Author Topic: A look at Peltier cooling  (Read 109067 times)

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XeonPony

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Re: A look at Peltier cooling
« Reply #165 on: April 14, 2015, 10:49:15 AM »
It uses water in its chemistry when it cures, just to explain that.

Good just so long as you're aware to never trust it to food storage!

And it can work, you need to stack the pelts and get agressive with the heat spreader and such, but in the end efficiency wise you can not beat the vapour compression cycle.

Going to some junk yards in areas with lots of RV's odds are you'll find a 12/120v compressor system.

Once the solar system is expanded I may even reconsider a pelt drive system, but they are very unpractical with out a ton of energy to toss at them.
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Nautilus1

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Re: A look at Peltier cooling
« Reply #166 on: April 26, 2015, 05:19:27 PM »
Tested my setup as described here.

Ambient temps inside home 20°C (68°F)
Fridge placed in the most shaded corner of the house
Peltier fed 12 volts / 3 amps from a laptop charger (placed away from the fridge) continuously
Load: ~4.5 liters (4.8 US quarts) of beer and juices
Various container types (2 x 0.5 liter plastic bottles, 1 x 0.5 liter aluminum can, 2 x 0.355 liter aluminum cans, 1 x 0.25 liter aluminum can, 1 x 1 liter aluminum can, 2 x 0.55 liter glass bottles)

Results:


- Cools the load (overnight) to the temperature of a glass front commercial fridge. (Which is slightly warmer than a classic home fridge, 7°C or warmer. Look at the bottom display next time you buy beer from the store.)
- Aluminum cans are coolest, glass bottles don't cool themselves as well, plastic bottles are worst.
- It doesn't matter if containers were already cooled when bought or just room temperature. Overnight they cool just as well, only the container material makes the difference. Insulative containers like plastic bottles did not allow enough cooling to happen, even overnight.
- The actual size of the load makes little difference either, it cools in a similar way with 2 bottles or 9 containers.
- Charger (power brick) temps were in the <40°C range, usually 36-38°C.

This makes it very suited to beer, juices or wine, but a rather poor storage method for food.

Mary B

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Re: A look at Peltier cooling
« Reply #167 on: April 26, 2015, 07:21:20 PM »
If you move to a larger peltier it will help. And I think your setup could handle one. Or stacked...

XeonPony

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Re: A look at Peltier cooling
« Reply #168 on: April 26, 2015, 09:02:52 PM »
Stacked, he could have a mega watt peltier the temp diffriential is the same.

Think of it like this, heat is water, the pelt is a pump, you got to lift the water up a hill but just one pelt can only get it half way at best, on average only a quarter of the way

One idea I was toying with is stacking them and wiring the pelts in series and driving them with 12V

it would make a stacked 24v pelt, under driving it to reduce waste heat.
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

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Nautilus1

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Re: A look at Peltier cooling
« Reply #169 on: April 27, 2015, 02:03:21 AM »
The Peltier does not seem overworked, warm side heatsink stays at room temps.

There may be another problem, which just a larger Peltier won't cure.

Top mounted Carnot fridges use a relatively large sheetmetal heat sink through which the cold coils run. In some cases, the entire inner surface of the fridge is a heatsink. This make the container material irrelevant. It cools slowly, but still (sooner or later) the beverage will loose heat and cool itself since there is no other place for the heat to go. My setup has a small heatsink and a fan to circulate cold air inside and shed a bit of heat each time air passes through the heatsink. The more conductive a beverage container is, the faster will the air cool it.

For these reasons, the most efficient way to use it is keeping all the contents in aluminum cans, keep it full for thermal mass and use it mostly for beverages. Just like glass fronted commercial fridges (wine coolers, beer coolers) do. It's too small for foodstuffs anyway.

XeonPony

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Re: A look at Peltier cooling
« Reply #170 on: April 28, 2015, 09:11:48 PM »
the origional fridge is absoprtion not carnot (Vapour compression) cycle. Pelts of small size are slow to move the heat making them easily over whelmed by leakage heat Vs actual cooling of product. Second pelt has insuficient Delta T for effective cooling (Unstacked)

A care fully sized stacked pelt system with a better heat exchanging system would be able to keep pace but the power draw will not be nice!



Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

Bruce S

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Re: A look at Peltier cooling
« Reply #171 on: April 29, 2015, 08:50:39 AM »
Xeon;
In the past I had actually looked at building a walk-in fridge ( Wife is a chef ! ( they NEVER have enough fridge space  :o) ). Using ammonia absorption style chilling.
A neighbor is an HVAC person and could do the proper install for me.
Space was near perfect for build-out , price to install was NOT.
I can understand the special needs for ammonia due to its corrosive qualities , but the price was just too much at the time.
 
