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Use Motor as Dynamo, Motor as a Brake, Dynamometer Test

Almost any permanent magnet motor can be made to work as dynamo, this article is only about using permanent magnet motor as dynamo.

In general the dynamos are designed to work at low RPM (Revolutions Per Minute) so that the energy can be produced easily. Apart from this, there are only slight variations in the design and manufacturing of dynamos when compared to motors, but however this doesn’t limit any motor to function as a dynamo.

In simple terms let us understand, what is a motor? And what is a dynamo?

A motor is device which converts electrical energy in to mechanical energy. In the above figure the energy conversion is explained with a motor and a power supply. So when a motor is given power supply the motor converts the electrical energy in to mechanical energy by rotating the motor shaft, the force at which the shaft rotates is called the torque of the motor.

A dynamo is a device which converts mechanical energy in to electrical energy. In the above figure the force is provided to rotate the dynamo shaft and the electrical energy produced is used to glow a light bulb. Since this article is about using the motor as a dynamo, the symbol for the dynamo in the above figure is kept as motor symbol M instead of using the generator symbol G.

In this article a dynamometer setup is used to study and understand various parameters of a dynamo. This is because we need a device which can generate mechanical energy and transmit the energy to the dynamo, so that we can study the dynamo output.

The dynamometer setup is shown in the above figure. Power supply is provided to the motor (Motor 1) and the energy transmission to the dynamo (Motor 2) is done with the help of a shaft coupler.

Watch the video of motor as dynamo, motor as break, dynamometer test

Specifications of the Motors used in the Dynamometer setup

Motor M1

Input Voltage  Units volts

Input Current Units Amps

Motor Revolution     Unit RPM

12

0.058

1806

Motor M2

Input Voltage  Units volts

Input Current Units Amps

Motor Revolution Unit RPM

12

0.058

1506

Power Efficiency of the this Dynamometer setup

The power supply to the Motor (Motor 1) is kept constant while the load (R) on the dynamo  (motor 2) is varied.

The observations are recorded in the above table. At a particular load (R) it is observed that the power efficiency is high i.e 25.35%.

Conclusion: Proper load (R) on the dynamo (motor 2) gives high efficiency.

 

Dynamo (Motor 2) RPM Vs Power

Conclusion: The increase in RPM of the dynamo (motor 2) results in increase in power generated by the dynamo (motor 2) .

(Note: There is a limit at which the RPM of the dynamo (motor 2) can be increased, which is dependent on the maximum current the armature windings can with stand. Exceeding  this limits the motor/dynamo may be subjected to over heating and causes permanent damage to the unit.)

Dynamo (Motor 2) as a Brake

 Any dynamo can work as a brake, this is possible because the dynamo can absorb the  mechanical energy provided to it  and the electrical power generated can be dissipated by shorting the terminals of the dynamo.

When the dynamo terminals are not shorted its runs at 1620 RPM, but when the terminals are shorted the RPM of the dynamo drop downed to 610. This significant reduction in the speed of the dynamo allows it to function as a break.

The amount of decrease in RPM is proportional to the amount of power dissipated by the dynamo. The dynamo with a different configuration(higher power dissipation) can increase the RPM drop to even more significant level. which means when dynamo terminals are shorted the RPM can even be lower than 610.

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