PRODUCT SPOTLIGHT:
PELTIER MODULES


Introduction

introduction image

Welcome to the CUI Product Spotlight on Peltier modules. Learn about CUI's Peltier module product line, while gaining a better understanding of Peltier module technology, including its principles, applications, structure, and advantages.

Objectives

  • Outline Peltier module theory, structure, and applications
  • Compare Peltier module advantages and limitations
  • Introduce the benefits of CUI's arcTEC™ structure found in its high performance Peltier modules
  • Review CUI's entire portfolio of Peltier devices

What is a Peltier Thermoelectric Module?

peltier function illustration

Early 19th century scientists, Thomas Seebeck and Jean Peltier, first discovered the phenomena that are the basis for today's thermoelectric industry. Seebeck found that if you placed a temperature gradient across the junctions of two dissimilar conductors, electrical current would flow. Peltier, on the other hand, learned that passing current through two dissimilar electrical conductors, caused heat to be either emitted or absorbed at the junction of the materials. It was only after mid-20th Century advancements in semiconductor technology, however, that practical applications for thermoelectric devices became feasible. With modern techniques, we can now produce thermoelectric "modules" that deliver efficient solid state heat-pumping for both cooling and heating; many of these units can also be used to generate dc power at reduced efficiency. New and often elegant uses for thermoelectrics continue to be developed each day.

Advantages

cross-section of peltier

Peltier modules offer several advantages over other thermal management solutions. They are compact, lightweight, and boast reliable solid-state construction with no moving parts, unlike typical fan cooled solutions:

  • Ideal for situations where forced air cooling is not an option E.g. in sealed equipment/environments
  • Offer precise temperature control and a fast temperature response
  • Capable of sub-ambient cooling
  • Compact form factor and lightweight
  • High reliability due to solid-state construction with no moving parts
  • Do not require refrigerants or use CFCs – environmentally friendly
  • Can be used for cooling or heating

Applications

Thanks to their precise temperature control, CUI's diverse line of Peltier devices are ideally suited for high density, high reliability medical and industrial applications as well as refrigeration and sealed environments where forced air cooling is not an option.

  • Laser Lab
  • Medical
  • Small Refrigerator Units

The Structure of a Peltier Module

peltier structure illustration

A typical thermoelectric module consists of an array of Bismuth Telluride semiconductor pellets that have been "doped" so that one type of charge carrier– either positive or negative– carries the majority of current. The pairs of P/N pellets are configured so that they are connected electrically in series, but thermally in parallel. Metalized ceramic substrates provide the platform for the pellets and the small conductive tabs that connect them.

When dc voltage is applied to the module, the positive and negative charge carriers in the pellet array absorb heat energy from one substrate surface and release it to the substrate at the opposite side. The surface where heat energy is absorbed becomes cold; the opposite surface where heat energy is released, becomes hot. Reversing the polarity will result in reversed hot and cold sides.

Understanding Key Specifications

Essential Datasheet Terminology

  • Maximum current (Imax) and maximum voltage (Vmax) are operating limits, not the module's absolute maximum rated values
  • Recommended operation only up to 70% of these limits
  • Operation beyond limits will result in decreased heat absorption and efficiency as Joule heating increases

Interpreting Function Diagrams

  • ΔTmax (maximum temperature difference) is the temperature difference between sides of the semiconductor when heat absorption is zero (0 W)
  • Qmax (maximum heat absorption) is attained when the temperature difference between sides of the semiconductor is zero
  • Relationships between current, voltage, temperature difference, and heat absorption are all illustrated by datasheet function diagrams

Design Using Function Diagrams

peltier function diagram

The function diagram for a Peltier module allows one to determine its performance under given conditions. More specifically, it can be used to determine how much heat can transfer from one side of a Peltier module to the other. In this example, let us assume there is a 12 Vdc power supply that can source 15 amps (180 W). Let us further assume this is CUI's CP150 series of Peltier devices, where the hot side will be held at 27°C and the cold side will be cooled down to 0°C.

  • Step 1: Mark the input voltage on the vertical axis at 12 Vdc.
  • Step 2: Mark the ΔT on the horizontal axis at 27°C.
  • Step 3: Drawing two lines to connect the dots, one can estimate that the Peltier module will consume 11 A of current.
  • Step 4: Mark 11 A figure on "Heat Pumped, Q(W)" section.
  • Step 5: By connecting that dot to the vertical axis, we can estimate that 65 W is being transferred from one side of the Peltier module to the other.

Mounting a Peltier Module

mounting a peltier illustration

Peltier modules do an excellent job of actively transferring heat from the cold side of the module to the hot side. However, once the heat has been transferred, if not removed, the Peltier module will heat up. This is because the electricity input into the module used to transfer heat across the device also has the unfortunate side effect of creating a considerable amount of heat. While very effective in transferring heat, Peltier modules typically consume more energy (in the form of electricity) than they transport (in the form of heat). For this reason, it is necessary to connect the module to a radiator such as a heat sink to efficiently disperse the emitted heat. A Peltier module fitted between a radiator and a heat extractor like an aluminum block for use as a cooling device is called a cooler unit.

