Love This

[Don.F.Broadus at ucm.com]

PWM of cooling fans is done almost exactly the same way injectors are fired,
more or less duty cycle to a transistor. 

> -----Original Message-----
> From:	Clarence L.Snyder [SMTP:clare.snyder.on.ca at ibm.net]
> Sent:	Tuesday, February 02, 1999 9:43 AM
> To:	diy_efi at efi332.eng.ohio-state.edu
> Subject:	Re: Love This
> 
> Ernst Denbroeder wrote:
> > 
> > > >That's a good question.  How do they PWM the coolant fans? I know I
> > > >can hear the relay clicking away..
> > > >Shannen
> > >
> > > I believe it's (the actual switching) done with an SCR, but that is
> coming
> > > from a total klutz in terms of electronics.
> > >
> >         Close... :)  SCR's are used for AC applications.  An SCR relys
> on
> > the 0V crossing to turn off.  And a TRIAC is two SCR's in parallel (sort
> > of).  :)
> > 
> >         Ernst.
> Also used (with commutation circuit) on DC controllers like the GE EV1
> motor controller used on forklifts and some electric cars. REAL tricky
> getting the suckers to turn off though!