"Jim Wilkins" wrote in message ...

"Richard Smith" wrote in message ...

Ideas to get a controlled temperature of around -40C (also -40F) in a
test sample?

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The lowest setting on my Alpicool C20 DC-powered freezer is -40C. Temps
below -20C are accessed with the E1 special setting.
https://www.amazon.com/Alpicool-C20-.../dp/B075R1LH8D

It works well enough but isn't as rugged or hands-off reliable as a normal
AC-powered freezer, and really should have thicker insulation.
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I confirmed it could be set to -40C but didn't leave it there, as it's full
of food and would have taken a long time to settle.

My Alpi wouldn't quite cool to -20C in a hot car so I made an insulated
enclosure for it, 1" foam lined inside with a yoga mat to catch and drain
summer condensation. The exterior is thin birch plywood joined at the
corners with sheet metal angles inside and truss head screws. The lid is a
flap of Harbor Freight moving blanket, doubled.