This is the best back-of-napkin application I've seen for TEJ's, ever and a 24v power supply is the perfect supply for it.<br><br>There are two problems I see:<br><ol><li>When you cycle them to maintain a temperature, the heat you moved to one side will quickly conduct back to the other.</li>
<li>In this process, a charge will be created and sent down the wire.</li></ol>How you handle this is a mystery to me.<br><br>Here's what I would do. I would NOT wire them in series. Instead, I would implement switching power supplies and use them to keep the TEJ's active at 16v when cooling or a lower voltage while maintaining the desired temperature. Then I would switch them relative to how far below the desired temperature they are. Any temp above desired, 16v; 1 degree below, 12v; 3 degrees below, 8v... or whatever.<br>
<br>I would NOT overdrive them because I imagine they just get even LESS efficient.<br><br>1 arduino<br>1 temperature probe<br>a fist full of switching power supplies<br>a capacitor just to keep power going to the TEJ to help resist the heat moving backward (I don't know if this is a problem, but it is a cheap solution.)<br>
whatever else (I am not even pretending to be an EE.)<br><br>YMMV<br><br><br><br><br><br><div class="gmail_quote">On Tue, Jul 6, 2010 at 9:35 AM, Sean Cusack <span dir="ltr"><<a href="mailto:sean.p.cusack@gmail.com">sean.p.cusack@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Oh yes...I know they are terrible at efficiency...but they are also the only thing that I know of that can get you to sub-ambient temperatures without using a (comparatively) giant refrigeration system.<br>
<br>I'm planning on using these to cool a few pieces of lab equipment. Typically, to get to sub ambient conditions, you have to use ice/water (gets you to 0C), or dry ice/acetone (gets you to -78C), or full on Liquid N2 which gets you too cold for most practical applications. It would be *awesome* to hit like -20 or -10 or even 5C repeatedly and controllably for a million and one different chemical reactions. <br>
<br>There is equipment that allows you to do this now, but pretty much its a standalone refrigeration system that pumps cooled silicon based oil through your reaction mixture. It takes up a ton of room on my bench, and since those refrigerators are on the order of $7k a pop, its tough to convince my boss to allow me to buy more than about 2 of them. In other words, longer hours for Sean in the lab = teh sux.<br>
<br>So, I'm trying to use these doodads as a way to run a bunch of reactions at a controllably cold temperature. I agree there's problems, but given the application, it may just work!<br><font color="#888888"><br>
Sean</font><div><div></div><div class="h5"><br><br><div class="gmail_quote">
On Tue, Jul 6, 2010 at 8:44 AM, Jonathan Foote <span dir="ltr"><<a href="mailto:jtfoote@ieee.org" target="_blank">jtfoote@ieee.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div>On Tue, Jul 6, 2010 at 4:17 AM, Corey McGuire <<a href="mailto:coreyfro@coreyfro.com" target="_blank">coreyfro@coreyfro.com</a>> wrote:<br>
<br>
> Messy, messy stuff. TEJ's are not efficient. This is fine by themselves. When you stage them, their inefficiencies > become readily apparent as they begin to compound.<br>
><br>
> May I ask what you intend to do with them?<br>
<br>
</div>Yeah, also curious. Corey is absolutely right: TEJs have terrible<br>
Carnot efficiency -- way less than 10%. This means to move (not<br>
remove) 5 watts of heat you have to put in 50+ watts of power, which<br>
turns into heat you ALSO need to remove.<br>
<br>
So they are only useful in a few applications where the small temp<br>
difference over a tiny scale is worth the waste. If they really were<br>
the magic refrigerators people think they are, they would be in every<br>
PC and laptop. And note that if you are trying to keep things cool,<br>
there may be far better solutions.<br>
<br>
"In this house we obey the laws of thermodynamics!"<br>
<font color="#888888"><br>
-J<br>
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