Author Topic: A look at Peltier cooling  (Read 78881 times)

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Madscientist267

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A look at Peltier cooling
« on: February 09, 2011, 11:40:05 AM »
I've been playing with these little Peltier modules for a little while now, and have come to realize their potential for use in the land of RE (and real life as well) for use as a source for chilling.

Translation? Refrigeration.

While they have been in use for many years now for just that, there's been a fatal flaw with them that for whatever reason was never addressed.

They are horrendously inefficient in their 'native' design specification, but I have found a cute little combination of hacks that make them potentially viable for use in this arena, even in RE.

I held out forever with this until I could prove to myself that it was viable. First hold up was that the idea of running them on reduced input didn't really cross my mind until recently. The other was time to set aside to play with them. Not that it was difficult to do the experiment, just hadn't gotten around to it.

Last night, I found out that they can be run in a 'maintenance' mode, using between 1/4 and 1/6 the power they are rated for (and even less with the right circumstances), and still keep things cool.

I have two of these modules, one is buried inside it's OEM implement, a new Coleman "44 can" cooler that I got from wally world recently, that can stand upright just like a micro-fridge. The other was removed from a much smaller cooler that I purchased years ago. The barebones assembly is the only thing intact, with the module sandwiched between the two heatsinks.

The Coleman module appears to use quite a bit more power than the other one, and so this was one of my motives for trying this. The power supply that came with the unit gets outrageously hot in operation, and I couldn't see the need for it.

Both modules are designed to run on 12V nominal.

Turns out, reducing the input to approximately 5V results in moderate chilling capability with much less power consumption than it is designed for. It was able to 'hold the cold' overnight, only gaining a couple degrees C over the entire span. On full power, it will hold the temp lower, but the return is nowhere near what it is given to do so.

I'm in the process now of designing a thermostat that will switch between 5, 12, and 15V (the output from the power supply that came with it) in an effort to economize this thing as much as possible.

I'm also looking into using very large heatsinks with multiple modules to work my way closer to the abilities that a carnot cycle fridge can provide, even though I'm aware that the overall efficiency will still be much lower. Efficiency, surprisingly enough, isn't the primary concern here. The lack of moving parts is what makes it so appealing. With a large enough hot-side heatsink, I may be able to even eliminate the fans altogether from the design. More on that at a later time.

The relationship between power consumption vs cooling ability is non-linear:

@ 5V : ~1.8A (~9W)
@ 12V: ~4A (~48W)
@ 15V: ~4.6A (~70W)

The couple of degrees of 'cool' that are lost by running it at 5V is trivial compared to the power savings.

I'm not sure if the module can handle much more than 15V, and at the moment, I don't really care to find out. Power consumption is apparently exponential as the input increases, with only marginal additional heat pumping abilities.

In 'maintenance' mode, the module cannot quickly recover much in terms of heat that has entered the chamber due to the door being opened, etc. So, I am working out a multi-stage thermostat (maybe even just a PWM design) to provide power based on how close the temperature is to the set (desired) temperature.

At the moment, this means 5V when holding, 12V for normal cycling (heat creep recovery), and a switch on the door to engage 15V to prep the heatsinks for maximum recovery ability when the door is open. Considering a timer for this as well, to hold the 15V for a short time after the door has been closed, at which point control would be returned to the thermostat.

Here are some pics:



The Coleman cooler, holding at 7 deg C (~45F). It flirts with 6 degrees C (~43F) regularly, even after sitting all night. This is cold enough to keep many foods from spoiling, at least in any immediate term. Not bad for 9 watts.




The inside, showing the bags of dihydrogen monoxide provided for thermal mass. This makes a big difference.  ;D




The immediate rise in temperature as seen by the probe in the short amount of time the door was opened to take the picture above. The probe is dangling below the tray, not really visible. The meter actually peaked out at 16C (~61F), and had already recovered to 14C (~57F) by the time I could take this pic.




