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To peltier or not to peltier, that is the question

There has always been lots of questions concerning using thermoelectric cooling for Cp's
A while back I bought a 300watt peltier chip. It didnt take long to realize that this was the easy part. The hard part would be a power supply for the thing as it would require a 12vdc/25amp power supply (and massive heatsinks) LOL.... cha-ching

Recently I came across a 50(?) watt chip, now the power supply becomes more resonable. This one only needs 4amps at 12vdc. With a couple heat sinks, a fan and a couple power supplies some of my students and I were ready to give it a try.

Here are the results of a simple bench top test

The setup:
peltier_test1.jpg


The DVOM meter is indicating voltage, the adjustable power supply's display is showing current in amps.

The large power supply is powering the peltier and the small power supply is for the fan.

Immediately it became obvious that the bench top power supply could not carry the load. The best it would do is about 3 amps at approx 12vdc. This was maxed out, the power supply's heat sink (not visible in the pic) could fry an egg.

The top heat sink of the peltier is the hot side and the lower heat sink the cold. Peltier's are very inefficent to begin with. Without the fanI belive the top heatsink would be hot enough to blister your finger.

Initially it seemed to take about 30 mins for the peltier temp drop to reach maximum. As the delta T max is reached efficiency drops even lower.

Room temperature is 68-70f

It wasnt long before condensation was obvious:
peltier_test2.jpg


Input power levels:
peltier_test3.jpg


After a half hour or so, temps stabilize:
peltier_test4.jpg


peltier_test5.jpg


I was curious if a greater delta T max could be acheived if I used a power supply capable of driving the peltier at full load.

I found one and hooked it up, current jumped to above 6 amps and voltage levels were regulated at 13.8vdc

Amazingly, it had very little effect on performance. Evidently somewhere around 3 amps a point of diminishing return was reached. Any additional temperature drop would come at a significant price in efficiency, power consumption and wear and tear on all components.

So, where does all this lead me... I believe that a small terrarium would be an ideal application. Maybe a 5 or 10 gallon aquarium. But beyond that and beyond a 50 watt peltier... the disadvantages far out weigh the advantages. In that application a typical vapor cycle cooling system would be far superior.

Having said all this, I will build a 5 gallon temperature controlled terrarium version using the setup shown. It should be the perfect nursery for N. villosa and other difficult Cp children. I have little doubt that I could use this to lower a 5 gallon aquarium to 50f, maybe even a 10 gallon.

Hope this helps shed some light on the debate

Cheers'
Av
 
Why not just get one of those 12v peltier chilled coolers and take the lid off and replace it with some glass for lights?

I have not done alot of research on them but my understanding is they are incredibly inefficient at converting electricity to cooling temperatures. A small dorm fridge with gas compressor would be cheaper and use less energy and chill a much larger area.
 
Why not just get one of those 12v peltier chilled coolers and take the lid off and replace it with some glass for lights?

I have not done alot of research on them but my understanding is they are incredibly inefficient at converting electricity to cooling temperatures. A small dorm fridge with gas compressor would be cheaper and use less energy and chill a much larger area.

LOL well heck Tony, that wouldnt be no fun :p
Actually, the main point was to play with the technology and see what the possibilities are and a 5/10 gallon aquarium is much more aesthetically pleasing

Av
 
Well dang it how can I argue with that? lol
 
update: I had an odd feeling about that 6.6 amp reading with the other power supply, verified with two diff ammeters and it was in fact only 4.7

That sounds much better, and works out better mathamatically
 
Mathematically, teacher. Never trust spell check, I swear microsoft is dummy-ing us down on purpose.
 
When it comes to my spelling, ya cant blame microsoft :p

Av
 
I did a little research on peltier coolers a few month ago. You have gotten much further than me as I lack the know how. I have more knowledge of programming languages.

I read that efficiency goes up if...

1. The temperature differential between the two zones is great.
- The cold side is in contact with heat and the hot side is in contact with cold.
2. There is fast dissipation of heat and/or cold.

Obviously #1 is not practical in a CP environment. More so for thier originally designed application of cooling electronic devices. With that said, have you measured efficiency in a very humid environment. Perhaps one that has a constant blowing of mist to transfer the heat from the mist to the cooling device? Air itself is not a very conductive material.

Very interesting stuff. Thanks for posting.
 
