Introduction

In this project we are making an electric tricycle, which operates by getting power from a battery source. The speed control mechanism used here makes the drive more safe and comfortable. It will be beneficial for the physically challenged people. The battery is charged by a solar panel.

Description

A motor is a device which converts electrical power into mechanical power. Machine reduces human effort and makes the work easier. The two transistor model speed control mechanism makes the rider to travel with a safe and smoothly adjustable speed.

Materials required

1. Battery
2. Switch
3. Transformer
4. Resistor
5. Variable resistor
6. LED
7. Capacitor
8. Diode
9. Motor
10. Wheels
11. Transistor
12. Connecting wires
13. Solar panel

Components Description

Resistor

A resistor restricts the flow of current. The 1kΩ resistor used here is carbon film and quarter watt type.

Capacitor

A capacitor stores electric charge. Capacitor used here is 1000 µF and it is an electrolytic type.

LED (Light Emitting Diode)

It is a transducer which converts electrical energy into light energy.

Transistor 

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit. BC 547 is a general purpose transistor. It is an npn epitaxial silicon transistor. Its maximum collector current (DC) is 100mA.

BD 140 is a pnp epitaxial silicon transistor produced by Fairchild Semiconductor. It is suitable for medium power linear and switching applications. Its maximum collector current (DC) is 1.5 A.

Transformer

It consists of two coils of insulated copper wire linked by an iron core. Transformers are used to step up (increase) or step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is   no electrical connection between the coils. Here we have used a shell type step down transformer which step downs 230 volt AC to 12 volt AC. It can supply maximum 1A current. The working principle of transformer is very simple. It depends upon Faraday’s law of electromagnetic induction. Actually, mutual induction between two or more winding is responsible for transformation action in an electrical transformer.

Diode 1N4007

These are general purpose diodes. These diodes have high current capability and low forward voltage drop. The average rectified output current is one ampere.

12 V Battery

We have used three number of 4 volt lead acid batteries in series to get 12 V. You can use  directly a 12 V battery if available.

BO Motor

BO stands for Battery Operated. BO motors are suitable for electronics hobby activities especially for small projects. It consists of small DC motor with gear arrangement to increase the torque. It is used in many DIY Robotic applications that are operated through batteries.

Solar panel

A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell, defined as a device whose electrical characteristics e.g. current, voltage, or resistance vary when exposed to light. Cells can be described as photovoltaic even when the light source is not necessarily the sunlight. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon or germanium. Electrons are excited from their current molecular/atomic orbital. Once excited an electron can either dissipate the energy as heat and return to its orbital or travel through the cell until it reaches an electrode. Current flows through the material to cancel the potential and this electricity is captured for our use.

Working

The components are connected appropriately according to the circuit diagram, proper alignment is done. Wheels are fitted to the motor shaft.

The full bridge rectifier converts 12 V AC into 12 V DC and filtered by the 1000 µF capacitor. The LED in series with 1 kΩ resistor is just for power indication purpose. The output is connected to 12 V battery terminals for charging. This charger is helpful at night and in a cloudy weather.

The speed control circuit operates through 12 V DC supply. Here we have designed simple circuit based on two transistors that can be used to control the speed of two 12V DC motors. The left LED series with a resistance in the circuit diagram is just a power indicator. A 10kΩ variable resistor is used to control the speed of motor. This project runs on 12 volt DC. Here we have used a 12 volt rechargeable lead acid battery.

When the resistance value of the variable resistor decreases, it increases the base current of transistor BC 547 which in turn decreases the collector voltage of the same transistor. Since the collector of BC 547 is coupled to the base of transistor BD 140, the decrease in collector voltage of BC 547  forward biases  BD 140 more and that’s why the speed of the motor increases. What actually happens here is the voltage across the armature of motor is controlled. There is an LED series with a resistance which is connected to collector of BD140. The brightness of the LED will be proportional to the speed of the motor. Heat sink is provided to protect bd140. In a DC motor, Speed of armature is directly proportional to back emf and inversely proportional to magnetic flux.

Mathematically,

N α (E_b /ɸ)

Where,

N  =  speed in rpm.

E_b  =  back emf

ɸ  = field flux

As we are using a permanent magnet dc motor, here field flux is practically constant. So, now

N  α  E_b

But E_b  = V – I_aR_a

Where,

V = voltage across the armature

I_a = armature current

R_a= armature resistance

Definitely R_a  is fixed here, when Vvaries E_b also varies. Thus, when voltage across armature is variable, the back emf varies accordingly. As back emf is directly proportional to armature speed, a variable back emf will provide us a variable speed. This is how the speed is controlled.

Application

1. This tricycle is used for physically handicapped persons. As there is an electric motor drive, the human effort is reduced to drive the cycle using muscle power.

2. It is completely pollution less and environment friendly as there is no internal combustion engine. As we are using solar panel, here we are getting energy from a nonconventional source.

3. It is more economic compared to fuel engine.