Are there any DC generators without brushes and a commutator?

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Quix270

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Are any generator that produce dc current without brushes or commutator?
 
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I don't know of any off the top of my head. Is this a theoretical musing or a more practical inquiry?
 

anorlunda

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Motors can be used as generators.

 

Quix270

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I don't know of any off the top of my head. Is this a theoretical musing or a more practical inquiry?
Practical Inquiry
So all needs commutator?
 
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Quix270

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There are no dc generator that produce dc current without commutator or brushes?
 
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You can make AC current without brushes and then rectify it. If you describe why you need to know this we can be more helpful.
 

Quix270

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So all generator are ac but some have commutators or rectifiers to produce dc?
 
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So all generator are ac but some have commutators or rectifiers to produce dc?
There are AC generators without brushes. Please: why do you want to know?
 

Baluncore

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What is this fascination with brushes? It is commutation that is important for DC.

A voltage is generated when a wire moves relative to a magnetic field. The voltage is proportional to the rate-of-change of magnetic flux through the wire loop. Obviously the flux cannot increase forever, so at some point the flux must be reversed, to make AC.

To make DC the connections must be reversed each half cycle, that is called commutation. That reversal can be done with brushes on a commutator, or with asynchronous rectifier diodes as used in a car alternator, or with a synchronous rectifier which senses the position of the rotating magnetic field and electrically switches the appropriate windings to the DC output.
 
You need to state your intended use. Do you want to produce DC current for welding? How many amperes and volts will you need?
Squirrel-cage AC motors and brushless permanent magnet motors have no brushes. Some electronics for safety and control will be needed. A DC generator with brushes and a commutator is a very old technology.
Rather than designing it yourself, it is much safer and less expensive to buy a DC power supply. You can buy a power inverter to generate DC electronically.
 
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Some Homopolar generators manage it. The ionic liquid / liquid metal variety have electrodes, but they do not erode like traditional commutator brushes.

Also, I don't know the internal configuration of a superconducting homopolar generator, but an early type also managed without brushes. I Remembered this from a 'classic' Scientific American article on research-grade superconducting electromagnets, where the 'test coil' was 'close coupled' to the generator stator...

FWIW, a multi-pole stepper motor plus diode rectifier array for the resulting polyphase AC will give you fair DC without brushes or mechanical commutation. As not engineered for this task, efficiency is likely to be sub-optimal...

Um, what are you trying to achieve ??
 

tech99

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Are any generator that produce dc current without brushes or commutator?
The very first generator, or dynamo, was made by Michael Faraday and gave a DC output. It did not have a reversing device (commutator) but it did have one rubbing contact. It can be seen in his laboratory at the Royal Institution, London.
 

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