Low temperature chamber (-60C and below) - Page 1
Forum section: electronics / general

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: July 18, 2021, 08:01:26 pm
content: Do we have any successful projects to build thermal chamber that goes down to -60C and below?I don't want to deal with dry ice or liquid Nitrogen.At the moment I am using a chest freezer that reaches -42C inside within an hour of turning on empty at room temperature.I put a small 12V car coolbox with its "electronics" removed and Peltier/fan connected to external PSU and this setup goes to -50C..-55C inside the coolbox.Maybe someone knows efficient and inexpensive car freezer that I can use instead.CheersLeo

author: Labrat101
author_rank: Unknown
timestamp: July 18, 2021, 09:13:12 pm
content: Hi Leo ,Did you try butting a 3rd box inside the -55 cooler box just a thought .even though in theory its possible to cascade Peltier cooling and each levelwill decrease in efficiency but adding a 3 level will give you hopefully anotherminus 8 to 12 degrees maybe more 15. would be about max...I did build a minus 80 cooler when I was working in Kinston for a company.for testing equipment before sending to the Antarctica . . That was a very long time ago early 80's . It was done by converting an R12 freezer and changing the gas to 13B1 which was very expense and I believe it is now been band from use in the UK .The freezer you are using is probably one of the new Green Gases . maybeR161 which is basically butane or R404 or similar .What I think you need is to get hold of a second hand lab freezers whichI believe use R508B and can go down to close to minus 80 .I am retired now so I have lost track on the new refrigerants .I would Try Cascading Peltier plates with an external power supply is certainly the cheapest way . You can sandwich Peltier plates but you needa very good thermal grease between each and a thin copper sheet .to help with thermal movement as they expand and contract the copper sheet will reduce the ceramic from cracking .with luck . and lots of Power amps.Note ( Make sure the Peltier plates are orientated hot,cold,hot,cold )placing 1 plate wrong it won't work . also the power has to be monitoredthe first sage will use more than the second .The first sage is the one within the -42 side (Edited due to Typo )second as final or if 3 stages and so on .I have only ever used 2 stages . as they become hard to mount .A tension plate with springs should be used to hold them together

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: July 18, 2021, 09:38:54 pm
content: Thanks, Labrat101.I have not had much success stacking Peltiers in the past. They quickly reach a point where they just pump the energy they generate themselves.The chest freezer is only a few years old so I assume it will be a modern green variety (and thus incapable of reaching high temperature differentials.)I will try to find a larger and smaller cool boxes but it is not dissimilar to stacking Peltiers. Outside freezer should be capable of removing heat at the rate that internal boxes generate.Leo

author: Labrat101
author_rank: Unknown
timestamp: July 18, 2021, 09:58:15 pm
content: Quote from: Leo Bodnar on July 18, 2021, 09:38:54 pmThat should also work ..Using the Russian doll effect . I guess your freezer will take the extra loading it may justtake a little long to cool . Turn the fast freeze switch ON . or if it doest have and has a mechanical thermostat just short it out so it runs continuously . The fast freeze switchjust shorts the thermostat out any way . this is ok for about 2 to 4 hours . or better stillreplace the thermostat with a programmable onePS put a bottle of vodka in the freeze as well . That for the end to Drink

author: Anders Petersson
author_rank: Regular Contributor
timestamp: July 18, 2021, 11:50:48 pm
content: Quote from: Leo Bodnar on July 18, 2021, 08:01:26 pmHi Leo. I'm also interested in reaching -60 C or thereabout. My research so far has only yielded expensive environmental chambers; The Chinese and therefore hopefully relatively inexpensivewww.lib-industry.comquoted their smallest chamber T-50 last year at USD 7300 for -70 C and USD 13800 for -86 C. And shipping weight is 180 kg so that incurs a real cost too. And then the hassle of moving and housing the 1 m3 unit (inner space is 320*350*450 mm). Interestingly, humidity control only added a marginal cost.Without being an expert, I doubt -60 C is possible with peltiers regardless how small the temperature delta is. In fact I'd be thankful if you want to share details/pictures of your current setup for -50 - -55 C? It's a good result as is.