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Nautilus1

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Re: A look at Peltier cooling
« Reply #172 on: April 29, 2015, 09:43:53 AM »
1. Ammonia cycle fridges are terrible energy hogs.

A lot of fridges built in the Eastern Bloc from the 1950s to the 1970s (ZIL, Saratov etc) were ammonia type. This principle had been chosen since they didn't need compressors, just a source of heat (metal-ceramic resistor). A medium upright fridge guzzled 3800 kWh/year, a large one 5000-5500! A modern compressor fridge of similar size barely takes 150-200 kWh/year.

2. The Peltier setup is quite good for beverages. Due to thick walls there is little heat creep, and sizable load (20-24 beverage cans) has pretty good thermal mass to cope with slow heat transport through the Peltier. For foodstuffs is rather poor.

I'm planning two more projects

- to fit a solar panel to feed the Peltier about 3 amps at 12 volts, with a battery fitted below the box to keep it running in the dark;
- to combine a small Carnot fridge (for foodstuffs) with a water boiler, by fitting the warm side coils to shed heat into the water. This has 2 benefits: it takes little energy to raise the temperature of already warm water, and on the other side, there is no heat shed into the house from the coils.

MattM

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Re: A look at Peltier cooling
« Reply #173 on: April 29, 2015, 11:18:48 AM »
Perhaps the idea of a multiple stage peltier fridge shouldn't be about stacking peltiers, but instead overlapped insulation zones.

1.  Your outer box is around the entire rig
2.  Secondary box around the freezer section

Your first peltier cools the refrigerator, the second cools the freezer and dumps its heat to the refrigerator.  Why heat the fridge?  To create a smaller delta for the freezer side and a larger one for the refrigerator so that it runs more often whereas the freezer side never experiences the heat backflow like the refrigerator.  You could still use heat pipes from the warm side of the outer peltier to a copper sheet on the back side of your unit.  Copper and stainless play well together, so corrosion isn't a big problem.  You would be hard pressed to measure much difference between a copper and aluminum heatsink when it comes to shedding the heat.  Aluminum doesn't play well with copper tubes, so I really recommend the copper.

Nautilus1

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Re: A look at Peltier cooling
« Reply #174 on: April 29, 2015, 04:38:35 PM »
MattM: Far too complex, useless as long as I don't have a fridge+freezer combo and it blows apart the basic advantage of Peltiers: lack of fluids, sealed ducts and moving parts.

Also did a second test, left the box disconnected from power for 3 days. Same conditions, ambient temps inside home 20°C (68°F), similar load, but all containers inside had been aluminum. Heat creep was slow enough to have the contents still colder by a few degrees C than ambient after 3 days.

This means two things: first, the wood + styrofoam + reflective material sandwich is a good enough insulator and second, the small size of the heatsinks, which are the only thermal bridge to the inside of the box, means the heat creep (from exterior and from the Peltier moving its own heat back in) is not enough to be a significant concern as long as power is cut and the fans don't move. In the future, the Peltier setup may be cycled on and off, or higher- to lower-voltage to save power, by a suitable thermostatic device.

XeonPony

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Re: A look at Peltier cooling
« Reply #175 on: April 30, 2015, 09:56:05 AM »
Perhaps the idea of a multiple stage peltier fridge shouldn't be about stacking peltiers, but instead overlapped insulation zones.

1.  Your outer box is around the entire rig
2.  Secondary box around the freezer section

Your first peltier cools the refrigerator, the second cools the freezer and dumps its heat to the refrigerator.  Why heat the fridge?  To create a smaller delta for the freezer side and a larger one for the refrigerator so that it runs more often whereas the freezer side never experiences the heat backflow like the refrigerator.  You could still use heat pipes from the warm side of the outer peltier to a copper sheet on the back side of your unit.  Copper and stainless play well together, so corrosion isn't a big problem.  You would be hard pressed to measure much difference between a copper and aluminum heatsink when it comes to shedding the heat.  Aluminum doesn't play well with copper tubes, so I really recommend the copper.

Sorry not gonna work Pelts are very specific device that is well knowed Td Per W.

YOU MUST STACK period end of discussion, if you want any usable cold, sooner we get this out of the way sooner we all can continue forward with functional devices.

