Author Topic: A look at Peltier cooling  (Read 109061 times)

0 Members and 4 Guests are viewing this topic.

Madscientist267

  • Hero Member
  • *****
  • Posts: 1181
  • Country: us
  • Uh oh. Now what have I done?
Re: A look at Peltier cooling
« Reply #66 on: April 01, 2011, 07:16:05 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, 07:18:29 PM by Madscientist267 »
The size of the project matters not.
How much magic smoke it contains does !

zap

  • Hero Member
  • *****
  • Posts: 1107
  • There's an app for that
Re: A look at Peltier cooling
« Reply #67 on: April 02, 2011, 10:37:32 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

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #68 on: April 04, 2011, 10:40:56 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
A kind word often goes unsaid BUT never goes unheard

Madscientist267

  • Hero Member
  • *****
  • Posts: 1181
  • Country: us
  • Uh oh. Now what have I done?
Re: A look at Peltier cooling
« Reply #69 on: April 04, 2011, 12:16:55 PM »
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
The size of the project matters not.
How much magic smoke it contains does !

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #70 on: April 04, 2011, 02:05:07 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, 02:09:07 PM by Bruce S »
A kind word often goes unsaid BUT never goes unheard

taylorp035

  • Hero Member
  • *****
  • Posts: 1204
  • Country: us
  • Stressed spelled backwards is Desserts
Re: A look at Peltier cooling
« Reply #71 on: April 14, 2011, 07:04:51 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

  • Hero Member
  • *****
  • Posts: 1181
  • Country: us
  • Uh oh. Now what have I done?
Re: A look at Peltier cooling
« Reply #72 on: May 24, 2011, 03:28:06 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

The size of the project matters not.
How much magic smoke it contains does !

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #73 on: May 26, 2011, 10:53:02 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?
A kind word often goes unsaid BUT never goes unheard

Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #74 on: October 30, 2014, 04:07:57 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 11°C while heated the hot side to 40-44°C in open air at 20°C 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 20°C ambient air, the cold heatsink inside cooled to 1-3°C 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, 04:17:38 AM by Nautilus1 »

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #75 on: October 30, 2014, 09:09:44 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
A kind word often goes unsaid BUT never goes unheard

Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #76 on: October 30, 2014, 09:50:34 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 20°C or for extended amounts of time, so I can't yet say if it can cool to 1-3°C 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

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #77 on: October 30, 2014, 10:09:31 AM »
Now that's what I call upcycling!!

A kind word often goes unsaid BUT never goes unheard

MattM

  • Hero Member
  • *****
  • Posts: 1167
  • Country: us
Re: A look at Peltier cooling
« Reply #78 on: October 30, 2014, 01:18:41 PM »
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

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #79 on: October 30, 2014, 03:15:58 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

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #80 on: October 30, 2014, 06:48:28 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 33°C 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.

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #81 on: October 31, 2014, 04:02:05 PM »
that is where you get a piece of copper plate the same size as the peltier(TEC). Make sure it is very flat on both sides, use high quality silver heat sink paste and create a spacer. That will let you get 1/2 inch of insulation(or more but the thicker you go the higher the losses) in between heat sinks. I plan on using some aerogel insulation board in between the heat exchangers of the 450 watt unit. Expensive but I am dealing with a lot of generated heat that I need to control. That 450 watt TEC is 62mm on a side, thing is huge. I figure a pair of them will cool the chest freezer I am going to be using as a fridge! They will be mounted outboard with liquid moved through a heat exchanger inside and outside, cool loop and hot loop. Still collecting parts, need another large PC water cooking radiator, 2 pumps, and the liquid blocks that will sandwich the TEC blocks.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: A look at Peltier cooling
« Reply #82 on: October 31, 2014, 05:59:37 PM »
The efficiency of a TEC is 1/4 that of Carnot cycle compressor driven units.

http://en.wikipedia.org/wiki/Thermoelectric_cooling

Also the harder you push a Peltier junction the less efficient it becomes as it has to dissipate it's own heat plus the heat it is moving from the other side. That implies you would do better with a lot of junctions with some being driven then allowed to rest in cycles.

http://www.youtube.com/watch?v=iCuNBY3hMwI This guy uses an aluminum rod to transfer heat to freeze water during the day and the melting ice keeps it cool at night. He has 3 inches of insulation all around.

Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #83 on: November 01, 2014, 02:34:55 PM »
Peltiers clearly have their limits; in my second test, I ran the Coleman full throttle with a load of 54 soda cans (not sure how I managed to do that, its technically a '44 can' cooler...?) and it took 3 days to get down to ~6C (~43F). It hit 8C (~46F) in two days. I haven't plotted out the curve yet, but it looks like the butter zone in terms of energy efficiency is about 10C (50F). This of course is above a 'comfortable' temperature for refrigeration, by 7-9C (12-15F). Ideal is just above freezing, "between 35 and 38 degrees F (1.7 to 3.3 degrees C)" according to one hit I peeked at

My own device, tested at 14-16°C ambient temp, took an inordinately long amount of time to cool a 3-pint bottle of mineral water, about 4-5 hours to reach 10°C.

Most likely a full load will take more than a day to cool down below 10°C and in summer temps it may even take 2-3 days to hit 6-7°C.

Reversed the cold side fan, to draw air from the sides and exhaust through the center, this way the air currents inside were much colder and could be felt farther. Hot side fan runs as it should, pushing air through the center of the heatsink and exhausting to the sides.

After the door was opened and closed, hot side warmed up enough to feel the difference by hand - the Peltier blew the heat it gained from the ambient air.

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #84 on: November 01, 2014, 04:14:07 PM »
You only have about 4 watts of actual cooling power with a 30 watt TEC block. Rest is dissipated as heat. So due the calculation of how much energy it takes to cool a pint of water from room temp to whatever temps your test is dropping to. If you started with a cold bottle of water then all you have to do is keep the water at that temp and that will require less energy.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: A look at Peltier cooling
« Reply #85 on: November 01, 2014, 07:45:54 PM »
A cold side fan is a waste of energy. I have a true Carnot cycle fridge made by Engel. It draws 35 watts running and has no hot side or cold side fan. It's all convention. The cold side surrounds the entire inside around the fridge. Only the bottom and top do not have coils.

The hot side is outside on the control side of the unit. This Engel will flash freeze and hold 0F at 86F ambient, all on 35 watts at 12v.

Insulation is what matters most. The Engel was designed for the Australian Outback. There is a thermal blanket option for better cooling/less power draw.

MattM

  • Hero Member
  • *****
  • Posts: 1167
  • Country: us
Re: A look at Peltier cooling
« Reply #86 on: November 02, 2014, 02:08:15 AM »
A few millimeters of this stuff is equal to an inch of conventional foam:

http://www.gizmag.com/polymer-aerogel-stronger-flexible-nasa/23955/

Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #87 on: November 02, 2014, 03:48:11 AM »
MattM: unaffordable. Aerogel based materials cost over $2000 per square foot ($90 for a 2"x 3" sheet). That is, $12000 for a small cabinet. The entire Styrofoam pack of 10 sheets was just $5.

dnix71: This happens because the entire interior of the Engel is a cold side heatsink. I had to do with a 5.5x5x5 cm heatsink in a 30x30x26 cm box. Because my Peltier was 3x3cm.

Someone may ask "why didn't you buy a bigger Peltier?" - I already had this one plus the heatskins and the wooden box, so they cost me nothing.

Waeco MF-15 draws 50 watts and could make 6-7°C in a 25°C environment (tested by myself), Waeco MF-6W draws 36 watts and Ardes TK45 draws 60 watts.

All have relatively thin, flimsy insulation, nonexistent cold side heatsink and an oversized hot size heatsink to dispense with the fan or run it too slow to be audible.

DamonHD

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 4125
  • Country: gb
    • Earth Notes
Re: A look at Peltier cooling
« Reply #88 on: November 02, 2014, 04:48:16 AM »
Aerogel need not be anything like as expensive as you suggest.

I have half my house wrapped in the stuff and did not rob a bank (just worked for one!) to pay for it.

So, very roughly, 40mm thick of aerogel was ~£150 per square metre including the plasterboard facing, so maybe you could get the Aspen 10mm aerogel blanket for $50/m^2.

This is a random link I found with Google: http://www.buyaerogel.com/product/spaceloft/

You can also construct (or buy) vacuum panels, such as used in fridge/freezers.

Rgds

Damon
Podcast: https://www.earth.org.uk/SECTION_podcast.html

@DamonHD@mastodon.social

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: A look at Peltier cooling
« Reply #89 on: November 02, 2014, 12:19:44 PM »
Laptops use a thin metal plate to move CPU and GPU heat to the shell. Instead of a heatsink with fins and a fan, you could use a plate. A thick plate of aluminum would move heat well and be cheap enough. Instead of one Peltier, four in series [one on each vertical side] would give much better efficiency.

