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<div class="moz-cite-prefix">John,<br>
</div>
<div class="moz-cite-prefix">My earlier message was wrong about the
signal direction of the white or yellow wire, but the signal wire
is not only for whether the fan is rotating or not (to check if it
is stalled to avoid too much compensation current) but to check
the current speed of the fan to determine whether to increase the
pulse-width or not, and to determine a synchronizing signal to
time pulse to the fan (generally not used in this fashion for a PC
fan, but in big motors like those cooling the braking resistors of
a railroad locomotive.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">If you didn't already know, PWM, or
pulse width modulation, changes the time on versus the time off of
a square wave without changing the frequency (called the Duty
Cycle).</div>
<div class="moz-cite-prefix"><img
src="https://circuitdigest.com/sites/default/files/inlineimages/pulse-width-modulation-duty-cycle.gif"></div>
<div class="moz-cite-prefix">(courtesy of Circuit Digest "What is
PWM?"
<a class="moz-txt-link-freetext" href="https://circuitdigest.com/tutorial/what-is-pwm-pulse-width-modulation">https://circuitdigest.com/tutorial/what-is-pwm-pulse-width-modulation</a>)</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">The full power during the on portion
overcomes the angular torque problem of turning the roters instead
of a gradual increase in voltage like that of a sine wave
(building up the magnetic field more quickly). The inertia of the
rotating blades acts to smooth and average the pulses into an even
movement - especially at higher frequencies of the pulse stream --
not as important for fans motors but really useful for things like
model trains. Electronically, the average amount of power
delivered to a motor is proportional to the duty cycle:</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><img class="caption caption-processed"
src="https://circuitdigest.com/sites/default/files/projectimage_tut/Pulse-Width-Modulation.jpg"
alt="What is PWM: Pulse Width Modulation" title="What is PWM:
Pulse Width Modulation"></div>
<div class="moz-cite-prefix">(ref: Circuit Digest)</div>
<div class="moz-cite-prefix">This works for dimming LEDs and other
devices or components that require full voltage to operate.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">This averaging effect can be done
electronically as well, passing it through a low-pass filter to
extract out the fundamental frequency components (a square wave is
an {practically} infinite sum of sine waves of the odd-harmonic
frequencies), and by rectifying the pulse stream and then using a
capacitor to smooth the ripple. This will result in a voltage
proportional to the pulse width.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">See also: Arrow Electronics: What is
PWM? Pulse Width Modulation Explained"
<a class="moz-txt-link-freetext" href="https://www.arrow.com/en/research-and-events/articles/what-is-pwm-pulse-width-modulation-explained">https://www.arrow.com/en/research-and-events/articles/what-is-pwm-pulse-width-modulation-explained</a></div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">See these videos:</div>
<div class="moz-cite-prefix">"Electronics Basics 23: Pulse Width
Modulation" <a class="moz-txt-link-freetext" href="https://www.youtube.com/watch?v=GQLED3gmONg">https://www.youtube.com/watch?v=GQLED3gmONg</a></div>
<div class="moz-cite-prefix">"What is PWM"
<a class="moz-txt-link-freetext" href="https://www.youtube.com/watch?v=B_Ysdv1xRbA">https://www.youtube.com/watch?v=B_Ysdv1xRbA</a></div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">- sgh<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 2/2/21 1:43 PM, John Vaughters via
TriEmbed wrote:<br>
</div>
<blockquote type="cite"
cite="mid:787047071.1667246.1612291403498@mail.yahoo.com">
<pre class="moz-quote-pre" wrap="">
Computer fans are almost always brush-less, actually never seen a brushed one. Because the electrical noise is too high. She 3 pin motors are simply two power pins plus one tachometer pin, which you generally only want to determine if the fan is failing. I could be wrong about this part, but I expect that they are single voltage and reducing the voltage may or may not affect the speed much and possibly could damage the fan over long use. However, I seem to remember some schemes to make 3 wire fans speed controlled. it's worth a look online I suppose.
John Vaughters
</pre>
</blockquote>
<p><br>
</p>
<pre class="moz-signature" cols="80">--
Scott G. Hall
Raleigh, NC, USA
<a class="moz-txt-link-abbreviated" href="mailto:ScottGHall1@GMail.Com">ScottGHall1@GMail.Com</a>
_Although kindness is rarely a job, no matter what you do it's always an option._
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