What is Dc motor: Definition and 321 Discussions

A DC motor is any of a class of rotary electrical motors that converts direct current electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current in part of the motor.
DC motors were the first form of motor widely used, as they could be powered from existing direct-current lighting power distribution systems. A DC motor's speed can be controlled over a wide range, using either a variable supply voltage or by changing the strength of current in its field windings. Small DC motors are used in tools, toys, and appliances. The universal motor can operate on direct current but is a lightweight brushed motor used for portable power tools and appliances. Larger DC motors are currently used in propulsion of electric vehicles, elevator and hoists, and in drives for steel rolling mills. The advent of power electronics has made replacement of DC motors with AC motors possible in many applications.

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  1. P

    Modelling the voltage measured across a dc motor

    Hi there, I have done an experiment measuring the voltage across the terminals of a dc motor, whilst running and then by holding it with my fingers to stop it. Done as demo for my high school class. The voltage reading was higher when the motor was running, which was against my expectations as...
  2. Z

    Questions about motion control and the moment of inertia referred to a motor shaft

    hello take a mechanism driven by a DC motor in automation books you find transfer functions such as : G(s) = k1/s(s+k2) normally it s assumed that the moment of inertia referred to motor shaft is a constant the point is that in general it is not a constant take for example a slider - crank...
  3. CarlPace

    Misc. DIY RC Boat with Parallel Impeller

    I'm not sure if you would call it a "Parallel Impeller," but the pics below should tell the story. I'm designing/3D printing my next RC boat from scratch, and I wanted to try something different from tried-and-true propeller and shaft system. Reasons? 1. Fun. 2. Using a "wet" brushless motor...
  4. Ranveer

    Engineering Homemade DC electric motor not working

    Summary : i have tried changing the batteries and wire,but still nothing. The wire is insulated and the coating is removed at the ends of the battery and the point where the wire touches the commutator. I have not counted the number of coils. This is required for a school project. If someone has...
  5. B

    Engineering Why Isn't My DIY DC Motor Turning?

    Hi so I'm making a DC motor for my school project and I have no clue why it doesn't work properly. I used copper wire to make the coil (around 50 windings) and put that around a wooden axle (the windings and the coil itself are secured using tape and cable ties), I have a split ring commutator...
  6. O

    I need help with a Baldor dc motor, 15kw 240 volt ,150 volt field

    I need help with a Baldor dc motor, 15kw 240 volt armature and 150 volt field, I don't need the 15kw and so want to feed it with 150 volts to both field and armature, does anyone know the effect this will have on the motor, can I cause damage, what would be the approximate power output, I know...
  7. K

    B Simple yet effective way to reliably control the DC Motor speed?

    As a part of our physics high-school self-study, we are making a stroboscope. We have a small 5-V DC motor that powers the strobe disk. It works as expected, but, clearly, the motor makes the disk spin at a constant speed. Is there an easy, but effective and reliable way to control its speed...
  8. Pipsqueakalchemist

    Engineering Separately excited DC motor problem (Electrical Engineering)

    Hello, so for this question I know how to solve it but I still have a few questions. First when the question means it's rated at 20 HP and 600 V, it's referring to the source voltage and Pin correct? Also in order to solve this question, the rotation loss Prot was neglected. This was because at...
  9. L

    Orbital shaker - DC servo or stepper motor

    Hi, I wish to build an orbital shaker (a bigger version of these examples: https://learn.adafruit.com/crickit-lab-shaker https://www.thingiverse.com/thing:2983846 As my aim is that it will work continuously for months around 100rpm what is preferred in aspects of heat and weight on top of...
  10. K

    Can a DC motor work without either a commutator or a controller?

    I am a mechanical engineer and my experience with electrical systems is almost nil. The concept of a simple DC motor explained here was quite interesting, especially the need of a commutator part: And then I checked this DIY simple DC motor here and was confused because there was no...
  11. SuperPat

    B How to Calculate Power and Torque for a 15kg Load at 15 RPM?

    Hi all I am Belgian and I have difficulty with english formulas. I'm trying to calculate the power and torque required of a motor to rotate a load. Here is the problem: I have a motor (axis up) on which is fixed a cylindrical load of 15Kg. The diameter of this load is 400mm Calculate the power...
  12. hi8192

    I getting my homemade DC motor to work (school project)

    hi everyone, i need to build a dc motor for my school project. I have used copper wire for the turns (60 turns), wood to build the structure of the armature and commutator. i have used neodymium magnets as my permanent magnets and paper clips as the brushes. I tried using a 9v battery with a...
  13. P

    Why is my homemade DC motor not working?

    Summary:: I have built a DC motor as a physics project, it has neodymium magnets, copper split ring commutator and insulated copper wire. It connected to a 12v power pack. There is definitely a proper current flowing because it creates sparks and the copper coil becomes hot. When I turned on...
  14. G

    DC Motor Efficiency: Why Does Efficiency Plot Look Like Parabola?

    So I am doing an experiement about DC motors, and I would like to know why the efficiency plot looks like a parabola. What is the structure behind that. Thank you in advance
  15. V

    LED module failing due to DC motor?