6C - 7C in a 25C environment isn't enough to store meat and cheese safely. 4C or less is usually recommended. If all you want to do is chill your beer, then a Peltier fridge will do.

http://www.wusa9.com/story/news/investigations/2013/12/17/4066323/   Here is a recent study on commercial models sold by big box retailers.
"By 85 degrees all had failed to maintain temperatures at 40 or below.

In response to our findings, both Sears and HH Gregg are taking products off the shelf, and one manufacturer has rewritten its owners' manual to acknowledge, dependent upon room temperature, its refrigerator would be too warm to meet food safety standards."

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: A look at Peltier cooling
« Reply #90 on: November 02, 2014, 03:10:50 PM »
Nautilus1  I have a complete unit scrapped working from a TEC someone in sales didn't want anymore. If you want it send me a PM and I'll mail it to you. No charge.




Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #91 on: November 02, 2014, 05:31:07 PM »
dnix71: Thanks. Maybe for a later experiment.

Right now, I had in mind two purposes for the "wooden fridge": first, to cool a sizable load of beer and juices next to my bed and desk. Second, to maintain the outer aspect, as I'm decorating my home step by step into a steampunk design. (Side note: the discovery of the Peltier effect in 1834 predates both ammonia cycle refrigeration - 1860 - and Freon cycle - 1914. So it's not a modern invention, but a rediscovery of a Steam Age technology  :D )

One of them (model #634) was going to originally be my hot-side sink, but I would have been stuck with buying a 15 foot chunk! Now THAT's a heat sink! Even though they would have cut it up into the pieces I need, I had no idea what I would do with all the excess, so I talked with them about what I needed and what they offered on various levels, and this is what I came up with (from a company called Accel - La Habra ) ...

For the hot side:

(Attachment Link)

Two each of 24 inch length.

If I get this straight, the problem is not drawing heat from an object via the Peltier, but dissipating the said heat to the atmosphere.

As the inefficiency of the Peltier design means the quicker the heat is dissipated, the better it works, since the smaller the temperature differential between cold and hot heatsinks, the better it moves heat. Delta T's look impressive on paper, but at nominal maximum delta T (if it can ever make it) the element moves no heat at all.

If we have a standard finned heatsink on the outside, we can enlarge it for a relatively small cost with L-shaped aluminum bars from the hardware store, set in a grille like rays. The heatsink is the "sun", the "rays" are bolted to it. A small number of bars can increase the heatsink surface and therefore the radiation of heat by a factor of 10 or more, keeping the mass low enough and leaving the noisy outer fan redundant. Enough bars and we can truly say there are no moving parts in the device, not even a fan.

kc7noa

  • Newbie
  • *
  • Posts: 39
  • Country: us
Re: A look at Peltier cooling
« Reply #92 on: November 02, 2014, 06:43:58 PM »
Nautilus1  I have a complete unit scrapped working from a TEC someone in sales didn't want anymore. If you want it send me a PM and I'll mail it to you. No charge.

(Attachment Link)

If  Nautilus1 isn't interested in it .. i think i would be ...

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #93 on: November 02, 2014, 06:48:24 PM »
To space your TEC cold side farther from the hot side get a copper heat spreader or a CPU cooler that uses heat pipes(sealed liquid) to get the heat away from the cold. That will help your system a lot. A small piece of Aerogel between the two will provide really good thermal management. Relatively cheap too accomplish. Heat leakage to the cold side is a big issue with any design.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: A look at Peltier cooling
« Reply #94 on: November 02, 2014, 07:25:10 PM »
kc7noa send me a PM with your address.

Nautilus1

  • Newbie
  • *
  • Posts: 17
  • Country: ro
Re: A look at Peltier cooling
« Reply #95 on: November 04, 2014, 07:06:32 AM »
TEC1-12703 is rated to a Qmax 30 W of heat (29.3 W to be very specific) at 15.4V / 3.2A (49.28 W of electrical power drawn).

Running at 12.4 volts and assuming the cooling to power ratio is more or less linear, it draws 34.65 watts to move 20-21 watts of heat. Usually efficiency is maximum at Vmax / Imax, so it should drop a little below Vmax, let's say a bit below 20 W of heat. The hot side has to dissipate around 56 W, power drawn by the Peltier, heat absorbed by the Peltier from the cold side and the small amount of heat generated by fan motors.