Limitations of Standard Peltier Modules

illustration of thermal-fatigue

Thermal fatigue affects the solder that is normally used to bond the copper electrical interconnect to semiconductor pellets and the sintering that forms the bond between the interconnect and the ceramic substrate. While these bonding techniques normally create a strong mechanical, thermal and electrical bond, they are inflexible and the repeated heating and cooling cycles of normal Peltier module operation can cause them to degrade and eventually fail.

Introducing the arcTEC™ Structure

arcTEC structure illustration

To combat the effects of thermal fatigue, CUI has implemented an advanced construction technique called arcTEC™ structure, which allows for higher performance and reliability when compared to conventional thermoelectric module designs.

Key Technology Benefits

  • Thermal Resin: Thermally conductive resin allows for repeated thermal expansion and contraction, resulting in: better thermal connection, superior mechanical bond, and no marked drop-off in performance over time.
  • Improved Solder: High temperature SbSn solder carries a 235°C melting point, offering superior resistance to thermal fatigue and better shear strength when compared to the 138°C melting point of typical BiSn solder.
  • Larger Semiconductors: Larger P/N elements made from premium silicon ingot are as much as 2.7 times larger than other P/N elements on the market, leading to faster, more uniform cooling.

Improved Reliability with arcTEC Structure

arcTEC comparison graph

The combined effect of the thermally conductive resin and the SbSn solder joints within the arcTEC structure has a dramatic effect on the reliability and life span of the Peltier modules.

The data shows the stark contrast between Peltier modules built with and without the arcTEC structure. After as few as 3000 thermal cycles, the conventional Peltier modules already show a dramatic change in resistance. In contrast, the modules built using the arcTEC structure show negligible change in resistance all the way out to 30,000+ thermal cycles.

Improved Thermal Performance

heatmap of peltiers

In addition to superior reliability and module longevity, modules built with the arcTEC structure also offer enhanced thermal performance, thanks to its larger P/N elements mentioned earlier.

IR inspection shows an even temperature distribution across the surface of the ceramic substrate for units built with the arcTEC structure. Conventional units, in contrast, exhibit multiple temperature variations, indicating diminished cooling performance and higher risk of a shorter working life. These temperature variations can result from inferior P/N element quality, smaller element size, or poor solder quality within the module.

In field testing, modules utilizing the arcTEC structure demonstrated a greater than 50% improvement in cooling time compared to competing modules. This dramatic difference can be attributed to both the size and quality of the P/N elements as well as to the improved reliability the arcTEC structure provides.

Standard Peltier Modules

standard peltier group

CUI's line of standard Peltier Modules are available in 0.8 A to 13 A current ratings with package sizes ranging from 10 mm to 50 mm. Compact models with profiles as low as 3 mm and low current draw are also offered.

  • 0.8 ~ 13 A current ratings
  • 10 ~ 50 mm packages
  • ΔTmax up to 75°C (Th=50°C)
  • Solid state construction
  • Compact, low profile models

Peltier Modules with arcTEC Structure

arcTEC illustration

CUI's line of high performance thermoelectric modules delivers superior cooling performance and a longer cycle life with its innovative arcTEC structure. Ranging in size from 30 mm to 40 mm with profiles as low as 3.15 mm, these Peltier modules are available with a ΔTmax up to 77°C (Th=50°C) and current ratings from 2.0 A to 12.5 A.

  • Enhanced reliability for high thermal cycling
  • Superior thermal performance
  • Silicon sealed
  • Wide ΔTmax
  • 30 mm ~ 40 mm packages
  • 2.0 A ~ 12.5 A current ratings
  • Precise temperature control

Multi-Stage Peltier Modules

two-stage peltier

CUI's line of multi-stage Peltier modules feature two modules stacked for improved heat pumping capabilities and are available in 2.8 A to 8.5 A current ratings with a high temperature delta up to 105°C.

  • Two-stage thermoelectric coolers
  • High ΔTmax up to 105°C (Th=50°C)
  • 2.8 A to 8.5 A current ratings
  • Precise temperature control
  • Solid state construction

Peltier Cooling Unit

pletier cooling unit

CUI's CPM-2F is a 6.0 A Peltier cooling unit featuring better seal structure for water resistance and absorption of thermal stress, along with easy installation.

  • Full Peltier cooling unit
  • Better seal structure for water resistance and absorption of thermal stress
  • Easy installation
  • Solid state construction

Summary


peltier group

Discovered two centuries ago, the principles for Peltier module technology still hold value today for applications where forced air cooling is not an option. Thanks to their precise temperature control, CUI's diverse line of Peltier devices has the variety of sizes and form factors to meet a variety of thermal management needs. Several high performance Peltier modules built with the arcTEC structure are also available, offering improved reliability, performance, and cycle life when compared to conventional thermoelectric coolers.

 
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