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<azonenberg> Welp, thermal characterization setup is proceeding nicely
<azonenberg> My old heatsink wasnt beefy enough
<azonenberg> now using an old core2quad heatsink and some arctic silever paste
<azonenberg> silver*
<azonenberg> At about 1.8 amps, in 23C ambient, the plate was measuring -5C and had a perceptible layer of frost forming on it
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<azonenberg> The peltier module can handle up to 6A but there's no way i'd actually run it that hard
<azonenberg> Point is, i totally have the power to get my DUT down to 0C Tj
<whitequark> azonenberg: interesting
<whitequark> for -20°C you could use a, hmmm
<openfpga-github> [yosys] azonenberg pushed 5 new commits to master: https://git.io/vQR1l
<openfpga-github> yosys/master 8952bd6 Clifford Wolf: Add chtype command
<openfpga-github> yosys/master 18c030a Clifford Wolf: Add $tribuf to opt_merge blacklist
<openfpga-github> yosys/master 5b95901 Clifford Wolf: Merge pull request #353 from azonenberg/master...
<whitequark> 1
<whitequark> 1:3 ratio of salt to ice
<whitequark> gives you a nice stable -20 until all ice melts
<azonenberg> whitequark: I don't need lower
<azonenberg> they're commercial temp range parts iirc
* azonenberg double check
<azonenberg> s
<whitequark> ah ok
<azonenberg> actually no, i take that back
<azonenberg> they're -40 to 85
<azonenberg> I may have a hard time testing at -40
<whitequark> no
<whitequark> sec
<whitequark> you can get ethanol, ethylene glycol and dry ice, right?
<whitequark> 60% ethylene glycol, 40% ethanol, frozen with dry ice
<whitequark> gives you -41°C
<whitequark> actually you can get any temperature from -5 to -78 this way
<azonenberg> interesting, but i want to go solid state if possible
<whitequark> you could use one of those water cooling contraptions, no?
<whitequark> or just use a copper cup, it's not like you need a lot of mixture
<azonenberg> The peltier lets me do scripted closed-loop feedback
<whitequark> ohh
<whitequark> well ok sure
<azonenberg> My plan is to put a die in the rig then run tests automatically across the supported T/V range
<azonenberg> then load another one and repeat
<azonenberg> i really dont want to be messing around with custom ratios of stuff and dry ice etc if i can do it solid state
<azonenberg> I have a peltier that may be able to pull this off
<whitequark> $48, DTmax=91°C, Qmax=1.6W
<whitequark> no single stage peltier will bring you to -40 afaik
<azonenberg> Depends on Tamb
<whitequark> room
<azonenberg> But i'll look at multi-stage
<azonenberg> So far I've managed to get it from 22C ambient to -5C at 1.75A or so
<azonenberg> it's rated for 6A
<azonenberg> let me pull up the datasheet
<azonenberg> Qmax is 66C at 27C ambient
<azonenberg> Which is -39C
<azonenberg> So if i can get Tamb a little bit lower., -40C may be doable
<whitequark> DTmax
<whitequark> not Qmax
<azonenberg> sorry yeah
<azonenberg> that's what i meant
<azonenberg> Qmax is 12.2W
<azonenberg> i was reading the wrong column heading :p
<azonenberg> This thing is rated for max 3.8V 6A, and i 'm pretty sure it's single stage
<azonenberg> I have the hot side on the copper slug of a 2U x86 CPU heatsink
<azonenberg> so i can easily dump 100W of heat into that
<whitequark> azonenberg: but you don't get DTmax at Qmax
<azonenberg> Correct, but i dont need to
<azonenberg> the Q is going to be near zero
<azonenberg> i basically just need to handle leakage from ambient
<whitequark> ok
<azonenberg> the heat generated from the DUT is infinitesimal
<whitequark> that is quite a bit at -40
<whitequark> so you'll need insulation
<azonenberg> we're talking worst case a few mW
<azonenberg> leakage from air will be greater
<azonenberg> The easiest option is probably just to buy a second of these peltier modules and stack them
<azonenberg> That should give me plenty of room on the low end
<azonenberg> I picked this one planning to test to 0C and somehow forgot the chips were rated for -40
<azonenberg> I plan to test at 0, 25, 45, 85 with my current setup
<azonenberg> then do say -20 and -40 once i get a second stage
<azonenberg> If one stage can get me from 22C to 0C running at 1/3 of the max current, i think two should be able to hit -40 quite comfortably
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