The post explains a simple solar electric rickshaw or E rickshaw circuit which can easily built by anybody at home and used with a locally fabricated vehicle. The idea was requested by Mr. Amit.
The Design
Selecting a BLDC
In one of my earlier posts I presented an idea which could be effectively used for making an electric scooter using a BLDC motor and associated circuitry.
In this post we discuss a similar concept but without using BLDC motor just for the sake of simplicity.
Although using an ordinary brushed motor could appear to be inefficient compared to its BLDC counterpart, a brushed motor nevertheless eliminates the need of complex BLDC driver circuitry and the involved complicated wiring with the motor making the design extremely simple and layman friendly.
Moreover, a brushed motor can be operated by using an ordinary IC 555 PWM circuit, quite unlike a BLDC motor which requires much sophisticated control ICs which are not only difficult to find in the market, but are always vulnerable of becoming obsolete, risking the guarantee period of a E-rickshaw which might have incorporated that particular chip.
PWM Controller
A simple PWM circuit using IC 555 can be used for controlling the speed of the E-rickshaw by controlling the speed of its attached control motor.
The PWM concept makes sure that the energy consumption of the motor is significantly reduced and the efficiency is increased to the maximum possible range.
The 100k pot associated with the two 1N4148 diodes becomes responsible for varying the output PWMs at pin#3 of the IC, which in turn determines the conduction rate of the TIP142 transistor and the speed of the connected motor. For higher current, the TIP142 could be replaced with equivalently rated mosfet.
The 100uF capacitor at the base of the transistor makes sure that whenever the E-rickshaw is initiated, it delivers a slow soft start to the motor, rather than with a jerk or at a higher initial torque.
The potentiometer should be of very high quality so that it is able to sustain the frequent speed control operations and may last for many many years without going through fatigue or mechanical wear and tear.
Typical specifications of the pot should be as given under:
Made up of Cermet or carbon moulded element.
Approved by BS and CECC
Rated at 2 watt at 70 degrees C, in Cermet
Rugged construction
Military standard layout
Container sealed with MC1/MH1 standards
Stiff, silver plated terminals.
How the Speed Control is Installed
The speed control pot knob could be favorably installed in the handle of the E rickshaw, near the thumb of the driver, so that controlling the speed of the rickshaw could be executed with maximum ease, and minimum effort.
The ON/OFF switch of the circuit should be also accessible near the thumb of the driver installed on the handle, so that the driver is able to switch OFF the system immediately during a critical or a catastrophic circumstance.
The Brakes
Th braking mechanism of the proposed electric rickshaw could be built using the conventional technique, however it must include a push-switch which may be in series with the supply voltage to the motor circuit, and must be configured in such a way that when brakes are applied the switch is first deactivated, switching OFF power to the IC 555 circuit and the motor.
This makes sure that before the braking system hits the wheel axle, the motor is disabled first preventing its interference in the braking procedure.
Solar Panel Integration
In order to convert the proposed E rickshaw into a power saving solar electric rickshaw, a solar panel may be integrated with the system, as explained below:
Although primarily the battery of the vehicle will need to be charged from an AC mains operated charger quite often, the solar panel will act like a secondary back up charger, and help reduce electric consumption of the vehicle which in turn will help to save power and money for the end user.
Preferably the solar panel could be mounted on the roof of the vehicle and therefore could be as big as the size of the roof top of the E rickshaw, and rated at around 30V, 5 amps which looks quite economical for the proposed system.
With the above specified solar panel, no additional charger controller would be required as the voltage from the panel would automatically self adjust with the 24V battery specs, making the unit even more cost effective.
The solar integration ensures that the vehicle battery is kept on a topped-up condition whenever the vehicle is idling and thus help to increase the efficiency of the vehicle substantially.
The Battery
For a reasonable three seater E rickshaw including the driver, a 24V 20 amp motor would be just enough (assumed value), and to operate this motor optimally throughout the day, a 24V 200AH battery would do just well, although the user could alter the AH specs according to the needs and suitability of the vehicle's operational schedule.
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