My other Peltier module, with heatsinks. This one uses a little less power by design, but doesn't have quite the cooling capacity either. Good for getting an idea of what to expect from the bigger module in the Coleman, however. They operate on the exact same principle, and so far, hasn't led me astray. The small sensor wedged in the center chunk of aluminum is some sort of temperature limiting device (I'm assuming for automatic defrost - this one had some minor issues with that when it was in it's original implement.


The probe's temperature recovery is good (within a minute or so) with the bags of water and soda bottle as shown. Recovery is very poor without these present.

Figured someone might find this interesting... More to come as the experiments continue...

Steve

EDIT -

Maybe even just as a supplement to a carnot system, a hybrid.

Haven't run the math to get an idea of how this pins up against a comparable sized conventional mini-fridge's average usage. No samples.  :(

May be worth it - a deep sleep that uses almost no juice.

FWIW
« Last Edit: February 09, 2011, 12:40:26 PM by Madscientist267 »
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dnix71

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Re: A look at Peltier cooling
« Reply #1 on: February 09, 2011, 04:27:43 PM »
There was one brand of Peltier junction cool boxes that works like you tried. It was almost as efficient as a real fridge. The cheap cool boxes have no real controls. This one did.

I can't find it on the web anymore. It was about $200 which is still much cheaper than an Engel.

Madscientist267

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Re: A look at Peltier cooling
« Reply #2 on: February 09, 2011, 05:10:13 PM »
Yeah I'm starting to think there really is something to this, but they get a bad rap because too much is expected from a single module.

I think spreading the power out among multiple modules is the answer here. A few designs have hit my mind's eye since I posted this; Seriously contemplating giving it a shot.

There's a place in china that has 40x40mm modules for like $4 US a pop, bought in lots of 10 modules ($40/lot), but I'm a little leary, something about the site doesn't really quite feel right, even though there's nothing outward that screams 'scam' either...

http://www.aliexpress.com/fm-store/901312/210188600-313416809/10-pcs-of-TEC1-12705-Thermoelectric-Cooler-Peltier-Plate-50W-free-shipping.html

What you guys think? $40 for 10 modules, but there are single modules for that much elsewhere on the webernets.

Traces of the PC repair geek in me always scrutinizes a little more than the average Joe, I suppose. But if it's real, I can think of a design I wouldn't mind trying using all 10 of a lot on one unit. Hope I can find as good a deal on extruded heatsinks too.  ;)

I mean either way, flop or scam - I'd be out only $40, so it's very tempting even if just for giggles to see what the possibilities are.

Steve
« Last Edit: February 09, 2011, 05:11:45 PM by Madscientist267 »
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joestue

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Re: A look at Peltier cooling
« Reply #3 on: February 09, 2011, 05:46:08 PM »
I think i paid $1.76 plus shipping for a 40mm square unit with the same part number as that lot you linked to just recently.
it works as good as the other ones.

The key here is turning the junction off when its cold enough.
The amount of heat transfered is pretty much linear. zero at 55-65C difference, maximum at zero C.
so its pretty easy to calculate the max thermal efficiency if you know how much heat you need to remove on average.

I'm not sure, but it might be more efficient to run one at 40 watts input with heat pipes rather than two with just heat sinks and fans.
the kind of fridges i've seen have two junctions, and heatsinks inside the fridge with two 0.3 watt fans inside the fridge.

if you were to use passive freon filled heatsinks rather than fans it would probably work out to be on par with normal refridgerators.

another issue is that when you turn it off, the heat in the heat sink is back fed into the fridge, at half the maximum rate you can remove it
(assuming a 40F fridge and the peltier is 35F at the cold plate, 80f ambient and heat sink temperature of 95F during operation.)
it isn't that much more efficient to pwm the peltier either.
one option is to use a water based cooling system.
that way when you turn the junction off, there is no heat back fed into the fridge.
« Last Edit: February 09, 2011, 05:57:02 PM by joestue »

Madscientist267

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Re: A look at Peltier cooling
« Reply #4 on: February 09, 2011, 06:41:03 PM »
I'm kinda there, only not. The multiple module design may draw more at some points than the single module would, but I think it would be much more efficient about it in the process.

