How to use DC motor as a generator? how to increase its output voltage

What is a Dc motor

A DC motor is an electrical machine that converts direct current electrical energy to mechanical energy most of the types rely on the forces produced by the magnetic field the same DC machine can be used as a motor or generator. DC motor speed can be controlled by using a variable supply voltage or by changing the strength of the current in its field windings. If a current carrying conductor is placed in a magnetic field it experiences a mechanical force and its direction is explained by Fleming’s left-hand rule and its magnitude is given by F=BIL

B=magnetic flux density, I = current, L = length of the conductor within the magnetic field

Fleming’s rule can be explained by an example like if we stretch our first finger, second finger and our thumb of the left hand to be perpendicular to each other

Then the direction of the magnetic field is represented by the first finger direction of the current is represented by the second finger and the direction of force experienced by the current carrying conductor is represented by the thumb

DC motor working


A DC motor with permanent magnets can easily be a generator it won’t affect If it is brushed or not. A motor without brushes make a great generator but we need to add a rectifier to get a DC output. When a motor has separate field windings in place of permanent magnet we will need to energize the winding from external DC source example a battery.

Another example is a car alternator uses Dc slip rings to supply small field current to the rotor and a three-phase stator winding if we need to get anything out we need to energize the field windings and then we get three phases Ac from the stator. In order to get DC, we must rectify it in order to control the output power it is done by modulating the field current.

DC motor can act as a generator if a DC supply is given to the armature then it acts as a motor converting electrical energy to mechanical energy. When permanent magnets are used in DC motors it can be used as the generator by spinning the shaft


A DC motor is 80% efficient as a generator and its output volts at 450 RPM is 14.4volts. A process that changes one dc voltage to another dc voltage is DC to Dc conversion a boost converter is used to step up the voltage it is like a switched mode power supply contains at least two semiconductors (diode & transistor) and one energy storage element a capacitor or an inductor or both to reduce voltage ripple filters made up of capacitors are normally added to the converter’s input and output



  • Lathes
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  • Electric traction
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  • Air compressor
  • Vacuum cleaner
  • Hair drier
  • Sewing machine