Coil Neutralization - ABB Scalable I/O Applications Manual

3.5 Coil neutralization

External devices
External relay coils, solenoids, and other devices that are connected to the I/O
devices must be neutralized and protected with external diodes for reverse
protection. The following sections describe how this can be done.
Clamping with a diode
The diode should be dimensioned for the same current as the relay coil, and a
voltage of twice the supply voltage.
+24 V DC
xx0100000163
Clamping with a varistor
The varistor should be dimensioned for the same current as the relay coil, and a
voltage of twice the supply voltage.
xx0100000164
Clamping with an RC circuit
R 100 ohm, 1W C 0.1 - 1 mF
>500 V max. voltage, 125 V nominal voltage.
+24 V DC
xx0100000165
Application manual - Scalable I/O
3HAC070208-001 Revision: F
Note
The turn-off time for DC relays increases after neutralization, especially if a diode
is connected across the coil. Varistors give shorter turn-off times. Neutralizing
the coils lengthens the life of the switches that control them.
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3 Hardware installation
3.5 Coil neutralization
53