>Hello Craig, I purchased a name brand 44qt? cooler with peltier
>device for $85.00 online and picked up at local sears. Keep an eye
>on their site and you can once in a while catch this price.
Yes, I'm sure the camping cooler module is the simple starting point.
The things to add to that are the ice tray/chest on the inside
(replacing the inside heatsink and fan) and the (as yet unbuilt)
smart control.
The 3" extruded polystyrene foam (house insulation, R5 per inch) is a
key to success with a minimal cooling unit, and shapes with minimum
surface area for the volume like an octagon (or ideally a geodesic
dome) are valuable.
With 3" of insulation, 3 one gallon ice cream pails of ice kept the
floor temperature at 5-6ºC for 2-1/2 days, and it looked like they'd
take 3 or 4 days to melt completely. So a simple large superinsulated
icebox should be good enough for weekend excursions. Call it a better
insulated cooler.
Polyurethane foam, R7 per inch, is even better, but I found it more
mess and hassle than it was worth to make walls of, at least for
flat, square shapes. However, cans of PU spray foam make an
excellent, crack filling glue for gluing the sheets of PS together.
---
To start from scratch, look up 'Peltier modules' or 'peltier cooling'
to find the thin, flat peltier wafers. The surfaces are white ceramic
and the thermocouples are within. (Mine is rated 8.4 amps at 15+
volts, and draws about 7.2 amps at 13 volts, BTW.) Aluminum extruded
finned heatsinks seem overpriced to unavailable. I make heatsinks by
(a) taking 2 fat bars of aluminum and clamping several pieces of thin
aluminum between (with bolts right across between the two bars), then
bending the thin pieces (eg, roofing flashing) into a fan shape,
\ top bar /
\ \ ======= / /
\--\-------/--/ <- fanned out
-------------- <- flashing
__/---------\__
========= <- bottom bar
[peltier]
=========
or (b) my new idea for the Peltier cooling with a fan blowing across
parallel fins: several 1/4" x 1/2" bars ("n") "stacked" together with
2" wide thin pieces ("|") for fins between them, bolted right across
from one side to the other: n|n|n|n|n|n|n|n... Or you might stack 2
fins per bar and bend them apart a bit.
Digikey is a bit pricey for peltiers (18$) compared to some people on
Amazon and other places (10$), but they have 12V fans from about 3$
up for the outside heat sink fan.
> I removed the exterior AL heat sink and replaced with a water
>cooled heat sink wi better fan ($38 online; used). Hope to find
>time next month to test for efficiency improvement (faster cooling),
>Also considered 'stacking peltier's but no time for that yet.
That should help a bit - keeping the outside cooler as with
circulating water gives you a few more watts of cooling energy for
the input watts, but making the ouside 10º cooler doesn't mean the
inside will be 10º cooler. (I mention this because I didn't realize
it at first. Heat is still leaking through the fridge walls at the
same rate and needs more watts for each degree cooler.) But there's a
Koolatron[.com iirc] cooler sized fridge unit (150-200$) with some
sort of passive refrigerant tubes heated by the Peltier outside unit
and they say it'll cool by up to 30ºC where most claim 20ºc.
Putting two Peltiers in series seems no more effective than a single
one - I tried it and then realized results were better with just one.
(If you want to have say 3 on the outside stage and 1 on the inside
colder stage it can get substantially colder, but for 4 times as much
electricity.)
Craig
===
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