2.6 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.
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.
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
0 V
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
0 V
xx0100000165
40
Application manual - Discrete I/O
3HAC070208-001 Revision: C
© Copyright 20192020 ABB. All rights reserved.
2 Hardware overview
2.6 Coil neutralization
Summary of Contents for Discrete I/O
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