What Is A Thermoelectric Module

What Is Inside A Module

A typical unit is a few millimetres thick by a few millimetres to a few centimetres square. It is a sandwich formed by two ceramic plates with an array of P-type and N-type semiconductor materials, commonly bismuth telluride alloys, in between.

The pellets are connected electrically in series and thermally in parallel. Copper conductors soldered to the inner faces of the plates join a P pellet to an N pellet at the top, then the next N pellet to the next P pellet at the bottom, and so on across the whole array.

That arrangement is what lets a low voltage supply drive a large number of junctions, and it is why the number of couples in a module sets its Vmax while the pellet cross section sets its Imax.

The Peltier Effect, Used For Cooling

When direct current passes through the junction between two dissimilar semiconductors, heat is absorbed at one junction and released at the other. Reverse the current and the hot and cold faces swap.

That is the whole basis of thermoelectric cooling. The module does not create cold, it moves heat from one plate to the other. Everything the module consumes electrically also comes out of the hot side, so the hot side always has to reject more than the load.

This is the single most important consequence for a designer: a thermoelectric cooler is only as good as its heat sink.

The Seebeck Effect, Used For Power Generation

Run the same physics backwards. Apply a temperature difference across the module instead of a current, and a DC voltage appears across the terminals. Connect a load and current flows.

This is what a thermoelectric generator does. It converts heat directly into electricity with no moving parts, no working fluid and no noise, which is why generators are used where reliability matters more than conversion efficiency.

Why Engineers Choose Thermoelectric

As solid state energy converters, thermoelectric modules have several advantages over competing technologies: high reliability potential, noise free operation, vibration free operation, scalability, orientation independence and compactness, meaning high energy density.

Based on those advantages, modules have come to dominate certain applications: temperature stabilisation, heat pumps for heating and cooling, large delta-T work and small scale power generation.

They are not a replacement for a large refrigeration plant. They are the right answer when a compressor cannot fit, cannot be heard, cannot be serviced, or cannot work in the orientation the product demands.

The Material Inside

The pellets are bismuth telluride based alloys for cooling and low temperature generation, useful up to around 450 K, and lead telluride based alloys for intermediate temperature generation up to 850 K.

Material quality is where module consistency comes from. We grow our own Bi2Te3 and PbTe at 99.99 % purity, slice it, cut elements with wire electrical discharge machining, and grade pellets on Seebeck coefficient and resistivity before assembly.

The published figure of merit for our P-type Bi2Te3 material is Z 2.55 to 3.4 × 10⁻³ K⁻¹ with ZT ≥ 1.1 at 300 K, and for N-type Z 2.34 to 3.2 × 10⁻³ K⁻¹ with ZT ≥ 1.0 at 300 K.

How To Read The Catalogue Values

Four values define a cooling module, and all of them are measured with the hot side at 30 °C:

Note the trap in those definitions. ΔTmax happens when the module pumps no heat, and Qmax happens when there is no temperature difference. Real operating points always sit between the two, which is why a module is normally chosen with Qmax around twice the working heat load.