[TriEmbed] laptop fan motor control question

Wed Feb 3 07:31:27 CST 2021

That makes sense Shane. Slow down that kick to the mechanical part with a cap to round off the jolt. Amazing how many problems a simple little cap can solve. Also makes sense that the fans have a position sensor to time the pulses. That is how they manage the timing. I couldn't remember the scheme for the brush-less motors, it's been a while since I thought about it. I just remembered you couldn't just simply apply a voltage to a brush-less motor. I know there are also schemes for running them without the sensor too. So that's the reason it's important to know the motor scheme. In general I suspect the PC fans have the timing method built in. But it begs the question if you pulse with the wrong timing it seems to me it will not energize the fan well.

Great article, I will remember this technique.

John Vaughters

On Tuesday, February 2, 2021, 07:48:50 PM EST, Shane Trent via TriEmbed <triembed at triembed.org> wrote: 

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 

919-348-0061 | shanedtrent at gmail.com 

ShaneTrent.com | Skype: skype:shane.trent1 

  Raleigh, North Carolina   

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