I’ve just been testing my second fridge setup today. All my SSRs and 12v supplies are mounted on a metal sheet. I have a 240v SSR (heat) on output B of my first SSR control board along with a 240v SSR (compressor) & DC SSR (condenser fan) on the two A outputs. I then have another DC SSR on a second control board (chamber fan). The second control board is daisy-chained off of the first.
The two AC SSRs seem to behave fine. But the two DC SSRs seem to interfere with each other. Enabling the chamber fan enables the condenser fan. Disabling it makes the switching of the compressor unreliable. The issue isn’t there when the either of the DC relays is disconnected from the control boards. I isolated the DC SSRs from the metal sheet they’re mounted on using double sided foam. This seemed to help when testing without load but doesn’t 100% solve it once a load is connected. I imagine that’s because the shared 12v supply might be providing an interference path once in circuit, or my make-shift isolation has stopped doing its job.
I have replacement DC relays on their way from Farnel. I’ve learned my lesson about ebay SSRs. I’m hoping more reputable SSRs won’t have any of their pins connected to the heat-sink. But I was wondering if there’s any other gotchas in the way the SSR control boards are designed that might be contributing to my issues?