twigss

Hi all, I am starting a project that has nothing to do with my PC... but everything to do with TEC cooling. I am trying to find a way to cool the air temperature in an aquarium.

Right now the plan is to find a TEC (I've read the ebay ones are crap and I should buy from Frozen CPU - which is fine) and slap heatsinks with 120mm fans on each side. I will put the cool side on the top or side of the aquarium and exhaust the heat to the room.

A few questions I have:
1) What watt TEC should I buy? Looking to cool from ambient (70F) to around 50F throughout the tank.

2) How can I attach the heatsinks to the peltier? I saw thermal adhesive (similar to thermal paste) on ebay, would this do the trick?

3) I think I have found the answer to this but, what is the easiest way to power this? I saw the sticky on turning an ATX PSU into a TEC PSU but is there an easier way?

billbartuska

Hope that helps start you in the right direction.

__________________
EDGE ...if you're not on it, you're taking up too much space.

zipdogso

Any TEC larger than your heating in the tank will suffice as air is very easy to cool. BUT a TEC larger then 100w Qmax will require water cooling on the hotside, use a lower wattage and a good heatsink fan combo will suffice.
You will need a thermostat or the TEC wil cool below the point you require.
If you havent any heating in the tank you can use quite a small TEC.
The heatsink inside the tank should be as large as you can get it (well perhaps big enough for two 120 fans.) with fins as tall as possible ( aluminium ones are quite cheap look on ebay. You may even need to cut one down to size.) and you mount one or two fans blowing into the the heatsink this will cool the air and circulate it round the tank.

With NO heating in the tank air actually is quite easy to cool but conversly is quite easy to heat as well.
I am assuming this is not an aquarium per se but a tank for keeping plants or land dwelling animals. A drop of 20ºF is equal to 6ºC roughly.
Let's say your aquarium is a 4 footer and 15" high and 12" deep it's volume is 48 x 15 x 12 = 8640 square inches which is 0.1415 cubic metres.
In an average room (average humidity.) it takes 0.339 watts to raise/lower a cubic metre of air by 1 ºC

So to lower 0.1415 cubic metres by 6ºC - 0.1415 x 0.339 x 6 = 0.2878 watt hours
If you want the temp drop to be quick say 5 minutes - 5 minutes is 0.084 of an hour so to achieve this cooling in 5 mins requires 0.2878/0.084 = 3.26 watts !!!

Of course this assumes the air doesn't heat up again in the 5 mins, which of course it will and assuming 50ºF is lower than you room ambient you will need extra wattage to counteract that too.
Also a high humidity will increase the power required, a very dry atmosphere obviously goes the other way.

So air is pretty easy to cool. In this instance, if you want to go cheap 80w TEC's are generally available, smaller ones you can get but they are expensive by comparison by going somewhere like this -http://www.shop.customthermoelectric.com/Standard-TECs_c2.htm;jsessionid=B3A3E385861215D2E1C6DC378DF 61201.qscstrfrnt01 I would aim about 45w or so BUT make sure you select one with a low current rating it will be easier to power.
If you are worried about efficiency go larger and undervolt the TEC BUT that's another story if you want to go that route you need more info.....I can give it but it starts to get complicated, I will need to know more about what your doing.

Ideally if you can you should bolt through the heatsinks to clamp the TEC between them. In the ideal world you need to clamp the TEC with a pressure of 150-300 p.s.i. but many heatsinks are not built to take this so the best you can do is tighten them so the heatsinks don't bend - they need to be flat against the TEC if they bow they wont have contact. You must make sure the heatsinks completely cover the surface of the TEC if you have ones with raised contact area you need to be sure this is big enough to cover the TEC's. Use a good TIM as already mentioned ceramique will do.

Well you might be in luck here....if you have no heating in the tank and you use a small TEC for cooling it will be very easy to use any generic power supply to power the TEC anything that can supply a constant 12v at the max current rating of the TEC. Ideally you want a variable one.
If you need a larger one it is best to use a dedicated supply like a meanwell or if that is too expensive look in the radio amateur section of ebay for a supply that suits the rating of the TEC you buy. The reason I say this is because the power will be variable so you can adjust the power of the TEC if you mod a PC PSU you will have no control it is 12v or nothing.

twigss

Thank you so much for the very detailed response!

You are right, it is for cooling a terrarium of plants - specifically highland Nepenthese and Heliamphora.

