What is coil surge?
It is a characteristic of the coil in which a large reverse voltage is momentarily generated when Relays are turned OFF. To deal with this problem, some Relays are equipped with surge-absorbing circuits.
When contacts are used for input, surge-absorbing circuits can be used to extend the service life of Relays, prevent the effects of noise, and minimize the production of carbides and nitric acid caused by arcing.
When semi-conductors, such as transistors, are used for input, reverse voltage is generated and may cause Relays to breakdown.
In most cases it is good to install a surge-absorbing circuit.
Some relays have a built-in surge-absorbing diode (for DC coils). These diodes can also be externally installed.
Comparison of Coil Surges in a 24-VDC Circuit
Comparison of Coil Surges in a 200-VAC Circuit
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