it—get started on making it. The coils above are ones I made for testing purposes, and all of them work. According to a friend named Randal Smith, the more turns you have, the longer your battery will last. He even wanted to send me a small ferrite core from America.

Parts List

Resistor      +- 100 Ohm                    1 Tk.

Transistor    BC 549/BC 548                3 Tk.

Coil             Homemade                        –

Power        1.5 V any battery                5-8 Tk.

Bulb            LED (ultra white is better)    3-5 Tk.

mamun2a at gmail.com