Manual flashlight without batteries, how to do?

A manual flashlight that does not use batteries is a very interesting solution for times of emergency as it does not require any type of battery or even be charged in an outlet. Of very simple construction and even being made in a homemade way, a manual flashlight is an excellent option for a camping trip, a night walks inside, a trail and even for when the energy in your home ends.

The flashlight will be composed of two main parts, the electronic part that will be responsible for activating the LEDs for lighting and mechanical assembly, which will be the structure that supports the flashlight, the components, and the actuation system of the engine that serves as a generator.

All components used are inexpensive and can be recycled from old electronic devices, simple to find.

Manual flashlight without battery.

Material list:

  • Motor with mechanical reduction:

The simplest motor to be found and the one we use in the project is the motor that rotates the microwave dish, it has a voltage of 120V, power of 4W and a mechanical reduction for 6rpm.

  • Rectifier bridge:

For a voltage of 200V and currently less than 1A, in this project, we used 4 diodes 1N4003 forming a rectifying bridge but a ready bridge can be used as the rectifying bridge KBU1010-G.

  • Capacitor:

An electrolytic capacitor with a minimum voltage of 50V and capacitance of 100μF, one can choose to increase the capacitance to keep the LEDs on for longer.

  • Resistor :

A 6.8KΩ resistor and 1 / 4W power will be enough to limit the maximum motor voltage to the LEDs while maintaining adequate current.

  • LED:

Six high brightness LEDs.

  • Beetle carburetor spring:

This spring is easily found in auto parts or scrap metal.

  • Cable fasteners:

Very easy to find in building depots or electrical supply store.

  • Self-tapping screws for wood.

Electronic assembly.

Most people in do-it-yourself assemblies or in English “Do It Yourself” (DIY), always complain about the electronic parts often because they do not understand the operation of each component, because they do not know how to dimension these components or even the difficulty of making connections.

This flashlight has a super simple electronic system and the step by step of each part helps to understand. Below the diagram with each part of what will be needed in the flashlight:

Scheme electronic system of the flashlight.

Motor.

A microwave motor that turns the microwave dish is the generator used for this flashlight. This motor was chosen because it already has a mechanical reduction, in which case fewer turns have to be made on the motor shaft to generate a good amount of energy to illuminate the LEDs. This motor, when its axis is rotated, generates electrical energy in the form of alternating voltage (similar to that of our socket), with a low current but sufficient for the LEDs to have a good brightness for a flashlight.

Microwave dish motor.

Rectifier bridge.

The voltage generated by the motor is of the alternating voltage type, the LEDs need this voltage to be transformed into continuous voltage and this is the function of the rectifier that can be built from 4 diodes or purchased ready-made (a very cheap component).

  • 4-diode bridge:

The diode is a component that lets the electric current pass only in one direction, so it is polarized, that is, it has to be connected in the correct position. The gray strip of the diode indicates the outlet side of the electric current, so when we connect the four diodes as in the diagram below the diodes create a path so that the current always leaves the positive side of the bridge and comes back from the opposite side creating a negative polarization.

4-diode bridge rectifier scheme.

  • Rectifier bridge ready:

In a rectifier bridge ready as one of the images below internally there are diodes already disposed of in rectification bridge format.

Rectifier bridge ready.

  • Electrolytic capacitor :

After passing through the rectifying bridge, the voltage is of the pulsating continuous type, that is, it is always positive but it is oscillating so that the current is exactly stable and continuous, it is necessary to use a capacitor that can store electrical energy and will discharge whenever the wave oscillation for the purpose of decreasing keeping the LEDs with continuous brightness and not oscillating.

The voltage that this capacitor supports must always be higher than the one that will come from the motor so we use a 250V one, the higher the capacitance, that is, the amount of energy the capacitor can store the longer the LEDs will go stay lit.

The electrolytic capacitor is polarized, that is, it has the right side to be connected to the positive and the right side to be connected to the negative, on the side of its body there is a gray strip that shows the negative side.

Electrolytic capacitor.

