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Peltier Cooling/Heating

SLOEIT

Cast Iron
Joined
Mar 28, 2004
Location
Granada Hills, CA
Hey everyone,

As a little bordom induced side project, im thinking of making a thermoelectric cooler/warmer with two thermoelectric junctions which i just got ahold of.

I was thinking something that i could plug into my lighter socket in my truck, and cool a can of soda or heat a can of umm...soup or something ;)

Any creative ideas? I was thinking some aluminum rounds, bored out, and a flat portion to mount the junction to.

Just thinking outloud, cant wait till i get back to school and have a machine shop handy!

Nick
 
At a past job we used ones from an auto store to keep data radios cool. They were big enough to hold a 6 pack. The outer heat sink had a fan for cooling. The inner sink got cold. In an inside lab test I believe the best I ever saw was 35 degrees under room temp. The heat sinks were about 4 by 5".
 
You might like this idea...its instructions on how to make it too
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http://www.stud.ntnu.no/~arnesen/peltierbeer/
 
These things are tricky. It uses a lot of power rather inefficiently. But if you use too much, it will heat rather than cool. Current has to be carefully controlled and depends on how well your fan-cooled hot side removes heat. You can't just hook it up to a battery and expect decent results.
 
I have played with these things myself before and have found that the ones I bought from allelectronics.com work great at 3 volts for a nice consistant temp. If you go to this link you can get them cheap and also the thermo chart on them form the downloads section.
http://www.allelectronics.com/cgi-bin/category.cgi?category=450&type=store

The nice thing about the junctions is that they are stackable and you can get higher temperature differentials with ~close to the same voltage operating each one. But as DaveG said, you want a cooling fan of vanes on the "hot" side so the device does not burn up when you are trying to cool an object. These suckers can get hot enough that it is like dropping a hot soldering iron on your thigh. (Don't, I repeat Don't solder in shorts!)

And if you just want to play around, here is a link for a Hilsch Tube, I have built one and I can get about 100 degrees F at one end and 50 degrees F at eh other at 4 atms (~60psi). (all numers are rough...
"Let me check my notes..." Riff

http://www.visi.com/~darus/hilsch/


[This message has been edited by jimm (edited 08-03-2004).]
 
I had one box with two radios in it. One assembly just wasn't doing the job. I put a second one in the lid with another fan. The current draw was about 3 amps for each junction at 14 volts.
 
As a reference a 6-gallon size Coleman peltier cooler draws 4 amps at 12V and will maintain about a 40 F difference indefinitely. In a car with the AC on it'll keep the blue "freeze blocks" frozen solid. Handy tool. Shouldn't take much to freeze a soda can, in a reasonably insulated container.
 
You'll have to know what voltage to feed them to get the current right. It might take 3 modules in series connection to run them directly off 12 volts. Check the specs, mine say 3.85 volts max, so 3 in series is about right, 2 in series will overheat the modules.

The second thing of importance is getting rid of the heat from the hot side. Fan cooling is ok, but there's a limit to how cool you can get, and the heat is discarded into the vehicle. Consider how hot it gets already, inside a vehicle. You would find that the cooler gets only less warm than the environment, and not cool enough to give you a refreshing drink. You might try to rig up water cooling the hot side of the modules, using copper tubing and a small circulating pump, and an oil cooler mounted where air can blow through it when the vehicle is in motion. Mount this finned module in front of the rad, so engine heat doesn't reduce the efficiency of the setup.

I'm in the process of converting an existing thermoelectric cooler to water cooling.

I had considered using an evaporative process to keep the water cooled, but that just means that I would have to replenish the water often, so my incarnation of this idea will be with using the oil cooler module, and I suppose antifreeze instead of water. I'm going to look around for a suitable core to use, maybe I'll find something with copper fittings that I can solder to directly to create a closed system. With of course, a pressure relief and filling spout, and a drain.

An alternative is to try getting some 'cool' from a component of the air conditioner, but I don't want to have to run it all the time.
 
