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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Pi-FAN for RPi4 with 4 (instead of 3) cables?
Date: Mon, 9 Dec 2024 13:11:34 +0000
Organization: A little, after lunch
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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:
>>>
>>>> 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.
>>>>
>>>> I dislike fans. They fail.
>>>
>>> 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.
>>>
>>> Fans fail.  Disc drives fail.  SSDs fail.  Batteries fail.  Reservoir
>>> capacitors fail.  But before they do, they are very useful.
>>>
>>
>> Such an ArtStudent™ view of life.
>>
>> Do you know what MTBF means?
>>
> 
> I was surprised you'd use MTBF for a component which is expected to 
> steadily deteriorate due to wear and tear.
> 
> I though MTBF was more a random failure thing.
> 
No it isnt that at all.


> 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.

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

> I don't know which it is for PC fans, but would assume it is more wear 
> and tear than random.
> 
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

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

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

-- 
For every complex problem there is an answer that is clear, simple, and 
wrong.

H.L.Mencken