[colug-432] Raspberry Pi Life

[jep200404 at columbus.rr.com]

On Tue, 2 Apr 2013 11:15:47 -0400, Scott Merrill <skippy at skippy.net> wrote:

> Someone told me recently that Raspberry Pis are not designed for 24/7 operation.
> 
> If one were to run a RasPi continuously, how would that effect that
> longevity of the device?

High temperatures shorten the life of electronics. 
The relationship is exponential. 

On an unenclosed Raspberry Pi, I measured the main chips[2] running 
about 50 F above ambient. A little breeze lowers the temperature 
much. So use heat sinks and/or fans to reduce the temperature for 
long life. It should not be hard to get the main chips down to 
10 F above ambient, at which they should last longer than your 
interest in using Pis. 

> I suspect the answer is "it depends" on things like workload,
> computational complexity, frequency of disk writes, etc. 

Heat is what counts as far as wearing out the Raspberry Pi itself. 

SDHC flash memory wears out due to writes also, 
but I consider that to be a separate issue. 

On Tue, 2 Apr 2013 13:07:11 -0400, Eric Floehr <eric at intellovations.com> wrote:

> So possibly thermal expansion/contraction causing shorts.

Thermal cycling is much more likely to cause opens than shorts. 

> Another thing could be capacitor degradation. 

Most of the caps on the board are ceramic, which last 
_forever_ as long as they are used within their specs, 
which is likely. I see three tantalum electrolytic caps, 
which will also last long enough to not worry about. 
There is one aluminum electrolytic cap, C2, in the 
power input connector. Those are known for failing[1]. 
Failure after two or three years of continuous use is 
common. That's mainly for the low ESR caps used in 
switch mode power supplies (SMPS) that are common in PC 
power supplies, on motherboards near the CPU, and in 
LCD displays. Since C2 is used with a linear regulator, 
not in a SMPS, it might not be the low ESR type are 
are more vulnerable. Nonetheless, C2 is likely the 
weakest part on the board. It's wear is also 
exponential with temperature[3]. I.e., fans will help 
extend its life. 

If I was running Pis for a long time, I would put a heat sink 
on the main chips and have a fan blow over the whole board. 
Even though C2 is the least reliable part, 
I wouldn't worry about it because it's easy to replace. 
The main chips can not be replaced. 

[1] https://en.wikipedia.org/wiki/Capacitor_Plague
    Also search COLUGs archives.

[2] IC2 is actually two chips, one stacked on top of the other. 
    The memory chip is on top. The brains is underneath. 

[3] See formula 48 of http://www.cde.com/tech/thermalapplet.pdf