Ok, now i gotta backtrak a little. I've just clued in again as to why I wanted to use an evaporative system to cool the circulating water. Circulating the cooling water through a core is not going to reduce the water temperature below ambient, so on a smokin hot day, the cooler isn't going to get as cold as you want anyway. It would be better than air cooling the heatsink, but maybe not worth the extra effort, materials, etc. I am starting to think again about using what is, I think, the evaporator component on the A/C system. Wrap some copper tubing around that and pump some water through, maybe get all the cooling that's needed without using peltier devices. I'll have to look under the hood tomorrow and see if that's even possible, and try to determine the effect on the A/C system.
 
I have to carry biological samples in my car and they must be kept relatively cool. I did just what you are suggesting with a Styrofoam cooler and two Peltier devices stuck in holes in the top.They run on 12volts a piece so are wired in parallel. They draw about 10 amps so I plug it into the lighter receptacle that is switched (off with the car not running). If you would like to know any particulars then let me know.
 
I'm curious about the amp draw of the various modules. My coolatron draws about 5 amps, including the fan current, which is only a small part of the total draw. There's two modules in series in it, so they must be ok running on 6-7 volts each. I have some similar modules I purchased from alltronics many years ago. I wonder if they have been made more efficient in continuing development, or if the limit has been reached because of the physical nature of the devices?

Checking over the van's A/C system, I find that a component, a cannister of sorts, is naked under the hood, and gets cold very quickly when the A/C is running. A sensor shuts off the compressor when this cannister gets near to freezing point of water, so ice won't build up in the air passages. I can easily wrap some copper tubing around this can to circulate cooling fluid through. It seems what will happen is that the compressor will run somewhat longer if I remove some of the cool from this component, and won't interfere with normal A/C operation. Being under the hood, one would expect engine heat to warm this part anyway, so I wouldn't be affecting much if I add the small ammount of heat removed from the contents of an on-board cooler. This is lower grade heat anyway, so I doubt if the A/C system would even notice.
I won't be able to freeze the cooler with the fluid pumped through the coils, but it will come close, based on the tempurature cutoff switch on the cannister. Great for drinks and fridge food, and this level of cool can also keep the hot side of peltiers cool enough to permit freezing from the cold side. Hmmm, I could have a fridge/freezer combo in my van, and the ice I make in the freezer can keep the drinks cool for a few days while I'm parked.
The only concern I have over this is the possible electrolytic action between the copper coils and the aluminum cannister. I will flatten the copper tubing somewhat, for a closer contact to the cannister, and probably coat the inside of the coils with something before mounting it. Anyone have any other ideas on this project?
 
Yeah, that's occured to me a couple of times today. It doensn't satisfy the urge to make something, but it's probably the most efficient overall. I have enough projects already.
 
what about heating with pelts. how hot can
the hot side get. could you boil water ,
saute' ,braise , sear ? what is the upper
temp of these things before self destruction.
i've been looking for compact heating devices
which can be quickly switched on and off to
get about 350'F for about 10-20 sec bursts.
 
TNMG, i dont think they can get that hot witout self destructing.

They do get hot enough not to be able to touch in a few seconds however, maybe 200deg.? tops?

Nick
 
I have a feeling something would melt. I seem to recall one of the metals involved has a low melting temperature, possibly within the range of boiling water. Heating something is best done using an element, when temperatures above 100 C are wanted. All the energy used is going into heat, anyway. Assuming nothing melts, you're only going to get a small ammount of extra heat by using peltier devices instead of an element. This extra heat comes from the environment, from whatever is warming the cool side of the module, in this reverse application of the module. I would think it would be less than 10%, probably less, and wouldn't justify the cost of the modules, and the concerns about damaging them.
 
Darryl, the canister you are referring to is the dryer, and you shouln't notice much effect on the car's airconditioning system. I don't think the switch you are seeing controls the temp. It is probably a low pressure switch that cycles your compressor out if the freon charge gets to low. James
 
Thanks, James. I'm not sure about the switch, I'm just going on what I've been reading about vehicle A/C. I'm going to study it more just out of interest.

Ironic I was just now thinking about picking up some copper tubing to fabricate a 'wrap' that I'll afix to the dryer (now I know what it is). I think I'll be soldering the copper coils to a copper sheet, which will be wrapped to fit the dryer. Should get good heat transfer that way, even with a thin insulating layer between the two. If I can make this 'wrap' in two pieces, I can just clamp then to the dryer, no unbolting or any interference to the A/C system at all. Now to figure out a small circulating pump and the rest of the plumbing.
 








 
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