Introduction to the Principle and Application of PTC Heater

1. Meaning of PTC: Positive Temperature Coefficient (PTC) is an abbreviation for the phenomenon that resistance increases with increasing temperature. In 1950, Haayman of Philips Company in the Netherlands first discovered the ceramic PTC phenomenon. He added a small amount of rare earth raw materials to BaTiO3 to transform the original dielectric material into a semiconductor ceramic, the resistance of which is proportional to the temperature. PTC thermistor is a typical semiconductor resistor. After exceeding a certain temperature (Curie temperature), its resistance value increases with increasing temperature. Ceramic PTC is a semiconductor ceramic made of barium titanate (or strontium. Lead) as the main component, and a small amount of rare earth (Y.Nb.Bi.Sb) elements and glass (silicon oxide. Aluminum oxide) and other additives. At present, the so-called PTC generally refers to various types of heating products with ceramic PTC heating elements as the core components.

2. PTC theory for ceramics:

The semiconductivity of ceramic PTC is donor semiconductivity, which usually requires the addition of some donor impurities such as Bi (bismuth), La (lanthanum), Y (yttrium), Nb (niobium). For Sb (antimony) oxides, double donor doping can obtain a PTC effect with better performance; in order to facilitate the formation of liquid phase during solid phase sintering, the commonly used sintering aid is Al2O3.SiO2, usually called AST phase. Mn and Cu oxides are acceptor states, mainly existing at the grain boundaries of BaTiO3 ceramics, which can significantly improve PTC performance.

The three main PTC effect bases are: crystal semiconductivity, ferroelectric transition, and grain boundary effect.

3.PTC principle: R-T characteristic refers to the characteristic of PTC resistance changing with temperature. When PTC is powered on, PTC generates heat and causes its own temperature to rise. In this way, resistance will decrease and heat will increase. When heating, if PTC heat is always greater than the heat it dissipates, PTC temperature will continue to rise to exceed NTC segment. In PTC segment, resistance and temperature change exponentially, and the rate of change can reach 30%/℃, showing a faster thermal compensation characteristic. As temperature rises, PTC resistance increases rapidly, causing current to drop rapidly, and PTC heat generation also drops rapidly. When PTC and PTC heat dissipation reach a balance, when PTC heat dissipation does not change, PTC temperature is constant temperature heating, that is, self-controlled temperature state; when the heat dissipation conditions around PTC change, when PTC temperature changes slightly, PTC temperature will change greatly and can quickly compensate for heat. This is the key to PTC being able to stabilize in a smaller temperature range under certain conditions.

4. Advantages of hot air furnace:

It has constant temperature, regulation and automatic temperature control functions: when AC voltage is applied to the PTC element or DC voltage increases, its resistivity is lower than the Curie point, that is, lower than the temperature of the Curie point; when the temperature exceeds the Curie point, the resistivity suddenly increases, causing the current to drop to a stable value, reaching the automatic control temperature.

Safe and reliable: PTC elements do not turn red when heated, there is no open flame (the heating wire turns red), and the temperature of the heating element is generally within 280℃, which will not cause other items to burn, and is very safe and reliable.

High heat conversion rate and energy saving: PTC only heats, not emits light, and has a low operating temperature and a thermal efficiency of more than 95%;

Long life: PTC elements themselves are oxidants, with stable internal structures and long lifespans, and the working time can reach 100,000 hours.

Simple structure: PTC element can automatically control temperature by itself, without adding automatic temperature control;

Strong adaptability to high voltage: When the voltage fluctuates by 20%-30%, the heating effect of PTC will not change much, and 100~240V dual voltage heaters can be produced without changing the structure;

5. Application of hot air furnace.

PTC heating furnace has a wide range of applications and can be divided into three types according to the application scenario:

1. Air heater: Use a fan to blow the hot air generated by PTC to the air to heat the air. Common application products of this type include air conditioners, dishwashers, electric heaters, warm quilt machines, mite removers, bathroom heaters, car defrosters, outdoor cabinet heating, etc.;

2. Liquid heater: Heat water or antifreeze through pipes. Common products include foot baths, egg cookers, steaming basins, hanging irons, electric boilers, wall-mounted boilers, bathtubs, and automotive thermal systems.

3. Contact heater: Heat the object by being close to the heated object. Commonly used products include hair straighteners, curling irons, rice cookers, coffee makers, car power battery heating plates, etc.