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AC-AC Solid State Relay or SSR - del30012

This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this.

These were used in controllers like this - Blind Dial Analog Temperature Controller

This is another common SSR which is used in Relay Logic too. In the Control Panel we could encounter a need to reverse the logic and drive a contacter. Sometime a relay has to operate when a Timer is turned on. This SSR turns on with the AC Power Signal and has High Impedance Input and drives a Motor, Heater Bank or Fan. The current rating has to exceed the load that you are using. Use a HRC fuse in Series.  

See how a Normal Magnetic Relay is Interfaced - Relay Driver - Electromagnetic

A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC control signal is available. The BTA series has the heatsink tab insulated from the Triac chip inside. The BTB needs electrical insulation to the heatsink.

AC-AC Solid State Relay or

PNG-Schematic  PCB - L1  L2  SS  M1  M2
AC-AC Solid State Relay or SSR - del30012

These devices BTA40600 and MOC3041 make SSRs very simple. They have proved very reliable and rugged in the field, overrate your designs, use heat sinks and seal the SSR with thermally conductive epoxy. Alumina with ciba araldite without any other filler or dye is the best way to hermetically seal.

See also some info here

                      Solid State Relay


The MOC303XM and MOC304XM devices consist of a AlGaAs infrared emitting diode optically coupled to a monolithic silicon detector performing the function of a zero voltage crossing bilateral triac driver. MOC3041

They are designed for use with a triac in the interface of logic systems to equipment powered from 115 VAC lines such as teletypewriters, CTRs, solid-state relays, industrial controls, printers, motors, solenoids and consumer appliances, etc.

  • Simplifies logic control of 115 VAC power
  • Zero voltage crossing
  • dv/dt of 2000 V/s typical, 1000 V/s guaranteed

MOC3041 Zero Crossing Triac Output, 6 Pin

See the original Motorola Application below.

MOC3041 Zero
                        Crossover Opto Coupler

The were used to control Heaters from DC control signal from a Proportional Temperature Controller. The Magnetic Contactors can be avoided for lower powers. At higher powers SCR banks become a bit expensive. The SSR has no mechanical wear and tear but heat up at high currents. So if we overrate by 5 Times then it is an excellent solution for lower power controls upto 5 Kilo Watts. The cycle time of Contactors must be 20-60 Seconds to make it last long. In a SSR a one second cycle time is possible as 10-20mS is the switching speed due to zero crossing.