On 28 Mar 2012 at 17:13, RussellMc wrote:

> The Freescale app note below suggests that a typical ceiling fan
> induction motor can be speed controlled using a basic phase controlled
> TRIAC "dimmer".
>=20
> Fan and dimmer and I are not to hand as I write, so rather than going
> and blowing uo a dimmer in the pursuit of knowledge, what do people
> think of this?
>=20
>=20
> http://cache.freescale.com/files/microcontrollers/doc/app_note/AN3471.pdf
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> If single phase motors can be speed controlled this was then people
> would do it in droves.
> I have severe doubts about this circuit.
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> But, Freescale must be right. No?
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> Thoughts.

Yeah, the correct way to do inductive motor speed control is to vary freque=
ncy, but=20
that's too expensive. But I'm thinking a fan load has something going for i=
t that migh=20
allow this cheap voltage chopping method to be of some use. The speed torqu=
e=20
curve of a fan slowly ramps up from 0 till fan gets up near operating speed=
 then=20
load rises dramatically. If the range of useful fan speeds was say 90-100% =
to give=20
say 25-100% air flow, variable voltage and fixed freq could probably be qui=
te=20
useable.
--=20
Brent Brown, Electronic Design Solutions
9 Titoki Place, Pukete,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz



--=20
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