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Author Topic: Are generators and electric motors the same?  (Read 2420 times)

Bill

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Are generators and electric motors the same?
« on: 27/08/2009 10:30:03 »
Bill asked the Naked Scientists:
   
I have a question about electricity; I read that a generator and an electric motor are basically the same, so for example if i spun the blades of a ceiling fan fast enough would it generate AC volts? 

thanks  ~ bill ~


What do you think?


 

Offline Turveyd

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Are generators and electric motors the same?
« Reply #1 on: 27/08/2009 12:16:13 »
I think you'd have to spin in reverse or it might just be a input that makes it work,  but yes basically.

Why Hybrid cars can re generate using there electric motor as a brake.

 

lyner

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Are generators and electric motors the same?
« Reply #2 on: 27/08/2009 14:04:35 »
If the motor has a permanent magnet then it could act as a generator. Most mains motors do not use a permanent magnet, though and use an electromagnet (field winding). In particular, the sort of motor used in fans would be induction motors, which operate a bit differently from the GCSE level motor and have no magnet nor do they have  a simple field winding. They are even less likely to generate a current. But, to be honest, you may get a  tiny, measurable voltage from one.
Hybrid cars will not have a permanent magnet but will get the magnetic field using a small amount of current, initially, from the battery (just like the alternator).
 

Offline syhprum

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Are generators and electric motors the same?
« Reply #3 on: 27/08/2009 19:50:34 »
I think that modern alternators on cars use a small a mount of permanent magnets to get them going as the transistors in the voltage regulators are reluctant to pass any current at the low voltage generated by the residual magnetism of the rotor.
The old system was to bleed in a small current from the battery but if this is quite dead you can't get things going. 
 

Offline techmind

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Are generators and electric motors the same?
« Reply #4 on: 29/08/2009 00:08:16 »
A small DC motor with permanent magnets, as used in toys and the like, is indistinguishable from a generator. Indeed if you connect one of the small grey Lego motors to a Lego light and flick the motor shaft between your fingers, you will find you can make the light glow momentarily. If you've got two motors, you can even link their shafts together, run one off the battery, and power a lamp with the other!

As others have pointed out, "big" motors and AC motors usually use "field windings" rather than permanent magnets, and these do require an external source of power to operate. You can use one of these motors as a generator in principle, but you may need to change the wiring so you can energise the field windings from an external power source (at relatively low power compared to the generated power).
You can vary the current in the field windings to control the voltage you get out of the generator.

In construction and mechanics, motors and generators are virtually identical.
« Last Edit: 29/08/2009 00:10:03 by techmind »
 

lyner

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Are generators and electric motors the same?
« Reply #5 on: 29/08/2009 00:30:51 »
techmind
Most 'big motors' are induction types. Just full of soft iron lamina and copper. Three Phase motors are such good value. No good as generators, tho.
Same for shaded pole types in fans, record players (history) and  all(?)refrigeration motors. No brushes / slip rings or moving parts (apart from the armature itself).
 

The Naked Scientists Forum

Are generators and electric motors the same?
« Reply #5 on: 29/08/2009 00:30:51 »

 

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