>-----Original Message----- >From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] >On Behalf Of Dave Tweed >Sent: 27 June 2007 22:22 >To: piclist@mit.edu >Subject: Re: [EE] Cheap solution for environmental chamber > > >Russell McMahon wrote: >> >>If you need to go VERY low then a Peltier device may not >have enough >> >>power. What is your target temperature range? >> > >> > If you need more delta T then stacked Peltiers are a possiblity. >> > This is what we use for over temperature testing in >production (way >> > faster than the environmental chambers we used to use). >> >> Stacked Peltiers do give extra temperature differential but at a >> substantial decrease in Watts of cooling as you use N layers and a >> reducing delta T per layer. For cooling you can get up to 6 >layers (I >> think I've seen) but the stack is shaped something like a Christmas >> tree with a very small unit at the top and very small cooling watts >> overall. > >The problem is that Peltier devices are not all that efficient >overall. Something like 30-40% IIRC. In other words, for every >Watt of heat coming out of the hot side, 300-400 mW of that >came from the cold side, the rest was the electrical energy >you put into the device. > >Even with stacked devices, you eventually get to the point >where all of the heat coming off the hot side is the >electrical energy you're putting into the stack, and there's >zero remaining capacity to remove heat from the target. > >-- Dave Tweed Absolutely, stacking the peltiers certainly makes the overall efficiency (or more correctly the coefficient of performance) much worse, and the heat pumping capacity is determined by the smallest peltier at the top of the pile. That said, if you need to production test a relatively low power device accross a wide temperature range it's a very effective solution, both in terms of test time and energy consumption when compared to sticking it in an environmental chamber and ramping it's temperature up and down. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist