TO-3, yeah, typo.  They&#39;ll go up to 1.5A, which is far more power than I&#39;ve ever used =)<div><br></div><div>The LM338 looks great.  I can&#39;t find them for less than $8, but that&#39;s still a really good deal.  I needed exactly this for a project idea I had recently... maybe it&#39;s time to revisit that idea.</div>
<div>--</div><div>/jbm</div><div><br></div><div><br></div><div><br></div><div><div class="gmail_quote">On Tue, Jul 6, 2010 at 11:37 AM, jim <span dir="ltr">&lt;<a href="mailto:jim@well.com">jim@well.com</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><br>
   i&#39;d tho&#39;t 7812s were only available in 1 Amp<br>
form; are there higher Amperages available for<br>
78XX regulators?<br>
   i&#39;m guessing you mean TO-3 rather than TO-2,<br>
yes?<br>
   there&#39;s a variable voltage regulator, LM338,<br>
that comes in a steel TO-3 package, will output<br>
from about 5 to a little over 30 VDC, very good<br>
regulation, and is rated at 5 Amps; i love &#39;em.<br>
on the order of $5 each.<br>
<div class="im"><br>
<br>
On Tue, 2010-07-06 at 11:07 -0700, Josh Myer wrote:<br>
&gt; 7812s are pretty standard for this sort of thing, and you can get them<br>
&gt; in beefy TO-2s, which take the silverpaste real good and have two<br>
&gt; places to bolt them to a big heatsink.<br>
&gt;<br>
&gt;<br>
&gt; That said, it&#39;s worth thinking through what jonfoote mentions about<br>
&gt; the Carnot cycle.  That is: if you use linear regulators, you&#39;re<br>
&gt; dumping half of your input power as heat right there, then dumping 90%<br>
&gt; of what gets through as heat off the peltier device.<br>
&gt;<br>
&gt;<br>
&gt; The exact math there is left an exercise for the reader.<br>
&gt;<br>
&gt;<br>
&gt; (Hint: leave room in your enclosure for a little muffin tin, and<br>
&gt; consider making some DIY versions of these:<br>
&gt; <a href="http://www.amazon.com/Easy-Bake-Super-Pack-mixes/dp/B00005C32X" target="_blank">http://www.amazon.com/Easy-Bake-Super-Pack-mixes/dp/B00005C32X</a> )<br>
&gt; --<br>
&gt; /jbm<br>
&gt;<br>
&gt; On Tue, Jul 6, 2010 at 10:57 AM, Corey McGuire &lt;<a href="mailto:coreyfro@coreyfro.com">coreyfro@coreyfro.com</a>&gt;<br>
&gt; wrote:<br>
&gt;         <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=527" target="_blank">http://www.sparkfun.com/commerce/product_info.php?products_id=527</a> times 18?  That sounds like a bit much.  Maybe there&#39;s a better regulator.<br>

&gt;<br>
&gt;<br>
&gt;<br>
&gt;         On Tue, Jul 6, 2010 at 10:14 AM, Corey McGuire<br>
&gt;         &lt;<a href="mailto:coreyfro@coreyfro.com">coreyfro@coreyfro.com</a>&gt; wrote:<br>
&gt;                 This is the best back-of-napkin application I&#39;ve seen<br>
&gt;                 for TEJ&#39;s, ever and a 24v power supply is the perfect<br>
&gt;                 supply for it.<br>
&gt;<br>
&gt;                 There are two problems I see:<br>
</div>&gt;                      1. When you cycle them to maintain a temperature,<br>
<div class="im">&gt;                         the heat you moved to one side will quickly<br>
&gt;                         conduct back to the other.<br>
</div>&gt;                      2. In this process, a charge will be created and<br>
<div><div></div><div class="h5">&gt;                         sent down the wire.<br>
&gt;                 How you handle this is a mystery to me.<br>
&gt;<br>
&gt;                 Here&#39;s what I would do.  I would NOT wire them in<br>
&gt;                 series.  Instead, I would implement switching power<br>
&gt;                 supplies and use them to keep the TEJ&#39;s active at 16v<br>
&gt;                 when cooling or a lower voltage while maintaining the<br>
&gt;                 desired temperature.  Then I would switch them<br>
&gt;                 relative to how far below the desired temperature they<br>
&gt;                 are.  Any temp above desired, 16v; 1 degree below,<br>
&gt;                 12v; 3 degrees below, 8v... or whatever.<br>
&gt;<br>
&gt;                 I would NOT overdrive them because I imagine they just<br>
&gt;                 get even LESS efficient.<br>
&gt;<br>
&gt;                 1 arduino<br>
&gt;                 1 temperature probe<br>
&gt;                 a fist full of switching power supplies<br>
&gt;                 a capacitor just to keep power going to the TEJ to<br>
&gt;                 help resist the heat moving backward (I don&#39;t know if<br>
&gt;                 this is a problem, but it is a cheap solution.)<br>
&gt;                 whatever else (I am not even pretending to be an EE.)<br>
&gt;<br>
&gt;                 YMMV<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;                 On Tue, Jul 6, 2010 at 9:35 AM, Sean Cusack<br>
&gt;                 &lt;<a href="mailto:sean.p.cusack@gmail.com">sean.p.cusack@gmail.com</a>&gt; wrote:<br>
&gt;                         Oh yes...I know they are terrible at<br>
&gt;                         efficiency...but they are also the only thing<br>
&gt;                         that I know of that can get you to sub-ambient<br>
&gt;                         temperatures without using a (comparatively)<br>
&gt;                         giant refrigeration system.<br>
&gt;<br>
&gt;                         I&#39;m planning on using these to cool a few<br>
&gt;                         pieces of lab equipment. Typically, to get to<br>
&gt;                         sub ambient conditions, you have to use<br>
&gt;                         ice/water (gets you to 0C), or dry ice/acetone<br>
&gt;                         (gets you to -78C), or full on Liquid N2 which<br>
&gt;                         gets you too cold for most practical<br>
&gt;                         applications. It would be *awesome* to hit<br>
&gt;                         like -20 or -10 or even 5C repeatedly and<br>
&gt;                         controllably for a million and one different<br>
