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

16

Sample Calculation 2

240-volt,18-amp load, 25 °C ambient air temperature

Model: 240D45

See the last two columns of the table on page 4 for thermal resistance and dissipation values for the 240D45. Also, see the note at

the bottom of the table.

Dissipation: 0.9 watts/amp

Thermal resistance: 0.67 °C/watt

Maximum junction temperature: 110 °C

The calculation would be as follows:

Duty Cycle Calculation

When solid-state relays are operated in an on/off mode, it may be advantageous to calculate the RMS value of the current through

the SSR for heat sinking or determining the proper current rating of the SSR for the given application.

This calculation indicates that you should

select a heat sink with a thermal resistance

of less than 4.6 °C/watt.

IRMS = RMS value of load or SSR

T1 = Time current is on

T2 = Time current is off

ION = RMS value of load current during on period

I RMS =

T1 + T2

(ION)

2 x T

1