🚀 go-pugleaf

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In article <266@ssc.UUCP>, markz@ssc.UUCP (Mark Zenier) writes...

>> In article <4486@optilink.UUCP> manley@optilink.UUCP (Dave Manley) writes:

>> >What is the physical mechanism whereby a thermoelectric cooler (TEC) 

>> >cools?  I been told it has to do with the Peltier effect.  
>> >
>> >(TEC's along with precision thermistors are used in diode lasers.)
> 

>There's a good writeup of thermoelectric coolers in Don Lancasters 
>Hardware Hacker column in the January 1990 Radio-Electronics
> 
>"And to further shatter some hacker dreams, no way will they
>make ice in the real world"
> 

  JC Witney markets several refrigerators for vans which are thermo-electrically
cooled. That is at least almost real world ;-) I've certainly formed 
frost on the front surface of one. Interestingly the ones manufactured for 
these purposes are a lot cheaper for the same heat capability than the ones 
made to cool chips. So far as I can tell there is no significant difference 
in the materials used. The company I bought from had a $100 dollar minimum, 
but I bought an assortment of  7 or 8 for slightly more than that, the company
was in NJ. If there is interest I'll dig up the address and a few 
representative prices.

  You can definetly make a good refrigerator with these puppies. It will
not be nearly as efficient as a compressor. But it can be small and
with a big heatsink no moving parts. The big thing to keep in mind
is you need a LOT of power to cool more than a small thing. Even an
eraser sized cooler needs an amp or two at 6-12 volts to work. If
you want to make a small refrigerator think TENS of amps, at low
voltage. Thats not surprising any reasonable fridge is a lot more
than 100 watts, and these things are less efficient than a CFC standard
fridge.

  I think the primary reason for their efficiency problem is that they
are thin (5mm) and the semiconductor junctions are wide. So the heat conduction
from the cold side to the hot side is quite large. Kind of like trying
to keep one side of a frying pan hot and the other side cool. Making them 
thicker helps minimize this heat loss since the heat has to flow farther. 
But since the current has to flow from one side to the other you lose on I^2R 
ohmic heating when you do that. Also you need more semiconductor ($$).


					Chuck@mitlns.mit.edu