Thinking something along the lines of an 'active insulation' kind of thing, with 1 module per ~sq ft of heatsink 'wall'.

With all 6 sides covered, the heatsinks can be thermostatically kept at 40F (or whatever) and the space inside will intrinsically meet up with this value at some point.

This is in contrast to the current designs; a single module, being force-fed full power, and struggling to keep up with just what is leaking through the walls.

A multiple module design would also be able to provide serious cooling power when needed, such as for initial cool-down and extended door-open induced temp spikes.

I also need a traditional carnot unit to compare performance to. Cost is already roughly comparable for identical size base units, about $80 US new for either kind, but the performance of the Peltiers lags severely, and I think it's simply due to design.

Edit:

9 watts flowing maintaining 7degC overnight? In terms of wH, I'd be willing to bet that the carnot system uses more than that when the on/off cycle is averaged over the same period of time.

Obviously, though, there is no contest when they are compared with the Peltier running at full throttle. Carnot wins, hands down.

This is where that whole PWM/Active Insulation idea comes in... if the duty cycle is continuously variable, it will only use as much energy as it needs to based on how much it needs to change the temperature at any given moment.

With 10 of the same Peltier module working in tandem, I'd be willing to bet that the power needed by each module drops even more significantly yet. They start to show a noticeable differential when being fed as little as 2.5V!

Steve
« Last Edit: February 09, 2011, 06:44:09 PM by Madscientist267 »
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dnix71

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Re: A look at Peltier cooling
« Reply #5 on: February 09, 2011, 07:31:19 PM »
I wonder how NASA does it? The EV suits all have some kind of solid state temp control, but maybe they are smart about it, since in space if you face the sun your back is to deep space.

One side hot, one side cold. You could run a Peltier backwards like that make power.

Multiple modules isn't done commonly because cheap is king in this world.

http://www.mobilegas.co.uk/mobilecoolbox/proelectriccoolbox/tropicool.htm   Here is a Peltier fridge with an "insulation bridge" to limit heat flow backwards in power off mode.
« Last Edit: February 09, 2011, 08:13:01 PM by dnix71 »

joestue

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Re: A look at Peltier cooling
« Reply #6 on: February 09, 2011, 08:37:18 PM »
what i'm saying is the amount of heat flowing backwards throught the junction depends on the temperature difference, the amount of heat flowing forwards depends on the current.

the two are independant. this is why at constant amperage the amount of heat flowing through the junction is linear. 0 at typically 60C temp difference, and x amount at 0C.


those small induciton motor driven compressors are exceedingly inefficient.
If you were to cut the top off, take the stator out and rewind it for three phase, hook it up to a small 3 phase motor driver (you could use those 24/48 volt airplane motor drivers, they aren't that expensive)
and drive it at say 600 rpm instead of 1700 or 3400 you'd use a lot less power.
« Last Edit: February 09, 2011, 09:15:32 PM by joestue »

DanG

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Re: A look at Peltier cooling
« Reply #7 on: February 10, 2011, 05:01:50 AM »
The best efficiency range from thermoelectric devices is 30 to 60%.

7 watts over 24 hours will chill 7 gallons of water 10F.

It takes .018btu to cool one cuft of (dry) air 1F, or takes 0.0002197 watt to cool 1 cuft of (dry) air 1F.

In worst-case real-world small-scale food refrigeration, say tropical oceans keeping hull at 90F, water temp at 86F, phase-change cooling regularly achieves 180% input-output gains while thermoelectric at its theoretical very best stays at 30 to 60%.

Space suits are cooled by allowing liquid water to seep through a porous plate and sublimate from solid to gas phase directly into space.

