What is Supplemental PTC Heating?
Electrical PTC heating elements are widely used for supplemental heating due to their simplicity, reliability, durability, and safety. PTC, positive temperature coefficient, characteristics make the small ceramic elements ideal for supplemental heating in a wide variety of applications.
PTC heating elements have recently gained even more popularity with the rapid development of electric vehicles. Both conventional and electric vehicles use PTC heating elements for supplemental heating.
Electrical vehicles found PTC heating to be the solution.
The stand for auxiliary heating in cars, construction vehicles, trains, and homes has always been electrical resistance to heating. The typical excess engine heat is too much time to warm up to heat the cabin and operating components.
Vehicles using resistive wire heating elements allowed quicker heating by the current flow through the resistive heating elements in line with the heating ductwork. This method solved the initial heating issues but wasn’t very efficient, created safety risks from combustion, took up a lot of space, and wasn’t as durable as needed for over-the-road vehicles.
EVs use heat pumps for heating and cooling in the passenger compartment, but have limitations for heating. At temperatures lower than 40 degrees F, their efficiency is drastically reduced and requires a supplemental heating system. Traditional electrical resistance heating took up space, added safety risks, and wasn’t very durable.
The answer was a solid-state heating system that took up little space, was very durable, provided voltage isolation, and had quick heating characteristics. That solution was adapted to PTC heating elements for automotive heating systems.
The difference between resistive wire heating and PTC heating.
Think of your standard light bulb compared to a new LED light bulb we use in our homes.
The traditional light bulb uses a small wire filament placed in a vacuum when an electrical current passes through the filament and heats up producing heat and light. The thin element needs to be in a vacuum to prevent it from burning out due to combustion.
An LED light bulb has a small solid-state electronic thermistor that produces the light and heat when the current passes through it. The solid-state device similar to a PTC ceramic element doesn’t need to be in a vacuum because no combustion is taking place.
Resistive wire heating
The resistive wire is hot enough when it comes into contact with something combustible that it can start a fire.
That is why resistive wire in toasters and other heaters is enclosed by insulation or protective barriers to keep human hands or combustible items away from contact.
The resistive wire is conducting current at a voltage and not insulated can cause burns, shock, or sparks if it comes into contact with metal or fingers!
Resistive wire heating, as you see in your kitchen toaster or space heater, is composed of bare wire with a constant resistance that heats up when current is applied. They don’t burn out when exposed to oxygen because they are larger in diameter than the light bulb filament.
Resistive heating follows Ohm’s Law where the current I = Voltage V / Resistance R is in a straight line. Another way of describing it is I = Constant x voltage where the constant is the resistance.
In PTC resistance the formula is I = a continuing changing variable x voltage because the resistance is changing as the temperature increases.
A resistive wire used as axillary heat in a home or automobile is also enclosed in a fin assembly to prevent direct contact and insulated from surrounding parts. When a thermostat or switch turns on the current, the resistive wire begins to heat. The resistance is constant, so the current remains the same until it is shut off.
Traditional heating requires a thermostat controller to maintain a set temperature, and not overheat.
PTC ceramic heating elements are similar to the LED as a solid material that has resistance to electricity. The LED energy is released as the current flows through the device, creating light rather than heat.
The big difference between resistive wire heating and PTC heating is the resistance to current changes with temperature. When current initially flows through the PTC ceramic element, the resistance is close to 0 ohms. As the element starts to heat, the resistance starts to increase in a logarithmic line, slowing down the current flow.
At the maxed designed temperature of around 158 degrees Fahrenheit, the resistance becomes so high that the current stops flowing and prevents overheating.
The surface is heated or the air flowing through the heating duct never reaches 158 degrees. The current decreases rapidly before reaching temperature and losses in the transfer of the heat from the silicone disc to the surfaces or air losses. The actual disc is embedded in a heat transfer medium that prevents direct contact with the PTC element itself.
When the ambient temperature is low the PTC heater heats quickly. If the temperature is higher the heater will heat slower because the resistance has already changed with the temperature.
PTC elements are also a great insulator of voltage such that there is no chance of coming into contact with voltages that power the devices. There is also no need for a temperature controlling system other than an on/off switch.
Who developed the PTC heating element?
