Technical information

Cautions for Use of SSR
13
ds_x61_en_ssr_technical_information: 011212D
Load Inrush Current Wave and Time
(1) Incandescent Lamp Load (2) Mercury Lamp Load
i/iO]3 times
(3) Fluorescent Lamp Load
i/iO]5 to 10 times
(4) Motor Load i/iO]5 to 10 times (5) Solenoid Load
i/iO]10 to 20 times
(6) Electromagnetic Contact Load
i/iO]3 to 10 times
(7) Capacitive Load
i/iO]20 to 40 times
4. Motors
When starting, an electric motor draws a
symmetrical AC starting current some 5
to 10 times the steady-state load current,
superimposed on a DC current. The
starting time during which this high
starting current is sustained depends on
the capacities of the load and load power
supply. Measure the starting current and
time under the motor’s actual operating
conditions and choose an SSR so the
peak of the starting current does not
exceed 50% of the SSR surge-on
current. When the motor load is
deactivated, a voltage exceeding the load
supply voltage is applied to the SSR due
to counter-EMF. This voltage is
approximately 1.3 times the load supply
voltage for induction motors, and
approximately 2 times that for
synchronous motors.
• Reversible Motor Control
When the direction of motor rotation is
reversed, the transient current and time
required for the reversal far exceed those
required for simple starting. The
reversing current and time should also be
measured under actual operating
conditions.
For a capacitor-starting, single-phase
induction motor, a capacitive discharge
current appears during the reversal
process. Be sure to use a current limiting
resistor or reactor in series with the SSR.
Also, the SSR should have a high
marginal voltage rating, since a voltage
twice as high as the load supply voltage
develops across the SSR in the reversal
process. (For reversible control on a 100
V AC line, use SSRs with a 200 V rating;
for use on a 200 V AC line, contact your
nearest our representative for further
information.)
For reversible motor control, carefully
design the driver circuit so the forward
and reverse SSRs do not turn on at the
same time.
Transistor-driven reversible motor
control circuit
5. Capacitive Load
A capacitive load (switching regulator,
etc.) draws an inrush current to charge
the load capacitor when the SSR turns
on. Choose an SSR so the peak of the
inrush current does not exceed 50% of
the SSR surge-on current. A timing error
of up to one cycle can occur when a
switch used in series with the SSR is
opened or closed. If this is a problem, use
an inductor (200 to 500 H) in series to
the SSR to suppress dv/dt error.
6. Other Electronic Equipment
In general, electronic equipment uses
line filters in the primary supply circuit.
The capacitors used in the line filters may
cause the SSR to malfunction due to dv/
dt turn on when the equipment is turned
on or off. In such an event, use an
inductor (200 to 500 H) in series with
the SSR to suppress dv/dt turn on.
Flip-flop
or manual
switch
SSR
2
(for
reverse
rotation)
R
2
R
3
TR
TR
R
1
R
4




SSR
1
(for
forward
rotation)




R
2
R
1
R
3
C
1
C
1
L
C
ZNR
Single-phase
induction motor
Load power supply
SSR
L

C
i
Approx. 1/3 second
Inrush current/rated current:
i/i
o]10 to 15 times
Incandescent lamp
i
o
i
i
o
3 to
5 minutes
The discharge tube, transformer, choke coil,
capacitor, etc., are combined in common
discharge lamp circuits. Note that the inrush
current may be 20 to 40 times, especially if
the power supply impedance is low in the
high power factor type.
Contacts
L
C
(for high power factor type)
io
i
10 seconds
or less
io
i
0.2 to 0.5 second
• Conditions become more harsh if plugging or inching
is performed since state transitions are repeated.
• When using a relay to control a DC motor and brake,
the on time inrush current, steady-state current and
off time brake current differ depending on whether
the load to the motor is free or locked. In particular,
with non-polarized relays, when using from B contact
of from contact for the DC motor brake, mechanical
life might be affected by the brake current.
Therefore, please verify current at the actual load.
Free
Lock
Load
Starting
Steady
state Braking
io
0.07
to 0.1 second
i
Note that since inductance is great,
the arc lasts longer when power is cut.
The contact may become easily worn.
io
1 to 2 cycles
(1/60 to 1/30 seconds)
i
io
1/2 to 2 cycles (1/120 to 1/30 seconds)
i