The fridge side pelt would need to be mega watts as well as the bulk of the current fed in is converted to heat as well.

Heatl + HeatP = Total heat of rejection + Dt  = Required sink.

I  make things cold for hobby, then loved it became work, pelts are beyond aluring for the fact no moving part, but yet at current so utterly useles in mission critticle cooling.

To sum up: Stacking, there is no way around this to get proper Tds, every pelt above the first must be of better wattage to make up for waste heat of the first + load that you are cooling.

« Last Edit: April 30, 2015, 10:00:15 AM by XeonPony »
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

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XeonPony

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Re: A look at Peltier cooling
« Reply #176 on: April 30, 2015, 10:06:41 AM »
Xeon;
In the past I had actually looked at building a walk-in fridge ( Wife is a chef ! ( they NEVER have enough fridge space  :o) ). Using ammonia absorption style chilling.
A neighbor is an HVAC person and could do the proper install for me.
Space was near perfect for build-out , price to install was NOT.
I can understand the special needs for ammonia due to its corrosive qualities , but the price was just too much at the time.
 

Absoprtion fridge: Amonia, Hydrogen, Sodium chromate, water, 3 out of the four are toxic and explosive.

Walk in is very easy, step one select area and make the best sealed well insulated box ya can! On the foundation of the box put in in floor heating tape.

Find your self an old 6k btu R-22 air con (3K will do aas well but for heavy loads the 6k will pull down room temp more quickly)  (More then good enough for a 10+10 well built unit.

Take off the shell of the air con, cut out its on board Tstat and just put in a pig tail (This connects to your fridge tstat inside) find the air mixing flap and seal it off, bolster the insulation on the evap side (It will be obvious once you see inside where it separates the hot and cold sides)

Put this in your box and seal it all up good!

This will work pretty good but won't be ultra efficient, if you have a good flaring tool set and access to a vacuum pump you can make a belt driven plant pretty easily.

For every watt you spend you move 3 watts out of the box with vapor compression cycle, for absorption it is .94w pumped for every w burned.
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

dnix71

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Re: A look at Peltier cooling
« Reply #177 on: April 30, 2015, 10:43:51 AM »
Peltiers are good for launching into space. No moving parts if the heat sink is large enough. Point one side at deep space and the other at the sun and you can make electricity. Peltiers are nice in transportation, again, no oil or moving parts, except a fan. But they aren't efficient compared to Carnot cycle refrigeration. No way around that.

Nautilus1

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Re: A look at Peltier cooling
« Reply #178 on: May 04, 2015, 02:54:25 AM »
PS Tested at the office in parallel with a glass front commercial fridge (Carnot) set to make 4.3°C (it doesn't). Both can cool to 5-7°C in 20°C ambient, but the Peltier takes a far longer amount of time for a given load.

A mobile 28-liter Peltier coolbox rated to draw 48W at 12 volts has similar sized fans inside and out and much bigger heatsinks. The inefficiency of which people complain comes from the very flimsy insulation (Styrofoam, but thinner than 20mm, in a paper-thin plastic shell) and the fact mobile coolboxes are dragged through open air, sunlight, left in cars to heat themselves from the sun, and so on.

XeonPony

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Re: A look at Peltier cooling
« Reply #179 on: May 04, 2015, 08:31:55 PM »
If you want to get serious get caltright load, and Keep right design tools, these are for designing fridge boxes.

The higher R values Only help in keeping the temp, but for pull down only raw BTU-H is going to help you.

In pelts that meanes 250w or better at start! to get the D^T you need to stack them.

Not all fridges are designed to meet the same temp, So glas display is usualy drink coolers, they are not meant to be food storage systems, (IN super markets the cooling plant is in excess of 6k BtuH at mid temp (Very powerfull motor 1/2horse to 1Hp)
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

Nautilus1

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Re: A look at Peltier cooling
« Reply #180 on: May 15, 2015, 03:48:13 PM »
Acquired rather cheaply in the meantime an adjustable power brick, able to give 4.5 amps while the voltage is set to 12, 15, 16, 19, 20 or 24 volts.

Tested each component with a K-probe. The interior fan created a small hot spot at the motor, it heated itself to >20°C and it could hit 32°C if the Peltier and fans were fed the nominal Vmax of 15.4 volts. Dropped the inner fan altogether.

Outer fan was in a poor shape and rather noisy. Removed it and fit a Sunon 80mm fan on an elastic mount to avoid vibration. New fan is visibly more powerful, air flow blown through the heatsink can be felt 2 ft away. Now the heatsink is much cooler.