The composition known as barium nitrate ceramic when it contains a small amount of rare earth elements Y, Bi, Sb, Nb, and Ta exhibited semiconduction that was disclosed in a German patent number. 631321 in 1951. In 1967 a Japanese patent No 42-3855 included doping with a small amount of Bi or Sb exhibited a high positive coefficient of resistivity.
In 1974, Panasonic Corporation (US3975307A) addressed the PTC thermistor composition and the method of making the small ceramic elements. The original patents were not for heating, but for use where the rapid inrush of current decreased rapidly was used for degaussing of the picture tube of color television.
The PTC element allowed for a rapid flow of current through an electrical coil that removed any residual magnetic residue on the tube’s surface. Residual magnetism on the surface of the tube would distort the three colored dots groups that made up the matrix on the face of the tube, producing images.
The distortion of curving of the individual colors making up each color pixel caused a blurring of the images that we viewed on the front of the TV tube. Today’s TV screens work much differently than the early cathode ray tubes and usually don’t require any degaussing.
Since then, the composition of the PTC thermisters has evolved for specific applications of heating and specific temperatures.
What are the characteristics of a PTC heater?
Positive temperature coefficient heating elements are best known for the relationship between current and resistance exhibited by the elements as they heat. Initially, there is low resistance to a high current rush.
The high current heats the element rapidly. At the same time, the increase in temperature increases the resistance of the device and rapidly reduces the current.
As important as the current resistance curve and automatic temperature control are the durability and safety of the devices. Since there are no moving parts unless a fan heater is utilized, there is no need for maintenance. The devices themselves coated with silicone and embedded in heat transfer housing are very rugged.
There is also no combustion taking place while heating and with the temperature limit no chance of creating igniting nearby materials.
While some of these heating elements run on 12/24 Volts, DC/AC higher voltage can be used for more output wattage. The elements have high voltage insulation characteristics that minimize the need for additional voltage isolation for safety.
No need for a temperature of current control circuitry.
The auto current controlling characteristic also controls the heating close to the desired temperature without other control circuitry to prevent overheating. Prior to the engine warming up in a conventional combustion engine vehicle, the element can heat the passenger compartment.
Conventional internal combustion engines use excess heat from the engines to heat passenger compartments. Without excess heat from the electrical motors in an electric vehicle, supplementary heat has to be available for heating the passenger compartment.
This supplemental PTC heating is also used for preheating and keeping the batteries warm for efficient charging in cold weather.
Many electrical vehicles use heat pumps for maintaining the temperature in the passenger compartment and cooling the battery assemblies in warmer weather.
Heat pumps can cool and heat but become inefficient under 40 degrees by making a supplemental heating system a necessity.
How are PTC heating element components constructed?
The small ceramic disk doped with the rare earth elements with PTC characteristics has to be embedded in heat transfer components and with wired connections to take advantage of its unique characteristics for heating.
The ceramic disk can be placed in silicon, a good conductor and voltage insulator, and pressed into an aluminum or stainless steel housing. Liquid silicon is often used to mold or attach to a heat-conducting surface.
PTC finned heaters or air heaters are composed of a matrix of small disks used in a square round of aluminum or stainless screen for duct heating. The air passing through the arrangement in the ductwork of a vehicle or home heating is heated as it comes into contact with the metal find structure.
Other types of PTC heating structures:
PTC heaters in electric cars.
Several PTC heater types are used in electrical and conventional vehicles for supplemental heating. For most of us, EV technology is new, and yet to be widely understood. The equipment and mechanisms for converting electrical energy to drive train power are complicated. Although the lower number of components required makes for less maintenance and more durability.
There are actually two separate voltage systems in electric vehicles. One is the typical 12 Volt system that provides power for all of the controls and operating systems. The second is a much higher DC voltage that is converted to AC voltage to run the motors.
PTC heaters can operate on AC or DC voltages at 12/24 volts or higher 110 - 240 Volt and higher if necessary. This provides plenty of flexibility for EV system designers.
Where can I get a PTC heating element for my vehicle?
These small compact heaters can be ordered online in numerous sizes and configurations for OEM or DIY modifications to current vehicles. Not getting enough heat fast enough in your old truck or car, 12C PTC heating elements are available at very reasonable prices.
Visit our PTC component store at DBKUSA.com, or click here to see products. If you have questions on applications, call us directly and speak with an engineer. Not a salesperson!
Call - 1-864-607-9047