author: TiN
author_rank: Super Contributor
timestamp: July 19, 2021, 03:34:49 am
content: If your heatload is low (<few watts) and you don't mind dealing with vacuum insulation, you could use stirling cryocoolers, such as popular in DIY scene STI SuperFilter RX.For heatloads in hundreds of watts, cascade phase-change system is an option too. Polycold make some units, sometimes they do pop up on secondary market. It's also possible to DIY if you don't mind few k$ investment and learning curve (typical systems are 2-stage cascades with two compressors and R404(507) + CO2 gases as refrigerants). I'm currently working on getting cryosetup for below -250, but that's rather exotic GM 2-stage cooler and still a learning curve for me (and it would be 100mW heat capacity at best for that temperature).

author: ConKbot
author_rank: Super Contributor
timestamp: July 19, 2021, 05:33:41 am
content: It all really depends on the heat load, as mentioned by others. Assuming under 5w, given you already have a -40 freezer, a 1 stage Peltier is viable, but a controller is needed. Just whacking 12v onto a peltier is almost always asking for disappointment. TECs that "oversized" can actually have a not garbage COP. I.e.https://www.lairdthermal.com/products/thermoelectric-cooler-modules/peltier-polartec-series/PT6-12-F2-4040-TA-RT-W6/pdf1A3V to move 5w across a 20C delta, with Thot at 27c, and this is on a 12-14v unit.The performance of TECs drop as they get colder, but even if it's still going to be better than just hitting it with 12v and seeing what happens.Your car cooler Peltier can probably work, just don't let it eat dozens of watts for no reason. That and upsize the heatsink as much as you can to get the hot side as cold as possible. But no heatsinks with heatpipes, as they generally use water unless they are specific low temperature heatpipes.

author: David Hess
author_rank: Super Contributor
timestamp: July 19, 2021, 06:02:47 pm
content: Liquid nitrogen cooling has the virtue of rapidly reaching significant negative temperatures and the exhausted nitrogen is not toxic and displaces water in the chamber preventing condensation.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: July 21, 2021, 05:53:59 pm
content: Quote from: Anders Petersson on July 18, 2021, 11:50:48 pmI use chest freezer like this:https://www.cateringhygiene.co.uk/shop/tefcold-se10-45p-low-temperature-chest-freezer.htmlIt reaches good honest -40C..-45C when started empty from room temperature in 2-3 hours.Then I use this sort of thinghttps://www.halfords.com/motoring/travel-accessories/coolboxes/halfords-8-litre-12v-in-car-electric-coolbox-291085.htmlI have modified it: cut out the switch and separated Peltier and the fan wiring to be able to control them separately. Grille around the fan has also been removed.I can reach -50C in 3-4 hours.The progress below -55C is very slow which is understandable but I feel that -65C is within reach if all the details are taken care of.Yes, I can use liquid Nitrogen or dry ice but it's hard to control the temperature without proper controller and too easy to inflict significant thermal shock onto the DUTs.Leo

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 21, 2021, 06:53:44 pm
content: I believe virology labs routinely use -70 freezers - might be worth looking at surplus/ebay.The problem with stacking peltiers is that each layer needs to pump the waste heat of the next, and the low efficiency means you get diminishing returns. A while ago I took apart a 3-layer stack from some sat-comms gear, and that used something like an 8x10" first layer to cool a postage-stamp sized third layer.

author: fcb
author_rank: Super Contributor
timestamp: July 21, 2021, 07:05:20 pm
content: If it's just the odd bit of testing, we've got a couple of chambers that go to -65oC (Design Enviromental & Votsch).They come up occasionally on eBay - but are mad money new. There's one on eBay (https://www.ebay.co.uk/itm/164955721747) at the moment for £5K - which if it works is a fair price.We tried domestic freezers but couldn't get more than -32oC.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 21, 2021, 07:29:03 pm
content: Quote from: mikeselectricstuff on July 21, 2021, 06:53:44 pmIn the US they like the -70 freeze, but this is -70 F which is -54° and thus about the dry ice temperature.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 21, 2021, 07:44:48 pm
content: Quote from: Kleinstein on July 21, 2021, 07:29:03 pmHere's a -86 freezer on ebay UK - bit priceyhttps://www.ebay.co.uk/itm/174815156594?hash=item28b3cb9972:g:9ZEAAOSwl-xgqN4K

author: Anders Petersson
author_rank: Regular Contributor
timestamp: July 21, 2021, 07:59:55 pm
content: Thanks for the details, LeoI think your setup can be refined by replacing the car cooler with an optimized custom build. One idea is to connect the peltier hot side to a metal plate pressed against the wall of the freezer. Then the heat transport would be more efficient, not going through the air. And you would get rid of the heat-generating fan.If my own experiments don't give enough cold, this is the way I'll go myself.Quote from: fcb on July 21, 2021, 07:05:20 pmSort of proves my point; that one weighs 550 kg and runs on 3 phase AC. It's a commitment.I found a middle road in lab freezer Porkka Lab Line PRO 11. It looks like a regular top-loading freezer, 130 liter capacity, goes to -60 C. Cost new (in Sweden) is USD 2800 plus VAT. I don't expect it to have the temperature stability or fine control of a climate chamber, so an inner chamber is still desirable.

