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Question on using a Peltier/TEC device for air temperature control - Help please.

I want to have some control over the temperature inside the Orchidium I'm designing and I thought it might be cool :) to use a Peltier Device (device aka module) (Peltier aka TEC or Thermoelectric Cooler). I find I need a lot of help! (Please!) Alright, this isn't a completed Instructable, it's a plea for help, and maybe if the subjects lie in some of your fields of knowledge then we can all enjoy and learn from it. So, the Orchidium I'm designing is an acrylic case 24"W x 18"D x 30"High. It's to grow species orchids indoors in a microclimate, with LED grow lights, proper humidity, air movement and temperature control. (Of course, other critters would like the case, too: poison dart frogs, newts, carniverous plants, etc.. But I'm going to call it the Orchidium.) I've got it all pretty well planned out so that it can be built for a very reasonable price (yes, including the LEDs) and still be aesthetically pleasing and real purdy, too. All planned out EXCEPT FOR THE TEMPERATURE CONTROL. I was looking for some way to cool my case and I stumbled across Peltier devices in eBay. They are CHEAP, costing about $5 or more, depending on the Wattage, etc. The eBay sellers intimated that all you have to do is plug them in and the device gets ice cold. Later, with diligent web-study I learned that actually ONE SIDE of the peltier gets cold, while the other side gets hot. Also, you MUST attach a heat sink and fan to both (?) sides of the peltier. Also, that these devices are not ready to be plugged in; you must attach a DC power supply to them. Oh, another trick that these miraculous devices do is reverse their hot & cold sides when you reverse the polarity of their juice. Ideally, I would like a Peltier device with heatsinks, fans, a thermostat and a DC wall transformer attached... the Peltier/heatsinks/fans would measure about 2" x 2" x 6" and would be mounted in the sidewall of the Orchidium. When the temperature is 65-85F degrees the orchids are happy and the device is Off. But when the thermostat senses the internal temp going over 85F it turns on the Peltier, cold side inside, and so the inside of the case doesn't go up to 90-95F like mine does now; it cools the case a little. Conversely, for someone with chilly orchids or sneezing newts the thermostat would switch the Peltier to hot-side-in to heat the Orchidium a bit. The retail cost for us to buy a Peltier device, 2 heatsinks w/fans and a DC transformer is cheap... roughly $30. The thermostat might be cheap, but I don't know enough about what's needed. If it's too expensive then the Orchidium can do without it. I was hoping I could find an off-the-shelf Orchidium cooler/heater. No such luck. These miraculous Peltier devices are still practically undiscovered -- relatively speaking. People want to use them to cool their computer chips but are hampered by condensation; my orchids welcome condensation. Pathetically, it seems the most common use for Peltiers now is to cool/heat the little boxes on your car seat... they plug into your cigarette lighter and keep your 6-pack cold. Come on! You folks at Instructables can surely help me figure out how to best make an Orchidium cooler with this barely-discovered and poorly-utilized device. I started out a few weeks ago writing to many of the Peltier manufacturers around the world in hopes they might help me in choosing which of their modules I might purchase for my Orchidium. None of them was any help. They wanted to know how many million Orchidiums I planned per year. They told me my basic plan was hopeless or inefficient cost-wise. A Swedish company wanted $800. An American company wanted $500. Some other company wanted $5,000 to $8,000. I wrote back and said I could get a Peltier on eBay for five bucks. The Swedes snottily claimed that their Peltiers were very high quality. No. No way is any svensker Peltier $795 better than ANY other Peltier in the known universe. They both get cold and grow ice crystals on one side. I just need to cool the case A LITTLE BIT, like from 90 to 80 degrees Fahrenheit. I am not trying to make a refrigerator or freezer. The case (Orchidium) is large, at about 7.5 cubic feet, and there is practically no insulation. Acrylic provides a little insulation, that's all. The temp of the interior of the case is derived from the ambient room temperature of your house... and the lights... which is why I designed it with LEDs. There is a constantly-operating muffin fan inside the case to provide air movement for the plants, but it does not provide any evaporative cooling since it's a closed case. So, first off what size Peltier do you recommend... do you think a 40 Watt would be enough, or what? Next, the placement. I envision the Peltier device mounted vertically through a hole in the side of the case. It might be a plan to mount it in the ceiling, but remember that the LEDs take up most of the ceiling. Next, the heatsinks. I confess I'm not totally clear on this, but I "think" that 2 heatsinks-with-fans may be needed, with one sticking out the outside and the other inside the case. I went ahead and got 2 heatsink/fans from Newegg for supercheap ($1 after rebate), but they aren't really what I want. They're actually shaped to fit some AMD chip. What I think I need is a copper heatsink with a flat bottom a little bigger than the Peltier, and fins... and a heatsink fan attached... and some way to attach it to the Peltier, and through the case to the other heatsink. See? Simple... well it should be but I can find nothing. Next, the power supply. I know it has to be DC, but I don't know which brick to get. I did find a bunch of DC or AC Wall Transformers for sale at alltronics... around $10 or so. All that stuff would be enough... at least to test the cooling power. But if we want to go whole hog then the icing on the cake would be thermostatic control of the Peltier. Well, I throw that out in case one of you is sharp in that field.

