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Old 03-07-2012, 06:06 PM   #11
scaryeyes
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Hi

Dont know if I missed something, but how many peltiers did u use? And how is the attachment? I plan to build a small fridge to fit 2 corny kegs and I can think its stupid to invent the wheel twice.
How big are those cooler elements, and did you make some calculations of how big they had to be?

Not only I find it hard to find big cooler elements, they are expensive too. But in your build, shouldnt it be better to use the bigger cooler on the out side to get more heat away from the peltier?

But I really like your build.

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Old 03-24-2012, 10:54 PM   #12
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Originally Posted by scaryeyes View Post
Hi

Dont know if I missed something, but how many peltiers did u use? And how is the attachment? I plan to build a small fridge to fit 2 corny kegs and I can think its stupid to invent the wheel twice.
How big are those cooler elements, and did you make some calculations of how big they had to be?

Not only I find it hard to find big cooler elements, they are expensive too. But in your build, shouldnt it be better to use the bigger cooler on the out side to get more heat away from the peltier?

But I really like your build.
Hi
sorry for the delay in my reply...

about the cooler I was quite lucky...I found an ebay surplus with 4 cells , heatsink and fan already assembled...I think the producer was supercool (http://www.supercool.se) .
It was a air/water exchanger that I have adapted air-to-air.
I don't perform specific calculation...just make the assembly and see the results...doing my best in insulating the carry on

About inner and outer heatsink again I have used what I was able to source budget price...and also trying to fulfil some mechanical constrains..

So not so much help...very empirical approach...hope you succeed to source your devices and got same results !

ciao
Davide
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Old 03-24-2012, 11:30 PM   #13
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That's pretty slick...

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Old 03-25-2012, 12:20 AM   #14
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I've been working on a peltier cooler but it's a much simpler and less costly design.

My biggest issue is, like someone else mentioned, dissipating heat. You have to dissipate the heat pulled out of the cabinet plus you have to dissipate the heat the unit generates. And between the two, the heat the unit generates can be greater.

Once the heat issue is solved and the design is done I will have a peltier cooler module you can just fasten to the side of your fermentation chamber, plug into the wall and dial in the temperature.

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Old 03-26-2012, 02:34 PM   #15
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thats the problem with peltier junctions; none are more efficient than 60-70% at best... most cheap ones are in the range 30-50%. meaning for every 100w of cooling power, you need to feed them with 200w or more of electricity. the differential in power is converted into heat that has to be removed.

so a 50% efficient TEC with 100w of cooling power will consume 200w of electricity, remove 100 (or slightly less, just because its not exactly 1:1) watts of heat from the cold side, but will produce around 200w of heat on the hot side. so your heatsink has to be double the size you would normally need to cool 100w.

cool project though. im suprised you arent using more than ~150w to cool that chamber.

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Old 03-27-2012, 03:29 PM   #16
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Originally Posted by thargrav View Post
I've been working on a peltier cooler but it's a much simpler and less costly design.

You have to dissipate the heat pulled out of the cabinet plus you have to dissipate the heat the unit generates. And between the two, the heat the unit generates can be greater.
Maybe my english is not so good... but I don't understand the point related to heat generated by the unit...unless you are talking about the heat generated by power supply and TEC controller with h-bridge circuit (that have to be dissipated)
Peltier cells as far as I understad works like a heat pump..generating a delta T between hot and cold face...so you have to dissipate heat from let's say the hot face (it can be reverted) ..the more heat you dissipate the cooler is the other face. Of course there is a concept of "efficency" like all thermal sistems.

If you are saying that "heat that unit generates" menas that peltier cells are low efficency you are right...!! this is the main disadvantatge of this solid state approach ...but the advantages are on other points...

hope to have understood
ciao
Davide
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Old 03-27-2012, 03:34 PM   #17
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Quote:
Originally Posted by audger View Post
thats the problem with peltier junctions; none are more efficient than 60-70% at best...
totally agree...peltier cells = low efficency

but...in homebrewing efficency is not the main target...

moreover the capabilty to reverse the hot/cold surface, the capability to drive continuosly the power (PWM modulation) , the compact and no mechanical part assembly...should be considered vs some more wat

Davide
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Old 03-28-2012, 12:42 AM   #18
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Quote:
Originally Posted by mysobry View Post
Maybe my english is not so good... but I don't understand the point related to heat generated by the unit...unless you are talking about the heat generated by power supply and TEC controller with h-bridge circuit (that have to be dissipated)
Peltier cells as far as I understad works like a heat pump..generating a delta T between hot and cold face...so you have to dissipate heat from let's say the hot face (it can be reverted) ..the more heat you dissipate the cooler is the other face. Of course there is a concept of "efficency" like all thermal sistems.

If you are saying that "heat that unit generates" menas that peltier cells are low efficency you are right...!! this is the main disadvantatge of this solid state approach ...but the advantages are on other points...

hope to have understood
ciao
Davide
They work like a heat pump plus they generate their own heat when working. Thie is because all of the PN junctions have resistance and they get hot. The end result is for every BTU you pull out like a heat pump the unit itself generates up to one BTU. This also means that the hot side heat sink must be much larger than the cold side heat sink.
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Old 03-28-2012, 02:18 AM   #19
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This also means that the hot side heat sink must be much larger than the cold side heat sink.
Here is the issue that halted my plans. Large heatsinks are hard to find. If I find , they are very very expensive.
I plan to use 4 millimeter aluminum for backside of my small corny fridge. Like 500 mm wide and 700 mm high. That will do as a heatsink for the cold side. Then.... The hot side.... Uh! Need to fill the entire back with expensive heatsinks and fans. The plan is to controll the cooler from a PID with PT100 sensor.
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Old 03-28-2012, 03:18 AM   #20
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Just buy what you need by the foot here.
http://heatsinkusa.com/

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