Author Topic: A look at Peltier cooling  (Read 79478 times)

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Madscientist267

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Re: A look at Peltier cooling
« Reply #54 on: February 19, 2011, 07:52:40 PM »
Got the sinks yesterday BTW!

Was easy, too... no digging. They had been stacking them all, some with fans still on them.

I'll be returning the fans (due to a glitch in communication and understanding of what was what on my part), but the sinks are mine! All 30 of 'em!



The heatsinks laid out before cleaning and de-fanning.





Detailed shot of one of them, with an old pack of smokes for size comparison.





All cleaned up (even ran them through the dishwasher). This is the rough configuration physically that they will be in.

Main difference is that I will probably use two rows on the cold side instead of three to make up for the inherent heat generation.

Still not entirely clear how I'm going to go about holding them all together and in place, although I'm thinking something like thermal epoxy on each sink to something like a 0.25 inch slab of aluminum plate for each side. The Peltiers would then be sandwiched between the two slabs with standard heatsink grease.

Or something like that.

At least it didn't cost me a thousand bucks!  ::)

Steve
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zap

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Re: A look at Peltier cooling
« Reply #55 on: February 19, 2011, 09:35:12 PM »
Still not entirely clear how I'm going to go about holding them all together and in place, although I'm thinking something like thermal epoxy on each sink to something like a 0.25 inch slab of aluminum plate for each side. The Peltiers would then be sandwiched between the two slabs with standard heatsink grease.

Or something like that.


Folks have been using JB Weld for many years for such things... the metal in it tends to conduct heat very well.

I think the sliding flap is Maxwell's demon!  B^>

Rgds

Damon

The design I posted is my intellectual property and mine alone... if Maxwell doesn't like it, Maxwell can sue me ;)
« Last Edit: February 19, 2011, 09:39:58 PM by zap »

Madscientist267

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Re: A look at Peltier cooling
« Reply #56 on: February 20, 2011, 01:24:20 PM »
Freezer got here today as well. Had to pull some strings - they were trying to deliver it next Saturday.

I don't think so.

Here it is with the heatsinks 'mocked up' on a board sitting on top of the unit...



Looks like with a little careful spacing and substrate management, I'll be able to cover the entire top. :)

Steve
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taylorp035

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Re: A look at Peltier cooling
« Reply #57 on: March 07, 2011, 05:26:54 PM »
I have been messing around with these last few days and there are so many variables that I just decided to make a spreadsheet that does it for me.  If you guys want to make a fridge, the biggest bang for your buck comes in the form of a bigger fan or bigger heat sink.  Getting the lowest C / W rating will let you lower your input power to the chip. 

I'm in the same situation right now, as I am trying to make a cooled seat, but I have some serious limits to how much power I can use.  At 25w of cooling, I can achieve a temp drop of 22.4 C at 300W input and 200 CFM on my 2"x5" heat sink.  But at 300w, my battery will die in 5 min.  Most likely I will end up with a 23 min run time w/ 2 batteries and a 9.5C temp drop.  I will have to update once I get the whole system working.

DanG

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Re: A look at Peltier cooling
« Reply #58 on: March 08, 2011, 07:00:34 AM »
Umnn - you have moving air already, and the auxiliary fan.. maybe you can go a little more basic..

Evaporating a gram of water at 106F in one minute absorbs 569 calories or 2.25646442627 BTU or 39.65 watts heat energy.

The same amount ice to evaporated vapor carries away 720 calories per gram or 2.8552801176 BTU or 50.17 watts heat energy.

An average sensible heat for a human standing might be 4 BTU per minute, with brisk activity that is 6 BTU.

If you can keep wicking from acting as an insulator then having just enough water holding vs. surface area might give ten minutes of coolth. The old dip seat in water, shake twice and ride trick.

taylorp035

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Re: A look at Peltier cooling
« Reply #59 on: March 08, 2011, 07:24:16 AM »
We could spray water on the heat sink, in which the water should evaporate fairly quickly.  Our idea will work, but we probably bought TEC's that were too large (Qc = 248 and 134w). 