Small DC powered freon compressors use an inverter module power adapter - most of them have an adjustment for RPM, some variable but most are a fixed value resistor that can be changed to control RPM.

zap

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Re: A look at Peltier cooling
« Reply #8 on: February 10, 2011, 08:13:26 AM »

In worst-case real-world small-scale food refrigeration, say tropical oceans keeping hull at 90F, water temp at 86F, phase-change cooling regularly achieves 180% input-output gains
???

ghurd

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Re: A look at Peltier cooling
« Reply #9 on: February 10, 2011, 08:26:27 AM »
I am not an expert on Peltiers, except on how to cook one in world record time.   :(

Am I following this correctly?
My take on it is 9W is better than 70W, and the things cost $4 each, and RE is expensive.
So $40 saves a lot of RE power.

I think the same way with LEDs.  Run more at lower power and higher efficiency to achieve the same result with less power for just a bit more money up front.
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Madscientist267

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Re: A look at Peltier cooling
« Reply #10 on: February 10, 2011, 08:57:55 AM »
Basically, yes. All of you are right from what I can tell.

Its not that they are more efficient overall, it's that when used to just 'keep the edge off', they can be throttled back to next to nothing. Very much like how an LED can 'break darkness' for very little juice. Like LED's, a Peltier's efficiency is determined by how much current is being forced through it. The harder it gets pushed, the more it will do (to a point), but the less efficient it is at doing it.

It doesn't take very much power at all to keep the heat where you (don't) want it once it's (not) there when using a Peltier module. For that, it appears that the a Carnot (phase change) would use much more power doing the same job.

The inverse is true for raw cooling power;  Carnot is much more efficient at pumping large amounts of heat than Peltier is. So for quick initial cool-down and heavy loading caused by open doors, etc, a compressor is the way to go, and Peltiers would still be painfully chugging along trying to move the heat load long after the compressor got done with it.

Quote from: dnix71
Peltier fridge with an "insulation bridge" to limit heat flow backwards

This is basically what I'm looking at doing, only with multiple modules, instead of a single. Just barely enough juice to prevent heat transfer from outside to in when in 'sleep' mode.

They will collectively also be able to pump more heat when needed to handle door loads.

First rendition of the unit would be only Peltiers (for that whole lack of moving parts thing), but eventually, I'd even like to see this combined as a hybrid with a standard Carnot cycle fridge. I think it would make a huge difference in the amount of energy the unit uses when it's just maintaining a temperature.

Another factor that affects both types of heat pump is external ambient temperature. The lower the external temp, the more efficient the system is, because it does not need as much power to hit such a high diffferential. In extent, ambient temps too high make the Peltier impractical, when it can not reach the desired cold side temp. Carnot has a little better response for this; depends on the refrigerant used.

So, G -

Quote
Am I following this correctly?
My take on it is 9W is better than 70W, and the things cost $4 each, and RE is expensive.
So $40 saves a lot of RE power.

Absolutely. If it's true. Need more data to determine the truths here, but it's looking that way by a rough gander from a distance. :)

Steve
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kevbo

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Re: A look at Peltier cooling
« Reply #11 on: February 10, 2011, 10:20:13 AM »
In a previous life, I got paid to play a bit with Peltier modules.  I found that they were inappropriate for what we were trying to do, so the boss gave the project to someone with a "better attitude" who went full speed ahead into a product that never worked.  Essentially they were trying to make a high power processor (a DEC Alpha) work in an environment that did not have sufficient cooling air available.

The OP is pretty good information.  The only big flaw I am seeing in this thread is in regard to using PWM to "throttle" the devices:

This is where that whole PWM/Active Insulation idea comes in... if the duty cycle is continuously variable, it will only use as much energy as it needs to based on how much it needs to change the temperature at any given moment.

