Want to build a 25C oven. - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 06, 2018, 11:03:56 am
content: I have some chips that I want to keep at 25 deg C but the PSU and other electronic in the case can sometime reach above that.So what I am looking for is a oven that can heat and cool. I am hoping to make an color changing LED that get a color when the temperature are within spec.Can anyone please help me?

author: Berni
author_rank: Super Contributor
timestamp: September 06, 2018, 11:55:42 am
content: Such equipment is called a "Environmental chamber"https://en.wikipedia.org/wiki/Environmental_chamberThey use refrigeration technology to both increase or decrease the temperature inside, most also control the humidity inside by adding or removing water from the air.As you might expect these are quite a expensive bit of kit. But you can do a similar job by simply putting your fancy temperature controlled oven inside a fridge and adding a fan.

author: exe
author_rank: Unknown
timestamp: September 06, 2018, 11:56:39 am
content: Sounds like a peltier element is a perfect candidate as it can both heat and cool. Watch out for condensed moisture. Also power efficiency isn't that great.BTW, what is the problem in the first place? You say you want keep something at 25C, what for? If it's a reference, then there are other ways to make it stable.

author: Zero999
author_rank: Super Contributor
timestamp: September 06, 2018, 12:35:25 pm
content: If it's a reference or oscillator, it's generally better to aim for a higher than ambient temperature, so cooling is unnecessary. The main disadvantage with higher temperatures is increased thermal noise.

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 06, 2018, 12:59:31 pm
content: My goal is to build a wary sensitive meter that detect changes in voltage for some plants.I am thinking of using the 25C (that temperature the chips work best) as a constant temperature, so I do not have to calculate drift due to temperature change.My meter do not have to tell me the voltage, only if it increases or decreases.To know if the meter is ready, it would be great to have an LED indicator, that tell me if the temperature is fine.

author: exe
author_rank: Unknown
timestamp: September 06, 2018, 01:18:40 pm
content: It would be great if you post schematic and requirements (e.g., how large temp drift could be).While it makes sense to build a temperature chamber to compensate for temperature drift, I bet there are ways to achieve same without it. For example, people don't often cool down devices (as it is more difficult than to heat up). Instead the temperature elevate above maximum operating temperature. Again, it's almost never needed to heat up the whole device, at most you need to heat up the reference voltage (think of lm399). But even then most of the time this is not needed if right components and schematic is used.And even if you have a chamber, it doesn't mean you'll get good accuracy. If it were so simple people would build benchtop DMMs that way. In reality you have to take into account humidity, aging, local hotspots, mechanical stress, EMI, etc.

author: David Hess
author_rank: Super Contributor
timestamp: September 06, 2018, 01:51:04 pm
content: Peltier thermoelectric coolers can be used this way but you have to beware of condensation when cooling below ambient. Linear Technology had a couple application notes about it and even made an ASIC specifically for this application.Linear version:http://www.analog.com/media/en/technical-documentation/lt-journal-article/Thermoelectric_Williams_Mar02_Mag.pdfNote that the LT1970 is just a power operational amplifier with a very flexible adjustable current limit. A discrete power output stage could also be used.High efficiency switching version:http://www.analog.com/media/en/technical-documentation/lt-journal-article/ltc1923_0901_mag.pdfhttp://www.analog.com/media/en/technical-documentation/data-sheets/1923f.pdf

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 06, 2018, 03:41:42 pm
content: I do not have a schematic yet, would first find out if it was even reasonable to do.It is just to experimentation at home, so a DMM with nV or even pV, would be fare from sane:-)humidity can maybe a problem, aging is first a problem after weeks or months?, local hotspots do not count if the device is at the same spot?, mechanical stress again not a problem for maybe 24 hour tests, EMI is properly a big problem!Thanks for the schematic, looks wary interesting! I am assuming that "laser tec" can just be considered as a generic load?

author: David Hess
author_rank: Super Contributor
timestamp: September 06, 2018, 03:46:20 pm
content: Quote from: FriedMule on September 06, 2018, 03:41:42 pmThat is right. The idea and circuit could be used with any thermal load. Lasers can be very sensitive to temperature which affects their mode and coherence.

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 06, 2018, 04:36:44 pm
content: But how would you implement the thermic censor that are needed instead of the build in censor in the laser?

author: coppercone2
author_rank: Super Contributor
timestamp: September 06, 2018, 07:38:08 pm
content: If you search my posts I posted some design (mechanical/thermal) details for building a good one in someones thread

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 06, 2018, 08:28:04 pm
content: coppercone2 I have tried to search but it seems that I can't find your post, do you have more info to search for?

author: coppercone2
author_rank: Super Contributor
timestamp: September 06, 2018, 11:54:48 pm
content: Quote from: FriedMule on September 06, 2018, 08:28:04 pmsearch just coppercone not coppercone2

author: FriedMule
author_rank: Frequent Contributor
timestamp: September 08, 2018, 03:53:21 pm
content: Sorry but I can't find your post, I have tried everything now.

author: iMo
author_rank: Super Contributor
timestamp: September 08, 2018, 05:53:51 pm
content: https://www.ebay.com/itm/7-5L-12V-Mini-Electric-Car-Truck-Cooler-Warmer-Refrigerator-Fridge-Travel-Home-/173372207521

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2018, 06:05:38 pm
content: https://www.eevblog.com/forum/projects/mini-tempco-characterization-rig/the guy did a decent job too