Here is the set up right now:







Things that majorly change the performance include where we put the fan and the power input.  Our fan is only 100 CFM, so we plan on buying a 250 CFM soon. According to my calculations, that will drop the temperature at least 10C.  The water pump pushes 2 GPM and the water block is 3" x 3" for scale.  The water pipes are 3/8" I.D, 1/2" O.D.

« Last Edit: March 08, 2011, 07:40:22 AM by taylorp035 »

taylorp035

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Re: A look at Peltier cooling
« Reply #60 on: March 11, 2011, 10:09:18 AM »
After messing around with the set up, we managed to get the temp down to 54 F.  Interestingly, we were shipped the wrong fan, which has an output of 2W instead of 6W, hence there is no way that the fan was putting out 100 CFM.  So we boosted the voltage on the fan to 21v and made a new shroud to direct the air.  To get the lowest temperature, we ran our TEC at 8A and 9v, so the heat sink wouldn't get too hot and the overall temp drop would be lower.  Yesterday I found a delta fan that puts out 252 CFM.  After watching a bunch of videos of it in action, I have no doubt that the performance of it will be up to the task of removing the heat.


taylorp035

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Re: A look at Peltier cooling
« Reply #61 on: March 16, 2011, 07:24:50 PM »
I got my new uber 252 CFM 120mm box fan, and I got the temp down to 50.77 F @ 12A and ~12.5v (total system power = fan + TEC + pump).  Then then hooked up the 40' of tubing and made myself a "cooled office chair".  It turned out to be very effective.  More of this will be posted hopefully in its own thread when more progress + time is allowed for (things are moving very fast  ;D ).

Madscientist267

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Re: A look at Peltier cooling
« Reply #62 on: March 17, 2011, 05:01:55 PM »
coolth... hmm... a highly technical term... ;D

I want to add that stacking the modules may provide more heat flow at a lower power input, just based on what I've seen so far. More bang for the buck.

I'm considering the concept myself, although I have to weigh all the variables because I am looking at running them anywhere from a trickle to full power, and stacked modules will cause the 'cold side' module to overheat because they are the same size. This wouldn't be a problem at lower power levels but at full throttle it is liable to let the smoke out.

I would think that the following combination would be the most efficient:

1 - Run two modules stacked at reduced power. You would of course need to experiment and make a curve for power input vs heat flow to find the butter zone. Maybe even individually adjust them and/or try two different capacity modules (the smaller on the cold side).

2 - Trickle water onto a wick material at the heatsink. The wick would extend out of the heatsink fins somewhat to provide better surface area.

3 - Allow free air that was ducted from the outside to flow over the heatsink and wick (that odd named duct comes to mind, cant think of the name right off the top of my head).

4 - Tweak the flow rate of the cooling water for minimum heat difference between the sides of the Peltier, yet provides adequate cooling to the entire surface of the seat (under load!)

By doing this, you'd eliminate the fan, further saving on power, and your modules would be running at an optimal power level.

Shouldn't be hard, you said you already have two different modules, just slap a piece of 1/4" aluminum between them to optimize heat transfer, and give it a shot. I'd be willing to bet you can get the same cooling for significantly less power. Maybe 30% or so?

FWIW

Steve
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taylorp035

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Re: A look at Peltier cooling
« Reply #63 on: March 18, 2011, 09:37:33 AM »
I found this website to be very helpful.  They have PDF's on the performance of the chips, so you can calculate things before you spend any money.  This is where I bought all of my stuff (the water block, heatsink, and TEC).
http://www.customthermoelectric.com/

I'm not sure that running the water pump at a slower speed will help you.  The C/W of the water block goes down as you increase the flow rate.  In my setup, I am loosing about 4C through the water block @ 2 gpm.

As for stacking the chips, they have a few setups like this, where the max delta T is around 80 C instead of 60C.  Under real operating conditions with a load, the delta T is generally much lower (20-30 C).  The graphs that they have demonstrate this very well.

I'm not sure how well the evaporative cooling will work, but I can say that increasing the fan speed will make your quest for colder temperatures much easier.  If you could have a stream of running water over the heatsink (slow flow rate), you could get colder temperatures much easier than using a fan (probably less power consumption too.  Maybe you could have a 10 gallon container of water that acts like a reservoir, and as long as the temperature stays below 80 ish degrees F, things should work well.  Reaching 40 F with fans and heatsinks would be very challenging, especially if you want more than 5w of cooling.  My cooled seat cools at about 25-50w.