    I use a 2 Relay Motor module to control Direction on a motor (linear actuator). When Relay A is active, actuator retracts. When Relay B is active, actuator extents and Led Module is activated. After some repetitions Led module fail. Cause of the fail? I believe Surge voltage, although i am not...
  16. E

    Is this the default set up of a DC motor?

    ^because in my textbook, the set up doesn't even show the direction of dot/cross at points A/D, so we won't know the direction of current. then how are we supposed to use fleming's left hand rule to determine the direction of force?
  17. Chriz3223

    Questions about DC motor drive calculations

    Hi Physics! And again, thanks for the membership! I’m about to build a robot just with some old parts I have. The main thing is the motors. I have 2 DC Motors Specs below. (It’s a MFA975D Series with gear ratio 49:1) Operation range(Voltage): 12V No load = 147RPM Nm = 1,8 Stall Torque =...
  18. H

    Calculating Required Torque for 12V DC Motor

    I am designing a reciprocating saw that I plan to use a scotch-yoke mechanism to convert rotational kinetic energy into linear kinetic energy. I want to spec out a motor and the final thing I need to calculate is the required torque. The motor must be 12 Volts and I need to know the required...
  19. L

    What is the best DC motor for spinning a vortex impeller at 3000 rpm?

    I am looking for a recommendation on the proper DC motor to purchase for a custom project. My project involves vortexing water using an impeller, which resides in a 1.5" OD stainless shaft residing in sealed bearings - not a whole lot of resistance, easily turned by hand. I need to spin this...
  20. PhysicsTest

    Please confirm the torque curve of a DC motor

    This is the explanation in the section of DC motor Based on the above explanation i have drawn the torque curve. Can you please confirm if it is correct? In the initial position the torque is maximum and when it reaches the diagram 2 the torque is 0 and then it is maximum.
  21. Y

    Engineering Equation for a DC motor driving an arm

  22. sophiecentaur

    What does this DC motor supply do?

    A few years ago, I bought a Accurite weather station which has a wireless connection (not wifi) to a unit in doors. I was standing near it on a quiet sunny day and I heard a motor running. It turns out that is's a fan that blows over the temperature sensor to make sure it measures the actual air...
  23. H

    Designing a DC Motor Torsional Spring Circuit with Arduino Uno

    I'm a relatively new entry into the world of electronics so my understanding of what is possible may not be an accurate one. In a nutshell, I would like to have a DC motor act as a torsional spring with some variable virtual spring constant (k). The motor, or "spring", would act against an...
  24. G

    DC Motor "TACHO ERROR": Solutions & Causes

    Sirs, Am facing problem in dc drive that is dc tacho fault . I have checked tacho and found values of armature resistance are same in all segments in commutator. But motor speed not in control. It is automatically varying and suddenly stopped. Is there any bypass method available for tacho...
  25. kolleamm

    Motor Choice for Belt Movement: Stepper vs DC

    I want to move a belt quickly with a geared motor and with a high torque. Given a limited space, what would be better? 1.Stepper with a gear box or 2.DC motor with a gear box? (Both gearboxes would be the same ratio) I believe the answer is a DC motor with a gearbox but I need someone to...
  26. sophiecentaur

    Silent DC Motor for Automatic Watch Winder | Feasibility Study Stage

    At night, the house is totally silent and I want to make a silent winder to keep my automatic watch topped up. At the moment, our clock radio makes a disturbing whine all night and it disturbs us (real princesses) . I'm in the feasibility study stage. A winder needs to rotate about 600 times a...
  27. B

    DC Motor Overspeed: Cause & Effect

    i don't get how a dc motor will overspeed when you don't give the field windings power cause you need flux to make the motor move so how will taking away the flux make the motor go super fast
  28. Z

    Increasing the output torque of a DC motor with gears

    Hello everyone, I see videos showing the output torque can be increased by using gears and this is usually demonstrated with DC motors (simple DC motors can be removed from toys). I understand the general logic: * The DC rotates in a high speed. * The gear system reduces the output speed. * If...
  29. PainterGuy

    Some basic questions about a DC motor and a DC generator

    Hi, The picture below shows a DC generator. The magnetic field is uniform. As the coil rotates clockwise, the right side of coil is moving downward and the left side of coil moves upward. Using Fleming's right hand rule, one can deduce the direction of conventional current in both sides of...
  30. P

    High Current 12V DC motor speed control

    Hi. I am new here. I have a question on how to speed control a DC motor running a pump. The pump is a seawater cooling pump cooling a large V8 motor. Therefore I need to control the RPM, based on the temp of the V8 Motor. Any ideas?
  31. N

    Engineering Calculating Efficiency and Speed of a DC Motor at Half-Load Torque

    First some basic figures which are very rounded as I'm interested in the approach to the problem rather than accuracy of the answer at this stage: The field current will be 500/220 = 2.2727 Amps, and so power is a fixed loss at 1136.36 Watts The armature current is 45 - 2.2727 = 42.72 Amps. At...
  32. K

    Troubleshooting a DC Compound Motor: Negative Effects and Solutions

    What are the negative effects (if any) of running a compound DC motor with the series field open? I’m troubleshooting a 100hp recoiler motor on a metal slitter machine that constantly blows line and load fuses. It is on a DC drive. The drive has been replaced and the motor has been rewound. The...
  33. M

    Two Different Designs of DC Motors

    Hello, I have two designs of DC motors. Which one is more efficient? I believe what is in question is the location of the communicator. Whether it should be closer to the out piece of the shaft turning the gears? Or should it be further away towards the end? Does this make a difference...
  34. UMath1

    DC Motor Working Principles: Are Both Explanations of the Rotor Valid?

