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Simple cooler

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And you also overstated the size of the insulated box Pommie (so it would be better with a small custom fitted box). All round you allowed heaps of safety margin, and I suggested a little more by adding bubblewrap, then a 80W peltier or a couple of 50W units for 100W total. I also agree the brewing heat from a long period of low temp fermentation will be close to nothing. :)

I have a 12v 6A peltier here and with a good sized heatsink on the hot side its ability to move heat is pretty impressive.

As a test for the OP, you could get a 12v peltier+heatsink and a car battery etc and press it on the side of your 20 litre container and strap it in place with some bungee straps. Then stick a thermometer in and do some simple tests. Blankets will do for insulation for testing.
 
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Hi Mike,


I do appreciate your taking the trouble to do some of the numbers to find out what will fly here, and also posting the link which i found which is very informative. Now what i propose is that you redo the calculation one more time but this time take into account the natural rise in temperature of the hot side once the thing is plugged in. Once the unit is plugged in the first thing that happens is the hot side starts getting hot as it pumps the heat through the device from the 'cold' side. Now it's unfortunate but that means the hot side gets hotter than the ambient and that means the hot side of the Peltier device itself gets hotter than ambient. The downside to this is that the temperature differential has to be more than simply the ambient minus the inside colder temperature because the temperature differential is not the outside air temp minus the inside air temp, it's the hot side surface temp minus the cold side surface temp. Add to that the problem of heat sink thermal resistance and we're suddenly working with a less efficient system.

My only suggestion here can be to build a smaller prototype and test it, then scale up from there. Build a small unit with one Peltier device and use two nice size heat sinks and two fans. One fan on the inside and one large fan on the outside. Start with a small styrofoam cooler (cheap) and cut a hole in the top to fit the Peltier and go from there. Measure inside and outside temperatures. This would also allow us to test the time it takes to get the mass inside the box down to the target temperature, using a mass with proportionally sized specific heat capacity or at least something to simulate the true object that will be inside the box in the final project.

As Ron pointed out, there seems to be more to this than we have considered so far (such as the heat of the hot heatsink and not just the ambient temperature) because i dont think those commercial units work as well as we would like. Lucky for us here though is that we dont need a huge ambient to inside temperature differential
 
6 litre cooler gives up to 40 degrees heat or cool (peltier driven) $39;
https://www.amazon.com/Wagan-EL2260-6-Liter-Personal-Fridge/dp/B000786JRI
**broken link removed**

It's not rocket science, just a decent sized peltier or two, some insulation and decent heatsinks+fans.

Here's an aussie built one from Ross Tester (Silicon Chip magazine) 2003;
www.k3pgp.org/sales/ck1500.pdf[\url... the heatsink assembly and cooling plate etc.
 
How about two of these TEMs with 2" styrofoam (I was actually thinking the 2" foamboard insulation from a home improvement store, no numbers on that though). I need heatsinks, fans, a temp controller, and the problematic beefy 12v power supply...
 
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Modern ATX power supplies have +12 volt rails so large you'll never want for power.
 
I'm only familiar with ATX supplies insofar as I have installed them in systems...so I could just check the pinout for the ATX connecter and cross some leads to get it to power up and stay on?
 
If you run the calculatior I think you will find you need a bigger one.
 
So here's a basic TEM question: Peltiers heat AND cool, correct? I am confused as to why some models by the same manufacturer are listed as "heating/cooling" and others are not. Does the design need to be different for a module that is reversible, or can I expect any module to work the same with the current reversed provided both sides are heatsink/fan equipped? I ask this because I'd rather be able to heat my cooler as well as cool it and I need a module that will allow me to do that.
 
I'm only familiar with ATX supplies insofar as I have installed them in systems...so I could just check the pinout for the ATX connecter and cross some leads to get it to power up and stay on?

Yeah, that is pretty close to it. Take all of the Yellow (+12 Volt) wires in the main power connector and tie them together and do the same for all the orange (+3.3 Volt) wires as well as black (Common). Run the orange through a 10 Ohm 10 Watt resistor to Common. The yellow give you your 12 VDC power. The main connector should show a green wire. That should be PWR_ON. Place a simple SPST On/Off switch between the green and common. The switch will place the PWR_ON at logic low and turn on the supply. The 10 Ohm resistor is likely optional but I would include it as I think (operative word think) ATX PSUs regulate off the 3.3 volt bus.

Ron
 
So here's a basic TEM question: Peltiers heat AND cool, correct? I am confused as to why some models by the same manufacturer are listed as "heating/cooling" and others are not. Does the design need to be different for a module that is reversible, or can I expect any module to work the same with the current reversed provided both sides are heatsink/fan equipped?
...

As far as I knew they are all heat/cool, you just reverse the current. You have to treat them gently to avoid thermal shock, so you should not slam the voltage (current) in reverse, and for the same matter it's not good to cycle them on/off with a switch either it's better to ramp the current and PWM it to get a constant smooth heat. I have seen specs for >2kHz PWM recommended to reduce thermal ripple. You can do that with a 555 timer or a simple comparator oscillator.
 
Two of the 80 watt units should do it. Or here is a combo that should work:

2 Tellurex C2-40-1509 using:
2 Masscool heatsinks PN 9T288B1N3G Or equivilent 0.4 degree C per watt heat sink.
 
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That is a great FAQ thanks for that! I had no idea the peltier was full of little alternating P and N nuggets, I thought all the little nuggets were the same.
 
So here's my plan for testing: I have an ATX power supply (or 10) laying around, and lots of different heatsinks. I will get an inexpensive TEM and attatch it to heatsinks for which I have specs, make a quick and dirty box and put a gallon brew inside.
As far as controlling the current, is this something I can put inline or will it require a specialized power supply?
 
To test it I think I would just hook it up to your 12 volt supply and let it run. Keep an eye on the hot side heat sink. If you can't touch it it's probably time to turn it off.
 
It's not a CPU, but a very thin layer of heatsink grease is probably a good idea. For TEM modules you don't generally control current, they're designed around a voltage. From what little I remember of valuing TEMS in the past though that they reach their rated power handling capacity at a set voltage, and that you better be sure of the power handling capacity of the TEM you're using at the voltage you're using as they're typically peak efficient near 16 volts, running one at stock 12 volts may drop it's power handling ability by a large amount.
 
I have an ATX power supply (or 10) laying around,
...
As far as controlling the current, is this something I can put inline or will it require a specialized power supply?

They are normally specced to run from 12v systems, so that should be fine. As Scaedwian said you would get a bit more power running from a bit higher voltage like 13.8v (ie automotive 12v). You can check the input wattage by W=volts*amps and compare to the rating of the device.

Remeber you need a BIG heatsink, even a big slab of metal for testing. Also since they are very thin you really need a small block of aluminium on the cool side going through your insulation, to provide some separation between your cool container and the big hot heatsink.

If you check that PDF I linked to earlier from the SiliconChip magazine article, it shows a photo of the peltier and heatsink and it is a unit from a commercial cooler, so you can see the design. :)
 
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