author: fcb
author_rank: Super Contributor
timestamp: July 21, 2021, 08:15:46 pm
content: Quote from: Anders Petersson on July 21, 2021, 07:59:55 pmDifferent horses for different courses. The medical sample/vaccine freezers don't have provision for getting signals in/out, and they can't change temperature easily and if your device generates heat then their cooling capacity might be insufficient. Of-course these factors might not matter in the OP's case.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: July 21, 2021, 10:31:03 pm
content: Quote from: Anders Petersson on July 21, 2021, 07:59:55 pmOf course, you are right, Anders. This was going to be my next move as well.Air is the worst kind of heat conductor (short of vacuum or aerogel.)If you think about:- ifthere is nopower source inside the freezer then it does not matter how efficient your heat transfer is. It will just take longer to cool down the contents. Same as charging an ideal capacitor via a resistor. Resistor value does not matter if you are willing to wait long enough.- ifthere isa power source inside the freezer then you have a classic situation similar to a voltage drop over the resistor that charges leaky capacitor. Any thermal resistance between the heat source (DUT, fans, Peltier module) and the heat sink (compressor) will create a temperature differential proportional to series thermal resistance times power removed by the sink (compressor)Leo

author: Labrat101
author_rank: Unknown
timestamp: July 22, 2021, 09:50:00 am
content: Hi Leo,From the freezer specs* Refrigerant R290 & refrigerant charge 40R290 is Propane and can go even lower your thermostat may have a limiter set on it.The temperature scales used for Low temp are in C. (-40F same as -40C ) scale coincide @ -40 .R290 will operate down to -60C . the only limitation are the freezer insulation and the compressormight not like being run with a suction return pressure -8.50 psig . So the compressor will need fan cooling will help . These small compressors when new can run under extreme conditions . But not GuaranteedUpdate Edit .If your compressor has 2 small pipes at the very bottom of the compressor these areOil cooling pipes and will give better performance @ lower suction cooling return.

author: Anders Petersson
author_rank: Regular Contributor
timestamp: July 23, 2021, 08:01:34 am
content: Leo, that's a good description.The one advantage of the air layer is the active circulation (convection) that exchanges heat with more or less all inner walls of the freezer. The solid thermal connection would work best if the freezer is designed to cool a particular wall.Another point is to minimize the size of the inner chamber, as the surface area determines the heat loss. There's also an optimal thickness of insulation: Too thin and the insulation is ineffective. Too thick and you lose more heat from added surface area than you gain from the extra insulation. Estimating calculations are fairly simple -- there are online calculators too.I guess you don't need theoretical pointers like these. If you build something, I'd be interested to see the results. I'll post my own results when I have time to finish my experiments.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: July 23, 2021, 09:17:10 am
content: Quote from: Labrat101 on July 22, 2021, 09:50:00 amInteresting, I am going to take it apart when I have more time and have a look.There are a few -86C freezers on eBay for £2k+ but they are huge for my purposes.Leo

author: Labrat101
author_rank: Unknown
timestamp: July 23, 2021, 10:09:42 am
content: Quote from: Leo Bodnar on July 23, 2021, 09:17:10 amThe main problem with chest freezers is that there are 2 types .One is the condenser pipes run around the outside of the case .And the evaporator pipes run round the inside of the case.So the insulation is the only separation. So there is a very high delta T across the insulation.Not overly efficient . But cheap and breaks down after a few years . Due to condensation and other chemical break down .The second type is that the condenser is mounted in the compressor compartment and has a small fan . This type of freezer is better.Your freezer was class 4 which is tropical rated . Which if you were lucky has the fan cooled condenser. And the you should get away with screwing the thermostat. To minus 70 CGiving a td at that temperature -60C and keeping the suction pressure to the compressor a little over spec ..Also if the condenser is NOT on the outside case extra insulation can be added. 8inch would be correct for -80 apx depending on grades Q .as the specs you upload don't give any real info .An ice cream freezers are better quality. The ones in the shops. Class C4 .