    I've seen two different explanations on the working principle of DC motors: One considers the rotor as a loop of wire that experiences a torque because current flow is perpendicular to an external magnetic field. The other describes the loop as an electromagnet which then experiences a torque...
  35. T

    Using a generator to charge 2 batteries

    My project is to create a circuit for a stroller that can store the mechanical work into electrical while moving around and with the push of a switch, use the electrically stored energy to assist the movement of the stroller. I’ve tried capacitors but it ended up not being enough voltage and I...
  36. IzitoI

    Physical units problem for a DC Motor with viscous friction

    Hi everyone, I'm trying to derive DC motor differential equations. I have some doubts: I have a viscous friction coefficient in terms of N*m*s. Is it possible to express it in terms of N*m*s/rad? And how? Some exercises show this value in Newton-meter-second and others in...
  37. K

    Choosing the right ESC for a Brushless motor

    Hello everyone. I have a RC helicopter (WLtoys V912) that recently had a crash. The main board was damaged and replaced and I got it working again but there is a problem. The main brushless motor is not as powerful as before and I have to apply 75% throttle to keep hovering above the ground. It...
  38. E

    Slowly Rotating Device For a Camera Pan Timelapse

    Hello all! I just discovered PF as I have been searching about a project I have been pondering for a day. The idea is to have a device that I can set my 3lb camera and have the device rotate left-to-right && || right-to-left over the duration of 2 hours for use in a sunset/cloud timelapse...
  39. J

    Torque on a DC motor spinning a wheel horizontally

    I need a 12v DC with appropriate torque. In my design, the axle of the motor would be pointed straight in the air and I want to affix a wheel to it and have the wheel spin flat, sort of like a pottery wheel sort of design. I know what the wheel is made of, its dimensions and approximate weight...
  40. nashikin58

    How to avoid a clash of magnetic charge and electric charge

    Hi, now I'm working on a project which involves a dc motor and high voltage. I'm developing a machine consists of a motor to rotate a platform disc and high voltage will be applied during the rotation. The problem is when I supply a positive high voltage at motor shaft during rotation, the motor...
  41. G

    Can a DC motor be made with one magnet?

    In a DC motor as I understand it, a current is passed through a coil of wire within a magnetic field. The magnetic field exerts a force on the current perpendicular to the direction of the current. This force causes the coil to spin. Is the coil is between the north and south poles of 2 magnets...
  42. G

    What factors affect the efficiency of a DC motor?

    Hi forum, I've been thinking about efficiency factors, I've read that they are more efficient at higher loads? I was wondering why this is... On the one hand at higher loads (maybe lifting a heavier mass) the rotation rate is reduced so this reduces energy losses due to friction? (so goes with...
  43. V

    Is it possible to convert a DC motor to a Stepper motor?

    I have doubt. Is it possible to convert DC motor to Stepper ? If yes then what is the procedure ?
  44. Juan Andrew

    Calculating Magnetic Field Strength in a Stator DC Motor

    Hey, I need a little help I know in a DC motor there are permanent magnet and also coil So my question is, what is the equation to calculate the magnetic field strength in a stator dc motor compound?
  45. Adem

    Need help with a homemade DC motor

    Hey guys I need help with my homemade DC Motor, as it doesn’t work, pic is uploaded Thanks
  46. C

    Engineering Mechatronics: DC Motor Position Control

    Homework Statement Write down the equations of motion and develop the continuous-time system. Homework Equations See my word doc. or PNG's. The Attempt at a Solution See my word doc. or PNG's. I assumed that there was no friction as no information was given. I can easily get the transfer...
  47. S

    Engineering Electrical Machine - Shunt DC Motor Problem

    Hi guys, can someone please have a look at the following problem that I am struggling with; An 8.25 kW shunt DC motor is supplied with a terminal DC voltage of 300 V. The armature resistance of the motor Ra is 0.25 ohms, and the field resistance Rf is 40 ohms. The field winding consists of 1500...
  48. D

    What generator/DC motor do I need for my wind turbine

    I am making a small wind turbine for my A-level RMT and wondering what kind of generator I need to charge a 12volt battery. The turbine is a vertical axis savonius turbine that will probably be about a meter high and half a meter wide. I know I can use permanent magnet dc motors and someone...
  49. D

    BLDC motor as generator to power eddy current brakes

    Hi everyone - here's a concept that I'd like a few opinions on: As part of a project, I'm looking at using a brushless DC motor mounted on a high-speed vehicle as a generator. Once the vehicle hits its top speed, the batteries should disconnect from the motor and the vehicle's own velocity will...