Re: Long life fan wanted

From: Bob Wilson (rfwilson_at_send_no_spam.intergate.ca)
Date: 07/11/04 

Date: Sun, 11 Jul 2004 04:24:41 -0000

In article <a7076635.0407091603.7f2d35b0@posting.google.com>,
bigcat@meeow.co.uk says...
>
>Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> wrote in
message news:<122qe0p744gobf6sd7u4jnv9lo47jht04q@4ax.com>...
>> On Thu, 08 Jul 2004 08:23:57 GMT, "Ban" <bansuri@web.de> wrote:
>
>> >> I'm currently using the Sanyo Denki 109L0812H402 which is great (100k
>> >> hours life), except that it doesn't have the option for a tachometer
>> >> wire. I need the tach so that I can know when a fan (in the bank of
>> >> three) fails.
>> >>
>> >
>> >If you put a self-heated PTC-pearl into the individual airflow, by
>> >monitoring the PTC current with a comparator you can reliably detect any
>> >flow threshold.
>>
>> Early detection of fan failure (in this case) involves comparison of
>> the speed vs voltage characteristic compared with the same
>> characteristic when new. I'd like to be able to detect changes of
>> only a few percent.
>> The ambient temperature may vary over a wide range, which makes any
>> temperature based measurement (e.g. using a PTC-whatever) useless for
>> my purposes.
>
>compare 2 thermistors, one in peak airflow, one not.
>
>
>> BTW, I wasn't asking for ideas on thermal management. I have a board
>> that's waiting to have three three-wire fans plugged in; I want to
>> know where to get a reliable three wire fan.
>
>I dont know either. In case you get stuck it might be poss to add
>another lil PCB to detect the fan frequency from its current waveform,
>and turn that into something that will feed your existing 3 wire PCB.
>I know its not what you want, just felt like saying it anyway... not
>sure why. Good luck.

What fails in almost all cases is the bearings. Assuming that the fan in
question has ball bearings, you might consider bonding a small transducer such
as the type if electret microphone used in cell phones to the frame of the fan.

Ball bearings get increasingly noisy as they wear out. Monitoring the bearing
noise may help predict approaching failure.

Sleeve bearings used in el-cheapo fans will also become noisier,but it is not
as pronounced.

Bob.

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