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Installation, Wiring,
and Specifications
2–21
Installation, Wiring, and Specifications
This figure shows the same circuit with a transorb (TVS) across the coil. Notice that
the voltage spike is significantly reduced.
+24 VDC
–24 VDC
Module Relay Contact
–42 VDC
+24 VDC
Use the following table to help select a TVS or MOV suppressor for your application
based on the inductive load voltage.
hh
Vendor / Catalog
Type (TVS, MOV, Diode)
Inductive Load Voltage
Part Number
General Instrument
Transient Voltage
Suppressors, LiteOn
Diodes; from DigiKey
Catalog; Phone:
1-800-344-4539
TVS
TVS
TVS
Diode
110/120 VAC
220/240 VAC
12/24 VDC or VAC
12/24 VDC or VAC
P6KE180CAGICT–ND
P6KE350CA
P6K30CAGICT–ND
1N4004CT–ND
Harris Metal Oxide
Varistors; from Newark
Catalog; Phone:
1-800-463-9275
MOV
MOV
110/120 VAC
220/240 VAC
V150LA20C
V250LA20C
Relay contacts wear according to the amount of relay switching, amount of spark
created at the time of open or closure, and presence of airborne contaminants.
There are some steps you can take to help prolong the life of relay contacts, such as
switching the relay on or off only when it is necessary, and if possible, switching the
load on or off at a time when it will draw the least current. Also, take measures to
suppress inductive voltage spikes from inductive DC loads such as contactors and
solenoids.
For inductive loads in DC circuits we recommend using a suppression diode as
shown in the following diagram (DO NOT use this circuit with an AC power supply).
When the load is energized the diode is reverse-biased (high impedance). When the
load is turned off, energy stored in its coil is released in the form of a negative-going
voltage spike. At this moment the diode is forward-biased (low impedance) and
shunts the energy to ground. This protects the relay contacts from the high voltage
arc that would occur just as the contacts are opening.
Place the diode as close to the inductive field device as possible. Use a diode with a
peak inverse voltage rating (PIV) at least 100 PIV, 3A forward current or larger. Use a
fast-recovery type (such as Schottky type). DO NOT use a small-signal diode such
as 1N914, 1N941, etc. Be sure the diode is in the circuit correctly before operation. If
installed backwards, it short-circuits the supply when the relay energizes.
Inductive Field Device
+
–
PLC Relay Output
Output
Common
Input
Common
Supply
Prolonging Relay
Contact Life
Summary of Contents for DL05
Page 1: ...DL05 User Manual Automationdirect com ...
Page 2: ...DL05 User Manual Automationdirect com ...
Page 436: ...1B DL05 Error Codes In This Appendix Ċ Error Code Table ...
Page 443: ...1C Instruction Execution Times In This Appendix Ċ Introduction Ċ Instruction Execution Times ...
Page 459: ...1D Special Relays In This Appendix Ċ DL05 PLC Special Relays ...
Page 464: ...1E DL05 Product Weights In This Appendix Ċ Product Weight Table ...