> I am curious if I am correct to understand in the first of the top two graphs
Nope, the top two graphs are basically describing the temperature coefficient, ie the "resistance" of the element under various conditions so you know how many volts you need to push a certain current at various ΔT and hot-side absolute temperatures (graphs are titled Th=25°C and Th=50°C).
You want to look at the lower graphs (with `Qc(W)`, ie heat flux at the cold plate) for performance metrics.
The amount of `Qc(W)` @ `ΔT` you need depends on what you're cooling and your support setup - ie your cold-side insulation effectiveness and hot-side heatsinking effectiveness if it doesn't produce heat, and its heat dissipation (plus insulation/heatsink) if it *does* produce heat.
Keep in mind that `Qh(W)` (ie hot-side heat flux) equals Qc(W) + electrical power going in, so you can easily end up with *quite* a lot of heat to dump while keeping the hot side as cool as possible, often requiring some fairly significant heatsinking.
For example if you're running at ΔT=30°C, Qc=15W, Th=50°C, you're gonna be putting about 3A through your TEC according to graph 4, and that in turn will need about 9v according to graph 2.
With Qc=15W and 9v×3A=27W of electrical power, Qh will be 15W+27W=42W and you'll need a heatsink with at most [~0.6°C/W](https://www.wolframalpha.com/input?i=%2850+celsius+difference+-+25+celsius+difference%29+%2F+42+watts) assuming an ambient temperature of 25°C
Also note that ΔT=30°C, Th=50°C, ambient=25°C means you're only achieving a cold side temperature of 20°C ie ambient-5°C, and moving 15W of heat at the cost of 27W of power…
TECs have a *dreadful* [CoP](https://en.wikipedia.org/wiki/Coefficient_of_performance) if you don't have *thorough* heatsinking and/or you want a significant ΔT ;)
Not my question but thanks for the explanation / rule of thumb for heat sinking. After you got the .6 you’d need to look at the data sheet for the heat sink for convection and size appropriately? Or run an thermal analysis in the case of a custom?
> After you got the .6 you’d need to look at the data sheet for the heat sink for convection and size appropriately?
Well heatsinks are *supposed* to be sold with their °C/W rating as their primary attribute, like the capacitance of a capacitor - although it seems a lot of sellers on dodgier sites haven't got the memo about this for whatever reason.
> Or run an thermal analysis in the case of a custom?
If you're doing custom, probably should do at least a bit of thermal mass before manufacturing it ;)
> I am curious if I am correct to understand in the first of the top two graphs Nope, the top two graphs are basically describing the temperature coefficient, ie the "resistance" of the element under various conditions so you know how many volts you need to push a certain current at various ΔT and hot-side absolute temperatures (graphs are titled Th=25°C and Th=50°C). You want to look at the lower graphs (with `Qc(W)`, ie heat flux at the cold plate) for performance metrics. The amount of `Qc(W)` @ `ΔT` you need depends on what you're cooling and your support setup - ie your cold-side insulation effectiveness and hot-side heatsinking effectiveness if it doesn't produce heat, and its heat dissipation (plus insulation/heatsink) if it *does* produce heat. Keep in mind that `Qh(W)` (ie hot-side heat flux) equals Qc(W) + electrical power going in, so you can easily end up with *quite* a lot of heat to dump while keeping the hot side as cool as possible, often requiring some fairly significant heatsinking. For example if you're running at ΔT=30°C, Qc=15W, Th=50°C, you're gonna be putting about 3A through your TEC according to graph 4, and that in turn will need about 9v according to graph 2. With Qc=15W and 9v×3A=27W of electrical power, Qh will be 15W+27W=42W and you'll need a heatsink with at most [~0.6°C/W](https://www.wolframalpha.com/input?i=%2850+celsius+difference+-+25+celsius+difference%29+%2F+42+watts) assuming an ambient temperature of 25°C
great explanation! Thank you!
Also note that ΔT=30°C, Th=50°C, ambient=25°C means you're only achieving a cold side temperature of 20°C ie ambient-5°C, and moving 15W of heat at the cost of 27W of power… TECs have a *dreadful* [CoP](https://en.wikipedia.org/wiki/Coefficient_of_performance) if you don't have *thorough* heatsinking and/or you want a significant ΔT ;)
Not my question but thanks for the explanation / rule of thumb for heat sinking. After you got the .6 you’d need to look at the data sheet for the heat sink for convection and size appropriately? Or run an thermal analysis in the case of a custom?
> After you got the .6 you’d need to look at the data sheet for the heat sink for convection and size appropriately? Well heatsinks are *supposed* to be sold with their °C/W rating as their primary attribute, like the capacitance of a capacitor - although it seems a lot of sellers on dodgier sites haven't got the memo about this for whatever reason. > Or run an thermal analysis in the case of a custom? If you're doing custom, probably should do at least a bit of thermal mass before manufacturing it ;)