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How Do I Choose the Best Electrical Relay?

An inductor generates a magnetic field when current is applied to it.
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  • Written By: L.S. Ware
  • Edited By: Melissa Wiley
  • Last Modified Date: 19 September 2014
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The electrical relay is a component in a vast array of technologies, from laboratory instruments to automobiles. Choosing the best electrical relay for a particular project can be daunting. They come in a myriad of sizes, shapes, and technologies. Some of the key factors to consider include the type of load, the speed necessary, and the budget of the project.

First and foremost, it must be determined what kind of load will be handled: resistive, capacitive, or inductive. The type of load will influence the preferred metal out of which the contacts are made. The contacts on an electrical relay can be made from a number of materials, with gold and tungsten being two of the most common. Gold contacts work best for low-voltage applications, while tungsten is preferred for high-voltage and high-current scenarios.

The speed with which the electrical relay needs to operate is another major consideration. Different types of relays provide different speed parameters. Electromechanical relays are one of the most common types of relay, but they are also among the slowest. Reed relays provide a faster speed, at about 10 times faster than their electromechanical cousin provides. Solid state relays (SSRs) are even faster and very useful for high-voltage applications.

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Budget, as with any project, is a factor to be taken into account. The cost of an electronic relay can vary dramatically, depending on the cost and availability of materials, among other things. The number of relays needed will alter depending on the type of relay used and can have a dramatic effect on costs.

Additional factors to consider are the desired lifespan of the electrical relay, the required voltage or current parameters, and the number of switch poles the relay will need to perform its desired function effectively. Lifespan is affected by a number of factors, such as the wearing down of mechanical parts and damage caused by excessive voltages or currents. It is imperative to ensure the coil of an electronic relay can be powered properly by the current passed by the controlling circuit.

Choosing the best electrical relay for a desired application can be tricky. For some projects, a large number of relays may be appropriate, while other projects may have only one or two relays that conform to all the required parameters. Be sure to apply all relevant measurements to ensure a proper fit with a given project. Consider the voltage and resistance ratings to avoid under- or over-powering the relay, the workload to be handled to avoid early failure of the relay, and the speed of switching to guarantee satisfactory performance of the electronic relay.

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