Nice investigation Butch. I was just doing some reading on cooling systems on my breaks at work today. Has anyone ever done anything with absorption chillers? I'm very curious about the feasibility of building an at-home model.
~Joe
 
  • #10
Dash,

The hot side is just a few degrees above ambient. I don’t believe any more can be done on that side. Now on the cooling side, yes if it had a fan on it the delta T would decrease and efficiency would increase.

If i understand your statements correctly, yes... the efficiency of the peltier module is inversely proportional to the DeltaT max form the hot side to cold side. The greater this difference the lower the efficiency.

Also, the greater the temp differential the greater the heat transfer (ref. the peltier to ambient)... so this comes into play as well. It also has to do with emissivity, reflectivity, absorbtivity and transmissivty of the materials in question and the temp differentials.

Thanks seed, and i don’t know... but if it is what i think it is, then i don’t think it would be feasible. But I honestly don’t know.

Butch
 
  • #11
what the heck is a peltier? :blush: ???
 
  • #12
It's an electrical device that produces a cooling effect with no moving parts. When you electrify certain metals sandwiched together just right, one side of the stack gets hot, and the other side gets cold. It's called a thermoelectric or Peltier effect, named after the scientist that discovered it.
~Joe
 
  • #13
Joe, I looked up absorption cooling... and yes it’s what I thought. I’ve only had dealings with a couple over the years and they were in travel trailers (Winnabago type)

My main concern would be the Anhydrous Ammonia. While I’ve only had a couple dealings with absorption systems, I've had a lot of dealings with industrial NH3/NH4 systems. (former hazmat responder and incident commander)

That stuff is wicked, I’ve put the bubble suit on several times to go in and fix leaks.. Just a few PPM's and you can’t stand it, somewhere around 450 (IIRC it's been quite a few years) is lethal

The two I worked on, I had to turn upside down and let them sit over night. Evidently they get a gas pocket trapped somehow and turning them upside down allowed it to escape???

I didn’t have a clue what I was doing. Luckily back then I knew someone who did.

Personally, I would not want a NH3/NH4 system anywhere near my house. I have felt the sting of its bite

Butch
 
  • #14
Yeah, it seemed a little too good to be true. But if I were to build one, it would be outdoors - the only part that would be near an enclosed space would be an external heat exchanger, to circulate cold water or some other coolant back indoors. Glad to hear your thoughts on it though. I should be happy with Peltier units, but there's something about 10% efficiency that I find very unattractive.
~Joe
 
  • #15
Load performance test

10 gallon load test, no insulation (on purpose).

Start:
10galpeltier1.jpg


One hour run time:
10galpeltier2.jpg


After one hour, temps are still dropping but at a very slow rate... I started to graph it out, but it was like watching water boil... :crazy:

I would estimate a mid 50f temp to be very likely after several hours

Obviously, insulating the sides, back and bottom would improve performance, as would downsizing to a 5 gallon tank.
 
  • #16
Hey, you stole my thermometer!
~Joe
 
  • #18
fantastic mate. If in the future I have to downscale my setup to something small and for a couple of plants...I would seriously do this....or more likely...get it done. lol! ;)
 
  • #19
Building a small peltier unit for a fellow CP'er

The first step is constructing/preparing the heatsinks and thermal spacer.
The primary causes of premature Peltier module failure is having it under sheer stress and/or moisture problems.
While it can handle compression loading it is very vulnerable to sheer.
It's important that there is enough "meat" in the heatsinks to prevent this problem. The bolt holes must also be close to the module for the same reason.
The thermal space is also thick enough for structural strength and separation the two temperature regions. All contact surfaces are true within +/- 0.001"

AMD socket 754 heatsinks were ideal for this project and required very little modification, the thermal spacer had to be custom made though.

yanns_peltier1.jpg


yanns_peltier2.jpg


yanns_peltier3.jpg


yanns_peltier4.jpg

Disregard the black tape, for demo purposes only

yanns_peltier5.jpg


Now just waiting on some #10-32 x2.5"stainless steel socket head bolts to arrive. Regular bolts would rapidly corrode due to galvanic conditions

Once everything is bolted in place, the module region will be coated with a heavy coat of epoxy for moisture protection. Then mounts will be added and everything in the middle insulated with high density foam.

Av
 
  • #20
Looking sharp! Those heatsinks look like they'll fit MUCH better than the ones previously. Looks like that this baby going to be purring pretty soon ;)
 
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