240D25 OPTO 22, 240D25 Datasheet - Page 21

• Manufacturer Part Number: 240D25
• Description: SSR, PANEL MOUNT, 280VAC, 32VDC, 25A
• Manufacturer: OPTO 22

Specifications of 240D25

• Control Voltage Range: 3VDC To 32VDC
• Operating Voltage Range: 24VAC To 280VAC
• Load Current: 25A
• Isolation Voltage: 4000Vrms
• Control Voltage Type: DC
• Relay Terminals: Screw
• Peak Surge Current: 250A
• Brand/series: DC Series
• Current, Rating: 25 A
• Current, Surge: 250 A (Max.)
• Dimensions: 1.75 in. W x 2.25 in. H x 0.77 in. T
• Function: Power
• Mounting Type: PCB
• Relay Type: Solid State
• Standards: UL, CSA, CE
• Termination: Quick Connect
• Voltage, Control: 240 VAC
• Voltage, Drop, On-state: 1 VAC
• Control Voltage Max: 32V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FAQ: SSR Applications
Q : What is a solid-state relay?
A: A solid-state relay (SSR) is a semiconductor device that can
be used in place of a mechanical relay to switch electricity to a
load in many applications. Solid-state relays are purely
electronic, normally composed of a low current “control” side
(equivalent to the coil on an electromechanical relay) and a
high-current load side (equivalent to the contact on a
conventional relay). SSRs typically also feature electrical
isolation to several thousand volts between the control and
load sides. Because of this isolation, the load side of the relay is
actually powered by the switched line; both line voltage and a
load (not to mention a control signal) must be present for the
relay to operate.
Q : What are the advantages of using an SSR over a
mechanical relay?
A: There are many applications that require a moderate
amount of power (W to kW) to be switched on and off fairly
rapidly. A good example would be the operation of a heater
element in a controlled-temperature system. Typically, the
amount of heat put into the system is regulated using pulse-
width modulation turning a fixed-power heating element on
and off for time periods ranging from seconds to minutes.
Mechanical relays have a finite cycle life, as their components
tend to wear out over thousands to millions of cycles. SSRs do
not have this problem; in the proper application, they could
be operated almost infinitely.
Q : What are the limitations of using an SSR?
A: SSRs have a few limitations when compared to the
capabilities of their mechanical counterparts. First, because
the relay is semiconductor-based, it will never turn all the way
on, nor off. This means that in the “on” state, the relay still has
some internal resistance to the flow of electricity, causing it to
get hot. When in the “off” state, the relay will exhibit a small
amount of leakage current, typically a few mA. This leakage
can conspire to keep some loads, especially ones with a high
impedance, from turning off! Additionally, SSRs are more
sensitive to voltage transients; while Opto 22 relays are very
well transient-protected, if a relay gets hit hard enough a
sufficient number of times, it will die or degrade. This makes
SSRs less ideal for driving highly inductive electromechanical
loads, such as some solenoids or motors. SSRs should also
never be used for applications such as safety power
disconnects, because even in the off state, leakage current is
present. Leakage current through an SSR also implies the
presence of a potentially high voltage. Even though the relay
is not conducting a large amount of current, the switched
terminal will still be “hot, ” and thus dangerous.
© 2006–2011 Opto 22. All rights reserved. Dimensions and specifications are subject to change. Brand or product names used herein are trademarks or registered trademarks of their respective companies or organizations.
Solid-State Relays
800-321-6786 • 951-695-3000 • FAX [phone] • [e-mail] •
Q : Do you make multi-pole or multi-throw SSRs?
A: Opto 22 manufactures only single-pole, single-throw SSRs.
If multi-phase operation is required, just use a relay on each
phase. Because of the limitations on semiconductor devices of
the type used in SSRs, it is not practical to build single-device
multi-throw SSRs. However, an alternative to multi-throw
operation may be accomplished with multiple relays.
Q : Can I hook up SSRs in parallel to achieve a higher
current rating?
A: No. There is no way to guarantee that two or more relays
will turn on simultaneously when operated in parallel. Each
relay requires a minimum voltage across the output terminals
to function; because of the optical isolation feature, the
“contact” part of the SSR is actually powered by the line it
switches. One relay turning on before the other will cause the
second relay to lose its turn-on voltage, and it won’t ever turn
on, or at least not until the first relay fails from carrying too
much current.
Q : What does a “zero-crossing” turn-on circuit refer
to?
A: “Zero-crossing” turn-on and turn-off refer to the point on
the AC wave form when the voltage is zero. It is at this point
that an AC SSR will turn on or off. All Opto 22 AC relays are
designed with a zero-crossing turn-on and turn-off circuit.
When the AC circuit voltage is at zero, no current is flowing.
This makes it much easier and safer for the semiconductor
device in the relay to be turned on or off. It also generates
much less electrical EMI/RFI noise.
Q : Can I use an AC SSR to switch DC?
A: No. Because of the zero-crossing circuit described above,
the relay will most likely never turn on, and even if it is on, it
will likely not be able to be turned off, as DC voltage typically
never drops to zero.
Q : Can I use a DC SSR to switch AC?
A: No. The semiconductor device used in Opto 22’s DC SSRs is
polarized. It may break down and conduct for the portion of
the waveform that is reversed in polarity.
Q : Can a DC SSR be used to switch an analog signal?
A: This is not recommended at all. First, the voltage drop across
the relay will cause signal loss. Second, the conduction
characteristics of the SSR are very non-linear at low operating
voltages and currents. Use a mechanical relay; it will work
much better.
Opto 22 • 43044 Business Park Drive • Temecula, CA 92590-3614 • www.opto22.com
800-835-6786 • 951-695-3080 • FAX [phone] • [e-mail]
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