Contact Transfer - Fuji Electric MICREX-SX series SPF User Manual

Section 3 Specifications
2) Suppression of counter-electromotive force
For the inductive load, whether in AC or DC power, suppression devices must be connected in parallel to both its ends to protect
the relay contacts and lower noise interference. The schematic diagrams for AC and DC powers are shown below, respectively:
PLC Relay output
R
PLC Relay output
R
Suppress by a diode in DC power load (for low power)
PLC Relay output
R
Suppress by a diode + Zener in DC power load (for high power and frequent ON/OFF)

(2) Contact transfer

Contact transfer refers to a phenomena in which one side of contact melts or evaporates and is transferred to the other side
because of on/off operation of the DC load. As the number of on/off times increases, the protruded portion on one contact grows
and the embossed portion on other contact becomes correspondingly large. Eventually the two contacts are locked as if contact
melting occurred. This phenomena may occur within the ratings of relay contacts. In particular, when a relay is used to turn on
and off a capacitive load, this phenomena may occur. In this case, use a resistor to suppress inrush current.
Inductive load
R C
Scheme of AC power load
Inductive load
D
Inductive load
ZD D
R: 100~120
C: 0.1 to 0.24uF
D: 1N4001 diode or
VDC equivalent device
D: 1N4001 diode or
equivalent device
VDC
ZD: 9V Zener, 5W
3-13