The PWM frequency has a big impact on the audible noise. If the motor and cpu can handle it, higher PWM frequencies will push a lot of the noise into untrasonic range. There’s downsides to that in that your parasitic impedance goes up. 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
Shane
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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