Love This

[Clarence Wood]

  Could you, or someone, please explain PWM (assuming that PWM=Pulse Width Modulation) of cooling fans?  I thought that cooling fans worked on an on/off system.  Under what conditions would you want PWM control, and what is the pulse width that is being modulated?  You guys really know how to humble a guy; I thought I had a lock on cooling fans!(:<

Clarence  


At 12:10 PM 2/2/99 -0600, you wrote:
>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!
>
>