This principle also applies to thermoelectric material. At a certain point, the heat generated can internally offsets the thermoelectric module’s ability to pump heat.
Each thermoelectric module has a heat-pumping limitation. This limit is referred to as Qmax.
The current associated with Qmax is referred to as Imax. The corresponding voltage across the coolers is referred to as Vmax.
If a TEC is completely insulated and isolated from the environment and running at Imax, it will produce its maximum temperature difference, dTmax. At this point, it will also be pumping no heat whatsoever.
As heat is applied to the cold side of the TEC, the temperature differential is suppressed. Effectively, one trades temperature differential for heat pumping. As such, if the temperature differential is 0, the corresponding heat load is Qmax.
The coefficient of performance (COP) is defined as the amount of heat pumping one gets for each unit of electrical power supplied.
When designing a thermal TEG system, this thermal resistance will often be used to select a TEG that thermally “matches” the heat sinks used in the application. VOC, or open circuit voltage, is the maximum voltage the TEG will ever produce.It is important to remember that the TEG voltage during operation will be considerably lower than this value; usually around ½ of VOC.
Efficiency is the ratio of electrical power produced by the TEG to the heat that flows through the TEG.
II-VI recommends taking an AC resistance measurement using a digital impedance meter or LCR. Using a standard ohmmeter with a DC input signal will not yield accurate readings, because DC voltage applied across the TEC will generate a temperature change and variations in resistance readings. Nominal AC resistance specifications for II-VI coolers are available upon request
Their compact size makes them well suited for applications with space or weight limitations, such as portable or airborne equipment. The ability to use thermoelectric modules to heat or cool suits applications requiring temperature stabilization of a device over a wide ambient temperature range such as laser diodes.
Voltage or current limiting should be used in order to ensure that Imax for the thermoelectric module is not exceeded. A bipolar power supply is required for those applications requiring both heating and cooling. Pulse width modulation may be used at frequencies above 1 kHz. A linear proportional, PI or PID control can also be used.
II-VI does not recommend an ON/OFF control. While this is the simplest control technique, temperature cycling within the thermoelectric module as power is cycled from full ON to full OFF may result in premature failure.
One side of the TEC contracts as it cools and the other side expands as it heats. This stresses the elements and solder joints. Since thermal expansion occurs on an inch per inch basis, the larger the cooler gets, the greater the stress becomes on the elements around the perimeter of the cooler.
In cases where the required heat pumping capacity exceeds that which could be provided by one TEC, additional TECs can be used side-by-side. In special cases, II-VI will manufacture TECs up to 60mm x 60mm.
For thermoelectric modules, it is standard to use “coefficient of performance”, not efficiency. The coefficient of performance (COP) is the amount of heat pumping divided by the amount of supplied electrical power. In other words, COP tells you how many units of heat pumping you will get for each unit of electrical power you supply.
It is possible, in certain situations, to pump more watts of heat than the watts of electrical power input. COP depends on the application, heat pumped, and temperature differential required. Typically, the coefficient of performance, heat pumped then divided by input power, is between 0.4 and 0.7 for single stage applications. However, higher COPs can be achieved with optimized, custom thermoelectric modules.
AC means Alumina ceramics. BC means Beryllia ceramics. AB means there is a mix of Alumina and Beryllia on top or bottom ceramics (or within the stages of a multi-stage thermoelectric cooler). AN means Alumina Nitride.
These key thermoelectric terms are used frequently by our engineers at II-VI, and across our website. Reference this glossary whenever you come across an unfamiliar term.
- ACR Test – Test to determine the resistance of a thermal electric cooler by powering it with alternating current
- ALO – Ceramics made of aluminum oxide
- Alloy – A melted mixture of two or more raw materials
- ALN – Ceramics made of aluminum nitride
- BeO – Ceramics made of beryllium oxide
- Bismuth Telluride – The compound name for thermoelectric material
- Cold Side – Typically, the top of the TEC, that gets cold as current is passed through the TEC
- Cooler – A thermoelectric cooler
- Couple – A pair of elements: one N-type and one P-type
- Elements – P-type and N-type semiconductor materials cut to a specific size
- Figure-of-Merit – Thermoelectric property which defines a material’s heat pumping capability
- GD&T – Geometric, Dimensions and Tolerance a symbolic language used on engineering drawings
- Hot Side – Usually the bottom of the TEC that heats as current is passed through the TEC
- Ingot – A cast alloy of thermoelectric material
- Lead Wire – Connection from the TEC to the power supply
- Metallization – The conductive pattern printed on the ceramics
- Plating – Applying a metal solution onto a substrate or element
- RGA – Returned Goods Authorization form required for all customer returns
- SEM – Scanning Electron Microscope: Allows viewing of objects at very high magnifications
- SPC – Statistical Process Control: A method of monitoring process performance and preventing defects
- Substrate – Base material (bare ceramics or bare TE wafers)
- Tab – A copper material which attaches to the ceramic and carries the current between the thermoelectric elements
- TE Material – An alloy of materials that produce thermoelectric properties
- TEC – Thermoelectric cooler (our primary technology)
- TEG – Thermoelectric generator, which uses a temperature differential to generate power
- TEM – Thermoelectric module (an alternate term for TEC)
- Tinning – Applying solder over the copper or tabbed pattern
- Wafer – A slice of an ingot