[TriEmbed] laptop fan motor control question

Shane Trent shanedtrent at gmail.com
Tue Feb 2 18:48:17 CST 2021


I am enjoying this thread. I was not familiar with the need for
pulse-stretching to accommodate tach sensor power. Fascinating. This seems
like a great time to share my favorite app note about reducing
acoustic noise when using PWM to control a BLDC fan. I found it when I was
controlling a large fan that sounded awful under PWM control.

*Suppressing Acoustic Noise in PWM Fan Speed Control Systems*
https://ww1.microchip.com/downloads/en/AppNotes/00771b.pdf

Shane


On Tue, Feb 2, 2021 at 6:25 PM Brian via TriEmbed <triembed at triembed.org>
wrote:

> I store my paste at room temperature.  I like to live dangerously!  (I
> also don't have room in my house for another refrigerator, regardless of
> size...)
>
> That said, I recently bought some fresh paste...although my old stuff
> (and I mean old...several years of room-temp storage) still reflows, I
> was amazed by how many fewer bridge problems cropped up with the fresh
> stuff.  My workflow had been stencil, place, reflow, clean up several
> bridges on all four sides of TQFPs...with fresh paste, there was almost
> no cleanup to be done.
>
> I still store at room temp, though. XD
>
> As an aside, I've been thinking about switching to a low-temp
> tin-bismuth alloy, but I hear even the tiniest bit of lead will really
> attack and weaken that stuff, and I can't guarantee there aren't some
> atoms of lead still clinging to my iron..
>
> -B
>
> On 2/2/21 5:14 PM, Pete Soper via TriEmbed wrote:
> > Thanks, guys. The connections were red for positive, blue for ground and
> > brown for what I assume is the PWM input. It spins up with 5V just fine
> > and I feel silly about the high resistance measurement. The fan cools a
> > pair of heat pipes from two IC sites side by side and the whole thing is
> > copper. The IC sites have faint markings but I can just make out "attach
> > Peltier devices here". After only eight years I may be able to store my
> > solder paste in something smaller than a dorm fridge. :-)
> >
> > -Pete
> >
> > On 2/2/21 2:34 PM, Brian via TriEmbed wrote:
> >> On 2/2/21 1:15 PM, Pete Soper via TriEmbed wrote:
> >>> The DC resistance between any two pins with any polarity is much
> >>> higher than I would have expected: thousands of ohms.
> >>>
> >>
> >> Others have already mentioned:
> >>  - It's probably a brushless motor
> >>  - Three wires are probably power, ground, and tachometer
> >>
> >> The reason you see an unexpectedly high resistance across the power
> >> leads is because there are active electronics inside the thing to
> >> commutate the brushless motor.  You're not measuring a motor winding.
> >>
> >> I say if you have a red and black wire, hook that up to +5 VDC and see
> >> if she spins.
> >>
> >> -B
> >>
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-- 
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*Shane D Trent*
Patent Agent

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