Peltier enviromental chamber builds

[TiN]

I'm pretty sure it will work horrid.
Many somewhat forgot that TEC on each W of power transferred between sides also adds same W of it's own heat.
That's why on commercial multistage TEC modules you see twice smaller module on top of bigger in the bottom, and every layer follows that.
On example with 2 TECs if top TEC (facing DUT) is 40W, then bottom TEC must be at least 100W to give enough margin.

I changed ambient side cooling to watercooling system, and now have things much better to go on range +18c to +50c with my chinesium 40W 40x40 TEC.
Example charts: https://xdevs.com/usac_fx1_test1/ and https://xdevs.com/usac_fx1_test2/

[rhb]

I looked at the commercial series modules,  They're a lot more money.  There is also the issue of asymmetry.  The small end is implicitly the cold side. so if the flow is reversed it's being fed far more heat than it can transfer.

I plan to  control the current to each TEC separately.  Obviously this build will not change temperature quickly.  The steel box has a lot of thermal mass.

This will be a bit of a bugger to insulate and still maintain good airflow.  So it's likely that I'll use water cooling for the big one.  This is based on stuff I have on hand aside from the TEC modules.

[ch_scr]

I finally managed to get my basic control & driver circuit to work. Guess who learned the hard way how important seperate regulation for load and control supply rails is when driving bigger loads  I tried to create an "elemental while reasonable" analog control circuit for my box, while designing from stock. The current mirror is in there like that because i did not have another OP07 at hand at the time.
I use an old CATV head unit power supply that has sturdy a 12.5V line to drive the Peltier, the 18V provides positive control rail and the 5V provide the -5V control rail via an isolated DC-DC module. It works reasonable for a first attempt, slight overshoot on the regulation but nothing serious. I literally just had success an hour ago, i tried alot to get it working on +12.5V alone and it would not stop oscillating Build pictures: https://imgur.com/a/KDYyZ8y The fan and big heatsinks are a mix of legacy, what was at hand and a safety measure to protect the mosfets. Sure did prevent me from blowing them up while messing around.

[ch_scr]

I had a bit of a further play with it today and logged the value of the LM335 with my K2100 every second. The plot & data is attached.
Took about 8.5 minutes to reach -6°, took 3.3 minutes to go to 38.5C from there. This is with 10V across an element capable of 15V.
I don't like the drifting once it closes in on to the setpoint, will have to investigate further. Logging and plotting was done with python.

Edit: I did a second run with higher P-Gain to see if that would help, it looks like that to me. Setpoints were a bit different which hinders comperability. I also added the complete plot, but there is not much to be seen there i think.

Edit2: Upon further pondering, i believe part of the problem is that the part of the voltage coming from the LM335 i try to regulate upon here is already in the 100's and 10's of uV. Also, for a remote sensor, a current based one should be better with regard to signal integrity. I think i should retire the LM335 together with the current mirror for a LM334 and an OP07 in transimpedance configuration.