Re: Pi-FAN for RPi4 with 4 (instead of 3) cables?

On 12/9/24 13:11, The Natural Philosopher wrote:

On 09/12/2024 12:28, Pancho wrote:

On 12/9/24 10:50, The Natural Philosopher wrote:

On 08/12/2024 19:50, David Higton wrote:

In message <vj1d28$31v9g$12@dont-email.me>
           The Natural Philosopher <tnp@invalid.invalid> wrote:
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It's an interesting thought as to why one would use a fan at all. If its
such a high compute task that you need one, maybe a bigger Pi or an
Intel based machine is indicated.
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I dislike fans. They fail.

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PC fans run pretty much all the time.  A fan on a RasPi is likely to
run less of the time, and could well last longer overall.
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Fans fail.  Disc drives fail.  SSDs fail.  Batteries fail.  Reservoir
capacitors fail.  But before they do, they are very useful.
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Such an ArtStudent™ view of life.
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Do you know what MTBF means?
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I was surprised you'd use MTBF for a component which is expected to steadily deteriorate due to wear and tear.
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I though MTBF was more a random failure thing.
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No it isnt that at all.
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For some relatively reliable components, such as people, you initially see a relatively low failure rate, but come 80 or 90 years they start dropping like flies, due to wear and tear.

 Yup. MTBF of peole is about 70 years.
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I read MTBF for people is about 700 years.

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For some things like atomic an atomic nucleus, the failure does seem random, so MTBF seems applicable.
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Never used.
 

Well yes and no,
Given f = failure rate (e.g probability of nuclear decay)
half life = ln(2)/f.
MTBF = 1/f.
Therefore:
half life = ln(2) * MTBF = ~0.69 * MTBF
essentially they are the same, apart from the 0.69 conversion factor.

I don't know which it is for PC fans, but would assume it is more wear and tear than random.
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In general fans fail for one reason only. Bearing failure.  The cheapos use phosphor bronze plain bushes and these dry out and seize up, wear out and get noisy and start slowing down  or get clogged with people's cruft.
 You can go for sealed ball races if you like, as in hard drives,  but the price goes up.
 In terms of drying out, its time elapsed, not time spent running. Same for cruft. Only bearing wear is time dependent.
 None of these are random., All if them are however dependent on conditions and maintenance
 

For a stingy old man like me, yes. I wait till things break. So MTBF is not particularly useful. I want long average life, not reliability until they get old.

MTBF is an attempt to get a handle on how long a collection of parts should stay operational given the spreads of failures in a spread of conditions  of the individual parts
 There will always be variations in conditions and manufacturing quality
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MTBF is the type of metric used by someone who will replace bits before they get old.
If I were managing a data centre and I knew human intervention was very costly (I suspect it is), I might  have a policy of replacing parts before the failure rate became high due to old age.
I know the companies I worked for hated investigating failure, or fixing stuff. They much preferred replacement. Essentially components were cheap, human intervention was not.
Obviously if the equipment is expensive, or you have cheap slave labour, the equation may change.

My experience of cheap fans is that 5 years was about the MTBF.

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