Positive Temperature Coefficient Heating Elements

Positive Temperature Coefficient Heating Elements

Publicado por Adelle Webber en

How does the PTC heating element work?

PTC heating technology is unique in the family of electrical heating systems.  As current passes through the ceramic element, the resistance to the current produces heat, just as in resistive wire heaters. 

Small BuffetPTC Fan Heaters are Used for Maintaining Food Temperatures in Serving Lines.

The difference between the PTC heating element and resistive wire heating elements is there is no combustion taking place.  The PTC element with no “glow” can not cause combustion.

Due to its PTC characteristics, the ceramic element offers little or no resistance to current when cold.  Because there is no resistance, the current flowing through the component will be high, initially creating heat with little lag time associated with other resistive heaters.

As the temperature increases, the characteristics of the heater cause the resistance to increase, slowing down the current flow helping not to overheat the device.  The self-regulating nature of the heating element keeps the heating device from overheating.  

Temperature sensors and controls are still required to control the output temperature and shut off the circuit when the heater is unnecessary.

Technically no external temperature controls are required for PTC heating in some applications, but most will need a thermostat and shutoff device.  See examples of temperature controllers that can be used with PTC heating elements.

More detailed information on how PTC heaters work. View the video on PTC heaters.

Define a PTC heating element.

A PTC heating element or positive temperature coefficient heating element is composed of advanced ceramic material or ceramic stones with a small amount of barium titanate.  The doping procedure sets the maximum temperature of the ceramic component and provides the PTC characteristics.  

PTC ceramic heater or self-regulating heater is a small ceramic element that produces heat embedded in heat transfer material to conduct heat away from the component itself.  The heat transfer material can be aluminum, stainless steel, silicone, or similar materials that are good conductors of heat.

Why use a PTC heater in an electric vehicle?

Electric vehicles use PTC heaters because of their safety and efficiency.  Buyers of electric cars think of the massive battery pack that runs the care and specifications for horsepower and range.  

Buyers forget that EVs with large high voltage batteries also contain a typical 12-volt car battery to power displays, controls, and heating or cooling systems.  It is difficult to harness 700 volt AC output used for electric motors that run the car for 5 - 12 volt electrical systems.

cars in snow

PTC heating elements can produce heat effectively at 12 volts AC/DC.  A PTC ceramic heater is self-limiting based on positive temperature coefficient resistance changes.  Limiting the current flow without a temperature control circuit improves the operating efficiency of the heat source.  

PTC heaters are a very cost-effective heat source due to the immense heat output for their size.

Another advantage of the PTC heating element is that it automatically adjusts to ambient temperatures, drawing less current to reach the same temperature.  Its ability to draw maximum current when the cold temperatures allow the heater to heat quickly with very little lag time.

An alternative heat source for electric vehicles is a heat pump. They are very efficient for heating and cooling. However, under 40 degrees Fahrenheit they become very inefficient. In homes and cars and the electrical heating element is required below this temperature.

What is the PTC heating element temperature range?

The temperature operating range of the positive temperature coefficient PTC heaters is 40 degrees C to 220 degrees or 104 degrees F - 428 degrees F.  Keep in mind that is the temperature of the actual ceramic heating element.  

Actual temperatures transferred to materials and air are much less accounting for losses in heat transfer.  A heater used in ductwork in HVAC systems with air flowing through the ducts has the heat from the fin structures being removed rapidly into the air stream.  

Smaller PTC fan heaters control air movement across the surface to meet the heating requirements of cabinets or compartments.

What is a positive temperature coefficient?

When the heat rises in the heater, the resistance also increases logarithmically. This fast-rising resistance curve reduces the current going through the heater and the resultant heat. 

Note on the graph how the curve indicates increasing resistance as the temperature increases, which decreases current automatically.  The system will no longer generate heat once it reaches the desired temperature

PTC Graph

These characteristics also make the PTC heating elements energy efficient since current decreases as the heater approach the desired temperature.  

What are the different types of PTC heaters?

The PTC ceramic heating elements are embedded in heat transfer materials that isolate the voltage and current from external contact and efficiently transfer the heat to other materials or air. 

In a PTC air heater, aluminum honeycomb or v patterned structures are set between conductive bars containing the heating element.  These structures are placed in ductwork where the air flows to transfer heat to the air stream.  HVAC systems for homes or commercial will have these heaters in the ductwork.  

Electric vehicles, construction equipment, trains, and buses use air heaters for heating operators and passenger cabins.

PTC fan heaters are used for similar purposes in vehicles where a separate fan isn’t practical or available to transfer heat to compartments.  Another use is in electrical enclosures, medical equipment, and other applications where small heaters may need to operate at lower voltages.  

Higher voltages are available for heating up to 800 watts.

PTC convection heaters are used in electrical enclosures and other applications where there can be natural convection of air passing through the heating elements fin structure.  These heaters are placed in the bottom of a vented or unvented electrical enclosure. 

The efficient heaters heat the cooler air at the bottom of the cabinet, which raises to protect components from moisture settling onto electrical components.

PTC surface heaters also have an aluminum fin structure that is attached directly to the surface of the object to be heated.  The heat generated by the PTC ceramic heating element transfers through the material to the surface to be heated.  

Silicone or other efficient heat transfer material is used for bonding between the aluminum fins and the surface to be heated.

PTC immersion heaters or cartridge heaters have the ceramic heater embedded in heat transfer material inside a round or square tube of stainless steel that is inserted into the side of a container with contents to be heated.  The heater is fitted with a screw-in or bolt-mounted seal with wires extended for connecting an external circuit.  

This device looks similar to typical resistive heating elements in water heaters but in better condition than this one shown here in a blog article about cartridge heaters.

How to Select the right PTC heater for your application.

Call our team of thermal management specialists.  You will talk with an engineer that is very familiar with all of the devices available and can walk you through finding the proper PTC heating device for your application.

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