SSR Attempt

[RyanG]

This is my attempt at a SSR to replace our old mechanical relays. The 12vdc is on when the machine is turned on. The 24vac is the current relay trigger. I don't know how the triac part of the circuit looks because I have never really done anything with them. The J connectors are screw terminals to replace the 8 contacts on the relays. The relays run motors. The terminals connected to the PNP are normally closed and the ones to the NPN are normally open. Does this thing look like it would work? If anyone has any improvements or ways to reduce the number of parts required that would be great.

[bktemp]

I see many problems with this circuit:
- This only works if there is no other connection between GND and 24V ac.
- Q1 does nothing useful and could replaced by a piece of wire
- The current is probably a bit too low for driving the optotriacs (check the datasheet, they require 5-30mA depending on the type)
- When the 24V is turned on, Q2 sees a base-emitter voltage of ~20V, but it will break down and get damaged somewhere less than 10V. Also the switching point is not defined exactly, there is probably a period when both NO and NC contacts are open or shorted.
- Using one optotriac for driving 2 triacs does not work.
- You should add a snubber circuit for the optotriac.

[RyanG]

This is the only connection on the 24vac. I removed the original Q1. I forgot to remove it after I changed it around from my original layout. I reduced the resistors going to the optotriacs. I added 2 more optotriacs so each triac has its own. I also added snubbers for each of the optotriacs. What should I use in place of the BJT to turn that part on?