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I got my peltier device three days ago and plugged it in as soon as I could with a heatsink. On the first few runs it got cold enough that there was condensation forming on it's cold side.

But now when I run it, it barely even gets cold, so much so that the side towards the +12v gets cold but the side towards the ground terminal out right gets hot to the touch.

I'm pretty sure this isn't a heatsink problem because it was working fine the first day. What could the reason be? Is my peltier malfunctioning or is something else at fault?

P.S. the humidity of the environment has been more or less the same the past few days so that isn't a reason.

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  • \$\begingroup\$ Did you seal your peltier and provide correct mounting pressure? Two most likely reasons seem that moisture or contaminants have shorted part of the circuit, or it's also possible if your peltier consists of 2 strings of bismuth cubes in parallel, each of which covers half the surface area, that one of the bismuth cubes has shattered or cracked or desoldered, opening the circuit. Humidity is culprit for this as well. If you have a factory sealed peltier, this is less likely. If you sealed it your self, the humidity when you sealed it is a factor. \$\endgroup\$ – K H Apr 29 at 1:45
  • \$\begingroup\$ If it is unsealed, if there is condensation on the outside of the plate, there is condensation on the inside of the plate. If you are operating at high temperature differentials, mounting pressure goes from important to crucial, and you may wish to purchase an element with grooved plates or attempt to groove your own. \$\endgroup\$ – K H Apr 29 at 1:46
  • \$\begingroup\$ If you provide the exact model and manufacturer and datasheet and possibly photo for your peltier, someone here may be able to speculate on the wiring arrangement of the elements. Is it precisely half of the peltier that is cooling or does it appear to be some other area of the element. If you label the parts that are heating and cooling on the photo, that will likely help. \$\endgroup\$ – K H Apr 29 at 1:50
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If There are a few problems that could be happening:

  • It's broken by mechanical or electrical stress
  • The thermal contact is wrong

One thing to do would be to check the resistance at room temperature with another module of the same make, it should be pretty close. Sometimes you can check the ohms of the module with the datasheet. With any module if the impedance is 1k or higher at room temperature, then there is most likely a problem.

Another thing that can kill peltiers is thermal expansion, ceramic (usually aluminum oxide) has a coefficient of thermal expansion, which means the hot side gets longer and the cold side gets shorter, this can break modules.

If the module is behaving differently, the most likely thing is because a physical change has occurred in the module, possibly reducing it's effectiveness.

Peltiers are fragile, most all peltiers consist of two pieces of ceramic sandwiched with a junctions made from positively or negatively doped bismuth telluride crystal. The junctions are all in series, if one breaks it reduces the efficiency of the whole module. Sudden shock from dropping or other objects can break modules. Peliters can also break by exceeding absolute maximum values listed on the datasheet, this usually happens through thermal stress. Run too much current through a peltier and you can kill it.

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