TEC Microsystems - Miniature Thermoelectric Coolers and Sub-Assemblies

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Thermoelectric coolers are used now in many applications. There are four key TEC parameters you may find in any specification from TEC vendor: dTmax, Qmax, Imax and Umax. The first two - dTmax and Qmax parameters - are the most important for TE cooler - they indicate TEC performance level. Second two - Imax and Umax - describe the required electrical current and voltage to reach the specified dTmax or Qmax level.


dTmax is the max possible temperature difference that TE cooler can create between its cold and hot sides at zero heatload. It’s essential to understand that dTmax is specified without heatload applied to TEC.


Qmax is the max TEC cooling capacity - the level of heat a thermoelectric cooler can pump from the cold side to the heatsink. And here we should bear in mind that thermoelectric cooler parameter Qmax is specified at zero(!) temperature difference between TEC cold and hot sides (dT=0).

Thus we got two “set points” - dTmax at zero heatload and Qmax at zero dT - both parameters from the TEC datasheet are connected, and the actual application operating point (with a heatload and required dT under this heatload) is somewhere in between.


These two key TEC parameters (dTmax and Qmax) are the first to check when looking for suitable TEC. Once obtained from the TEC datasheet, these parameters are accepted as trustful by default, precisely as the TEC manufacturer specified, no doubt on the customer side.


But where are these parameters initially taken from by TEC manufacturers? Interestingly, the TEC manufacturer estimated the parameters dTmax and Qmax using initial Bi-Te material properties and Figure-of-Merit value. The critical question is about verifying these estimations, at what conditions they are specified and how close the estimations are to reality. In the real world, it’s always possible to face specific differences between theoretical estimations and actual results in the real world. In the case of thermoelectric coolers, there are many factors with more or less beneficial influence on actual TEC performance after assembly. And the estimated TEC performance level may have certain differences from actual TEC parameters.

Moreover, some TEC manufacturers may apply the quite simplified mathematical model and estimations to calculate TEC performance parameters and power consumption (and it's close to actual values as, say, car fuel consumption in the advert brochure - attractive, but let's say far from real). Thus the actual TEC performance is to be measured by direct testing and compared with initially estimated values. This is how it has to be done by an experienced and reliable TEC manufacturer, by default. Such proof requires advanced R&D equipment and high experience in TEC analysis to exclude all distortions and take into account all corrections during measurements.


There can be situations when the TEC manufacturer skips the actual proof of TEC performance level and simply specifies the estimated data. And there are also certain tricks to attract customer attention - making a bit higher values to demonstrate better performance. For example, setting TEC dTmax=75K instead of dTmax=72K looks good in the TEC datasheet. It creates a good impression, and once it's dTmax (specified at absolute zero heatload) - nobody needs the precision proofs. The same is about the Qmax parameter - it's specified at zero dT. In the real application, there is no absolute zero dT. Thus why not specify Qmax=10W instead of 9.5W? It looks better, shall we? There is another trick - performance values specified at higher ambient temperature (specified usually as Tamb or Thot in TEC datasheets): TEC Qmax and dTmax values grow with ambient temperature. Thus let's specify dTmax and Qmax at ambient higher than competitors and create an eye-catching effect. Why not? It's all about making a good first impression.

In most cases, big projects require several TEC vendors, and the initial choice of vendor is made under the impression of initially provided technical datasheets and parameters estimations. The same TEC solution, with even slightly higher performance, looks better. Thus some slight “advantages” in TEC specs give certain benefits for the TEC vendor (and the price, of course). Usually, TEC consumer has no actual ability to prove the exact TEC max performance level. TEC consumer simply relies on datasheet values as specified. TEC max performance parameters are required for the initial TEC choice and very rough analysis only. They technically create an initial impression and start next-level negotiations, while actual TEC performance is to be tested later in real application conditions. Marketing tricks are used for the thermoelectric industry, same as in many others.

