Control of MOC3021 Solid State Relay Using PIC16F877

[Asabzi2000]

Hi
Am designing Microcontroller Based Autmatic Transfer Switch for a gen set. I want to use solid state relays (MOC3021) for the control of the engine starter relay. The relay should be powered to start the engine starter when utility power is lost. I want to use about 4 of the relays. How do I connect them to the MCU. Any help (including circuits) will be much appreciated! Kindly find attached my design (the MCU and the AC Voltage sensors)

 

[Kripton2035]

moc3012 is not a solid state relay but an opto-triac.
you need another triac to switch the load. there are lots of examples, the first one is in the moc3021 datasheet
regards,

 

[crutschow]

If the engine start relay is DC then you will need a DC output opto-isolator or solid-state relay, not one with a TRIAC, such as the MOC3012, which can only operate with an AC output. The opto-isolator you show in your schematic is a DC output type.

To drive the isolator or relay from an AC source you need to put the diode in front of the resistor and add a capacitor from the junction of the diode and resistor to the opposite input terminal to filter the AC. Otherwise the relay will turn on and off 50/60 times a second.

 

[Asabzi2000]

Thnx a million times Crutschow, could u kindly help me with a schematic? Thanx in advance

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Thnx Kripton, is it the combination of the opto-triac and another triac that make the SSR? Kindly expatiate to me.

 

[Kripton2035]

Thnx Kripton, is it the combination of the opto-triac and another triac that make the SSR? Kindly expatiate to me.

wikipedia is your friend ! https://en.wikipedia.org/wiki/Solid_state_relay

 

[Asabzi2000]

Thnx, could u kindly help me with schematic?

 

[crutschow]

Is the input control AC or DC and is the output signal being controlled AC or DC?

What is the output load?

 

[Asabzi2000]

The starter motor is run on 24V DC (Generator starter motor)

 

[crutschow]

The starter motor is run on 24V DC (Generator starter motor)

For that you can use a DC-DC solid-state relay such as this.