Author Topic: Making Do with What You Got/ Building a Thermal Stability Fixture  (Read 16361 times)

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Offline Anders Petersson

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #75 on: April 02, 2021, 05:55:48 pm »
Great that the loop made such difference!
I don't have time to continue my own project right now, but I will post details when I do.
 
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Offline coppercone2

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #76 on: April 02, 2021, 08:24:29 pm »
try loctite tite foam for making this, its slightly less insulating but the materials parameters in terms of toughness is vastly superior to normal crappy expansion foam.

it is around 7$ a can vs the normal 4$ but it is worth it
 
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Offline Anders Petersson

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #77 on: April 12, 2021, 09:16:18 am »
Shodan, not quite sure what the plan is, but if the cost of milling holds you back I can share what I did. I bought blocks and cylinders of aluminium and managed to saw and drill them at the local makerspace. Copper should work too, except I heard that drilling deep holes in copper is hard.
 

Offline ace1903

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #78 on: April 12, 2021, 01:01:15 pm »
I do machining on a small lathe for fun in free time. When I do design most often I tend to over engineer designs.
Manual lathes are often available in each city and hourly rate is much lower.
Maybe it is worth redesigning coper part in order to be doable on lathe?
If I need to do something like this I would redesign coper part to only have circular features and few bores that doesn't need to be precisely aligned.
Will increase size of coper part and will replace aluminum part with plastic part that can be produced on 3d printer.
If aluminum thermal bridge is needed, then will make it as cylinder and plastic part around it.
It will not look so fancy but it will have comparable performances.

 

Offline Kosmic

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #79 on: April 19, 2021, 12:49:38 am »
Article for Russian EEVBlog readers: https://ampnuts.com/deep-cold/
(sorry, my English too poor to create big text...)

No worries, google translate is doing a good job. Always interesting to read your post Shodan  :-+
 
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Online dietert1

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #80 on: April 19, 2021, 10:24:18 am »
Some people even use web translators to read the russian description linked above.
When doing that, i thought about your little theory about reducing air convection losses by cooling from above. Think about it again: The coolest spot is your cooler, so it should be at the bottom. I know the cooler has a hot side but that's another problem to solve by air tight and thick foam isolation. The heat "buffer" you insert between the two TEC stages will help with that.

Regards, Dieter
« Last Edit: April 19, 2021, 11:10:54 am by dietert1 »
 

Online dietert1

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #81 on: April 22, 2021, 03:50:38 pm »
I like those nylon screws. A pitty we don't have nylon wires.. But seriously, what is the heat conduction of a TEC in comparison to some wires or screws?

Regards, Dieter
 

Online ch_scr

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #82 on: April 22, 2021, 07:17:23 pm »
Ok, report: The China control module arrived & I had a play. It's the "TCB-NE PT100" which is specified at 12V/12A up to 24V/10A. The unit operates as a buck converter with switchable output polarity with +-1000 steps resolution. It can reduce maximum power going to the peltier, at the expense of control resolution by setting a lower maximum allowed duty. The duty is calculated by PID from temperature difference "Set Value"-"Read Value" at an interval between 100ms to 3s. To have stable regulation, the interval has to fit the speed of your thermal feedback. Each time a new duty value is calculated, it reports over serial. Also you can have manual interrogation instead. So far I did run it at 12V/4A max and it stayed totally cool so I have no reason to doubt the numbers. PCB seems well made, "Sam Young" capacitors. The unit has two error & ready logic outputs and a disable logic input. The Aliexpress seller send only the chinese manual, but shafan-oe.com seem to be the primary source and I got a prompt response in good english and the english manual from them. The official seller is shafan-store on taobao. PID values can be modified on the fly and will be used on next cycle, so with a bit of scripting on the pc side more complicated stuff (different P for heating and cooling as a first step?) can be wrapped around.   All in all it is a simple unit without much bells and whistles, seems to be originally made for industrial temperature stabilisation of optical elements. Verdict: It does deliver for its price, at ~1/5 compared to more professional units I am happy with it.
Edit: Also, if you have hints on how to optimally set interval with regard to thermal feedback delay, I'm all ears ;)
« Last Edit: April 23, 2021, 07:45:19 pm by ch_scr »
 
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Offline Kleinstein

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #83 on: April 22, 2021, 09:23:13 pm »
The update interval sets the upper frequency limit, as the 4th (often hidden) paramter to a real word PID regulator.  As a rule of thumb one wants upper limit frequency about 5-10 times the P to D cross over. So the PID sampling / recalculation should be at something like 1/5 the thermal delay.
Faster calculation would increase noise of the D term - some noise may be actually wanted to get some kind of dithering to avoid the 1000 steps quantization.

Normally the same PID paramters should work for heating and cooling. This is at least true if the PID loop include linearization of the TEC. The TEC is nonlinear with a power level about a parabola with the maximum cooling near the nominal current. So if no linearization is used, one may consider to adjust the overall gain depending on the power level, e.g. less gain for heating and maybe more close to the lowest temperature.
 
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Offline Kleinstein

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #84 on: May 03, 2021, 07:38:27 am »
I would not torture the low temperature setup with so high temperatures. Some +100 C should be plenty.  Of cause for some commercial test a -40 to +125 C range in a single setup is nice. Some of the stress comes from the temperature span.


The action of the PID is nonlinear, giving more gain when heating. For a very large range one may have to take that into account and reduce the PID gain for higher heating power, or directly add linearization for the ouput part if one has it's own PID controller with full control.

Instead of 1 higher power water pump one could just use 2 (and a 2nd heat sink).
 

Online dietert1

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #85 on: May 07, 2021, 03:12:13 pm »
Did you find a RS-232 programming manual for the AE-800?

Regards, Dieter

Edit: See here: https://www.kepcopower.com/support/cotek_communication_protocol_spec_a5_0928.pdf
« Last Edit: May 07, 2021, 06:31:45 pm by dietert1 »
 

Online dietert1

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #86 on: May 14, 2021, 08:42:02 am »
Those mosfets are specced with Rdson = 1.4 milliOhm typ and 1.8 milliOhm max, a pretty solid build. When looking at your image and thinking about heat, i found the solution for low output operation of my Cotek AE-800. As of the AE-800 spec sheet operation below 10 % of nominal 30 V output isn't recommended, but i can use the polarity switch to implement PWM between -3 V and + 3 V. With a little bit more firmware one can keep "linear" operation of the AE-800 outside of +/- 3 V interval. Have to try yet.

Thanks again for sharing the info!

Regards, Dieter
 

Offline Kleinstein

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Re: Making Do with What You Got/ Building a Thermal Stability Fixture
« Reply #87 on: May 14, 2021, 09:18:57 am »
A TEC is quite nonlinear, and even the parabola approximation is not perfect (this ignores the resistance going up with temperature). So I would not worry so much about the linearity of the output stage.
 


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