Re: Hey, Wingerr , got PWM ?? - Saab 9000 Bulletin Board - Saabnet.com
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Re: Hey, Wingerr , got PWM ??
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Posted by udderslate (more from udderslate) on Mon, 10 Sep 2007 06:32:26 Share Post by Email
In Reply to: Re: Hey, Wingerr , got PWM ??, Wingerr, Sun, 9 Sep 2007 21:31:15
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Hi , great to hear from you .
I built this;
http://www.solorb.com/elect/pwm/pwm1/

Switching is 400hz.
I imagine that a low duty cycle would be very audible
when used on the Fan motor . too low of a switching speed has its issues too . If the pulse rate and motor RPM is same , you power only one
commutator per rev . I figure 3pulse min X 3 commutators ..10x or so min .

amazed that R-shack had what I needed .

Procastiation ..that me .
I intended this to replace a resistor pack , that blew the Temp Fuse .
I just wired across it , and of course it works , so there went my
ambition too .

I strongly suspect , the fuse blows at startup ( its a 10A rating ) .
Old motors likely spike a bit extra current at turn on , the PWM is
a soft start by design .
My prototype has a trimpot to vary PW , in actual use , I would hoble
the dash knob , to switch discrete resistors ?

Did you ever measure the motor voltage at the fan motor ,
at each dash setting , 1-2-3 ( 4 is 12v ish ) .

Heat??? I dunno .
0.007*19A is the dissapated power in the FET. 0.133 W
Its the Schottky that has me guessing , as I don't know the specifics
about the fan motor inductance . The schottky gets slammed with back EMF .

Unknown is the EMI of this .


posted by 137.71.2...

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