TEC key parameters in the datasheet can be specified at, say, 50ºC ambient, while other vendors can rate it at 27ºC by default - and there will be a valuable visual difference in terms of dTmax and Qmax. It will be valuable enough to attract customers at the initial TEC choice stage. Some TEC manufacturers go far more and specify TEC max performance parameters at much higher ambient temperatures. It looks excellent in the datasheet, while the performance is the same (or even lower) as other vendors have if to specify it at 27ºC ambient temperature.

HINT: The first thing to check when looking at performance parameters in TEC datasheet is the ambient temperature, at which TEC performance data is specified. In most cases, it's noted as "Tamb", "Thot" or "Th" in the datasheet ("Thot" and "Th" means the temperature of TEC hot side, which is accepted equal to ambient temperature in optimal conditions). When it's not specified, it's essential to ask the TEC manufacturer to avoid any misunderstanding. Most TEC vendors specify TEC performance data at +27ºC and +50ºC.

Example - fragment from TEC Datasheet (Japan)

The next critical moment for the TEC performance datasheet study is the ambient conditions - gas or vacuum. TEC demonstrates the best performance in a vacuum, without a passive convectional heatload from the gas ambience. In the case of a gas-filled atmosphere, its convectional heatload has a particular effect on TEC parameters, directly proportional to TEC size. The larger the TEC size is, the more effect from convectional heatload. Traditionally TEC vendors specify performance parameters at +27ºC in a vacuum and +50ºC in Dry Air or Dry Nitrogen. This historically comes from typical TEC applications: X-Ray or IR-detectors in vacuum-sealed packages operating in near room conditions, and typical laser (LD) applications with operating temperatures closer to 50ºC, with gas-filled controlled ambiance. And if for the case of single-stage TE coolers, there is no significant difference in max performance in vacuum or gas-filled atmosphere for single-stage TE coolers, while multi-stage TECs are pretty much sensitive for such things.

In the case of professional support from the TEC vendor, all the estimations about TEC'sTEC's actual power consumption in the operating mode can be provided. The actual testing results in operating mode have to match the estimations, ideally. But it is the real world, and the actual results may differ from the estimations. All these may lead to certain debates between TEC suppliers and TEC consumers. Here is a pretty typical situation: TEC consumer specifies application requirements (in terms of TEC size, operating conditions, heatload level and required dT), TEC vendor suggests optimal TEC solution and provides necessary estimations; consumer installs TEC and observes higher power consumption than estimated by TEC vendor, or lower TEC performance level. TEC vendor is pretty sure about estimated values. TEC consumer is pretty much sure about the design and specified application conditions. Where is the problem? There can be various reasons for that. Incorrectly estimated application conditions: higher ambient temperature; overheating due to improper heatsink or poor thermal contact; excessive heatload to TEC; ambient influence (unexpected convectional and radiational passive heatload), etc. Also, it is possible to get TEC performance drop because of specific impacts or damages during the device assembly / TEC integrating stage. Or the compelling case - actual TEC performance may have a particular deviation from datasheet values or TEC manufacturer estimations because of an insufficient or simplified mathematical model in estimations.


Thus, there should be a reliable TEC performance verification and approval mechanism - a laboratory testing system where you can make actual TEC application operating conditions and apply a precisely controlled heatload to test TEC's actual performance level directly, in praxis.


Once such a verification approach is implemented (realized), it is easy to analyze the results and get the real, verified TEC performance level. Then it is possible to analyze the reasons for obtained deviations with theoretical estimations - if it's about unexpected application conditions like overheating or excessive heatload, or actual deviation of TEC real performance values from the estimated values.


TEC Microsystems GmbH, with already ten years of experience in thermoelectric coolers analysis, development and manufacturing setup, offers the unique service - direct testing of TEC performance and power consumption. All TEC performance parameters can be analyzed and measured directly. The analysis is made with a specially developed professional TEC testing system - DX8020 TEC Expert (available also for ordering).