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junits156 years ago
Here is my experience with thermoelectric units, for a box THAT large you will need a lot more than 40 watts to cool the case especially without any insulation. I have a 1.57" X 1.57" (40mmX40mm) 168 watt TEC that I got off of ebay. It is extremely in efficient as it draws 14 amps max ( a real PTA to find a power supply for) I have never been able to provide the full 14 amps...yet. the closest I've ever gotten was with 10 amps from an old computer PSU, and even when it was underpowered (the PSU extremely overloaded) I had to watercool the Hot side before I got any ice on the cold side. So anyway lets say, hypothetically, that you changed your mind and bought a more powerful TEC You would need a much more beefy PSU for it. An xbox 360 PSU works nicely because it can put out 16 amps on the 12v rail. ( =0) then in order to cool the air in the box you would need a heatsink with large fins so they wont frost up and clog the fan but to heat the box you would need to resist some of the current to the TEC (you dont want to fry your plants do you?) then comes the problem of actually switching the current around, we are talking 12+ amps here depending on the TEC. That means you will also need some fairly powerful relays or transistors and resistors to control everything. So in conclusion, from what I see, this project looks like it could take right off and be a really nice featured instructable. It just needs to be re-planned to be compatible with the TEC idea.
Neurotoxin8 years ago
Just as an FYI, 'Peltier Junctions' (aka Thermoelectric Modules) are, as you've already figured out, nothing more than solid state heat-pumps. While they vary in efficiency -- drastically, in my experience -- those in use for Government/Military purposes are EXCEPTIONALLY efficient, being run at anywhere from 3-12VDC, and I've personally seen those which run at the higher voltages and which draw *less* than one (1) amp -- no joke. Availability of a unit remotely *close* to that kind of efficiency, however, is either A) very pricey, or B) Restricted.

Check out this Military unit designed in 1961, with the report finished in 1962. Note the EER, the thousands of BTU's per hour, and that the dimensions were 1' x 1' x 3" -- yes, that's correct: a foot by a foot by three inches (!!!!). Compare the stated EER achieved with that of, say, a comparable refrigerative AC unit with the same approximate BTU hours available to the public *today*.

If that doesn't blow your hair back a little, again, note that this was stuff being done the moment the materials were available, and which the military was already working with/putting into commission in the 1960's (!).

So, to repeat NachoMama, you ARE on the right track; while Tech-King is correct in that the majority of the TECs available (e.g., on ebay, etcetera) are garbage -- they suck HUGE amounts of current, nearly as badly as the early Mil-tech ones did, IME, the fact remains that not *all* of them do....Whether they're publicly available or not is mostly an open secret, if one knows the principle manufacturers, and understands their varying part-numbering schemes (e.g., group XX-XXXX is Govt only; group XX-XXXX is unrestricted).

All comments about them needing to be properly heat-sunk ('cold-sunk') on both sides are correct: without the appropriate amount of area for heat-dissipation/absorption, they WILL be destroyed, or at least have their effective lifespan shortened). Forced convection (fans) are a good idea, as well.