Nvidia GeForce GT440 chip is rated to draw a maximum of 65 W, part of which gets dissipated as heat by the heatsink. But it is also rated to a maximum of 98°C and it usually operates above room temperature. So the hot side heatsink may be enough to dissipate many more watts than Peltier can do, but not quickly and not to room temps.

I'm not trying to cool in 20°C temps, this has already been done right now, but in summer temps, which may raise to 35°C sometimes.

Step one: The backside of the box, currently 5mm wood panel + 22-28 mm of Styrofoam, is to get at least one more layer of insulation on the outside.

Step two: the outer insulation at the backside is to get a reflective outer layer, most likely aluminum foil.

Step three: the outer heatsink should be enlarged by bolting aluminum "rays" to increase radiative surface by a factor of 8 or 10.

Rays can easily by done from hardware store aluminum blades, which are cheap and light, therefore increasing also surface to mass ratio (the better the ratio, the quicker heat is dissipated).

If the outer heatsink grows large enough, two nice things can happen:

1. the fan can be eliminated altogether and I get completely silent operation;
2. the Peltier can do the same with less current, and therefore it can be throttled down to 5 V or 9 V and fed from a small solar panel and a battery, and I get my beer chilled for free  ;)

Further pics coming soon.

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: A look at Peltier cooling
« Reply #96 on: November 04, 2014, 10:57:55 AM »
Sorry late coming back to this thread!
I have been lucky enough to be able to test 3 different makers of the counter top fridges.
All of them suffer the same problems when the ambient temps reach above 78F.

All of them also seem to have woefully under-sized fans to move the heat away from the heat side.
I have tested a few things you might want to look for.
The heat pipes can be had for free (possibly) go looking for the older HP laptops, these use pretty good sized heat pipes in-relation to the fans on the older larger units, plus they're copper.
I have gone away from using the standard computer fans and am now using the squirrel-cage style fans, these I can mount on one or both sides of the fins, they seem to push the heated air away in a better fashion than a small localized fashion.
I get them free from older Dell and Compaq desktop computers  ;)
I like the way you are staying within that very nice piece of furniture! and using what you have on hand and free  :)
Cheers

A kind word often goes unsaid BUT never goes unheard

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #97 on: November 04, 2014, 02:40:45 PM »
In order to get efficiency with a larger aluminum heatsink you need to use a copper heat spreader. In RF amplifiers I have built and worked on the transistors are first bolted to the heat spreader then that is attached to the aluminum heat sink

TEC1-12703 is rated to a Qmax 30 W of heat (29.3 W to be very specific) at 15.4V / 3.2A (49.28 W of electrical power drawn).

Running at 12.4 volts and assuming the cooling to power ratio is more or less linear, it draws 34.65 watts to move 20-21 watts of heat. Usually efficiency is maximum at Vmax / Imax, so it should drop a little below Vmax, let's say a bit below 20 W of heat. The hot side has to dissipate around 56 W, power drawn by the Peltier, heat absorbed by the Peltier from the cold side and the small amount of heat generated by fan motors.

Nvidia GeForce GT440 chip is rated to draw a maximum of 65 W, part of which gets dissipated as heat by the heatsink. But it is also rated to a maximum of 98°C and it usually operates above room temperature. So the hot side heatsink may be enough to dissipate many more watts than Peltier can do, but not quickly and not to room temps.

I'm not trying to cool in 20°C temps, this has already been done right now, but in summer temps, which may raise to 35°C sometimes.

Step one: The backside of the box, currently 5mm wood panel + 22-28 mm of Styrofoam, is to get at least one more layer of insulation on the outside.

Step two: the outer insulation at the backside is to get a reflective outer layer, most likely aluminum foil.

Step three: the outer heatsink should be enlarged by bolting aluminum "rays" to increase radiative surface by a factor of 8 or 10.

Rays can easily by done from hardware store aluminum blades, which are cheap and light, therefore increasing also surface to mass ratio (the better the ratio, the quicker heat is dissipated).

If the outer heatsink grows large enough, two nice things can happen:

1. the fan can be eliminated altogether and I get completely silent operation;
2. the Peltier can do the same with less current, and therefore it can be throttled down to 5 V or 9 V and fed from a small solar panel and a battery, and I get my beer chilled for free  ;)

Further pics coming soon.

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: A look at Peltier cooling
« Reply #98 on: November 04, 2014, 02:43:11 PM »
If you want a deeper t/max stack a smaller TEC on top of a larger one with the larger cooling the smaller. You then need to make sure your hot side thermal management is very very good but you can achieve a 50+c differential in temps.