  • Resistor.

The resistor will be responsible for limiting the voltage that will be delivered to the LEDs and will be connected in series with them. For this project we need a 6.8KΩ resistor, the resistors have their resistance defined by the colors printed on the resistor itself, in the case of the 6.8KΩ resistor, a blue, gray, red and gold resistor is required.

6K8 resistor.

Unlike the capacitor and the diode, the resistor has no polarity, that is, it can be connected from either side, either positive or negative.

  • LED

The LEDs are like small lamps that will emit light for our flashlight, the LED is a polarized component, that is, it has a positive terminal and a negative one, if it is connected, it does not work and depending on the situation it burns.

In this project we use 6 high brightness LEDs, they must be connected in series with each other, that is, the negative terminal of one connected to the positive terminal of the next one and thus the six must be connected.

LED polarization.

Step by step:

  1. The cables coming out of the motor must be connected to the rectifier bridge at the terminals that indicate alternating current, just look for the letters AC in the ready bridge, in the case of the bridge with diodes at the central terminals as in the diagram.
  2. From the positive and negative terminals of the bridge, two cables must be connected connecting the capacitor terminals (carefully look at the polarity of the capacitor, negative and positive cannot be inverted). The capacitor will be connected in parallel with the cables.
  3. The resistor must be connected to the positive terminal of the capacitor, it will be in series with the circuit, the resistor has no polarity so it does not matter which side of the resistor will be connected.
  4. From the other terminal of the resistor connected to the positive terminal of LED 1 then connect the negative terminal of LED 1 to the positive terminal of LED 2 and so on by connecting the 6 LEDs in series.

    Serial connection of LEDs

  5. From the negative terminal of the last LED connect a cable to the negative terminal of the capacitor closing the circuit.

The diagram below details the entire wiring diagram:

Electric manual flashlight scheme.

This video list has an exact explanation of each of the electronic components used in the flashlight.

Mechanical assembly.

The mechanical assembly of the lantern was made in MDF 6mm and on one side MDF 15mm for fitting the motor.

Basically a box with the following dimensions

Dimensions of the hand torch.

In the side cover where the motor will be fitted, MDF 15mm was used to hold the motor and a hole was drilled with the 50mm cup saw and the motor shape made with a file as in the drawing below:

Details of the hole for fixing the motor.

The handle that will be used to charge the flashlight was made with 15mm MDF and cut on the tic tico, it must have a hole to fit the motor shaft, a 7mm drill will make a tight hole for the shaft and a screw will lock to the motor shaft.

Detail fr fixing the drive handle.

There are two models of springs for the fuselage carburetor, in which case we will use the following spring

Beetle carburetor spring.

And the cable fasteners are of the type to be fastened by nails or screws:

Cable fasteners.

The image below shows how the spring will be attached to the handle.

Fixing the spring to the handle.

Once inside the box, just put the motor in place and fix the other end of the spring using a screw or even another cable fixer.

A retractor was placed so that the handle is not too tight with space inside the box, it can be glued with hot glue

Complete spring fixation.

After the LEDs are already fixed on the front cover of the flashlight it is time to close and place the circuit inside the box. The electronic circuit can be fixed with hot glue.

Fixing the electronic circuit to the box.

Now the flashlight is ready, just put the last side of the lid and close.

With this mechanical assembly, it is possible to use the flashlight with only one hand, the handle has spring return which does not require the use of a crank (which would make the flashlight have to be used with both hands, one to hold the flashlight and one to turn the crank), the stroke of approximately 1/4 of the motor rotation ensures a sufficient voltage to activate the electronic circuit and the capacitor ensures that the lantern has a longer illumination time before it is necessary to activate the handle again.

An excellent project to be used in school science fairs and also to satisfy the pleasure of curiosity in the functioning of a flashlight and the various physical, electronic and mechanical concepts that this project involves.

About the author

Henrique Mattede is a Professor of Electrotechnics and a technology enthusiast. Creates videos and articles about electrical on the internet to bring free knowledge to those looking for it.