8 Points to Selecting the Best Relay
Do you know how to avoid the most common relay problems? Everything begins with really knowing your application before you select a solution! Data sheets are only part of the process when selecting a relay. They provide basic facts about the construction, capability, and functionality of a relay, but other factors must be carefully considered as well to assure the best possible solution and avoid relay failure.
1) Actual Maximum and Minimum Operating Temperature
Temperatures affect a relay's operation in several ways. It is crucial to know ambient (surrounding) temperature in any application utilizing an electromechanical relay. The ability of the relay's coil to function properly, for example, is directly affected by surrounding temperatures, and coil functionality is essential to the relay's proper switching. At extremely high temperatures, the insulation on a coil can be damaged, causing malfunction in the relay. The materials used in a relay's electrical contacts can also be greatly affected by temperature, so knowing the minimum and maximum temperatures is essential.
2) Continuous Current Draw
This is the amount of electricity in amperes being used in the circuit, and an essential piece of information when selecting the correct relay for the application. Current flow is also a heat generator, which can affect a relay's functionality and contact materials, and a vital piece of information.
3) Switching Current
This is the amount of electricity in amperes that is actually being switched by the relay during its operation. Depending upon the type of electrical load being switched, transient voltages can occur, potentially affecting the relay's switching performance under certain conditions. For example, closing a contact on a highly capacitive load, such as lighting, may create initial currents 12 times as high as the operating current. As well, opening an inductive circuit such as a winch motor may create transient voltages that can result in damage to the contacts.
4) Load Voltage
The level of voltage and the type of voltage affects the relay system. The power is in direct proportion to voltage and current.
5) Control Parameters
Other questions about the control system containing the relay(s) can contribute to the selection of the proper relay. Are the control voltage and power sufficient to drive the relay properly? Is the supply voltage regulated? Is the control output a relay contact or solid-state switch? These questions provide good examples of details that will be helpful when discussing the relay selection process.
6) Load Type- see switching current
Exactly what the relay is switching will determine the type of electrical load, and will provide valuable information for the relay selection process. Electrical loads vary, but play an important role in choosing the proper relay. Resistive loads are commonly seen in heating equipment and incandescent lighting. Inductive loads are common to electric motors, transformers, and coils. Capacitive loads are seen in energy-storing circuits; such as, certain electric motors, power supplies, radio and telecom equipment.
7) Cycle Rate
Some temperature controllers may demand that a relay open and close faster than it's designed to respond. Rapid cycling adds heating effects that can hinder relay performance at high ambient temperatures.
8) Connection Method
Exactly how a relay is connected into a circuit can create its own challenges, and factors into the relay selection process. The integration of wiring terminals into the circuit can create resistance heating, and wire must be properly sized to provide maximum heat dissipation. If the relay is PCB mounted, soldering and wash downs are factors to be considered. A variety of sockets can also accommodate most relays.
* Discuss your application with a DURAKOOL Relay Applications/Sales Engineer
REMEMBER- Datasheets can't be used to select a solution. At best, they just get you in the ballpark. Datasheets are constructed to present generalized information about relay capabilities. Assumptions made about the applicability of a relay in a given application cannot be made without clear definition of the application parameters and the specific capabilities of the relay chosen from the generalized data.
If you have solid information about the 8 factors listed above, we can guide you to the most robust and efficient solution there is.
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