Cheapest way to make a cooling chamber?

that's somewhat unclear, I'm assuming you mean that you need to go colder.

A freezer should be capable, the standard set-point is -18C, but that's controlled by the thermostat, you could adjust that or shim the sensor with a nearby resistor.

I'd recomend a CO2 cold plate or a small Tenny chamber. Freezers in a fridge just barely go below Zero, while a standalone freezer may do better. But a real environmental chamber will compensate for the added heat of the gadget and the cold plate can get to below zero rather quickly. I've used both and wouldn't bother messing around with something else unless the DUT is big, then it's a double compressor large HVAC system.

Cheers

Freezers typically have a "freeze" button for quickly freezing new items to at least -25 C and then maintain it at -18 C,

For testing larger objects, the big outdoor freezer can be used. In Finland there are test tracks (near 70N) that car and tyre manufacturers use for winter testing. This winter here has been weeks with neatly -40 C and more than a meter of snow this early this winter, On the South Coast (at 60N) the temperature as been +5 C and no snow, so you can find suitable temperatures for the tests between

My product is 20x20x20 cm

I live in Denmark and the last couple of years we have had extremely mild winters, averaged 5.4 degrees in January, a all time record

So I need a chamber that works a room temperature

Cheers

Klaus

The sort of freezer intended to keep dry ice in would probably do that easily and the volume of the smallest ones is about right too.

There are some issues with electronics in cold temperatures.

One problem with any processor based (or sequentially logic) system is starting the clock oscillator at extreme low temperatures. This can be quite unreliable. Once the clock is running, the electronics will generate some internal heat warming the components in the box to higher temperatures. Thus, even i some components are initially out of specs it will be within specs after a while.

When doing cold testing, let the device cool to the lowest temperature obtainable with equipment power turned off. Once the lowest temperature has been achieved, turn equipment power on and verify that the clock starts. Once running, make sure the box outside temperature remains in your case at -20 C despite the 5 W heating,

When doing indoor cool chamber tests, the initial air contains some absolute humidity. While the chamber cools down, the relative humidity RH increases, finally reaching 100 %, after which condensation or frost will accumulate. Do not put the equipment directly on the bottom of the chamber, since there might be some condensation water on the bottom. The condensation or frost may cause problems with uncoated PCBs.

This is not much of an issue when doing outdoor tests in the cold, in which the absolute humidity is already quite low.

A beer fridge for the chamber, a resistive heater, and a jug of liquid CO2 for cooling. Back when I was a real RF engineer, we had an environmental chamber that worked like that. Round here you can get your CO2 at a sporting goods store that sells paintball gear.

Cheers

Phil Hobbs

On Sunday, February 2, 2020 at 3:37:03 PM UTC+1, snipped-for-privacy@downunder.com wro te:

We have big, super expensive chambers at work, where we always do that LOL and UOL (Lower Operating Limit and Upper Operating Limit), which has the pu rpose you mention to find when it really fails. We would normally have the LOL at -50 and UOL at 150. But for my own business if I can do a minus 20 t est and 150 then I feel pretty safe

Yes. Also, don't open the chamber when at -40, tried that, won't do it agai n (heavy condensation)

Cheers

Klaus

Klaus Kragelund wrote in news: snipped-for-privacy@googlegroups.com:

Place the UUT in a Fluorinert bath.

I wanted to do an entire motherbaord that way and go down below and clock up above what the OC boys do. Some of the videos are amusing watching some dude pouring LN2 over a CPU.

My solution would work, and for long term too, not "I OC'd my PC to 10GHz" (for 1 minute long enough to run the benchmark). It is funny watching them make claims. My PC in a fish tank method would

When it is cold outside, the outside air dew point and absolute humidity is low too. When heating indoor air to +20 C the dew point and absolute humidity remains the same, but the relative humidity drops to perhaps 30-40 %. When starting an indoor cold chamber the chamber temperature can sink to outdoor air temperatures and even lower before the dew point is reached and condensation starts. To avoid some of the condensation problems, do the test on a day with low outdoor temperatures, the dew point will be even lower.

;-)

Also, don't leave a pile of Li batteries in the chamber and accidentally set it to +150degC. John

Liquid CO2 would be a first. It might even get you a Nobel Prize.

Phil probably means liquid nitrogen. Pouring that into a jug might create e nough thermal stress to break the jug. A thermos works better, but you may need to drop a resistor into the liquid and boil off enough liquid nitrogen gas (at -195.8 C or 77.2 K) to counter-act the heat flow in from the outsi de world.

Getting liquid nitrogen is like getting milk delivered, but you need a big enough container to store about a week's worth, well insulated enough to le t it last a week. Foamed polystyrene may not hack it.

Maybe, maybe not. I recall an outfit that was working on cooling military electronics. They used something like Fluorinert but instead of immersion which actually provides thermal barriers from limited conductivity of the f luid, they sprayed it on using patented nozzles to obtain optimum droplet s ize and used the heat of vaporization to cool. While that would not cool t

ction issues of the liquid.

Rick C wrote in news: snipped-for-privacy@googlegroups.com:

Fluorinert does not vaporize and the immersion unit would have the fluorinert always flowing over the parts. And oh fluorinert has very good thermal conductivity. It would work well in seal, conduction cooled designs as well, where no movement happens or is needed. They work far better than a friggin thermal pad or even a directly attached air flow heat sink.

clock up above what the OC boys do. Some of the videos are amusing watching some dude pouring LN2 over a CPU.

PC to 10GHz" (for 1 minute long enough to run the benchmark). It is funny watching them make claims. My PC in a fish tank method would work down to

Of course it vaporises if you get it hot enough.

If they didn't get too hot. "No movement" is unlikely. Convection in a liqu id can shift quite a lot of heat - if nowhere near as much as evaporation a nd condensation.

They'd work even better in a heat-pipe set-up, but water is mostly good eno ugh there.

Yes, that's the point. It does a much better job of cooling if it does eva porate. In the system I was talking about, they tried to make sure there w as no or very little surface layer of liquid. If there was, the cooling ef fect would be dramatically reduced due to the higher thermal resistance.

"very good" is a judgemental term with no quantitative value. The point is it is not as good as it needs to be to equal what can be achieved with a s pray and vaporization rather than immersion.

Don't care. I'm talking about systems that require much better cooling tha n either of those. One of the things they talked about was using a synthet ic diamond substrate to mount components to provide a thermal path for cool ing in a very high density package.

There are more technologies in mil-spec gear Horatio than are dreamt of in your philosophy.

Bill Sloman wrote in news:285c10e9-ef32-4d0b- snipped-for-privacy@googlegroups.com:

Not in a useable way. Its latent heat is plenty to use in a single phase.

Bill Sloman wrote in news: snipped-for-privacy@googlegroups.com:

Fluorinert is NOT a good candidate for the ingredients of a heat pipe.

Depends which Fluorinert. There are several. For a heat pipe it makes sense to use a single component liquid

The latent heat of vaporisation is lower than for water, which isn't an advantage, but it freezes and boils at rather lower temperatures.