Just over a year ago, I began the conversion of an old (circa 2003) Igloo thermo-electric cooler (TEC) ice chest into a nice, electrically cooled humidor. First, since I really enjoy the rich aromatic fragrance of properly seasoned Spanish Cedar, I lined the unit with 1/4" thick pieces of the wood wherever allowed by the cooler's design. Then I constructed a couple of trays to store loose sticks in and to act a shelves. All in all, the job took a little longer than I anticipated, but went quite well; my new, nice-looking and great-smelling humidor was finished.
However, soon I was wondering if I really *was* finished since I'd been thinking of some sort of temperature control using the built in TEC unit. The closer summer got, the more important it sounded to me. No worries, I thought, I'm an electronics guy, I can completely roll my own controller if I want. Soon though, I found a brand new, normally expensive process controller for cheap on eBay; normally costing around $330, I snatched it up for a mere $35. Then I ordered a matching temperature probe from the controller's manufacturer ($38), so for a cash outlay of only $73, I was ready to very accurately control the temperature of my new Igloodor.
The controller and the temperature probe are made by Omega Engineering, a name well known in the process control field; I've been using their stuff on various projects for the last 25 years or so. With the necessary control parts now on hand, all that was needed to complete the project were a few odds and ends collected over the years that were presently collecting dust in my junk box and the ambition to get off my lazy butt and do it.
I dug out three old Radio Shack relays, a few 1N4001 diodes for control line isolation, a power cord, and a fuse holder to complete the unit. But with no spare room in the Igloodor to mount the control stuff, what to use for a electronics case? Then an epiphany hit while smoking a 601 Blue; what, I mused, would be more appropriate than using an empty cigar box? Perfect! Thus the controller was begun.
A little head scratching, some elbow grease, and a couple burned fingers later, I finally have my completed controller - one that controls both cooling *and* heating, that's accurate to within about one degree, and that can maintain the temperature to within 0.1 degrees of set point if desired! Overkill? Definately! But
awesome cool (pun intended) so I did it anyway!
But, you ask, how can a mere "cooler" regulate both the high and low temperatures? Easy - a TEC is really a semiconductor heat pump that sucks heat out of the cold (source) side and moves it to the hot (sink) side, which also must dissipate the TEC's own operating heat. That's why good heat sinks are a must for both sides of the TEC and fans should be used, too, especially in our application to heat and cool the inside of our Igloodor and all our nice cigars too.
The great thing about such a semiconductor heat pump is that when the supply voltage applied to the TEC has it's polarity reversed, the source and sink sides swap too; cool becomes hot and vice-versa! Therefore it's relatively simple to use the TEC as both a cooler and a heater since all that's needed is some sort of polarity reversal device - that's a relay in this design.
There's not much else to say here except that point to point wiring was used to construct the project. Safe construction techniques must be used on the mains (120VAC) power side for the Omega controller. Also various control parameters need to be set properly to use the Omega controller for this task. If there's interest, I'll add to this thread post later and let you know which control parameters were set and what they were set to. In case anyone is interested, here's a higher resolution version of the schematic presented with the pictures of the complete unit in the Igloodor photo album:
IgloodorSchem.jpg and here's a link to the album itself:
Igloodor
Finally, the unit keeps temperature controlled flawlessly, and with the inclusion of several 4 ounce bags of HCM (Shilala) beads the RH stays right smack-dab at 68% where I want it. So enjoy - I am!
:-)
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