Summary of TEC used in Free Space Optics
TEC devices are used in some CableFree FSO products to cool the actual laser devices. Free Space Optical communications systems are typically mounted in exposed outdoor conditions, subject to temperature variations, and depending on local climate, huge differences in regional temperatures. Lasers are temperature-sensitive devices and to ensure consistent performance and lifetime, TEC devices can be used to keep the sensitive laser devices operating within an acceptable temperature range
FAQ on TEC devices
“I’m curious, exactly what is a thermoelectric module?”
A thermoelectric module is a small solid state device that can operate as a heat pump or as an electrical power generator. When used to generate electricity, the module is called a thermoelectric generator (TEG). When used as a heat pump, the module utilizes the Peltier effect to move heat and is called a thermoelectric cooler (TEC).
“It sounds familiar, but…what is the Peltier effect?”
The Peltier effect was discovered in 1834. When current passes through the junction of two different types of conductors it results in a temperature change. However, the practical application of this concept required the development of semiconductors that are good conductors of electricity but poor conductors of heat – the perfect balance for TEC performance. Today, bismuth telluride is primarily used as the semiconductor material, heavily doped to create either an excess (n-type) or a deficiency (p-type) of electrons.
“How does a TEC work?”
Very simply, a TEC consists of a number of p- and n-type pairs (couples) connected electrically in series and sandwiched between two ceramic plates. When connected to a DC power source, current causes heat to move from one side of the TEC to the other. Naturally, this creates a hot side and a cold side on the TEC. A typical application exposes the cold side of the TEC to the object or substance to be cooled and the hot side to a heatsink which dissapates the heat to the environment. A heat exchanger with forced air or liquid may be required. (As clever as TECs are, they can’t eat heat – only move it!)
“What happens if I reverse the direction of the current?”
If the current is reversed, the heat is moved in the opposite direction. In other words, what was the hot face will become the cold face and vice-versa.
“How much heat can it pump? Could I cool my house with it?”
The maximum amount of heat the largest single TEC can pump is about 125 W. So, you couldn’t cool your house with it! However, our modular design enables you to use several TECs per application, allowing you to move more heat.
“So, I can use more than just one?”
Sure! They can be used side-by-side to increase the amount of heat pumped, or they can be stacked on top of one another to increase the temperature difference across the TEC. When stacked, they are called “cascades”, or multistage TECs. When the temperature difference between the hot and cold faces doesn’t need to be more than about 60°C, single-stage TECs can normally do the job. If the temperature difference needs to be greater than 60°C, cascades should be considered. Some cascades are listed in the Multistage Specification table. Many others are available.
“When should I use a TEC…is a TEC as good as a compressor?”
TECs are absolutely perfect for some applications and completely unsuitable for others. Depending on the application, a TEC can be much, much better than a compressor or no match at all. TECs are very small, very light weight, and completely silent. With no moving parts, they are extraordinarily reliable. TECs generate little, if any, electrical noise and can provide precision temperature control when used with an appropriate controller. They can be operated in a vacuum or weightless environments, and in any physical orientation. On the other hand, TECs tend to lose their competitive advantage when cooling loads exceeding 200W. Under some special circumstances, however, TECs are used to pump loads of tens of kilowatts.
“Is it hard to design a TEC for my application? Do I need special equipment or training to install a TEC? ”
Using a TEC does require some understanding of heat transfer and a good grasp of your application. Our experienced engineers are available to help you. Proper installation is extremely important but not very difficult. And, we can build custom subassemblies for specific applications.
“What about temperature control and power supplies?”
TECs are DC devices. The amount of heat pumped through the TEC is directly proportional to the power supplied. Temperature is controlled through manual or automatic means. The automatic controller can range from a simple on-off thermostat to a complex computer controlled feedback circuit. Precision TEC control systems are built in as standard to FSO products available from CableFree.
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