Be sure to filter the PWM  supply to nearly pure DC.  Raw (unfiltered) PWM is a loser with Peltiers because during the "on" part of the waveform they are running full power, which as you noted, is not very efficient, and during the "off" part they are not pumping any heat, but _are_ still leaking it in the reverse direction.  Running a Peltier cooler on raw PWM actually decreases the efficiency below the full power mode.

Also, if the raw  PWM is low frequency, then you are thermal cycling the modules which can lead to reduced life due to mechanical failure.

To avoid resistive losses the filters need to be L-C type.  To keep the inductor (L) small you need to keep the frequency pretty high. Not too high though, or switching losses become a problem.  I'd probably shoot for 25 KHz or so...just high enough that humans can't hear it.

A filtered PWM controller is essentially a switch mode power supply, but there is one big difference:  Power supplies are designed to run at one output voltage, but this thing needs to vary it's output voltage as commanded by thermostat.  The effective loop gain depends on the output voltage, and becomes very high at low output voltages.  This means that if you are using feedback to control the output voltage, it becomes very difficult to maintain loop stability at low output voltages.

Fortunately, great precision in the output voltage is not needed, and you can run it open loop or feed-forward, and just close the overall loop with the thermostat.

ghurd

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Re: A look at Peltier cooling
« Reply #12 on: February 10, 2011, 11:11:17 AM »
Good call!
I think I recall someone else telling me raw PWM and Peltiers did not get along.
Its been a long time, but seems like even with low duty cycle the junctions failed?
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Madscientist267

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Re: A look at Peltier cooling
« Reply #13 on: February 10, 2011, 12:54:47 PM »
Yep, filtered. Thought I mentioned it... LOL

PWM referring more actually to 'buck'...  ::)

Was more or less eluding to integrating the thermostat with the natural characteristics of the feedback loop.

Tomato, Tomato.

(damn, that still doesn't work...)

 ???

Start out with 15V/module and back it down to ~ nothing. I'm not going to be too worried about a little instability at the bottom, probably won't see it; chances are I will run these things in series anyway with a set or group collectively running at a higher voltage together (4@60V at 'full' throttle). Might make switching 'cheaper' too; less current. Thinking maybe just going line-to-module, direct conversion for the 120/240V version...

The only thing I wonder about is would current interactions (due to temperature differences among modules) cause some form of runaway (ie, one getting too cold, or never cold enough)... ?

Steve
« Last Edit: February 10, 2011, 01:20:16 PM by Madscientist267 »
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dnix71

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Re: A look at Peltier cooling
« Reply #14 on: February 10, 2011, 04:16:10 PM »
There is a video on the web of a regular hack-a-day group that took 4 Peltiers and sandwiched them between two cast iron skillets. They were wired 2 series x 2 parallel, to double both the voltage and current out. The skillets were back to back with the Peltiers in between. Water was poured in the top and the bottom was set over a campfire. The thing only produced 2 or 3 volts.

That suggests that they don't need much voltage at all to work. If you had 12 in series that were identical and fed the string 12vdc they would each see 1 volt. That might be efficient at the expense of initial cost.

Plus, there is a hack I see no one doing. Peltiers will frost over if you run them hard or without a fan on the cool side. A small fan on the cool side might bring big gains in efficiency if the fan was dc/variable speed and was controlled by a thermostat on the Peltiers. The best heat transfer occurs at the greatest Delta T between the air inside and the surface of the module, but any frost will insulate the module. Run the fan as slowly as possible without frost to maximize heat transfer.

One other hack would be to place a paperboard wick under and around the cold side to transfer condensation to the hot side through a fine slit in the back wall of the fridge. All normal a/c's shuttle condensate to cool the hot side because cold water represents a lot of energy spent to make but has no practical value otherwise. Most of the energy cooling air like that is just getting it past the dew point.

Madscientist267

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Re: A look at Peltier cooling
« Reply #15 on: February 10, 2011, 05:51:12 PM »
Quote
Run the fan as slowly as possible without frost to maximize heat transfer.

This applies more to 'high power' mode than anything right? Recovery etc. ?

