The function of a power resistor is to withstand and dissipate large amounts of power. These power resistors are made from materials with a high thermal conductivity which also allows efficient cooling. In order to dissipate high amounts of power, these power resistors are designed to be coupled with heat sinks. There are resistors that need forced air or liquid cooling while under maximum load. The common thing for all power resistors is that they are built to dissipate the most heat while keeping their size as small as possible.
There are many different types of power resistors according to their construction.
The wirewound resistor is made by winding a metal wire around a solid material which is often made of ceramic, fiberglass or plastic. They are attached with metal caps and metallic leads at the ends. The wirewound resistors are often coated with non-conductive paint or enamel to offer protection from the environment. They are built to withstand high temperatures of up to more than 400 degrees Celsius. They are built to tight tolerances made possible by the materials used which is nichrome, an alloy of nickel and chrome. Then the device body is coated with non-conductive paint, enamel or plastic. Click this link high power resistor to see more information.
There are also grid resistors which are large matrices of metal strips connected between two electrodes. They have different sizes but there can also be very large. These are used are brake resistors and load banks for railroad vehicles, natural grounding resistors, load testing of generators, and harmonic filtering for electric substations.
One type of resistor look like integrated circuit chips and are called chip resistors. Surface mount power resistors are made from different materials such as pressed carbon, ceramics, and metal or metal foil. There are also wirewound chip resistors. Surface mount device (SMD} resistors are small, surface mounted chip resistors. It consists of a metal oxide film deposited onto a ceramic substrate. The resistance is determined by the thickness and length of the film. They have low power dissipation ratings and can dissipate just a few watts provided they have appropriate cooling. Witness the best info that you will get about current sense resistor.
Water resistors consist of tubes filled with a saline solution with an electrode at both ends. The resistance of the resistor is controlled by its salt concentration. Water provides a large heat capacity which allows high heat dissipation. High power water resistors use copper sulfate solution instead of saline solutions.
Liquid rheostats or salt water rheostats are visible resistors in which the resistance is controlled by submerging electrodes into saline solution. By adjusting the electrode position inside the liquid, the resistance may be raised or lowered. In order to stabilize the load, the mixture must not be allowed to boil. These are slightly outdated but are still constructed is some diesel generators.
