Peltier cell questions

[lithopsman]

Hello all,
1) I was wondering whether all of the heatsinks on eBay said to fit computers would work with a peltier cell?

2) Also, If you can hook up a peltier cell like a CPU fan with just an adapter, or if the power is to great?

3) Do you think just one cell is enough for a 24 gal tank?

4) If not, do you think I could get a smaller second one and hook it up to the same heat sink?

5) How would I go about waterproofing the peltier cells and or heat sinks, or should I just try to pipe in the cold air?

Thanks!!  

 

 

Here is the heatsink

here is the peltier cell.

 

[Tony Paroubek]

The coleman and igloo portable coolers that can work plugged into a car lighter socket work on peltier cells. I know of one person that has built a mini ultrahighland grow chamber using one of these coolers. Essentially the same as using a chest freezer setup but on smaller scale and different cooling system.

Peltier cells get pretty cold. They also generate alot of heat on the other side. To cool a terrarium you would need to figure out how to get the cold off the peltier and into the grow chamber and also effectively cool the heat sinks on the other side. I would imagine the effectiveness of the set up would depend on many factors. Such as:
How much of a temperature drop are you trying to achieve.
How large is the area needing to be cooled.
How effective is your system to move the cold off the peltier and also remove the heat from the other side.
How well insulated is the grow chamber.

 

[lithopsman]

Thanks Tony!! Here are my plants, unless you have any suggestions... It is a 24 gallon tank. I would put styrofoam around the back and sides. I plan to have the unit mounted on top and have the heat sink blow the warm air most likely into a water reservoir, or pipe it to the lowland tank. the peltier cell would be just inside the top of the tank, and I would mount a fan on the top side next to it to blow the cold air around the tank. I am aiming for a 15-20*F cooling effect. If you think it would work, I could just wrap it in aluminum foil where it would be in the tank, to enlarge the area dissipating cold, and water proof it from humidity. Do you think it works on power adapter plugs like a CPU fan? Thanks again!!

 

[Tony Paroubek]

Thoughts on your plans:

Blowing the warm air off the heatsink side into a lowland terrarium: Fine for warming the terrarium but will drastically drop the humidity of the lowland chamber as you pump all that air into it. So need to address that issue if you plan to use the warm air for that purpose.

For best efficiency you should have a heatsink on the one side disipating the heat and on the growchamber side a cold sink to better disipate the cold off the cell. As far as I know (which is only minimal when dealing with peltier cells) The better the heat and cold sink the better they operate. Quality copper or aluminum cpuheat sinks with integrated cpu fans mounted right to the peltier with thermal conductive glue would be best. So basically you need a hole in the grow chamber to place the cold sink through and seal up around the edges. I am guessing that a 250watt computer power supply would do nicely to run up to 2 peltiers and 4 fans if you wanted to add a second one.

I have no idea how much cooling effect you could achieve with one cell. Insulating around the sides and back will help alot. I think it is highly dependent on the quality of the heat and cold sinks and their ability to move the heat and cold off the surface of the cell.

 

[lithopsman]

Thanks Tony. I've never heard of a coldsink before, but wouldn't the aluminum foil wrapped around the cold side fairly thickly do the same thing? Also, I'm not enough of a computer person to know the difference between a CPU power supply and a normal one. All I know is that the fan that I run for air circulation is hooked up to an adapter that I connected to the CPU fans wires, and it works fine... Thanks again!!

 

[BigCarnivourKid]

The key to a heat/cold sink is surface area. A lump of foil has less surface area than a heatsink made out of the same amount of foil. Instead of a lump of foil, hook up a heatsink to it or reverse the polarity of your hook up and the heatsink becomes a coldsink and the flat side of the peltier becomes a miniature heater/hotplate.

Maybe an overclocker out there will have another idea.

 

[lithopsman]

Ok, but I could use a LOT of foil, and I have an idea for surface area, but its hard to explain... Thanks again!!

