Motor with generator

Most of conventional motors today are bidirectional devices. If you apply electricity the motor converts it to mechanical rotation. However if you rotate the motor shaft it generates electricity. This phenomenon is used in our experiments with an electric generator.

Electric generator kit consists of the precision made electric motor, hardware for connecting it to our motor kits and light emitting diodes (LED) – super bright red LED and a regular green diffused one (see their specifications at the end – super bright LED is 300 times brighter!).

So what experiments could be done with such a simple generator? The answer depends on the complexity of your project.

Here is a simple approach for the beginners. First of all it provides the perfect way to check that you have built a motor capable of doing some work.

  • You may see how electricity is converted to mechanical rotation and mechanical energy is converted back to electricity.
  • Motor connected to generator slows down. You may observe that connecting an LED slows down the motor even further; and if you connect both LEDs in parallel motor may not even provide enough speed to light them.
  • If you can measure input and output voltage and current you may calculate input and output power and explain why they are so different based on the fundamental physics law of conservation of energy.
  • The generator motor is a DC motor and generates DC power. The LED is one way device. You may experiment with LED connection. Note: LED anode has longer lead and should be connected to “+”.
  • If in your kit motor the rotor axle is at the same height level as the electromagnet and the sensor, motor may spin in both directions. In this case LED will light up only when rotation generates correct polarity. You may connect the second LED with reverse polarity and get an indicator for direction of rotation:

Direction indicator - green Direction indicator - red

For advanced experiments with the generator see Torque and Efficiency Calculation.

The generator is designed for use with kits #1-10 but could be also connected to QuikLock motors built from kits #13-14:

QuikLock motor with generator

Not every motor could be used as a generator with our kits. Even if we ignore the power loss in it, the motor will generate the voltage it was designed for only at nominal speed. Most of the small industrial motors are high speed motors at low voltage. Unless we rotate their shaft at this high speed we will not get enough output voltage to light up an LED. Kit motor slows down significantly (to 1000 rpm or even less) when connected to generator. The generator should be able to generate at least 1.8 Volts of electricity at this speed – most motors cannot do it. In other words the motor used as a generator should be designed for relatively high voltage (6-12 V or even more) and have relatively low speed. Also it should not require too much torque to rotate the shaft.

After experimenting with more than 20 different motors we found two of them that provide acceptable results when used as generators. These are high quality industrial motors with precious metal brushes used in CD/DVD players and VCR. The model numbers are RF-500TB-12560 and RF-520C-17410; their technical data could be found in Links or on the Internet.

Here is the technical data for red and green LED provided with the kit:

Super bright clear red LED:
Nominal voltage: 2.1 V (starts working at 1.8 V)
Current at nominal voltage: 20 mA
Maximum current: 50 mA
Typical luminous intensity (brightness): 12000 mcd (They are really bright – Do not look straight through the lens!)
Viewing angle: 15° (so it is safe to look at it from the side)

Green diffused LED:
Nominal voltage: 2.2 V
Current at nominal voltage: 20 mA
Maximum current: 25 mA
Typical luminous intensity (brightness): 40 mcd
Viewing angle: 30°

Luminous intensity of the LED is measured in mcd (microcandelas). So for the red LED it is 12 candelas; prior to 1948 this would be roughly comparable to 12 candles of specific size. Oh well… they did not have LED technology at that time.

New! Watch Simple Electric Generator video on our YouTube channel.

1 Comment

  1. Thank you for sharing the facts of how electricity is converted into the mechanical rotation and then back into electricity. This information is very helpful.

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