Simple Experiment Showing Dynamo and Diode Functions Using a Toy Car!

 This is a remote control toy car which works on four AA batteries. The remote control operates in the 27 MHz license free Citizen Band. Todays experiment is not on the remote control function, but another interesting feature which was noted by chance.

See that currently there is no battery in this car and the experiment is to be conducted without batteries.

When the car is moved forward manually at a good speed, we can see that the headlights light up, with brightness corresponding to the speed! During the process, the motor in the toy car is functioning like a dynamo or generator, producing an electric current which runs in the circuit and lights up the headlights made of light emitting diodes. We know that when a coil of wire in the motor moves in a magnetic field or if the magnet moves relative to the coil, an electric current is generated within the coil. It is that current which lights up the LED headlights. 

Now see what happens when the car is run manually in the reverse direction. Even while running it at the same speed in reverse direction, the LED headlights do not light up. That is because when the direction of movement of the car is reversed, the direction of current generated also gets reversed. LEDs have the basic function of diodes, which do not allow electricity to conduct in reverse direction. That is how rectifier diodes are used to convert alternating current to direct current in power supplies. In summary, this simple experiment with a toy car run manually illustrates both the principle of a dynamo or generator and a semiconductor diode. Instead of using a multimeter to measure the current, we are using the built in LED headlights to show generation of electric current with movement of the car.

Almost same principle is used to charge batteries in hybrid cars while braking, in the process of regenerative braking. Regenerative brakes work by driving an electric motor in reverse to recapture energy that would otherwise be lost as heat during braking, turning the traction motor into a generator. The power generated is fed backwards through the system and allows energy harvested from deceleration to charge a battery or capacitor.