Flashlight using Dead Discharged Battery

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The portable equipment always needs power supplies batteries and batteries that we use and through away so much that Mother Nature can't recycle them.

We use ordinary or saline batteries everywhere everyone knows that they have a voltage of 1.5.

There are different form factors and they have a different service life depending on the price and manufacture.

Also, there are alkaline batteries which are usually more expensive, but they have a longer service life.

Nevertheless, all these batteries are disposable if the voltage on them becomes less than 1 volt as a rule the device in which they were installed stopped working.

Many people know that there are batteries of similar sizes that are rechargeable, unlike ordinary batteries.

The disadvantage is their price they are more expensive but will serve much longer because you can always charge them.

As a rule accumulator capacity is indicated in milliamp-hours reservoirs, and they have a voltage of 1.2 volts unlike ordinary batteries of 1.5 volts.

But most portable electronics work with them without problems.


What about the batteries that are already dead? The answer is simple if there is no place to utilize them, you can squeeze all out of them.

We throw away the batteries when they are discharged but they can still serve for quite some time.

Let's make a simple extra-low voltage converter or rather a whole flashlight that will work from dead batteries.

The trick is that such a simple circuit will allow you to collect a good flashlight with your own hands for the minimum time.

This will pump out all the juice from the dead battery.


Components List

The following components are needed for this project:


  • 1.5V discharged Battery (1 pcs)
  • NPN transistor - C945, BC547, KC507, etc. (1 pcs)
  • Ferrit core EE or ring type (1 pcs)
  • 0.05 - 0.2 mm insulated copper wire
  • 1K resistor (1 pcs)
  • 100nF capacitor (1 pcs)
  • 8mm LED (1 pcs)
  • Breadboard/PCB (1 pcs)
  • Connecting wires

Flashlight Circuit Diagram

Schematic of low voltage converter flashlight circuit shown below.


Circuit Working Explanation

This low voltage converter (driver) provides power for LEDs (eg, white, blue, UV, but also any other) from 1.5 V or 1.2 V single cell (battery), but the LED starts to shine when the supply voltage is only 0.4 V.

LEDs have polarity roughly speaking +ve and -ve, if they are connected incorrectly they will not work.

You can use low batteries, which are useless for any other equipment.

The voltage drop of a LED diode is approximately 3V.

Therefore, it is necessary to use a low voltage boost inverter.

The circuit is very simple, it works on the principle of the self-oscillating inverter.


The coil has 2 x 50 turns of a thin wire (about 0.05 to 0.2 mm), both windings are wound simultaneously, and the working frequency is about 50kHz (not critical).

Ferrite transformer wound on two E ferrite pieces.

You do not have to do it exactly the same way, it is just for inspiration.

The capacitor 100nF is not strictly necessary, the drive works without it.

Demo and Testing

The assembled circuit works immediately!


The number of LEDs can be increased by connecting them series or parallel, in this case the battery will be discharged faster but the flashlight will emit more light.

The presented circuit begins to work from a voltage of 0.4 to 0.7 volts which means that it will discharge the already dead battery to the specified voltage.

If you will use the old germanium transistors then the circuit will discharge the battery to almost zero or more precisely to 0.2 volts, this is more preferable since we will use the maximum life of the battery.

This compact converter can be built into any cheap flashlight with a battery compartment for different batteries.

The lanterns themselves can be used for their intended purpose or as a nightlight, where LED from one battery will be illuminated for many days.

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