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Q: Electric motors ( Answered,   1 Comment )
Subject: Electric motors
Category: Science > Instruments and Methods
Asked by: steller-ga
List Price: $50.00
Posted: 06 May 2006 16:15 PDT
Expires: 05 Jun 2006 16:15 PDT
Question ID: 726154
Can an electric motor on a room fan be used to generate electricity if
spun backwards rapidly? What kind of common electric motors can
generate current? Are there DC motors that will do so?
Subject: Re: Electric motors
Answered By: sublime1-ga on 06 May 2006 18:00 PDT

A review of book available from, titled, 'How to Make
Home Electricity from Wind, Water, Sunshine', by John A. Kuecken,

"[the author] goes as far as to say almost any motor can be used
 as a generator..."

Here's a post in a Yahoo Group on Home Energy Systems Discussion
in which the writer talks of having used a ceiling fan motor as
a generator:

A regular room fan motor would function similarly, but require 
higher rpms to produce electricity. A typical house fan is 
powered by a four pole AC induction motor. Here's a page from 
the Hyperphysics website at Georgia State University that shows
the workings of an AC induction motor:

A useful discussion on the forum clarifies many 
things about the various types of motors which can be used
to generate a voltage:

"...I thought of AC induction motors. These can be controlled
 with an inverter but I'm not sure whether they will operate
 as a generator when at high speeds. I have seen induction
 motors used as generators buty they need to be run at their
 rated speed ie. 3000rpm for 50Hz because when you move away
 from this speed the motor stops generating."


"I have found this company:

 They make brushless DC motors of 6KW or 12KW ratings (and
 might even be scalable beyond that). They look very attractive.
 Await to hear back for a price. They have speeds of up to
 6800rpm and voltages as high as 72v."


"you can use a DC motor as a generator. The simplest is a
 standard brushed DC motor as it produces DC voltage that
 can be used to charge batteries or power circuits with very
 little electronics needed. Other motors such as brushless
 DC motors or AC induction motors can also be used as
 generators, but they will produce an AC output which will
 need converting to DC before it can be used to charge batteries.

 Your DC motor will have two terminals, lets call them A and B.
 Say you connect +ve to A and -ve to B and the motor turns
 clockwise, then when you use the motor as a generator; when
 you turn the motor clockwise A will be the +ve output. Simple.
 The voltage at the output terminals is proportional to the
 speed of rotation."

More on the page:

And here's a useful post on the Scoraig Wind Electric site:

"The best I've found for use as low-RPM generators are the
 permanent-magnet "servo" motors such as those sold by Surplus
 Sales in Lincoln, NE.  For about $30 they will sell you a
 permanent-magnet motor that will put out about 5-10 amps at
 battery-charging voltage, at an RPM consistent with direct

Much more on the page:


Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.

Searches done, via Google:

"almost * motor * as a generator

"motor as a generator"
Subject: Re: Electric motors
From: myoarin-ga on 07 May 2006 08:09 PDT
If you wanted test the above, take a plug-in fan, turn it on, put the
prongs of the plug in your mouth and spin the fan  - either way.  No,
you won't electrocute yourself, just get a slight sting from the power

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