Bruce S

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Re: A look at Peltier cooling
« Reply #64 on: March 18, 2011, 09:55:01 AM »
For Madscientits267's freezer setup the water-bath of even wick method may be the better way to go since water is able to wick away heat better than a mere fan.
On Taylorp035's vehicle and the need to keep weight at a minimum, I believe the fan to be the better route, unless its leads to added battery weight to keep up with the demand.

I'm following both posts and both are moving along with great info.
I have a 1CF beer fridge that has a traditional cooling system that gave up its last pump.
I plan on using this to work with the 4 4x4inch TECs I have been saving for just this something  :D

Thanks you guys for all the information and on-going tests!
Bruce S
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taylorp035

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Re: A look at Peltier cooling
« Reply #65 on: March 18, 2011, 09:58:50 AM »
No problem.  Its a lot of fun  ;D

Power drain will be around 150w, or about 11 min run time on 1 battery.  Each extra battery will add 3/4 lb or so.  Also, having water being sprayed around all of our electronics is probably a bad idea.

More progress will be made tonight.

Madscientist267

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Re: A look at Peltier cooling
« Reply #66 on: April 01, 2011, 05:16:05 PM »
Ok, adding tid-bit by tid-bit, another interesting little factoid popped out of the woodwork at me while I was working with the Coleman cooler.

For a while now, it has been sitting upstairs (next to the bed heh) with a computer power supply holding it at 5V. I was losing more in the power supply than what was to be gained by running the Peltier at reduced power. But that's another story. I recently changed the supply over to a power brick rated at 5V/4A and it runs nice and cool. The entire thing is practically silent in operation now because the fans spin so slow, and there are no longer any power supply fans to add to the noise profile.

At 9W, it's cooling capacity as it turned out wasn't nearly as limited by the lack of power, as it was lack of air circulation inside the cooler.

As I've been 'enjoying the fruits' of my labor, I've not been replacing the stock that once was 54 cans (somehow, in a 44 can cooler...?) that had it packed to the gills.

I noticed early on that an auxiliary fan inside was helping to keep things chillier, but it does even better with less in it.

This is seemingly conflicting with classic knowledge that keeping a fridge (or freezer) as full as possible increases it's efficiency.

Maybe it's because a standard fridge cycles, and the Peltier does not. The module runs 25/8/366 at 9W. Maybe more like 7 or 8, plus the power needed by the fans... anyway...

It actually is doing a fairly amazing job at such a low power, and has decent 'recovery' time too. When I finally DID get around to adding another 12 pack to it, they cooled off rather quickly (in less than a day's time).

It's possible that effective cooling may take place at an even lower input than 9W!

FWIW and more to come as I get it... Still trying to find a slab of 1/4" thick aluminum that I can use as a heat spreader for the bigger design...

Steve
« Last Edit: April 01, 2011, 05:18:29 PM by Madscientist267 »
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zap

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Re: A look at Peltier cooling
« Reply #67 on: April 02, 2011, 08:37:32 AM »
Steve,
It sounds like the little cooler is working well enough to think about investing in some aerogel or maybe vacuum insulated panels?
Both are pretty expensive... R50/inch anyone?

Here's a kit for an ice box:
http://www.glacierbay.com/Bbox.asp

Bruce S

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Re: A look at Peltier cooling
« Reply #68 on: April 04, 2011, 08:40:56 AM »
Steve;
 The fewer items in the fridge, may be allowing a better circulation of cooling air. This would make sense for having the fan circulating to cool air and allowing the items to chill quicker.
It will be interesting to find out what the lowest wattage will be to keep the items chilled or cold.
Question? Without digging all the way through the posts. Is there an external fan cooling the outside of the chip? and is it blowing air across the chip or exhausting the heat away by vacuuming ?
Just wondering if using an air-tunnel with dual fans to vacuum heated air away is something to be looking at rather than bigger heatsinks.

