Advantages and Trade-offs both ways
For a simple "no moving parts" version,
Oversize the heat sink and attach a 10 Watt resistor to it whose voltage is
controlled to keep the Heat sink temperature constant
ws
****************
Bill Harris w7kxb at msn.com
Bert:
Something to be said about "no moving parts".
Bill-w7kxb
*********
From: EWKehren at aol.com
Date: Sat, 17 Sep 2011 21:22:30 -0400
To: time-nuts at febo.com
Subject: [time-nuts] temperature control
Recent comments on dewier flasks bring me back to test I conducted last
year using a nice flask that I tested extensively using the guts of a
10811
as a constant heat source. What I found and reported was that the ambient
inside changed as much as .4 C with 8 C changes on the outside. The tests
ended when it fell off the pedestal that I mounted on my balcony in order
to
take advantage of the large overnight changes. Since then I have focused
on
temperature control by fan cooling. Shopping for small fin heat sinks I
ran
across a VGA cooling assembly at our favorite supply site 370537089468
for
a total of $5.92. At that price I said what the heck. It came in 4 days
and I mounted it on the back of a FRS. After 4 hours without cooling, the
back plate was 59.7 C with an ambient of 29.2. the fan assembly without
fan
running was actually already cooling the back plate, because without it
mounted, the temperature was 62 C. 6 minutes after powering up the 12 V
80 mA
fan, temperature had dropped to 45 C and 30 minutes after power up the
back
plate is 40.6 C again with 29.2 ambient. The fan is very quiet and it is
amazing what can be done with a small amount of moving air. This fan with
a
single op amp will be able to hold the back plate within .1 C at 45 C.
Eventually all my time/frequency units will have some kind of moving air
temp.
control. Lower temp. will also extend life.
Now my dilemma is whether to use my original design with an array of small
heat sinks with the fan off the side not part of the Rb or stay with this
super simple design.
Bert Kehren Miami
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