Minimizing frost while maximizing transfer seems tricky anyway - two options I see:

Statically run the cold side sink as close to just above 32F as possible (via the buck regulation)?

Or keep enough heat going into it (regardless of heatsink temp) to prevent the frost from forming (by tweaking air flow rate, eg fan speed)?

Combination?

This end of thermodynamics is where I start to get a bit on the hazy side, and for pretty good reason too... :(

Under the right circumstances, the laws can twist and bend. This was illustrated to me by at least one 'magic trick' that I've experienced for myself up close and in person, and occasionally gets a good head scratcher going -

Heat pipes can do some wierd crap that isn't readily explained by logic. For example, when you heat one end, it's possible for the non-heated end to reach a higher temperature than the end with the heat on it! Found that one out trying to repair a heat pipe CPU heatsink assembly for a laptop one day... Blew my mind! Whiskey Tango Foxtrot Charlie?!?!

How can this be? LOL

Steve
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dnix71

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Re: A look at Peltier cooling
« Reply #16 on: February 10, 2011, 06:28:10 PM »
I don't know about heat pipe behavior. Just keep the temp on the module at 35F and you should have no frost to deal with.

Or don't go cheap like most maunfacturers who use the inside wall as the cold side heat sink. Actually mount a decent heat sink on the inside and put a temp sensor directly in front of the sink and set it to 35F or so.

joestue

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Re: A look at Peltier cooling
« Reply #17 on: February 10, 2011, 07:51:34 PM »
@kevbo

You're right about the pwm.
but specifically its the resistive portion of the junction is what's creating your I^2R losses.

Quote
Plus, there is a hack I see no one doing. Peltiers will frost over if you run them hard or without a fan on the cool side. A small fan on the cool side might bring big gains in efficiency if the fan was dc/variable speed and was controlled by a thermostat on the Peltiers. The best heat transfer occurs at the greatest Delta T between the air inside and the surface of the module, but any frost will insulate the module. Run the fan as slowly as possible without frost to maximize heat transfer.

err.. no, you want to run the fan at the upper limit of where the heat produced by the fan (.2 to 1 watt) is adding more heat to the fridge than the extra heat delivered to the junction.
basically, you want the temperature difference between the cold plate and the fridge and the junction as LOW as possible.
a nice big freon heat pipe/heat spreader inside the fridge is the best way to do this.
look at it this way:
At 45C temp difference you have a peltier moving 20 watts of heat from the fridge to the ambient air.
and lets say you have passive heatsinks on ether side.
you now add a 0.2C/watt heat sink to each side of the peltier chip, and it takes a 1 watt fan to get that. (figure a 5 heat pipe cpu cooler off newegg for $40 will get you that)
now the 45C temp difference is now reduced to say 35C, and the the peltier is pushing 27 watts of heat.
net gain of 5 watts. 
if you can get the hot side of the junction to hardly 5C over ambient, and the cold side to no less than 5C cooler than the inside of the fridge, you'd be doing pretty good, and these fridges would be efficient enough to use in more situations

Madscientist267

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Re: A look at Peltier cooling
« Reply #18 on: February 10, 2011, 09:14:35 PM »
Quote
inside wall as the cold side heat sink

Actually, this is exactly what I was going to do, only it wouldn't be just a flimsy piece of aluminum. Full on heat spreading sinks, with a small amount of finning on the inside to contribute as much to convection as possible. Both inside and out. The entire framework would be one giant heatsink more or less.

Thinking something like one module for every square foot of sink, with something like aerogel between the two sinks as insulation.

Might crop up first though as just several modules on one large heatsink.

Either way, actual bonafide heatsinks, yes.