On 12 volt setting (about 36 watts counting the fan motor as well), the fan is less noisy and it can be left overnight to cool. The Peltier can run in 15 volt (15.4 actually) or 16 volt (real 16,2 volts) to cool relatively quickly the content, in a few hours. This raises the power consumption in the 50-watt range. It may run as well in higher voltages, but the amps raise just as quickly, to the point the power brick heats itself and can no longer supply the current.

Now the load can be cooled in a few hours for the cost of energy and noise, and left in a maintenance mode around 12 volts for most of the time, fan turning slower and less energy spent.

micropv

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Re: A look at Peltier cooling
« Reply #181 on: June 14, 2015, 07:58:30 PM »
Been playing with this old (circuit board bad) 12V cooler that I purchased at a thrift store for a couple $.  TEC and fan are still good.  Managed to hit 47.7F inside the "cooler" feeding it 5V/1A directly to the TEC and using a 6V battery pack to run the fan.  It took about 2 1/2 hours to reach that temp (ambient in the basement is 69.4F to 69.8F on the floor).




Today, tried to cool 3 room temp cokes, from 8 AM until 5:30 PM or so, lowest I could get them was 52.4F.  Might try again placing cold items in it and see how it does. 

Just something to do more than anything really..


Nautilus1

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Re: A look at Peltier cooling
« Reply #182 on: June 15, 2015, 09:30:34 AM »
This is quite a problem: cooling from room temps to 7-8°C (44-46°F) takes a lot of time in a Peltier cooler, maybe even 2-3 days, which is quite wasteful.

Taking the beer or juice bottle already cooled to a reasonable temp from the store and using the Peltier to just keep away heat from creeping in (active insulation) works much better.

Feeding the Peltier higher voltages works up to a point, where the heat generated is above the heatsink's ability to dissipate it and the cooling process is much hampered.

Bruce S

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Re: A look at Peltier cooling
« Reply #183 on: June 15, 2015, 09:40:57 AM »
When trying to do active cooling , it's better to have the TEC to it's near maximum rating to get the cooling cycle working, then use intelligent programing to step the power down to keep contents at or near set temps.
 Those little fridges are cute, but I think it's TEC is a 12V unit, but it would be better to check it's rating with the marking on the chip (IF you can get to it).

Cheers
Bruce S
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micropv

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Re: A look at Peltier cooling
« Reply #184 on: June 21, 2015, 02:06:41 PM »
Hey Bruce,

Yes, it is a 12v 5a TEC.  Interesting to experiment with, I have it hooked directly to "50W" of solar at the moment, I am running the fan from a 12v battery.

As you view the photos, keep in mind nothing is "final", just playing more than anything. 












Bruce S

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Re: A look at Peltier cooling
« Reply #185 on: June 22, 2015, 08:51:52 AM »
While running the fridge, put a temp probe over the exhaust fan to see what it is has, I'll bet there's too much pretty coverage around that back fan to let the heatsink get rid of excess heat.
I took the back off mine, found a 120mm fan to replace the smaller one ( I also tried to get a lower current rated one) and see if it keeps the contents cooler.
Of the contents I see inside, the metal ones will cool much better/quicker and I'm thinking the gel ice units are taking up too much space.
Also, metal lined on the inside should help wick away to heat from the other contents.

NICE use of foam board! I like the idea of using a portion as a door, better than opening the entire door.

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micropv

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Re: A look at Peltier cooling
« Reply #186 on: June 25, 2015, 10:16:55 AM »
I agree, a metal lined interior would really help!  I wonder if storing some items in those old aluminum "Coffee, Sugar, Salt, etc." containers would help some?  They were all the rage in the 70's and 80's.  I see them at thrift stores sometimes.  The gel packs do take up some room, kind of a in progress test, idea from the no longer made Sundanzer bfr105.

So far it is holding well, I use a small inverter upstairs, to feed the juice downstairs...  full throttle during the day (when sunny), and trickle at night.





It was aprox. 1.3CF before the addition of 1" foam.  4.8v to run the fan when on trickle.  An AA pack would make it 24hrs, just switched over to a D pack this morning.



I seriously need to start cleaning up the wires and connections!

