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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/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>
1:3 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>
actually no, i take that back
<
azonenberg>
they're -40 to 85
<
azonenberg>
I may have a hard time testing at -40
<
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>
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
<
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>
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
<
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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