Question
We are building a prototype laser cooling system that needs to control the temperature of two thermoelectric coolers (Melcor part: CP1.4-127-10L) connected in series. Each TEC has the following operating specifications:
Qmax = 33.4 Watts
Delta Tmax = 68°C
Imax = 3.9 Amps
Vmax = 15.40 Volts
Module Resistance = 3.44 Ohms
Will the HTC3000, 3.0 Amp product and its evaluation board be a suitable controller for this application since the TECs won’t really be driven too hard (except maybe at start-up)?
Would a 24 V power supply be sufficient to drive these TECs if they were connected in series?
Answer
The HTC3000 and its evaluation board would not be the best choice for this configuration. In this case, the HTC3000 would have several problems that suggest another temperature controller would be more appropriate for this application.
The HTC3000, even with the full 3.0 Amp output current would not be able to drive the TEC to its maximum 3.9 Amps and therefore each TEC would not be able to produce the full 33.4 Watts of power (Qc) to the thermal load. Therefore the load might be slow to reach the desired operating temperature and may exhibit stabilization issues once it did finally get to temperature.
Using a 24.0 V power supply with the HTC3000 and two of these series connected TECs would exceed the internal power dissipation value of the controller and would destroy the controller. The HTC3000 maximum internal power dissipation value is rated at 9.0 W. Internal power dissipation levels higher than the rated maximum will exceed the output stage transistors’ junction temperature and the transistors will fail, often almost instantaneously, but they can also fail after a period of operation. Always utilize the online Safe Operating Area (SOA) Calculator to check system designs. In this configuration we can expect about a 6 V drop within the controller at full current. Therefore the amount of internal power dissipation within the HTC3000 would be 18 W (internal voltage drop times the series current, 6 V * 3 A = 18 W).
The best possible Wavelength temperature controller solution would be to use the PTC10K-CH Temperature Controller with an 18 V power supply. The PTC10K-CH offers up to 10.0 Amps of TEC current, but more importantly, it is rated as having an internal power dissipation value of 60 W. Therefore we could use the 18 V supply to produce a compliance voltage that would accommodate the maximum 15.4 V that the TECs may draw.
Actually, the optimum configuration would be to parallel connect these TECs such that they could each be driven to their maximum operating potential. In a parallel configuration the two TECs would have the following operating parameters
Qmax: 66.4 Watts (33.4 W * 2 = 66.4 W)
Imax: 7.8 Amps (3.9 A * 2 = 7.8 A)
Vmax: 15.4 Volts (parallel configuration means the single voltage rating)
Module Resistance: 1.72 Ohms (3.44 Ohms || 3.44 Ohms = 1.72 Ohms)
Because of the parallel configuration a supply voltage of only 18 V would be required to drive the TECs to their full potential and with sufficient compliance voltage from the controller. This configuration would allow the TECs to be driven to their full potential and there would not be any problems of exceeding the maximum internal power dissipation value of the controller.