&gt;                         chemical reactions.<br>
&gt;<br>
&gt;                         There is equipment that allows you to do this<br>
&gt;                         now, but pretty much its a standalone<br>
&gt;                         refrigeration system that pumps cooled silicon<br>
&gt;                         based oil through your reaction mixture. It<br>
&gt;                         takes up a ton of room on my bench, and since<br>
&gt;                         those refrigerators are on the order of $7k a<br>
&gt;                         pop, its tough to convince my boss to allow me<br>
&gt;                         to buy more than about 2 of them. In other<br>
&gt;                         words, longer hours for Sean in the lab = teh<br>
&gt;                         sux.<br>
&gt;<br>
&gt;                         So, I&#39;m trying to use these doodads as a way<br>
&gt;                         to run a bunch of reactions at a controllably<br>
&gt;                         cold temperature. I agree there&#39;s problems,<br>
&gt;                         but given the application, it may just work!<br>
&gt;<br>
&gt;                         Sean<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;                         On Tue, Jul 6, 2010 at 8:44 AM, Jonathan Foote<br>
&gt;                         &lt;<a href="mailto:jtfoote@ieee.org">jtfoote@ieee.org</a>&gt; wrote:<br>
&gt;                                 On Tue, Jul 6, 2010 at 4:17 AM, Corey<br>
&gt;                                 McGuire &lt;<a href="mailto:coreyfro@coreyfro.com">coreyfro@coreyfro.com</a>&gt; wrote:<br>
&gt;<br>
&gt;                                 &gt; Messy, messy stuff.  TEJ&#39;s are not<br>
&gt;                                 efficient.  This is fine by<br>
&gt;                                 themselves.  When you stage them,<br>
&gt;                                 their inefficiencies &gt; become readily<br>
&gt;                                 apparent as they begin to compound.<br>
&gt;                                 &gt;<br>
&gt;                                 &gt; May I ask what you intend to do with<br>
&gt;                                 them?<br>
&gt;<br>
&gt;<br>
&gt;                                 Yeah, also curious. Corey is<br>
&gt;                                 absolutely right: TEJs have terrible<br>
&gt;                                 Carnot efficiency --  way less than<br>
&gt;                                 10%. This means to move (not<br>
&gt;                                 remove) 5 watts of heat you have to<br>
&gt;                                 put in 50+ watts of power, which<br>
&gt;                                 turns into heat you ALSO need to<br>
&gt;                                 remove.<br>
&gt;<br>
&gt;                                 So they are only useful in a few<br>
&gt;                                 applications where the small temp<br>
&gt;                                 difference over a tiny scale is worth<br>
&gt;                                 the waste. If they really were<br>
&gt;                                 the magic refrigerators people think<br>
&gt;                                 they are, they would be in every<br>
&gt;                                 PC and laptop. And note that if you<br>
&gt;                                 are trying to keep things cool,<br>
&gt;                                 there may be far better solutions.<br>
&gt;<br>
&gt;                                 &quot;In this house we obey the laws of<br>
&gt;                                 thermodynamics!&quot;<br>
&gt;<br>
&gt;                                 -J<br>
&gt;<br>
&gt;                                 _______________________________________________<br>
&gt;                                 Noisebridge-discuss mailing list<br>
&gt;                                 <a href="mailto:Noisebridge-discuss@lists.noisebridge.net">Noisebridge-discuss@lists.noisebridge.net</a><br>
&gt;                                 <a href="https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss" target="_blank">https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss</a><br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;                         _______________________________________________<br>
&gt;                         Noisebridge-discuss mailing list<br>
&gt;                         <a href="mailto:Noisebridge-discuss@lists.noisebridge.net">Noisebridge-discuss@lists.noisebridge.net</a><br>
&gt;                         <a href="https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss" target="_blank">https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss</a><br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;         _______________________________________________<br>
&gt;         Noisebridge-discuss mailing list<br>
&gt;         <a href="mailto:Noisebridge-discuss@lists.noisebridge.net">Noisebridge-discuss@lists.noisebridge.net</a><br>
&gt;         <a href="https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss" target="_blank">https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss</a><br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt; --<br>
&gt; Josh Myer 650.248.3796<br>
&gt; <a href="mailto:josh@joshisanerd.com">josh@joshisanerd.com</a><br>
&gt;<br>
&gt; _______________________________________________<br>
&gt; Noisebridge-discuss mailing list<br>
&gt; <a href="mailto:Noisebridge-discuss@lists.noisebridge.net">Noisebridge-discuss@lists.noisebridge.net</a><br>
&gt; <a href="https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss" target="_blank">https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss</a><br>
<br>
<br>
</div></div></blockquote></div><br><br clear="all"><br>-- <br>Josh Myer 650.248.3796<br> <a href="mailto:josh@joshisanerd.com">josh@joshisanerd.com</a><br>
</div>