Heating resistors
(56)Resistors are basic components that are found in every electrical or electronic device. They have many uses in circuits, but the main one is to limit current flow, accompanied by heating of these components. The greater the resistance, the less current can flow through the resistor.
Why are the resistors heating up?
The heating of the resistors is caused by the increase in current - higher currents result in more electrons and more collisions between them within the resistor. In any electrical or electronic circuit, overheated components are considered undesirable. The amount of heat that a resistor will dissipate depends on its physical size, as well as its power rating. Smaller resistors heat up more quickly due to the lower power rating. One of the easiest ways to stop the resistors from heating up is to limit the amount of power it is subject to. To limit the power to a resistor, you can reduce the voltage. Other ways to prevent resistors from overheating include the use of heat sinks. However, the heat generated by a resistor is not always a negative phenomenon.
What are resistive heaters?
Resistive heaters are used when an electronic device needs to generate heat for some reason. They are designed to provide a reliable and controlled heat source. The resistive heater may generate convection heat, which means that it heats the surrounding air or radiation heat, i.e., it heats other objects directly. Radiant heating requires the resistive heater to be placed near the object to be heated, while convection heating sometimes uses fans to blow air over the heaters to increase the heating efficiency. Resistive heater is a special type of power resistor, whose main function is to convert electrical energy into heat. They are offered in the form of thin strips, which can be easily glued in an optimal place inside the devices. This makes them ideal, for example, for stabilising the operating temperature of precision electronic components.
230 V resistive heaters - most common applications.
- Electric convection heaters: They have a heating element that is exposed to the air. When the air comes into contact with a hot object, it heats up, and because the hot air is less dense than the cold, it rises, leaving more room for contact with the heater from below. Sometimes they are fitted with a ceramic heating element. This process is called air convection. Electric convection heaters sometimes do not directly heat the air; oil heaters can serve as an example. In such devices, the heating element is in direct contact with a special oil that distributes the heat throughout the heater. The heat is then transferred to the environment by convection. A special type of convection heaters is underfloor heating, in which the resistance wires heat the entire floor area of the room. The heat is then transferred to the environment by convection.
- Fan heaters: They are similar to electric convection heaters, except that the air is forced over the heating element by an electric fan. These heaters are used to heat enclosed spaces, such as rooms or vehicle interiors, while the engine is still warming up to operating temperature. The downside of using fan heaters is that they are noisy compared to traditional convection heaters, although recent advances in technology have reduced fan noise. The heating element is often made of a PTC thermistor.
- Immersion heaters: Resistive heaters for heating liquids. They are electrically insulated to ensure safety and prevent the electrolysis of the heated liquid. These are often bent heaters and look like traditional immersion heaters. Many applications and devices require immersion heaters; these include domestic water heaters, water boilers, and aquarium heaters, which are equipped with a thermostat and maintain a constant temperature. If the immersion heater is in constant contact with hard water, as is the case in domestic water heaters, scale (calcium carbonate deposits) will eventually build up on the heating element. When the appliance is switched on and off, thermal expansion and contraction of the element break up the scale, which falls to the bottom of the container.
Electric heating resistor - less known applications
The number of interesting applications of resistance heating wires is countless and only some of them will be mentioned here. Resistive heaters can be used in heated motorbike grips or car windows. Other useful applications include surveillance cameras. The resistive heater is placed close to the glass cover and lens. Its heat keeps the glass temperature above the dew point, which prevents fogging and snow build-up, making the camera useful in all weather conditions. Some medical devices, such as blood analysers, also require constant temperatures to function properly.
What to look for when choosing resistive heaters
First of all, it is important to choose the power rating, because this will determine whether or not our equipment will break down; we have a wide range to choose from here, from 20 W up to 500 W. Of course, dimensions are also important - thick film resistors are only 1 mm thick. Another important parameter is the maximum voltage. If our equipment requires a 12 V resistive heater, using a different voltage may consequently damage the resistor or the temperature may be too low, depending on the component used. There are mounting options to choose from: the heating resistors can either be glued on or screwed on.
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