Quote
temperature difference between the cold plate and the fridge and the junction as LOW as possible

Gotta tend to agree on this part, however. Forcing the modules as close to frosting as possible might be a tactic for recovering from a door opening or warm item placed inside, but uses way too much power for what is gained out of it. This is why the spreading out among multiple modules. You can get very close to the same temperature differentials at very low power input, just without the ability to do it quickly. But for maintenance, pump rate is not very relevant. They just need to be able to keep the inside surfaces as cold as the target temperature of the items inside; ultimately, so that no heat can get in.

Doing this with as little power as possible is the goal, not Carnot-like performance out of a Peltier. Only insulation leakage will actually need to be continuously pumped out, so as always, the more effective the insulation, the better, but only will affect the amount of juice it takes to sustain the gradient between the two temps.

I've already proven that extended maintenance at reasonable temps and power levels can be done with just a single module. It's my theory that by spreading the juice even thinner, that the total energy requirements to maintain a temp with the door closed (ie sleep mode) will be even less, since Peltiers appear to do more with less, down to a certain point. Below a couple watts somewhere, they cease to function to any useful capacity, but exactly where that line is has yet to be discovered, particularly as it would apply to multiple modules working in tandem.

Need a really high quality cabinet to go full out with this... With some really nice heat sinks above and beyond that.

I'm thinking that modding an existing Carnot mini-fridge may be the way to go, especially since I can then directly compare apples to oranges and see which one is better suited for which contribution to the overall highest operating efficiency of the entire box. Benchmark both technologies with both in place, and come up with a controller that brings out the butter zone. ;)

Steve

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Madscientist267

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Re: A look at Peltier cooling
« Reply #19 on: February 16, 2011, 11:00:57 AM »
Well, against my (ahem) better judgement, I went ahead and ordered the lot of 10 Peltier modules, they should be here in a couple of weeks.

Did that whole escrow thing on top of paypal, so we'll see how that works out.

Still in the process of hunting down some heatsinks. I have my eye on some, but have yet to determine the cost (need to call the company).

I also bought a Carnot cycle deep-freezer that will be leaving the warranty department almost immediately after it arrives in my presence, and I determine it works as designed.

It's a 5 cubic footer, not much of anything, but I think will fit exactly what I intend to do with it.

The interior is all sheet aluminum, with the freon coils apparently wrapped around the outside, in close contact with the aluminum.

The door is nothing more than just that, a door. Lots of insulation, and a seal. Plenty of real-estate for me to build my playground.

This of course means that I'm not going to be able to do the 'whole-unit' active insulation thing, but might give me a close enough idea of whether this is worth pursuing or not.

All in all, I'll have about $250 USD (if I'm calculating my heatsinks right), so worst case, I got a 'back to the future' looking deep freezer that can still be used.  ;D

More to come as the parts arrive; the freezer is supposed to be here Saturday (along with the wife's new side-by-together fridge... why can't I just go in and get only what I intend to get?!).

Happy Valentines Day Baby!!! (not that she reads this hahaha)

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

Madscientist267

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Re: A look at Peltier cooling
« Reply #20 on: February 16, 2011, 01:47:22 PM »
Okie, put the quote request into a company that does heatsinks...

Hopefully what I'm doing here is 'allowed'. I apologize if it isn't; I don't know how else to get my points across.

Please note that I have NO affiliation with ANY of these companies, they are simply my sources for materials and equipment for this project!

Now then...

I was rather limited in what I can get from them, because they apparently only sell certain lengths of the various models.

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:



Two each of 24 inch length.


For the cold side:



Also two each of 24 inch length.



The idea is 5 Peltiers per set, two sets.

Here is the freezer (destined for hybrid fridge status) that all of this is going into:

Freezer (link shortened for ease of reading)



Also, considering using some 'aerogel' based insulation to give it that final space-age touch (the 'SpaceLoft' blanket, near the bottom):

http://www.buyaerogel.com/

Anybody have any experience with this stuff? Claims to be a couple times more insulating than styrofoam... and only a minor irritant to various body parts.