Hope that proves helpful, and let us know your progress :)

~J
I tried the link you have listed and I get a 404 Error. When I try to use just the Navy link nothing there. Do you have any updates?
Although I know even less about Orchids than I do about electricity - I was pleased to read this question since it comes topically close to my own dilemma... I have frequent need to warm/melt buckets of honey. The recommended means (cheap) is to put a 60 watt bulb in an old fridge and leave for 12-24 hours. I'm interested to know if I could mount one or several of these little peltier thingies inside the outside fridge, possibly using the fridge skin itself as a large heatsink (yes??) and then run it/them from a standard car battery recharged with a solar panel. If this CAN actually work.. how does the wattage of the units affect temp/electricity usage? and... could I mount one of the units on the underside of the lid of a honey bucket and plug it into the ciggy lighter of the car to be able to melt during long drives? Any help would be appreciated. tonyreay@kidhugs.com
. It should work. You'll probably want to plan for collecting the condensation from the cold side when you're in the car. . The more watts you have, the faster your 'fridge will warm up - and the bigger power source you will need. I'd install in 2 or more banks and switch them on/off as needed - use a thermostat if you want to get fancy.
Thanks.. how much condensation should I expect - about...? how does this thing function... do I just glue it to a piece of the exposed outer skin by stripping out a section of the interior insulating stuff? How do I know which is the right way to do it.. I haven't been able to find any actually "how to" pages anywhere (that's how I found this site..) I don't understand how to install two banks... or more. I would be willing to pay for actual diagrams and instructions and advice, since this is currently a difficult and expensive task. What do you mean "build a power supply" - regulated or otherwise..? AAAaaaarrrrrrggggghhhhhhh I feel SO DUMB sometimes..
1) expect a lot: that way, you will not be or be pleasantly surprised by the condensation 2) you attach it with thermal adhesive to one side of the skin, cold side touching metal. you use more adhesive and mounting screws to secure a decent size aluminum heat sink/fan assembly to the hot side 3)peltiers are powered of 12 volts. your wall has 110 or 220 volts in it. you need a power supply capable of around 5 amps. it depends on the peltier.
this is also a reply to NachoMahma - since you are both helping me stumble towards enlightenment here... I BELIEVE that I'm actually getting to grips with this system but, as always, have a few more questions... 1. If I attach the cold side directly to the outer skin... does it also need a heat sync and a fan? 1b How do I know which is the cold side - just wire it up and feel it.. or are they marked in some way? 2. How big a heat sink do I use on the interior "hot" side? can I just pull one from an old car cooler/heater thingy? What's a "decent" size? 3. Does a fan on the interior simply disperse the heat around or is it more designed to keep the peltier from bursting into flames? 4. Assuming that I only use one unit (mainly) can it indeed run from a car battery, kept up to snuff with a solar panel? 5. Is there a limit to how long one can continuously run juice through the unit without it ... breaking, I guess, in some way? A little clarification about some other comments in this thread please. It has been noted that one is ill-advised to buy units off'n ebay since they are inferior quality.. where does a neophyte get such things here in the UK then? It has also been noted that one shouldn't use thermostatically controlled switches to turn the current on and off... is this true? It certainly would be great if I could, y'know? Hotdarn this baby might actually work.
1) It may not _require_ one, but it will work MUCH better with one. The skin of the 'fridge may provide enough heatsink. Since you are not moving a lot of heat and it's not a critical application, I'd try it without and see what happens. 2) See t-k's answer. Since you only need ~60W, I'd go with unit(s) designed for CPUs/GPUs/&c - fan and heatsink already attached to the hot side. 3) See t-k's answer, but I'd rate them as pretty much equal. 4) If you are doing this more than a few miles (or whatever comfortable walking distance is for you) from civilization, I wouldn't recommend using your car's starting battery. A car battery should work fine, but as t-k points out, TECs can pull quite a bit of current. You could strand yourself in the boonies if you discharge your car battery too far. Maybe an extra battery in the trunk? If it goes dead, your honey is a little thick, but you can get home. 5) With the proper voltage and heatsinks, they are continuous duty. I had one on an old 68030 Mac that ran 24/7. Keeping the voltage below the max will help extend the life. . . I haven't heard of not using switches/thermostats, but I'm definitely not an expert. My experience is limited to the aforementioned Mac, some industrial "cabinet coolers," and a couple of small units that I fiddled around with on my workbench for a few hours. . > Hotdarn this baby might actually work. . I believe it will. It may not be terribly efficient when you get done, but it ought to work. . . PS: when you select a glue, not only should it conduct heat well, but it should be able to put up with the thermal cycling (expansion/contraction). For your application, neither one is critical, but keep them in mind.
a good glue is thermal adhesive by arctic silver, but is a bit pricey. look for gpu peltiers. cpu peltiers start at 80-120 watts.
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