 

[Tony Paroubek]

Think of a coldsink the same as a heatsink except instead of trying disipate excess heat your disipating excess cold ;>

Aluminum is a good conductor of cold/heat (copper is even better) but aluminum foil is to thin to do it well. You will also have a hard time getting good contact with the peltier. Ideally you should have a heat/cold sink bonded to the entire surface so you can maximize it's abilities.

I only mention a computer power supply because they are easy to find along with heatsinks and cpu fans. If the fans and peltier are 12v (which they most likely will be) then any 12v powersupply will work as long as it has enough watts to run everything.

 

[lithopsman]

I guess the thing that I need to clarify is that it wold be at least 30 layers of aluminum foil, the first few attatched by that thermal what ever stuff... Thanks again, I plan onsetting this soon, I'll keep you updated!!

 

[Tony Paroubek]

30 layers of aluminum foil won't help. You will basically be insulating the peltier with air space between the layers.

You need a cpu style heat sink that is carved out of a solid block of aluminum. One goes on the hot side and one goes on the cold side. Something like this cpu heat sink
The trick will be getting the peltier sandwiched between them.
This page shows thermal grease which might be all you need if you can physically machine screw the two sinks together with the peltier between them. Or perhaps the silver epoxy to glue each sink to each side of the peltier thermal compounds

 

[Casper]

This is right up my alley, I have used pelts many times to cool my cpu.

First of all, a 250w PSU would be streatched pretty thin to run 2 pelts and 4 fans. I would definatly get at least a 350w.

Second of all, the more heat you remove from the hot side, the cooler the other side gets, so depending on your price range, I would get a quality heatsink/fan combo. (Thermalright SK800 is probably the best on the market, but can run 30-40 bucks) couple that with a nice 80mm fan, OR you can get an adapter and put a 120mm fan on it (larger area, so the fan spins slower and moves more air READ: it is much quiter)

Now, if this was my project, I would put a waterblock and a cheap pump on the cold side. The TEC would cool the water, then run it through some copper tubing (kind of like a radiator) and put a large 120mm fan on it. This will in effect, give you a MUCH larger cooling surface in which to remove the cool air from, ortherwise you can simply put another HSF on the cool side, but you will not be using it to its full potential.

If you decide to do this, shoot me a message and I can help you with a whichever setup you decide to go with.

Also, if you get an AT Powersupply, you will have to mod it to make it work. ( they are designed to turn off and on by a computer, hence they won't work unless the ATX cable is connected to a motherboard, this is easily fixed by jumping two of the wires on the ATX leg)


Casper

PS: As far as the HSF, you really want to stick with copper, instead of aluminum, the heat transfer is much better with copper, and for thermal compound use Artic Silver 3, one 6 dollar tube should last you forever.

 

[lithopsman]

I wish that I had a better way to describe this... I could also melt down the aluminum if that would be better... I want this to be as simple, effective and cheap as possible, and since I soon plan on expanding to a bigger tank, I want to get it right in here first. Thanks again, I am still working on it...  

 

 

EDIT: </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Now, if this was my project, I would put a waterblock and a cheap pump on the cold side. The TEC would cool the water, then run it through some copper tubing (kind of like a radiator) and put a large 120mm fan on it. This will in effect, give you a MUCH larger cooling surface in which to remove the cool air from, ortherwise you can simply put another HSF on the cool side, but you will not be using it to its full potential[/QUOTE]<span id='postcolor'>

I can't find anything about waterblocks, are they cheaper/more expensive, and do they work better/worse? THANKS again!!

 

[lithopsman]

Ok, I am going to slightly change these questions to accomidate a well welcomed 50 Gallon Long!!

Anyways, the tank itself is: 50 Gal. Long 48L x 18W x 13Tall It is made of Acrylic, and when fully setup, will have 2 48" Florescent tubes on top, and a Tropic Aire with a 55 Gallon pump for humidity, you will see why it's neccessary in a sec.

