<div dir="ltr">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.<div><br></div><div><b>Suppressing Acoustic Noise in PWM Fan Speed Control Systems</b><br></div><div><a href="https://ww1.microchip.com/downloads/en/AppNotes/00771b.pdf">https://ww1.microchip.com/downloads/en/AppNotes/00771b.pdf</a></div><div><br></div><div>Shane</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Feb 2, 2021 at 6:25 PM Brian via TriEmbed <<a href="mailto:triembed@triembed.org">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I store my paste at room temperature. I like to live dangerously! (I <br>
also don't have room in my house for another refrigerator, regardless of <br>
size...)<br>
<br>
That said, I recently bought some fresh paste...although my old stuff <br>
(and I mean old...several years of room-temp storage) still reflows, I <br>
was amazed by how many fewer bridge problems cropped up with the fresh <br>
stuff. My workflow had been stencil, place, reflow, clean up several <br>
bridges on all four sides of TQFPs...with fresh paste, there was almost <br>
no cleanup to be done.<br>
<br>
I still store at room temp, though. XD<br>
<br>
As an aside, I've been thinking about switching to a low-temp <br>
tin-bismuth alloy, but I hear even the tiniest bit of lead will really <br>
attack and weaken that stuff, and I can't guarantee there aren't some <br>
atoms of lead still clinging to my iron..<br>
<br>
-B<br>
<br>
On 2/2/21 5:14 PM, Pete Soper via TriEmbed wrote:<br>
> Thanks, guys. The connections were red for positive, blue for ground and <br>
> brown for what I assume is the PWM input. It spins up with 5V just fine <br>
> and I feel silly about the high resistance measurement. The fan cools a <br>
> pair of heat pipes from two IC sites side by side and the whole thing is <br>
> copper. The IC sites have faint markings but I can just make out "attach <br>
> Peltier devices here". After only eight years I may be able to store my <br>
> solder paste in something smaller than a dorm fridge. :-)<br>
> <br>
> -Pete<br>
> <br>
> On 2/2/21 2:34 PM, Brian via TriEmbed wrote:<br>
>> On 2/2/21 1:15 PM, Pete Soper via TriEmbed wrote:<br>
>>> The DC resistance between any two pins with any polarity is much <br>
>>> higher than I would have expected: thousands of ohms.<br>
>>><br>
>><br>
>> Others have already mentioned:<br>
>> - It's probably a brushless motor<br>
>> - Three wires are probably power, ground, and tachometer<br>
>><br>
>> The reason you see an unexpectedly high resistance across the power <br>
>> leads is because there are active electronics inside the thing to <br>
>> commutate the brushless motor. You're not measuring a motor winding.<br>
>><br>
>> I say if you have a red and black wire, hook that up to +5 VDC and see <br>
>> if she spins.<br>
>><br>
>> -B<br>
>><br>
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