PTC Convection Heater

PTC Heater Using Natural Convection

What is convection heating?

Heaters utilizing convection to conduct heat from a heated surface into the surrounding air is one of the least complicated ways to heat electrical enclosures and spaces conducive to heat convection. The natural convection of heated air or water rising and cooler airdropping is the basis of thunderstorms.

Floor heating or baseboard heating in homes is an excellent example of convection heating. The heat source in or near the floor uses convection of heated air rising and cold airdropping to heat the space. PTC air heaters could also be viewed as convection heaters depending on the orientation of the heating device.

What are industrial applications for convection heating?

The number one enemy of electrical components is moisture. Too much humidity in an electrical enclosure at the right temperature will cause condensation to form on the surface of electrical components.

One of the ways to prevent condensation is to add heat to the enclosure when the temperature starts to drop. Cold air in a cabinet will fall to the bottom, like in a thunderstorm. When a small heater is placed at the bottom of the cabinet, it will heat the cooler air, which will rise. This warmer air prevents moisture from forming on the components.

PTC heaters are used for this purpose because they automatically turn on when temperatures decrease and stop producing heat as the temperature increases without external sensors and controls.

Why are PTC heating elements used for convection heating?

A PTC, or semiconductor, is a ceramic-based electrical component with temperature-dependent resistance as a heating element. Its positive temperature coefficient allows electrical current to flow better at low temperatures than at high temperatures. 

As the temperature rises, the PTC's natural resistance increases while its current conductivity and power output decrease until a state of equilibrium is reached, and the current can barely flow anymore. 

That's the PTC effect. In addition, PTC heating elements cannot overheat thanks to their self-regulating characteristic, which makes this heating technology exceptionally safe and reliable. 

Characteristics of PTC Temperature to Resistance Curve

The typical resistance curve of a semiconductor as a function of temperature is called PTC curve. The initial resistance of the PTC first decreases slightly with increasing temperature until the lowest resistance value Rmin is reached. 

The actual PTC behavior begins as the resistance increases non-linearly up to the nominal temperature Tc. At this point, also known as Curie temperature, the PTC’s resistance increases significantly. 

The operating range of the PTC extends from the nominal temperature Tc to the maximum final temperature Te, where hardly any current flows. 

The maximum temperature of a PTC depends on its ceramic composition and can therefore be determined in advance. Another characteristic of the PTC is its inrush current. 

As the resistance of the PTC is at its lowest value in Rmin, a large amount of current can flow there, causing it to undergo an increased inrush current for a few seconds each time it is switched on.

What is an example of a PTC convection heating device?

All PTC heating devices exposed to the air have some degree of convection heating, but several heaters are explicitly made for convection heating built to keep the heat from adjoining surfaces or human touch.  

Examples of these convection heaters are the Blizzard and Nimbus series of heaters from DBK USA.  The primary purpose of these heaters is moisture control in enclosed cabinets.

Each device is enclosed in a high-temperature plastic housing, making it a touch-safe heater. It is designed to fit onto a 35 mm DIN rail at the bottom of an electronic cabinet. The housing with a finger guard has an easy connection terminal block. The small size and high watt density make them a very efficient heat source.

Nimbus series of PTC convection heaters.

This series of DBK USA heaters come in a wide variety of configurations and higher wattages than the Blizzard series. Off-the-shelf models use 110 - 240 Volt power with output ranging from 30 - 175 watts. In addition, it is possible to custom order 12-24 volt AC/DC input units.

The Nimbus B series is enclosed in a case that lowers the external temperature profile with thermal decoupling. The device operates on a chimney effect for convection heating which optimizes the heating and retains the self-regulating effect of the PTC technology.

This series comes in four output voltages; 50, 60, 75, and 100 watts. They are exceptionally reliable, with no moving parts or exposed heating elements. 

The case provides IP20 finger protection and has a pre-wired connecting cable with strain relief. 

These units are small in size ranging from 3.54 - 7.87 inches in length and 3.2 X 1.38 width and height. They all have a mounting clip for mounting on a 35mm top-hat rail.  

See the complete Nimbus B specification sheet here.

The Nimbus E series of PTC convection heaters are similar in design to the Nimbus B series with higher wattage output. This series output ranges from 80 to 150 watts. Voltage ranges are the same as the B series at 110 - 240 volts. This series also comes in custom voltages of 12-24 volt AC/DC by special order.

These units come with VDE, UL, and CE approvals. Their case is isolated from the internal heating elements and the outside temperature but provides maximum chimney effect heating through the device. It is designed for mounting on a 35mm DIN rail.

The dimensions are 3.5 - 7.87 in length and 3.23inches in width X 1.38 inches in height. The external temperature profile doesn't exceed 266 degrees F. These dimensions and power provide a safe and reliable high power density device. Ideal for small cabinets in the lab or medical devices. Also, traffic controls, ATMs, or ticket machines operating in cold climates.

Nimbus E specification sheet.

The Nimbus D and NG series of PTC convection heaters are made with an aluminum fin structure for convectional heat transfer.  The heat generated by the internal PTC ceramic heating elements is conducted to the fin arrangement surrounding the device.  As the fins heat the surrounding air it raises and draws more cold air from the bottom of the cabinet.

The surface area of the aluminum fins on the Nimbus D and NG series are isolated from voltage and current but not temperature.  Anything, including human fingers touching the fins, could be subject to high surface temperatures.  

A finger guard is offered as an option that protects from unintentional contact.  The guard includes a DIN clip for mounting and a push release terminal blog for easy connections.  The two series of Nimbus NG include less than 100 W and greater than 100 watts up to 240 watts.

Nimbus NG specification sheet can be found here.

Nimbus NG Typical                             Nimbus B Typical               

What are other types of PTC heaters?

Learn more about PTC heaters and how they are used in our blog "What are PTC Heaters." See the applications in a wide range of industries at "Heating Up Industry.  If you need to learn more about how to use industrial heaters in your application, call our engineering center at 1-864-607-9047 and speak directly to an Industrial Thermal Management engineer.

We love to talk about applications for thermal management in the industry. Our engineers can determine if you need additional control devices for your applications to control humidity, moisture, and even cooling. 

DBK USA has a complete line of off-the-shelf control devices to provide effective industrial thermal management.