MattM

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Re: A look at Peltier cooling
« Reply #187 on: June 25, 2015, 12:13:46 PM »
So line the interior insulation with tin foil.  The use of foil on insulation is purely related to stopping infrared radiation and does really almost nothing as far as spreading out the cool.  Entropy does it already.  Blocking infrared light is very important as all heat-excited objects tend to radiate in the infrared band.  Not all, but most.

dewzenol

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Re: A look at Peltier cooling
« Reply #188 on: January 21, 2016, 12:30:02 AM »
I just built a peltier-based cooler using two peltiers, two heat sink / fan combos, a 1'x1'x2' Styrofoam cooler, and some 2"x1/8" aluminum plate.
Initially I made a 'T' using two (inverted) 'L'-shaped sections of plate (about 10" long each) and placed the cold side of one peltier on each of the two 'L's bases.  I then stuck another length of flat on top of the 'T', bridging the two hot sides, and placed my monster CPU cooler/fan (from an old Dell XPS) in the center. 
The vertical of the 'T' (or the legs of the 'L's depending on your perspective) were shoved through a snug slot into the Styrofoam cooler.  A smaller CPU heat sink / fan was placed on the aluminum bar inside the foam cooler.  Thermal grease was used on every junction.

The net result of this was a whole lot of current being used and a whole lot of heat being generated and no noticeable cooling effect.

Just like any bad hobbyist would do, I changed not one, but several variables in an attempt to correct this.  I ditched one of the 'L's and the flat bridge on top, and stacked the two peltiers directly between the big heat sink and the base of the remaining inverted 'L'.  In the process, I noticed that my thermal grease had squeezed out and onto the sides of the peltiers.  I think this was a big factor in my failure.  I believe the goo was conducting the heat right back to the cold side.  I thoroughly cleaned the excess paste and assembled as I described. 
Another variable I changed was to switch from 12v in parallel to 12v in series, giving each peltier only 6v.

The net result was that with the device running, the temperature inside the cooler dropped about 2 degrees centigrade per minute.  I'm curing meat so I didn't try to get to freezing -- I'm sure the rate would have dropped the closer I got to that.  I only went from 70F ambient to 55F.

I don't know if the extra aluminum plate on the hot side (and its surface area fractions of an inch away from the cold side) was a big factor in my initial failure.  I think the excess thermal paste was a/the huge factor.

I am also not sure whether switching to 12v in parallel would greatly speed the cooling.  I suspect it would pump heat faster than my sink/fan could dissipate it and would therefore be much less than twice as fast.  So I'm keeping it as is.

Hopefully my story will have some value to you.

Good luck! 

dewzenol

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Re: A look at Peltier cooling
« Reply #189 on: January 21, 2016, 12:46:18 AM »
Just wanted to add before and after photos..



Mary B

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Re: A look at Peltier cooling
« Reply #190 on: January 21, 2016, 03:25:09 AM »
What model Dell is that from? I have a 350 watt peltier I am building into a water chiller for the laser cutter and need a monster heatsink to remove heat

Bruce S

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Re: A look at Peltier cooling
« Reply #191 on: January 21, 2016, 01:51:30 PM »
Mary B;
I have some of those very same heat sinks, mine came from a Optiplex 620 and Optiplex 760.
Hope that helps
Bruce S
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Mary B

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Re: A look at Peltier cooling
« Reply #192 on: January 21, 2016, 08:25:46 PM »
Thanks! Found one on ebay cheap. Need to measure the peltier and see if it is a big enough contact patch.

Bruce S

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Re: A look at Peltier cooling
« Reply #193 on: January 21, 2016, 08:35:38 PM »
Mary B;

Let me know what they go for on ebay, I could send you one FREE!! just pay shipping.
OR let me know what size you're looking for I'll dig into my grab bag of stuff .
At the FD we MUST trash older computers , being in their IT dept  8) I get first pick. I think I have about 6 of these!

Bruce S
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Mary B

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Re: A look at Peltier cooling
« Reply #194 on: January 22, 2016, 04:45:41 AM »
Think it was $15 shipped... but my Peltier is huge... 62mm square! The one I was looking at had a ~ 57mm square contact patch... so back to the drawing board. I may go with a water cooled unit but they are not cheap!

Bruce S

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Re: A look at Peltier cooling
« Reply #195 on: January 22, 2016, 08:50:43 AM »
Mary B;
That's not huge! IF google is correct, 62mm is only 2.5 inches. Let me dig into my stash and see what I've got.

I know for sure my wife would love to have some of these out of the way  ::).
They don't weigh much at all, I'm certain the fans that keep them cool are 3x3inches.

Bruce S



 
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Mary B

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Re: A look at Peltier cooling
« Reply #196 on: January 22, 2016, 08:56:28 PM »
the aluminum fin area is huge, the copper heat spreader is smaller!