KEVOS® MAKEOS · Engineering
Thermoelectric Cooler Check (TEC Module Constants from the Datasheet, Heat Pumped, Power, COP, Hot-Side Heat)
At my current and hot- and cold-side temperatures, how much heat do these thermoelectric modules pump, what power and voltage do they take, how much heat must the hot-side heat sink reject, and is that enough for my load?
Thermoelectric cooler (TEC) performance from the ideal module model: the module Seebeck coefficient, electrical resistance and thermal conductance worked out from the datasheet maximum current, maximum voltage and maximum temperature difference at the rated hot-side temperature, then at your operating current and temperatures the heat pumped from the cold side (junction heat less half the Joule heat less conduction back), the electrical power and voltage, COP, the heat to reject at the hot side, the current for the most heat pumped, and checks against the heat load and the module ratings.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Module rating (datasheet) | ||
| Maximum current | A | Current at which the module reaches its maximum temperature difference, from the datasheet (I_max). |
| Maximum voltage | V | Voltage across the module at the maximum current, from the datasheet (V_max). |
| Maximum temperature difference | K | Largest temperature difference the module can hold with no heat load, from the datasheet (ΔT_max). |
| Hot-side temperature for the ratings | °C | Hot-side temperature at which the datasheet ratings are given, usually 25 °C, 27 °C or 50 °C. |
| Operating point | ||
| Operating current per module | A | Current through each module at the operating point, from your driver design. |
| Hot-side temperature | °C | Temperature of the module’s hot face, which depends on the heat sink: heat sink temperature plus the interface rise. |
| Cold-side temperature | °C | Temperature of the module’s cold face, a little below the temperature of the part or air being cooled. |
| Number of modules | Number of identical modules sharing the load, all at the same current and temperatures. | |
| Heat to be pumped from the cold side | W | Total heat that must be removed from the cooled side: the electronics dissipation plus heat leaking in through insulation and seals. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Module rating (datasheet)
What this means: Maximum current
- What it is
- The datasheet current at which the module produces its largest temperature difference with no heat load. With the maximum voltage and temperature difference it fixes the module’s resistance and thermal conductance.
- Units and format
- Enter a number in A: amperes. The form accepts 0.001 A to 1000 A. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 A as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger rated current gives a lower fitted resistance and a higher fitted conductance, which act in opposite directions on the heat pumped.
- Get it right
- Take all three maximum ratings from the same datasheet table and hot-side temperature.
What this means: Maximum voltage
- What it is
- The datasheet voltage across the module at its maximum current. Divided by the rated hot-side temperature in kelvin it gives the module’s Seebeck coefficient in the ideal model.
- Units and format
- Enter a number in V: volts. The form accepts 0.001 V to 1000 V. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15.4 V as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Scales the fitted Seebeck coefficient, resistance and conductance in proportion, so heat pumped, voltage and power scale with it.
- Get it right
- Use the module voltage, not the supply voltage of a recommended driver.
What this means: Maximum temperature difference
- What it is
- The largest temperature difference the module can hold between its faces with no heat load, at the rated hot-side temperature. It fixes the module’s thermal conductance in the ideal model.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts 0.1 K to 300 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 68 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger rated difference means a lower fitted conductance, so less heat leaks back from the hot side.
- Get it right
- Do not confuse it with the temperature difference you need; real loads always run well below it.
What this means: Hot-side temperature for the ratings
- What it is
- The hot-side temperature at which the datasheet’s maximum ratings were measured, often 25 °C, 27 °C or 50 °C. The module constants are fitted at this temperature.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -100 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 27 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Changes the fitted Seebeck coefficient, resistance and conductance, and so all operating results.
- Get it right
- Datasheets often list two sets of ratings for two hot-side temperatures; enter the one you took the ratings from.
Operating point
What this means: Operating current per module
- What it is
- The current driven through each module at the operating point. The junction heat pumped rises with current, while the Joule heating rises with its square, so there is a current giving the most heat pumped.
- Units and format
- Enter a number in A: amperes. The form accepts 0 A to 1000 A. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3.5 A as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises voltage and power; heat pumped rises up to the optimum current and falls beyond it.
- Get it right
- Running near the maximum current gives little extra cooling for much more power; check the COP.
