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A contactor is basically a large version of a relay. It is designed to carry large currents and controlled by an electrical current. Typically areas where contactors are used is in motor control, controlling lightning and other high power switching circuits.

Physical size can be from 5-10 cm up to a meter, handling currents from a couple of amperes up to thousands of amperes.

To handle large currents the contact surfaces is usually made up of silver, silver-tungsten or silver-molybdenum alloys. The two latter alloys are good to handle high temperature and large currents.



Larger contactors often have the silver alloy contact surfaces brazed to the copper or brass conductors. It is easily removed with a torch but care is needed because cadmium is often used in the braze. Do not breath the fumes from melting the braze.

Pure silver or silver-copper alloys can be refined in traditional ways.

Silver-tungsten alloys

Silver and tungsten isn't possible to alloy in the classical meaning. It is made by sintering silver and tungsten powder. To get the silver out it needs to be boiled in nitric acid for a prolonged time. The tungsten will keep the overall shape of the original button. When the silver is dissolved the remaining button can be broken in half without problem.

Silver-molybdenum alloys

Silver molybdenum is also hard to refine. The molybdenum will be converted into greenish yellow molybdite by nitric acid. It takes a long time and in the end only yellowish powder should be left. The process is working faster with diluted nitric acid.


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