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Old 03-10-2016, 01:23 AM
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luka
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Join Date: Apr 2007
Location: Perth, Australia
Posts: 1,164
I found my notes regarding the sensor heat generation, including the heat transfer through pins:
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The sensor itself is probably negligible. 7mA@15V = ~0.1W.

I am more worried about the heat leaking from the main PCB via the sensor pins. It is a metal connection via 34 pins. Let's try to get a reasonable estimate:
Q = k * A * dT / d (ignore convection, radiation)
k = specific heat = 66 for beryllium copper
A = area (sensor pin = 0.46mm diameter (assume round), A = Pi * r^2 = 0.17 * 10^-6 m^2)
dT = delta T = 40C
d = thickness - how tall are our pins? Assume 10mm??? Longer pins will help.
We get Q = 0.05W for beryllium copper per pin. Multiply by 34 pins to get Q = 1.5W.

So it looks like our heat load for dT = 40C is about 1.6W. Double that as a safety margin to 3.2W.
(for dT = 60C we have 2.3W, 4.6W with double safety margin)
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and then here are more notes regarding a particular TEC from ebay:

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TEC2-19003, 12V, 3A, Qmax = 35W, Tmax = 80C, dual stage, 30x30x6.5mm

We should expect best case scenario of deltaT = 73C. Sounds really good if you believe the ebay specs.
Note that this deltaT would require the total heat load that our cooler needs to deal with 5.2W + (12V*3A) = 42W(note that 5.2W is the doubled heat load at 73C temperature differential).
That will require a smallish CPU cooler. However, we will likely never run the Peltier at this power.
For comparison QHY8L uses 30W max power.
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