The efficiency of a Peltier element application depends first on the type of power supply—this is discussed here—and second on the coefficient of performance (COP), what is covered in our TEC / Peltier element design guide.
TEC controllers are used for thermoelectric cooling and heating in combination with Peltier elements or resistive heaters. Peltier elements are heat pumps which transfer heat from one side to the other, depending on the direction of the electrical current. TEC controllers are used to drive the Peltier elements.
In this article we discuss the advantages of direct current (DC current) and disadvantages of PWM as power supply modes for driving Peltier elements with TEC controllers. Thermoelectric coolers operate by the Peltier effect and pump heat from one to another side. To maintain the direction of the heat flow, DC current is required.

TEC Controller Product Overview

Introduction

In the first part we show a direct comparison of a Meerstetter Engineering TEC controller with some other PWM TEC controller available on the market. The second part consists of example calculations.

Manufacturers of Peltier elements suggest using direct current and limiting current ripple for the regulation of the output current. They explicitly advise against the usage of direct PWM control of Peltier elements:

  • Ferrotec: "However we recommend limiting power supply ripple to a maximum of 10 percent with a preferred value being <5%."
  • RMT: "TEC [Peltier elements] controlled by PWM operates less effectively than at DC current. The PWM control is always less effective than TEC operation at the same average DC current and power consumption."
  • Marlow: "Thermoelectric coolers require smooth DC current for optimum operation. A ripple factor of less than 10% will result in less than 1% degradation in ∆T. [...] Marlow does not recommend an ON/OFF control."

Comparison of Two TEC Controllers

We compared a Meerstetter Engineering TEC controller with DC current (case 1) against a PWM TEC controller (case 2) from another manufacturer to emphasize the difference between thermoelectric cooling systems powered by DC current and systems using PWM. The goal was to compare the overall energy efficiency.
Both controllers fulfil the same need, but in terms of efficiency the difference is quite striking.

The setup consists of the following components:

  • power supply for TEC controller
  • TEC controller
  • object to be cooled (1 W load)
  • Peltier element
  • heatsink
  • fan to cool the heatsink

As target temperature for the 1 W load as object to be cooled, we chose in both cases 10 °C in an ambient temperature of 24.5 °C.

The results are presented in the following illustration and are discussed below.

DC TEC Controller vs. PWM TEC Controller with Losses

Remarkable differences and observations are:

  • The power needed to cool the object down to 10 °C was in case 2 more than six times more (56 W vs. 9 W)
  • The heatsink temperature in case 2 was 5 °C higher. This can lead to a higher temperature in the thermoelectric cooling system, especially when it is enclosed in a case.
  • In other words, the total amount of heat to be dissipated of the system using a PWM controller was more than 4 times larger. Hence, this results in the necessity of a much bigger heatsink for case 2.
  • A more efficient system allows also the usage of smaller components, like power supply, heatsink etc.
  • Using a more efficient TEC controller, smaller power supplies can be used.

PWM vs. Direct Current Driven Peltier Elements

In many applications, PWM is used for power supplies. This means in general simple logical control of the output power with a microcontroller and flexibility. For high frequencies the PWM current can be taken as direct current of the same amplitude value. However, TEC modules controlled by PWM are always less efficient than TEC applications controlled by direct current. Using the power input directly to generate a PWM signal makes a circuit prone to interferences, can lead to high transient voltages and is less efficient.

Another issue is that PWM may cause electro-magnetic interference (EMI) in the wiring to the TEC device. That effect could disturb measuring systems or cameras, e.g. when used to cool CCD sensors.

In the following example we compare a direct current driven and a PWM current driven Peltier element. We will calculate the current, the losses and the cooling capacity for both cases.

Please refer to the page Peltier Element Model for a better understanding of the following example.

Diagram PWM and DC current duty cycle
The direct current and the PWM current vs. time

Current of the Peltier Element

Direct Current PWM Current

Cooling Capacity of the Peltier Effect

Direct Current PWM Current

Conclusion: The cooling capacity PP is identical for both cases as IAVG is the same.

Ohmic Power Loss of the Peltier Element

Direct Current PWM Current

Notice that IRMS2 is five times higher for PWM current in this example.

Remember the formula for the effective cooling capacity at the object.

Conclusion: Using direct current for driving a Peltier element, Pel is low and therefore PO is higher.

Using PWM current, Pel is high and therefore PO lower.

For this reason, it is inadvisable to use PWM current to drive Peltier elements mainly because of the ohmic losses.

Peltier Element Current Ripple

To achieve stability, it is important that the direct current is constant and smooth with low ripple and low noise.

If the direct current has ripples, the cooling capability of the Peltier element is reduced. The reduced typical values of a Peltier element can be calculated by the following formula in case of sinusoidal ripples.

As an example, we take a Peltier element with a Tmax of 72 °C a DC power supply with a ripple factor of K=0.2 (20%).

Usually it's recommended to limit the ripple factor to less than 10% to reduce the loss in performance to less than 1%.

Meerstetter Engineering's TEC controllers have output stages that deliver DC current with less than 1.5% ripple.

Linear vs. SMPS TEC Controllers

How to generate the desired DC current for the Peltier element? To use a linear power supply is one solution – but not an optimal one.

Linear TEC Controllers drive Peltier elements with direct current. Therefore, the Peltier elements are working optimally.

But linear TEC controllers have a poor efficiency for themselves – the electronics generate great losses.

SMPS TEC controllers drive Peltier elements with direct current. Therefore, the Peltier elements are working optimally.

SMPS TEC controllers have a high efficiency for themselves. (>90%) The electronics generate few losses.

The Meerstetter Engineering's TEC controller family works in SMPS mode.

- Peltier elements are driven by direct current

- Electronics works with high efficiency

TEC Controllers

Overview
Model
Detailed Data
Output Current
(no PWM, bipolar)
Output Voltage
Output Channels
 
TEC-1092 image TEC-1091 image TEC-1089 image TEC-1090 image TEC-1122 image TEC-1123 image
TEC-1092 TEC-1091 TEC-1089-SV TEC-1090-HV TEC-1122-SV TEC-1123-HV
more... more... more... more... more... more...
±0 – 1.2 A ±0 – 4 A ±0 – 10 A ±0 – 16 A 2 x ±0 – 10 A 2 x ±0 – 16 A
0 – 9.6 V 0 – 21 V 0 – 21 V 0 – 30 V 0 – 21 V 0 – 30 V
one two
 
 

TEC Controller Product Overview

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+41 31 712 01 01

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