Anyways, I was wondering if I would need 2 or 3 peltier cells/heatsinks? I would like a drop from about 72-75*F down to 55-48*F

Here is how my setup would work:
Click here




FIGURE 1:

Yes, the tank is sealed, that's why I said the Tropic Aire is important... That way the fan can't make the air dry out...

Figure 2:

I am trying to see if I can get around cutting up the lid of my Growchamber, by integrating the lid into the peltier to coldsink connection... If you have any opinions, I could go into more detail... THANKS!!

 

[jalan kayu]

Just a further suggestion:

Place all peltier cells/heatsinks together at one end of the tank (but not too close to the end wall) using one set of fan to blow at the cells to create a cool air circulation in the tank. Place another fan set on top of the lid to cool the heatsinks.

 

[lithopsman]

Ok, thanks!! That's one nice suggestion! How about the question about figure 2? Thank you for all of the input!!

 

[Casper]

I must disagree, you want to place a fan directly on the pelt. blowing air down.

You see, pelts work on heat transfer. The more energy transfer, the colder it gets. So.. in easy terms, the more heat you pull off the top, and the more cold you pull off the bottom, the cooler it gets. Having a fan blowing accross it from a distance will yield cool temps, but having a 5 dollar heatsink/fan combo actually attached to the pelt will yield much better results. Now, if you wanted to blow the air sideways like in your diagram, you could probably use a pvc elbow to change the direction of the airflow for next to nothing.


Casper

P.S. You better have a serious power supply to run 3 pelts and the fans, and you DEFINATLY want to make sure its grounded (don't cut off the ground to fit it in a cheap timer)

 

[Casper]

Sorry, missed your post about the waterblocks.

Yes, they are more expensive, but they work 10 times better. You see, its all about surface area. If you have a larger surface area to move air accross, then you get a larger amount of heat transfer. Same reason there is a radiator in your car, only difference is, this is the reverse. You would have to buy a pump (for this application you don't need a high flow pump, some $20 job from your local pet store works fine) and you can get a heaterblock from autozone for $15 and you could probably find a waterblock on e-bay for the same.

I am actually going to set up a highland tank using this idea, the best thing is the waterblock has 4 holes in it with tension screws that you can screw directly into your heatsink/fan. Basically sandwiching the pelt inbetween for better contact.

Basically, the waterblock is cooled by the pelt, water is pumped into a radiator which then cools the copper fins, air blows accross the fins and into your tank.


Casper

 

[lithopsman]

Hello Casper,
Thanks for the input!! I am no electrician, so I don't know squat about grounding things, I plan on doing what I did for my air circulation fan, just sauter it to a standard power supply converter (AC I think) like you can get at Radio Shack... Also, I didn't notice last time I was in there, but does anyone know of they sell heatsinks? Thanks again!!

P.S. Copper, I don't know whether I want MAXIMUM squeeze out every last drop of cold, because I only want between 55-45*F, but maybe I do, because I don't know to much about them... I am still working on ideas for figure 2... Thanks!!

 

[Tony Paroubek]

Not sure about the arrangement. Putting them in the hood sounds easiest but might conflict with light placement. You mention 2 tubes but might want to consider 4 tubes for highland Nepenthes. They will enjoy the extra light.

My other thought is to get things operational and monitor temps etc. Don't want to be freezing the plants if the peltiers work better than expected!

Tony

 

[lithopsman]

I may do a comprimise at 3 tubes, currently they are on one in a 24 gallon tall, and are pretty darn colorful, and I don't want it to be to much of a difference, although I think that they could take a little more... Also, remember that the tank is only 13" tall, so they would be darn close to the lights since their pots are about 4" tall. Also, there are reflectors on three sides of the tank, so the light is bouncing around well. Also, when I'm gone I often put a reflective cover on the front to help out with the light reflection... (BTW, I am referring to my current tank, but would do the same with this one...) THANKS AGAIN!!