Glad you're able to enjoy those fruits too <LOL>

Bruce S
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Madscientist267

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Re: A look at Peltier cooling
« Reply #69 on: April 04, 2011, 10:16:55 AM »
Yes, there's an external fan.

The external is a 100mm, the internal is a 60mm.

Both are attached in the same manner as a typical CPU heatsink fan, forcing air down through the center of the heatsink, exhausting to the sides.

I've come to the conclusion that using the largest heatsink that is physically feasible for the hot side is almost a requirement. Forced air being a strong second.

The chips don't do much unless the hot side is kept as cool as possible.

It may or may not be worth two fans on the hot side to force as much air as possible; in one of my next tests, I want to try a heat pipe system instead since most of the time, they have exaggerated heatsinks on them.

Fans are fairly power hungry, so it's easy to undo the progress made by backing down the power on the chip. It's all a very delicate balancing act.

Zap -

Not quite ready for the aerogel... I'd like to see how multiple modules in cooperation with each other handle a given volume/temp/power scenario first. That stuff is expensive! :(

Steve
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Bruce S

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Re: A look at Peltier cooling
« Reply #70 on: April 04, 2011, 12:05:07 PM »
Steve;
Since you're doing ALL the work.
I could send you a "test" heat-pipe unit that has fan installed. It is very similar to the one I installed on my Chefmate.



It allows the unit to get much colder that it did stock I don't even have it at max cold and stuff  stays good & cold.



The fan can be a "fuel" hog running at 12Vdc at 2.65A  :o. The fans on these originally are for keeping low-profile Dells cool running.
If you want to do a little more testing  ;D you could swap the fan out and reverse the airflow to vacuum to heat out and let the fins pull air into them?
Let me know if you would like to give it a try. PM me with address I can ship it out.

Cheers
Bruce S
Edit the heat-pipe NOT my fridge or lunch :-)
« Last Edit: April 04, 2011, 12:09:07 PM by Bruce S »
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taylorp035

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Re: A look at Peltier cooling
« Reply #71 on: April 14, 2011, 05:04:51 PM »
Quote
and reverse the airflow to vacuum to heat out and let the fins pull air into them?

This makes a lot more sense.  Adding the heat from fan motor will only make it harder for the chips to lower the inside temp.  Unfortunately, I think the fan blade shape is rather bad for creating any significant type of pressure difference.

The fan I bought uses 4.8 amps, and it will supply 1 psi at 0 cfm.  (delta fans website has some really good information on the performance figures and cfm rates).


Madscientist267

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Re: A look at Peltier cooling
« Reply #72 on: May 24, 2011, 01:28:06 AM »
Ok Bruce -

I'm ready.

But I need two of those fans, rather than one.

Baking out some efficiency numbers here and this thread is about to explode with activity, but I have one more piece of the puzzle to solve first.

How much will it hurt? ;)

Steve

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Bruce S

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Re: A look at Peltier cooling
« Reply #73 on: May 26, 2011, 08:53:02 AM »
Ok Bruce -
I'm ready.

But I need two of those fans, rather than one.

Baking out some efficiency numbers here and this thread is about to explode with activity, but I have one more piece of the puzzle to solve first.

How much will it hurt? ;)

Steve
Steve!!
Sorry, I saw this then had a few things going on and let this slip without answering.
I have two, that I've been holding onto while you decided. ;D
Can you send me an email or PM with your address?
I'll pack 'em up and ship.
The Cost? Let me think on that...won't be first born or anything like that  ;)
 IF it was up to my boss I'd be paying you to get them out of my office!
Shipping shouldn't be too bad we get a pretty good deal from UPS,even cheaper if you have a business address.
Is it okay if the fans are still attached to heat pipes?
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Nautilus1

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Re: A look at Peltier cooling
« Reply #74 on: October 30, 2014, 02:07:57 AM »
Hello everyone

I've tried myself to build a small, portable Peltier cooler for my car. Used a TEC1-12703 Peltier, 30x30mm, rated for 15.4V / 3.2A / 30 watt of heat.

After some unsuccessful attempts, found out the Peltier will not work with any sort of heatsink that fits its own size. Tried from ice cubes and ice gel packs to old fashioned chipset coolers.

