Love This

[Don.F.Broadus at ucm.com]

Actually an AC light dimmer delays the firing of a triac so that only a
portion of the sine wave goes to the lamp.
For Dim the triac is on for 30 degrees of the 180 degrees positive peak and
30 degrees for the negative peak.
PWM deals exclusively with square waves and DC applications. AC Motor
control usually are variable frequency drive types.
No harm intended.    

> -----Original Message-----
> From:	Van Setten, Tim (AZ75) [SMTP:Tim.Van.Setten at CAS.honeywell.com]
> Sent:	Tuesday, February 02, 1999 5:11 PM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	RE: Love This
> 
> > Subject: 	Re: Love This
> > 
> > >  Could you, or someone, please explain PWM (assuming that PWM=Pulse
> > Width
> > Modulation) of cooling fans?
> > 
> > Subject: RE: Love This
> > 
> > >  Could you, or someone, please explain PWM (assuming that PWM=Pulse
> > Width
> > Modulation) of cooling fans?
> > 
> > Here's my .03 cents worth... Look at it from this angle.  The light
> dimmer
> > is your house uses PWM to control the intensity of the light.  The
> reason
> > the "brightness" of the light changes is because the "average power"
> > dissipated changes, ie. 1/2 bright, 50/50 duty cycle, full bright, 100%
> > duty cycle.
> > 
> > In an electric motor, the start currents etc. are very high, so PWM is
> > used to overcome most of these losses.  Again, the reason the motor runs
> > at 1/2 speed at 50/50 duty cycle is because the average power dissipated
> > is 1/2 of full power.
> > 
> > Hope this helps....Tim.
> >