What this means: Hot-side temperature
- What it is
- The temperature of the module’s hot face at the operating point, set by the heat sink temperature plus the temperature rise through the interface material.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -100 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A hotter hot side widens the temperature difference, cutting heat pumped and COP.
- Get it right
- Do not use ambient temperature: the hot face runs above the heat sink, which runs above the air.
What this means: Cold-side temperature
- What it is
- The temperature of the module’s cold face, a little below the temperature of the part, plate or air being cooled because of the interface between them.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -200 °C to 300 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A warmer cold side narrows the difference and raises heat pumped and COP.
- Get it right
- Below the dew point the cold side collects condensation; seal and insulate it.
What this means: Number of modules
- What it is
- The number of identical modules sharing the heat load, each carrying the same current between the same hot- and cold-side temperatures.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The total heat pumped, power and hot-side heat rise in proportion; per-module results do not change.
- Get it right
- Modules in series share the supply voltage; check the per-module voltage against the driver.
What this means: Heat to be pumped from the cold side
- What it is
- The total heat that must be removed from the cooled side: the dissipation of the parts being cooled plus the heat leaking in through walls, insulation, seals and wiring.
- Units and format
- Enter a number in W: watts. The form accepts 0 W to 1000000 W. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 W as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Moves the pass and fail line only; the module results do not change.
- Get it right
- Heat leaking into a cold enclosure is often larger than the electronics load; estimate it from the wall heat flow.
Method and formulas
- At a junction between two conductors the heat absorbed or released by a current is proportional to the absolute temperature, Π = S T (Bryan §164, equations (301)–(303); the Kelvin relations), with S the module Seebeck coefficient.
- Ideal module model: cold-side heat Q_c = S I T_c − ½ I² R − K ΔT, power P = S I ΔT + I² R, voltage V = S ΔT + I R, hot-side heat Q_h = Q_c + P and COP = Q_c ÷ P, with ΔT = T_h − T_c.
- From the datasheet point (Q_c = 0 at I_max and ΔT_max, hot side at T_hr): S = V_max ÷ T_hr, R = (T_hr − ΔT_max) V_max ÷ (T_hr I_max) and K = (T_hr − ΔT_max) V_max I_max ÷ (2 T_hr ΔT_max), all temperatures absolute.
- The current for the most heat pumped is S T_c ÷ R.
- Example: a 6 A, 15.4 V, 68 K module at 3.5 A between 40 °C and 10 °C pumps 22.9 W for 29.7 W of power (COP 0.77) and rejects 52.6 W; two modules pump 45.8 W.
Limitations
- Constant S, R and K fitted at one rated point; real module properties vary with temperature and the Thomson effect is neglected.
- The hot- and cold-face temperatures are inputs: the heat sink, interface materials and insulation must be designed so they are reached.
- Steady state only; condensation on the cold side below the dew point must be prevented separately.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size thermoelectric modules for an electronics or sensor enclosure, a sample cooler or a small cold plate
- Find the hot-side heat the heat sink must reject
- Choose an operating current between capacity and COP
Who it is for
- Electronics and product designers
- Thermal engineers
- Instrument and test rig designers
What you get
- Module Seebeck coefficient, resistance and conductance
- Heat pumped per module and in total
- Voltage, power and COP
- Hot-side heat to reject
- Verdict against the heat load and the ratings
Interpreting the result
- COP falls steeply as current rises towards the maximum: running below the current for maximum heat pumped, with more modules, usually saves power and heat sink size.
- The heat sink must reject the heat pumped plus all the electrical power, in the example more than twice the heat pumped.
Before relying on the result
- Compare the result with the module maker’s performance curves at your hot-side temperature.
References
- Bryan G. H., Thermodynamics: An Introductory Treatise Dealing Mainly with First Principles and Their Direct Applications (B. G. Teubner, Leipzig, 1907), Chapter XVI §§164–166 (junction and Kelvin thermoelectric effects; junction coefficient proportional to absolute temperature), pp. 167–173. Public-domain source; the method is restated in original words and no text, tables or figures are reproduced.
- Rowe D. M. (editor), CRC Handbook of Thermoelectrics (CRC Press, 1995): thermoelectric refrigeration, module performance equations.
- Ioffe A. F., Semiconductor Thermoelements and Thermoelectric Cooling (Infosearch, London, 1957).
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