So I've tried to use a small wooden cabinet as a cooler box. Heatsinks were a cooler removed from a Gigabyte GT440 graphics card, with 80mm fan, on the hot side, and an old CPU cooler (think it's from a Pentium II), about 55x50x50mm, on the cold side.

Measured the amps draw of the Peltier at various voltages and the temps it can achieve.

At 14.1-14.4 volts, it drew about 3.0-3.2 amps and cooled the cold heatsink to 11C while heated the hot side to 40-44C in open air at 20C ambient.

At 12.4-12.6 volts, it drew 2.75 amps and achieved roughly the same temps. Decided to feed it ~12 volts to be able to use a solar panel for an energy source in the future. The cooling power must have decreased, from the original 30W at 15.4 volts, to maybe 20W. Total power draw in the 34W range, fan included.

Insulated the wooden cabinet (~20mm wooden walls) with multi-layered Styrofoam (~28mm, 4 layers of 7mm each, glued with polystyrene glue) and sealed each crack with RTV silicone (white). The inner space shrunk to about 0.9 cu ft, enough to fit about 12 one-pint bottles of beer or 20-30 cans of soda. Styrofoam R-value is about 5 and average R-value for wood about 1, so if both layers are 1 inch or so, it should have a total R of 6. There was no way to fit a rubber band seal on the door, due to rough surfaces of the Styrofoam edges, so used a "labyrinth seal", let the inner layer of the door protrude slightly inside and poured multiple parallel "ropes" of RTV silicone around edges.

Fed electrical power from a laptop charger, rated to a maximum of 12 volt / 5 amps, which made 12.4 volts in practice.

In 20C ambient air, the cold heatsink inside cooled to 1-3C and ice began to form on top of the fins. But the bottle placed inside stood warm even after 2 hours. Still air is insulative, even when cold.

Fit a 50mm fan rated to 11 cfm to the cold heatsink, to draw air through the center and exhaust to the sides. The plan was to use inner air as a cooling fluid: draws heat from the bottles, releases heat to the cold heatsink, draws again heat and so on. As long as there are no leaks, permanently churned air inside should cool a bit each pass through the heatsink, down to freezing.

Repeated the test with same bottle. Heatsink temp did not decrease as low and quickly and ice did no longer form, but after 15 minutes the bottle was noticeably cooler.

So the roughly 20 watts of heat drawn away by the Peltier should allow cooling to fridge temps after a few hours, assuming a load of 12 bottles. Ambient conditions should be better compared to a normal upright fridge: it stays in the most shaded corner of the house, there is no hot kitchen around to draw heat from, door should be open infrequently.

There will not be any thermostat fitted, 34 watts of electrical power is affordable and if a 35W-60W solar panel can be used, power is nearly free.
« Last Edit: October 30, 2014, 02:17:38 AM by Nautilus1 »

Bruce S

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Re: A look at Peltier cooling
« Reply #75 on: October 30, 2014, 07:09:44 AM »
Very well explained!
I have found that the solid state chillers do take quite a bit longer to cool things down.
I like you have found that using the ones that are rated for higher voltages are much easier to work with. I am currently gathering parts to build a "cake" delivery container that is roughly a 14" cube to accommodate the cakes that my wife get orders for.
I'll be looking forward to your update and pics .
Cheers
Bruce S
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Nautilus1

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Re: A look at Peltier cooling
« Reply #76 on: October 30, 2014, 07:50:34 AM »
Thank you

The idea to use the cabinet as a small beer / RedBull cooler came after I've read Madscientist267's original post a few months ago. The wooden cabinet was for free (I've inherited it :D ), restored it just for fun and found no use for the inner space, about 33 x 33 x 30 cm (13" x 13" x 12"). If a 44 can fridge could be kept cool with 9 watts, the much smaller "30 can" box could have done at least as well.

Sought the most insulative material which could be bought for reasonable money and chose Styrofoam, after laying four inner layers got an interior space about 30x30x26 cm (23.4 liters, or 0.82 cu ft).

