Re: Detectig fan failure - modes of failude

From: Spehro Pefhany (speffSNIP_at_interlogDOTyou.knowwhat)
Date: 09/15/04 

Date: Wed, 15 Sep 2004 15:31:15 GMT

On Wed, 15 Sep 2004 08:02:02 -0700, the renowned Jim Thompson
<thegreatone@example.com> wrote:

>On Wed, 15 Sep 2004 13:02:49 GMT, Spehro Pefhany
><speffSNIP@interlogDOTyou.knowwhat> wrote:
>
>>On Wed, 15 Sep 2004 15:00:02 +0200, the renowned "SioL"
>><Sio_spam_L@same.net> wrote:
>>
>>>I'm designing a device with two convenient solder pads on the PCB
>>>providing LC filtered power to the fan to. This will be a smallish 1W
>>>12V fan, with only two connections (those are cheaper and I can't get
>>>the 3-pin version of 40x40x20 easily).
>>>
>>>It occurred to me that it might be great to have failure detection. Now
>>>it'd be easy if these were the 3-pin fans, but they're not. I wonder whether
>>>someone has some experience on modes of failure. Does it consistently
>>>draw more current, no current or should I watch for some AC ripple on
>>>supply line during normal operation, I'd expect there would be some and
>>>it'd stop if the fan stopped rotating.
>>
>>Yes, that will work. It might be patented however.
>>
>>>I'll possibly settle for a NTC if everything else fails, but I have some
>>>PCB real-estate left for other solutions.
>>>
>>>SioL
>>
>>
>>
>>Best regards,
>>Spehro Pefhany
>
>They have horrible current ripple, so bad that I once designed a
>quick-fix circuit to fill-in the ripple, because the ripple was
>disturbing a nearby CRT in a piece of OmniComp/GenRad portable gear.

No capacitors inside them. ;-)

>Did someone actually patent looking at the ripple ?:-)
>
> ...Jim Thompson

Seems kinda obvious. I had a vague notion M*x*m did, but I've never
had a reason to delve into it further. More expensive fans can have
tacho output or locked rotor output, of course. Here's one of M*x*m's
chips:

http://pdfserv.maxim-ic.com/en/ds/MAX6684.pdf

Best regards,
Spehro Pefhany 

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