Switches & Pilot Lights Signaling Lights Relays & Sockets Timers Contactors Terminal Blocks Circuit Breakers
817
800-262-IDEC (4332) • USA & Canada
Operating Instructions
Relays & Sockets
Operating Instructions
Driving Circuit for Relays
1. To ensure correct relay operation, apply rated voltage to the relay coil.
2. Input voltage for the DC coil:
A complete DC voltage is best for the coil power to make sure of stable relay
operation. When using a power supply containing a ripple voltage, suppress
the ripple factor within 5%. When power is supplied through a rectification
circuit, the relay operating characteristics, such as pickup voltage and dropout
voltage, depend on the ripple factor. Connect a smoothing capacitor for better
operating characteristics as shown below.
+
–R
Smoothing
Capacitor
Relay
Emin Emax Emean
DC
Ripple Factor (%
100%
Emax –
Emin
Emax = Maximum of pulsating current
Emin = Minimum of pulsating current
Emean = DC mean value
Emean
3. Leakage current while relay is off:
When driving an element at the same time as the relay operation, special
consideration is needed for the circuit design. As shown in the incorrect
circuit below, leakage current (Io) flows through the relay coil while the relay
is off. Leakage current causes coil release failure or adversely affects the
vibration resistance and shock resistance. Design a circuit as shown in the
correct example.
Incorrect Correct
R
Io
TE
R
4. Surge suppression for transistor driving circuits:
When the relay coil is turned off, a high-voltage pulse is generated, causing a
transistor to deteriorate and sometimes to break. Be sure to connect a diode
to suppress the back electromotive force. Then, the coil release time becomes
slightly longer. To shorten the coil release time, connect a Zener diode
between the collector and emitter of the transistor. Select a Zener diode with
a Zener voltage slightly higher than the power voltage.
R
suppressing diode
Relay
+
–
Protection for Relay Contacts
1. The contact ratings show maximum values. Make sure that these values are
not exceeded. When an inrush current flows through the load, the contact
may become welded. If this is the case, connect a contact protection circuit,
such as a current limiting resistor.
2. Contact protection circuit:
When switching an inductive load, arcing causes carbides to form on the
contacts, resulting in increased contact resistance. In consideration of contact
reliability, contact life, and noise suppression, use of a surge absorbing circuit
is recommended. Note that the release time of the load becomes slightly
longer. Check the operation using the actual load. Incorrect use of a contact
protection circuit will adversely affect switching characteristics. Four typical
examples of contact protection circuits are shown in the following table:
RC
Power CR Ind. Load
This protection circuit can be used when the load
impedance is smaller than the RC impedance in an
AC load power circuit.
•R: Resistor of approximately the same resistance
value as the load
•C:0.1 to 1 µF
This protection circuit can be used for both AC and
DC load power circuits.
R: Resistor of approximately the same resistance
value as the load
C: 0.1 to 1 µF
Diode
+
–
D
Power Ind. Load
This protection circuit can be used for DC load power
circuits. Use a diode with the following ratings.
Reverse withstand voltage: Power voltage of the
load circuit x 10
Forward current: More than the load current
Varistor
Varistor
Power Ind. Load
This protection circuit can be used for both AC and
DC load power circuits.
For a best result, when using a power voltage of 24
to 48V AC/DC, connect a varistor across the load.
When using a power voltage of 100 to 240V AC/DC,
connect a varistor across the contacts.
3. Do not use a contact protection circuit as shown below:
Power
CLoad
This protection circuit is very effective in arc suppression when
opening the contacts. But, the capacitor is charged while the
contacts are opened. When the contacts are closed, the capacitor
is discharged through the contacts, increasing the possibility of
contact welding.
CLoad
Power
This protection circuit is very effective in arc suppression when
opening the contacts. But, when the contacts are closed, a current
flows to charge the capacitor, causing contact welding.
Generally, switching a DC inductive load is more difficult than switching a DC
resistive load. Using an appropriate arc suppressor, however, will improve the
switching characteristics of a DC inductive load.
Soldering
1. When soldering the relay terminals, use a soldering iron of 30 to 60W, and
quickly complete soldering (within approximately 3 seconds).
2. Use a non-corrosive rosin flux.
Operating Instructions