[time-nuts] DIY FE-5680A lobotomy (disable temp compensation)

Angus not.again at btinternet.com
Mon Aug 18 20:58:36 EDT 2014


On Fri, 04 Jul 2014 02:35:41 +0100, you wrote:

>
>Hi Bert,
>
>I am thinking about testing a heat pipe on a fan cooled setup I use.
>The first temp controlled chassis I did used a peltier and works very
>well, but was a lot more work to do and is much more power hungry. 
>
>The main problem I find is not the temp controller itself, but rather
>the change in the temperature across the chassis as the ambient
>changes. However good the temp controller is, it only controls a
>single point, but other points further away from the sensing
>thermistor can vary a lot. 
>I noticed you posted a picture of a heat pipe cooler a couple of weeks
>ago - did you happen to compare the temperature across the unit with
>direct fan cooling and the heat pipe cooler, or with different heat
>pipes?
>
>Angus.
>

I finally got around to playing with a couple of laptop heat pipes,
fixed to a 25x50x75mm block of aluminium which is fixed to the 12mm
thick baseplate. 
On a quick test of it, a sensor near the end of the baseplate showed
1.5-2x greater variation with temperature compared with just having a
fan blow directly onto the baseplate. 
The oscillator also had to be allowed to run a few degrees C hotter
for the heatpipe coolers to work to the same max ambient temp.

One cooler had two heatpipes with about 12cm between the aluminium
block and the heatsink fins (cast in this case) The other had a
single, wider heat pipe with about 5cm between the block and the
heatsink (this time with a lot more fine fins) 

The second cooler was rather more efficient, allowing a extra degreee
of cooling at the top end, but more problematic was that it entered
'bang-bang' mode with the analogue temperature controller even sooner,
and the temperature fluctuations there were greater. Both were rather
worse than with the fan just blowing onto the baseplate.

Using a PWM fan controller would help a good bit, but getting more
creative with a microcontroller would be better. That way you can give
the fan a minimum of a small kick every so often, and vary the
repetition rate as well as the duty cycle as more cooling is needed.
With feedback from the fan and even air temperature monitoring, you
could get a good idea of exactly how much cooling was being applied.

Another problem is that the overall temp control range is lower with
the coolers - barely 8-9 DegC compared with 12+ DegC with the fan
blowing directly on the baseplate. That's mainly the result of the
poorer cooling at the top end of the range.

The Rb osc fitted during this test was a SA.22c which takes a good bit
less power than a 5680A, and the fan blowing onto the baseplate was
normally a 60mm one fitted about 50mm away from it. The baseplate was
horizontal with the fan blowing onto it from below.

Maybe fitting a heatsink directly onto the base would help further
with the maximum temp, but it would increase the convection cooling at
the minimum temp, reducing the overall benefit. It could also be more
susceptible to drafts, and would make the fan control much more
delicate.

Anyway, that's the results I got with my setup. Other setups and more
fine tuning could change things a good bit, but I just wanted to get
an idea of how the two cooling methods compared on the same setup.

Angus


>
>On Sat, 28 Jun 2014 12:37:37 -0400 (EDT), you wrote:
>
>>Will someone beside us use heat pipe. Would love to have an impendent  
>>input. What does it take to get a test going. Scott has done a lot of work, how  
>>about some one else step up to the plate. There are a lot of time nuts out 
>>there  with the 5680A,many for the first time will have a very good 
>>reference and some  of our experts with proper equipment can make a big difference.
>>Bert Kehren
>> 
>> 
>>In a message dated 6/28/2014 12:20:12 P.M. Eastern Daylight Time,  
>>newell+timenuts at n5tnl.com writes:
>>
>>At 04:32  AM 6/28/2014, wb6bnq wrote:
>>
>>>monitoring process ?  In other  words have you traced out the 
>>>connections to see what is driving the  pin you think is the temperature 
>>input ?
>>
>>No. I've only traced back from  the ADC input to the voltage divider.
>>
>>
>>>The next big question is  have you monitored the frequency and its 
>>>stability, externally, to  observe what effects are taking place when 
>>>you disable this input to  the A/D ?
>>
>>I have not.
>>
>>
>>>That sounds complicated and messy  but may be easier than it 
>>>appears.  An appropriate container  would be:
>>
>>It does sound messy. I don't think I'm willing to dunk one of  my units.
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