Positive Temperature Coefficient (PTC) heating elements are small ceramic stones with self-limiting temperature characteristics. PTC stones have fast heating response times and plateau once the pre-defined reference temperature is reached. It is possible to form the stones into a square, rectangular, circular or ring shape. Above the reference temperature, the semiconducting and ferro-electrical properties of the ceramic are utilized to produce a rise in resistance of several orders of magnitude, and thereby creating it's self-limiting properties.
The rise in resistance is experienced within a fairly small temperature window of a few degrees centigrade. This attribute of the PTC results in a heating element that self-regulates to a pre-set temperature and automatically varies its wattage in order to maintain that pre-set temperature. In a given application, a greater degree of thermal dissipation (cooling) will result in a lower resistance being maintained by the element. This effect increases the power output of the heater, during operation in colder temperatures. Inversely as ambient temperature increases and less heat is dissipated, the resistance of the element will increase culminating in a near zero current draw at its designated temperature.
The dynamic resistance and output of PTC heaters makes them an excellent choice for providing controlled electrical heat. In many applications it is possible to do away entirely with thermostatic controls. Simplification of design and reduced energy consumption represent significant cost savings for a given application. The removal of failure prone components such as thermostats can also add significantly to the reliability of a product. Safety is an added benefit, since no matter how much current is applied to the PTC, it will never surpass its intended surface temperature.
PTC stones are doped polycrystalline ceramics based on barium titanate. The Stone is formed after a process that involves blending, milling, drying and sintering. To facilitate electrical connection, metalized contacts known as electrodes are applied to the surface of the PTC.
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PTC Features & Benefits
- Temperature limiting characteristics ensure safety
- Dynamic, self regulating and energy efficient
- All voltages from 12 V to 240 V; special voltage applications up to 800 V
- Dual voltages 12-24 V, 100-240 V possible
- PTC surface temperatures can be set from 40° C / 104° F to 280° C / 536° F
- Temperature tolerances +/- 5° C
- Compact design
- High power density
- Long lifetime
- UL, CSA and VDE recognized
- Custom configurations available in regards to size, inrush current, temperature, voltage, and power output
PTC Design Guidelines/Considerations
Listed below are some items that should be taken into consideration when a specifying a PTC heater:
- What is the target temperature to be maintained?
- What is maximum allowable temperature?
- What is the time required to heat the media to target temperature?
- Identify the type of media to be heated.
- Identify any potential thermal barriers between heater and media.
- Specify the maximum allowable inrush current at startup of element.
- What is the supply voltage or voltage range?
- What is the inlet air temperature/CFM rating?
- What are the space/size constraints for the heater?
It is often times possible to eliminate temperature controls in applications where the following conditions are met:
- When there is not a heat up time requirement that would exceed the dynamic range of the PTC by requiring many more watts than what is necessary to maintain temperature once the medium is at it's target temperature.
- If the medium to be heated does not require a min and max temperature window that is tight. For example in an outdoor application, the medium must not fall below 50° F /10° C and never exceed 140° F / 60° C.
- When the temperature tolerance of the medium can accept +/- 5° C.