# Is There Truly a DC Electric Motor or Generator?

• Crazymechanic
In summary, there are truly DC motors and generators. They work by maintaining a static magnetic field between the stator and rotor.
Crazymechanic
Hi , maybe a pretty simple question and about things that we have long used and know well but is there a electric motor or generator that is truly DC? As much as I think there isn't because either to create , induce electricity in windings (generator) u got to have a changing magnetic field which in turn creates changing alternating current AC right?

And in dc motors like the BLDC (brushless dc) again the moving of the magnetic rotor is made by changing the phase and PWM, sorry if I make some mistakes.

The brushed dc motor operates from true DC I guess.
Tell me how much am I right and is there something to add?

P.S. Also doesn't in BLDC the rotor bearings experience very little friction as the rotor is held precisely in middle all the time when it operates by the magnetic field ?

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Answer is as simple as asking uncle google - there are truly DC motors and generators (brushed).
How DC field can make rotor moving ? Current is switched by commutator as rotor moves to keep rotor and stator DC fields static to each other.
Two fields (from stator and rotor) interact witch each other and creates torque spinning rotor faster. It can be seen form left hand rule.

http://en.wikipedia.org/wiki/Dc_motor
http://en.wikipedia.org/wiki/Commutator_(electric)
http://en.wikipedia.org/wiki/Fleming's_left-hand_rule_for_motors

About BLDC motor bearings.. so you say rotor levitates in the middle of stator ? Nonsense.. resulting force from magnetic field (on rotor) is zero - if rotor is perfectly in axis of stator (in other cases there is a "unbalanced magnetic pull" acting on rotor).

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Yes I understand that you need to reverse the polarity to keep the rotor going otherwise it would just move like 180 degrees at best and stop, but isn't reversing polarity what AC is all about, so from this kind of perspective I was asking about is there a true dc motor?
As it seems to me that true dc without any polarity change done by commutator both mechanical or electric(transistor) one is impossible as static magnetic field cannot create motion. Am I correct by saying this?

You do not reverse polarity of supplying DC current (it remains almost constant). This should be taken from this pont of view.

Hi there,

Thank you for your question. I can confirm that there are indeed electric motors and generators that operate on DC (direct current) rather than AC (alternating current). In fact, many modern electric cars and hybrid vehicles use DC motors for their propulsion systems.

DC motors operate by creating a constant magnetic field and using commutators to switch the direction of the current, which in turn causes the rotor to rotate. This is different from AC motors, which use alternating current to create a changing magnetic field.

As for BLDC motors, you are correct that they use a combination of changing phases and PWM (pulse width modulation) to control the speed and direction of the motor. However, the rotor bearings do experience some friction due to the rotation of the rotor, but this can be minimized through proper design and lubrication.

I hope this helps answer your question. Please let me know if you have any further inquiries. Thank you.

## 1. How do electric motors and generators work?

Electric motors and generators work by converting electrical energy into mechanical energy. In a motor, this is achieved by using an electric current to create a magnetic field that interacts with a permanent magnet, causing a rotational motion. In a generator, the process is reversed, with the mechanical motion being used to create an electrical current.

## 2. What are the main differences between electric motors and generators?

The main difference between electric motors and generators is the direction of energy conversion. Motors convert electrical energy into mechanical energy, while generators convert mechanical energy into electrical energy. Additionally, the design and components of a motor and generator may vary, but both rely on the principles of electromagnetism.

## 3. What are some common applications of electric motors and generators?

Electric motors are commonly used in household appliances, such as refrigerators and washing machines, as well as in industrial machinery and vehicles. Generators are often used in power plants to generate electricity for homes and businesses, as well as in portable devices like camping generators.

## 4. How efficient are electric motors and generators?

The efficiency of electric motors and generators can vary depending on their design and usage. On average, electric motors have an efficiency of around 80-90%, while generators typically have an efficiency of 90-95%. However, advancements in technology are constantly improving the efficiency of these devices.

## 5. Can electric motors and generators be powered by renewable energy sources?

Yes, electric motors and generators can be powered by renewable energy sources such as solar, wind, and hydro power. These sources provide clean and sustainable energy to power these devices, reducing our reliance on fossil fuels and helping to mitigate climate change.

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