[time-nuts] Re: Z3801A Temperature

[Magnus Danielson]

Hi,

Well, "ambient temperature" as per telecom terminology means the
temperature of the surrounding air in the aisle of the rack. The
Bellcore/Telcordia GR-63 and ETSI EN 300 019 (series) would stand for
the formal definition. This is also in line with the AT&T Reliability
manual. It is expected that the ambient temperature of the rack causes a
raise of 25 degrees C as you get into the components on the circuits
boards, giving the 70 degrees C commercial spec, raising it from the
normal 45 degrees C of Belcore/Telcordia GR-63. Other specs is used for
non-central office locations, but about the same reasoning of ambient
temperature applies. The ambient temperature of the rack then boils down
to how the individual equipment was built. Some use fans, while others
doesn't. The Z3801A for sure is not built with a fan, but then it is not
a direct rack unit device, but an odd-factored sub-rack unit. I kind of
doubt that the rack-unit that the Z3801A slides into had a fan to it,
but then this goes back to the day and age when some of the rack units
was allowed to be so spaceaous that no fan was needed, so that self
convection could work. We do not do that very often these days, as rack
space is expensive and the power we push into a design is such that
forced convection is the way we need to go most of the times, unless
someone goes for liquid cooling. There is a fine balance between cooling
to keep component ambient temperature down and keep the oven current low
and with that the oven controller wear down.

I would consider not stacking the Z3801A to densly with other things, so
there is a reasonable chance to keep cool.

Cheers,
Magnus

On 2021-07-19 15:19, Bob kb8tq wrote:
> Hi
>
> The implicit assumption on pretty much all telecom gear these days 
> is moving air. How much moving air? You would have to get into the 
> spec for the OEM that bought it. It might be listed there, it could easily 
> have been in somebodies notes from a phone conversation …..
>
> As long as the case temperature in your stack does not get much above
> 50C, the device should be happy. MTBF wise, the hotter it gets, the 
> quicker it fails … sorry about that. 
>
> Bob
>
>> On Jul 19, 2021, at 8:29 AM, Hal Murray <halmurray+timenuts at sonic.net> wrote:
>>
>>
>> I have one sitting on a shelf.  No air-conditioning.  The top plate is warm, 
>> far from hot.
>>
>> Will they be happy if I stack another one on top of it?
>>
>> The users guide says 50C.  What does that mean if they don't specify the air 
>> flow?  Is there an assumption that it is floating with lots of empty space 
>> around it or something similar?
>>
>>
>> -- 
>> These are my opinions.  I hate spam.
>>
>>
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