The Peltier with heatsinks in the shape of a sandwich fits as a "cooling cartridge" - a removable unit fitted with screws in wood, so it can be removed and upgraded at will. The "filling of the sandwich" is a 6" x 4" plate of Coroplast, inside which the Peltier sits, with heatsinks assembled on the plate with plastic ties, to avoid bolts which are conductive and turn into thermal bridges. Used white thermal grease between Peltier faces and heatsinks. Sealed all holes with RTV silicone.

Due to the cold season, could not test it in ambient temps over 20C or for extended amounts of time, so I can't yet say if it can cool to 1-3C in summer temps. As the cooling power of the Peltier can't be more than 20W at these voltages, the box has to be ridiculously insulative to prevent heat creep - there will be more layers of insulation on the outer back wall.






Bruce S

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Re: A look at Peltier cooling
« Reply #77 on: October 30, 2014, 08:09:31 AM »
Now that's what I call upcycling!!

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MattM

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Re: A look at Peltier cooling
« Reply #78 on: October 30, 2014, 11:18:41 AM »
That styrofoam is probably good for about R1.5 to R2 per inch.  It's cheap, but it's not very effective.  Going with better insulation will certainly make it easier to hold the cold.  No amount of insulation will improve your limited amount of cooling.

Mary B

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Re: A look at Peltier cooling
« Reply #79 on: October 30, 2014, 01:15:58 PM »
you need the best insulation you can buy in between the heatsinks holding the Peltier. Try add a copper heat spreader to both sides then a larger heatsink, the cooler the hot side the better. You can also stack them to get deeper temperature gradients. I have a 450 watt peltier to play with, going to need liquid cooling on the hot side to keep it from self destructing. Actually have 2 of them, want to stack them to achieve real cold and use them as a dump load, each draws about 40 amps. Can see 60-80c temp differentials stacked. Some good reading material for anyone playing with them http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.lairdtech.com%2Ftemhandbook%2F&ei=pYxSVO7tEIuiyASa3ICwBg&usg=AFQjCNEusLCK9t1bePikp06jxEzQsRGmiQ&sig2=vQ8mEvTqGqolqzAb-0LYww&bvm=bv.78597519,d.aWw

Nautilus1

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Re: A look at Peltier cooling
« Reply #80 on: October 30, 2014, 04:48:28 PM »
Sorry, there's no space for proper insulation or copper plates in between the heatsinks - the Peltier is 3.3 mm thick.

The "insulation" is an air space between the two layers of plastic: the Coroplast plate (luckily, the same thickness) has a square hole for the Peltier and heatsinks pressed on the sides. The ends are sealed with RTV silicone. So the air inside the two layers of plastic is trapped still and acts as an insulator.

There's a "wick" of cotton string around the cold heatsink which should draw condensation through a small hole to the hot side, but in practice there should be no water-vapor filled air inside and very little or no condensation.

The cold heatsink has been pushed inside the wooden box through a carefully cut hole to be nearly the same shape as the heatsink itself, so to avoid any contact of the warm heatsink with the interior of the box.

For me, the greatest problem is not cooling - if Madscientist267 achieved cooling of 50% larger space with just 9 watts of power, for 34 watts in a small space it should be a piece of cake - but prevention of heat creep over time.

Car travel coolers with Peltiers in the lid and desktop fridges with Peltiers in the back have similar electrical properties, since they draw about 33 watts at 12 V, but they perform poorly due to cheap construction: either miserable insulation, or no inner heatsink and just a steel plate inside, or the transformer/power brick inside and slowly heating the box around it, or all of them at once. Most likely all of them at once.

The cooler should be filled with beers and juices already a bit cool - carried from the store in a travel cooler - held 24/7 under power and opened rarely to get a can from the inside.

PS I've also modded a 10-liter travel cooler (the cheapo $8 model with plastic outer box and a flimsy Styrofoam insulation, thinner than 20mm). Devised a cover with a layer of felt which can be soaked in water to keep the exterior cool by evaporation and a reflective outer layer to keep the heat away. During testing in 33C ambient, filled with 10 lbs of ice cubes, held half of the cubes after 25 hours and the last of them melted after more than 48 hours. With no power source at all. The crappy plastic cooler unmodified in normal conditions can barely keep cool for 12 hours.