DX8020 combines direct TEC performance parameters testing and measuring parameters of thermoelectric single-stage and multistage modules. The testing process with DX8020 allows checking the following parameters:


DIRECT TEC PARAMETERS TESTING

Measured Parameter 

Designation 

TE module temperature difference versus electric current at zero heat load 

∆T=f(I) 

TE module maximum temperature difference at zero heat load 

∆Tmax 

Electric current at which ∆Tmax is achieved 

Imax 

TE module electric voltage versus electric current at zero heat load 

U=f(I) 

Electric voltage at which ∆Tmax is achieved 

Umax 

TE module temperature difference versus heat load available at electric current fixed (loaded plots)

Q=f(∆T) 

Maximum heat load capacity at Imax (∆T=0) 

Qmax 

Actual TEC Power consumption under specified heatload Q0

P

Actual TEC ∆T level under specified conditions (ambience/heatload)

∆T

TE module Figure-of-Merit 

Z 

TE module electric resistance 

R 

TE module time constant at 0.01Imax 

τ 

Average Seebeck coefficient of TE material 

α 

Average electric conductivity of TE material 

σ 


TEC testing with DX8020 provides the automatic capability to measure the full specifications of a TE module at one measuring cycle in given ambient conditions. It’s intended for acceptance, qualification and research testing of TE coolers. The direct analysis is made on an anonymous basis. TEC vendor names are not required for testing. TEC Microsystems laboratory analyzes on a “Sample A, Sample B” basis. There are three types of direct TEC testing services provided by TEC Microsystems:


     1.     Standard tests, simple TEC verification - direct testing of actual TEC performance level (max parameters), comparison with TEC vendor estimations/datasheet values.

     2.     Expert mode tests - detailed TEC analysis with direct performance and power consumption testing in operating conditions specified by the customer.

     3.     Advanced comparison analysis of multiple TECs, optimal solution finding - direct testing of several provided samples to find the most optimal one, comparison of the performance level and power consumption at specified operating conditions.


Expert mode and advanced comparison testing also include TEC material and performance analysis - direct measurement of pellets material Electrical conductivity and Seebeck coefficient.


TEC Microsystems direct TEC testing services save time and budget for TEC consumers, solve the disputable situations about different testing results and help to understand the actual TEC performance level. Professional analysis with high-end laboratory equipment simplifies optimal TEC search and gives precise and accurate results about actual TEC performance level and power consumption.

Here are some examples of direct TEC testing stories:


Story #1: Customer observes significantly higher power consumption in application conditions, different to estimations initially made by TEC vendor. Direct TEC testing in the laboratory proved the correct estimations of TEC vendor, estimated values matched direct testing results. Following the detailed analysis of customer application and design revealed significant passive heatload level, not taken into account. Problem solved.


Story #2: Customer observes lower performance level of TEC in actual application conditions, had doubts in TEC parameters specified by the vendor. Direct TEC testing was ordered as 3-rd party expertise. Laboratory proved the problem. Customer design had no mistakes despite the TEC vendor statement. The actual TEC performance level was found ~15% lower than expected. The customer switched to a reliable TEC vendor.


Story #3: Customer claimed higher TEC power consumption, much higher than expected from estimations provided by TEC vendor. Direct TEC testing in the TEC Microsystems laboratory proved the performance level of TEC. The detailed analysis of customer design revealed a 2-wires measurement scheme for TEC voltage and severe voltage drop on header pins connected to TEC. Problem solved.


Story #4: Scientific center ordered detailed TEC performance analysis in vacuum conditions and possible risks of performance drop in case of leakage and gas-filled ambiance. Research made, optimal TEC solution with cooling capacity reserve was found and approved.


Story #5: Customer ordered detailed comparison analysis of thermoelectric coolers made by bulk and thin-film technology in various application conditions. Significant advantages of bulk TEC technology were confirmed in specified application conditions.


Story #6: TEC vendor applied changes in technology with related PCN to customer. TEC parameters remain the same, but the customer observes specific performance differences with the new solution and initiates an RMA discussion with the TEC vendor. Direct TEC's testing was ordered and used as 3-rd party expertise. Direct TEC testing revealed moderate changes in the updated TEC solution. Both sides agreed, the problem was solved.