Input welcome, even though half the stuff is already on it's way!  ::)

Steve

UMM... As I was typing this up, the quote came back... Let's just say nevermind on the heatsinks! LMFAO ----

If I'm reading correctly, I'm looking at over $1K for the heatsinks ALONE ! ! ! ! !

Yeah, uh... anybody have some old heat sink they want to part ways with?  :o  :'(

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

Bruce S

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Re: A look at Peltier cooling
« Reply #21 on: February 16, 2011, 02:20:49 PM »
MS267;
  Couple things, so far all the stuff you're putting up here is okay and way cool  8)
I do have a couple heatsinks that look like this I would be willing to donate in the interest of science  :P

They look like this one. I currently have two, put will dig around the office for more if they will help. None 2 foot long though  :P


That's a squirrel cage fan on it.
PM me with address for shipping  if they'll help
Bruce S
A kind word often goes unsaid BUT never goes unheard

Madscientist267

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Re: A look at Peltier cooling
« Reply #22 on: February 16, 2011, 10:49:43 PM »
No doubt cool, and of much appreciation...

But alas, unless you have 20 (yikes!) of them, they aren't of much good.  :'(

I fortunately used to work where PCs were (and are) in high supply.

Old units get demanufactured constantly, to supply the need for boards and power supplies.

One can imagine that heatsinks don't really go bad.  ;D

The result is, they pile up, and get tossed.

The silver lining is that I am still on good terms with everyone there (it's said that they would hire me back if a position were to open), and I am being granted a chance to look through these boxes for the ones like I have. They're pallet waste boxes, so I have my work cut out for me, but the price is right. :D

I do appreciate the offer however, and heat pipe is one of my interests, so if you insist...  ;)

I'm going to assume since you have even a few of these though that you may be familiar with this weird 'dump side is hotter than source side' thing...? Ever seen that?

Strangest behavior...

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

joestue

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Re: A look at Peltier cooling
« Reply #23 on: February 16, 2011, 10:58:05 PM »
heatpipes..

i have yet to find a supplier that can deliver 6mm 270mm long heat pipes for less than i can buy them off newegg.
specifically there's a heatsink on there right now. normal price is 48 but occasionally it drops to 40$. has 8 of them in it. each is at least 240mm long.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835185142
http://www.newegg.com/Product/Product.aspx?Item=N82E16835185147

cheapest i've found is $6.75 each for 6mm 270mm long if i order 41 of them.. 12 each in unit quantity
no thanks..

anyway, its unlikely you can get passive heatsinks to match the C/w of a single cpu heatsink such as those two above; without fans. Even if you wrap the entire fridge with heat pipes.
there just isn't enough surface area/airflow.
« Last Edit: February 16, 2011, 11:08:31 PM by joestue »

ruddycrazy

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Re: A look at Peltier cooling
« Reply #24 on: February 16, 2011, 11:15:44 PM »
G'day Steve,
                  I had a look at that link to the peltiers you gave way back and they do have a nice selection so after you get yours a good review will be great as I am tempted to go for TEC1-12716 16A 15.2V 65degree 40*40*3mm 150W  ones and $93 for 10 of sounds like a seriously cool dumpload for a decent wind genny.

Cheers Bryan

Madscientist267

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Re: A look at Peltier cooling
« Reply #25 on: February 17, 2011, 12:00:22 AM »
Quote
its unlikely you can get passive heatsinks to match the C/w

Yeah, unfortunately fans are going to be a fact of life with this regardless of what I do... :(

Quote
cool dumpload for a decent wind genny

LOL Sweet! Hadn't thought about it that way! Most people (myself included) are intent on just dumping the surplus juice as heat... why not cool with it?!  8)

Good call man!

Steve
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How much magic smoke it contains does !

Simen

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Re: A look at Peltier cooling
« Reply #26 on: February 17, 2011, 12:25:21 AM »
Steve:
Think of heatpipes as a kind of passive heatpumps; they have a liquid running through the pipes in complete vacuum that evaporates and condenses when temperature differences occur.
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)