Solid-State Relays

Opto 22 • 43044 Business Park Drive • Temecula, CA 92590-3614 • www.opto22.com

SALES 800-321-6786 • 951-695-3000 • FAX 951-695-3095 • sales@opto22.com • SUPPORT 800-835-6786 • 951-695-3080 • FAX 951-695-3017 • support@opto22.com

© 2006–2014 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.

PAGE

19

Heater Loads

Care should be taken in selecting a SSR for driving a heater

load if the load is cycled on and off in a continuous manner as

might occur in a temperature control application. Constant

cycling can cause thermal fatigue in the thyristor chip at the

point where the chip bonds to the lead frame. Opto 22

employs a thick copper lead frame for mounting the SCR chips

in the power series SSRs to eliminate thermal fatigue failures.

In addition, Opto 22 recommends operating any SSR at 75%

rated current for cycling heater loads to ensure complete

reliability.

The following table is a guide to selecting the proper SSR for a

given heater load.

Single-Phase Reversing Motor Control

The circuit diagram below illustrates a typical 1 Ø motor

winding inductance and the phase shift capacitor can cause

twice-line voltage to appear across the open SSR. A 240-volt

SSR should be used for a 120-volt line. During the transition

period when one SSR is turned on and the other SSR is going

off, both SSRs may be on. In this case, the capacitor may

discharge through the two SSRs, causing large currents to

flow, which may destroy the SSRs. The addition of RL as shown

will protect the SSRs from the short circuit capacitor discharge

current.

Single-Phase Reversing Motor Control (cont.)

The resistors are unnecessary if the control circuit is designed

to ensure that one SSR is off before the other SSR is on.

Three-Phase Motor Control

Three-phase motors may be controlled by solid-state relays as

shown. A third SSR as shown is optional, but not necessary.

The control windings may be connected in series or parallel.

Care should be taken to ensure that the surge current drawn

by the motor does not exceed the surge current rating of the

SSR.

Nominal SSR

Curren t Rating

Maximum

Recommended

Heater Current

2-Amp

1½-Amp

4-Amp

2½-Amp

10-Amp

7½-Amp

25-Amp

18-Amp

45-Amp

35-Amp

10 480V

8-Amp

10 480V

8-Amp

240 Volt Three-Phase Motor

SSR MODEL

MOTOR

Z240D10

3/4 HP

240D10

3/4 HP

240A10

3/4 HP

240D25

2 HP

240A25

2 HP

240D45

3 HP