----- Original Message -----
From: "Murray Greenman" <[email protected]>
To: <[email protected]>
Sent: Tuesday, June 09, 2009 6:42 AM
Subject: [time-nuts] FE-5680A thermal management
Leigh,
I agree with Chuck. I have both an FE-5650A and an FE-5680A. With
the
former I was concerned about the heat, and so ran it only for short
periods, until I understood what was going on. I had the impression
from
the data sheet that there were different heatsink options for
different
temperature ranges, and I now believe this led me astray.
With the FE-5680A I had the opportunity to study things in more
detail.
There is no temperature range specification that I could find, and
no
particular advice in the manual regarding installation. I ran the
unit
from regulated 15V DC, and monitored the supply current. With no
extra
cooling, the steady state current was about 700mA. With air blown
over
it, the current increased. With the unit placed in a poly bag, the
current decreased to about 650mA. By the way, the current also
decreased
when operated from 17V DC.
This tells me that the whole structure is part of the thermal
package,
and we should not attempt to force down the case temperature just
because the unit runs hot. My experience with high performance OCXOs
tells me that the thermal environment is carefully designed, and
part of
the calibration process - if you modify this environment (by cooling
or
extra insulation) you modify the thermal environment, and are at
risk of
modifying the performance.
I'd leave well alone, and run the unit in an open, breeze-free
environment.
73,
Murray ZL1BPU
Murray et al,
The package of both units is clearly meant to be mounted on
something-the real question is how much heat sinking would that
something have provided? Changing the external heatsinking to achieve
the nominal supply current at the nominal supply voltage would appear
to be the only simple way to operate the units as intended.
I've not gone through this exercise yet with the 5650, but I suspect
the amount of heatsinking used is not that critical. Using a variable
speed fan to determine the 'correct' mounting plate temperature
(corresponding to nominal supply current/voltage) might be a good way
to start. The design of a heatsink to achieve the same base plate
temperature should be a trivial exercise.
Constraining the 'ambient' air temperature to an appropriate range in
the vicinity of the unit should certainly help as well.
Regards
DaveB, NZ
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