I am using a
SPF240D25R Solid State Relays - PCB Mount PCB SIP 240VAC, 25A load current and 4-15VDC trigger voltage. This is being triggered from a ULN2003A and used to drive a motor (pump).
On the same board I am driving a 5V coil relay which has 12VAC across its contacts with no load, this two is driven from another transistor with the same ULN2003A device.
When I fire the relay the SSR is firing. When I turn off the relay the SSR turns off. This ONLY happens when the load (motor) is connected to the SSR. For example, if I fire the relay and the measure the O/C load on the SSR it does not fire.
I cannot figure out the problem. I have a 100 ohm || 1uF capacitor snubber on the input to the SSR. I have a 1N4001 flywheel diode across the relay coil (even though the ULN2003 has them).
The main thing which is confusing is what does it not fire in error when no load is connected to it?
This is part of a large system and the schematics are over multiple pages. I have provided the various snippets below.
This is the SSR circuit. Please note that the SSR is a SPF240D25R (ignore the name on the schematics). Also note that the "pump relay" is not the offending relay. In fact when this relay is fired the same problem is NOT witnessed.