The main concern is a temperature drop at night. (like certain plants see in their natural habitats on mountains) This means there is no heat generated from within the terrarium itself, only ambient temperatures to deal with. I don't have an exact size, but the 4' by 15" by 12" should be a decent ballpark figure.

Do you have a suggestion on what to use as a thermostat? The ones I found from a quick google search were plugged into a wall outlet. This would mean it would have to turn off the entire PSU - is this healthy for the PSU to cycle on and off so often?

After reading your post, this project seems much more feasable than it did before. There have been a couple of people that tried using TEC's as cooling for a terrarium and many came to the conclusion that it was possible but nobody ever implimented a decent setup. I hope to show them all up with your help!

zipdogso

To start with where are you ? I am in the UK so I tend to find things in the Uk which isn't too helpful if your USA. But if your USA I will still see what I can find. Thinking about it now you quoted fahrenheit...hmmm...you must be USA. Oh yes you are - just seen your PM.

Ahhh.....carnivorous plants, nice one. Depending on your species of Nepenthes 15" high migh not be enough. I don't know much about pitchers BUT I do know some get pretty big.

Great your jobs a bit easier then....out of interest what is the average ambient of the room where the tank is. I am assuming it is not much more than the terrarium internal temperature.

Your right about the thermostat what you need is something like this - http://cgi.ebay.co.uk/TC-10-DIGITAL-...item35a3c6848c

I have one of these and they are very good to use them with a PSU you have to wire the unit slightly differently to what the manufacturer says in the advert. Don't worry it is only a case of connecting different wires to the screw conections on the back and it was the manufacturers that told me how to do it.

On the subject of heatsinks to go inside the terrarium you want something like this but no where as big this one is collossal....6cm deep...wow. -
http://cgi.ebay.co.uk/Thermoflow-MON...item230348ebb1
You need something more reasonably sized..... at the other end of the spectrum there is these but they are a tad small - http://cgi.ebay.co.uk/Brand-New-Cool...%3D5%26ps%3D63
The picture isn't working but trust me, problem is they only take an 80mm fan but you could use a couple of them. You can find them on the cooljag (USA) site they are 78mm x 86mm x 26mm high with skived fins and are all copper.
For the hotside of the TEC ideally placed on the outside of the terrarium you could just use standard computer CPU heatsink and fan combo, seeing as you wont be using big TEC's.
Once I know where you are I will find you a good place for the TEC's.

Unfortunately the desire by many to NOT seek decent information before using TEC's means few actually implement decent setups even here in the computer world.

Ultrasonic2 (muffy)

Sounds like just about every TEC project .. to be frank to get a TEC project to work you HAVE to do it right which means it's gonna cost a lot. You'll be doing it for love more than anything else

__________________

zipdogso

Twigss...I hope you will excuse my drawing but the attached is something like what you should be aiming for. It is based on how they build commercial TEC air chillers. You need the fans blowing air into the heatsink so it comes out sides. It needs to mounted centrally, near to the top of one of the sides this should give you good air circulation with cold air falling and hot air rising with air going out both sides down the length of the tank then coming back towards the centre.
As these are living things you wont be able to seal the terrarium otherwise you would get better results but I am assuming air intake is restricted somewhat the free-er the air in to the terrarium the harder the TEC's will have to work to maintain temp and this of course is where the room ambient temps will come into play.

Attached Thumbnails

 

twigss

Zip, That is a perfect setup. I think that mounting the unit will be ok if I use supports for the heatsinks. I have already found a few heatsinks on ebay that will provide plenty of heat exchange.

That thermostat is ideal, but I can't find anything like it in the US. I did find this http://shop.vetcosurplus.com/catalog...oducts_id=1542

Which looks like it would go between the PSU and the peltier, but I'm not sure exactly what the "Relay power rating: 24V DC/AC 3A" refers to. That is too much power to provide to the peltier

I did read something about using a programmable home thermostat($10-15) to control light cycles. They did a mod on it to remove the thermostat for their purposes, but I think a home model might actually work.

I will have to do some more research tonight.

Thank you all for your help

flak-spammer

You'll need some really powerful heatsinks like less than 0.1C/W, I've already looked into air to air heat exchange.

rpm666

Why not use an aquarium chiller? $300 and temp control on it.

Easier setup, easier maint., better control, less expensive to run 24/7.

__________________